Aust. 1. BioI. Sci., 1985, 38, 393-403

Gastro-intestinal Tract Function in Sheep Infused with

T. N. Barry, A,B G. J. Faichney, A and Carolyn Redekoppc

A Division of Animal Production, CSIRO, P.O. Box 239, Blacktown, N.S.W. 2148. B On leave from: Invermay Research Centre, Mosgiel, New Zealand. Present address: Department of Animal Science, Massey University, Palmerston North, New Zealand. C Department of Endocrinology, Princess Margaret Hospital, Christchurch, New Zealand.

Abstract The effect of a 5-day continuous intravenous infusion of somatostatin (4·6 ng min- I kg-I) was studied, using anoestrous ewes given 791 g dry matter per day of a 60: 40 lucerne hay: oat grain pelleted diet from a continuously moving belt. 5ICr-EDTA, I03Ru- and lignin were used as markers to determine digesta mean retention times (MRT) by a continuous infusion-total sampling procedure. The somatostatin infusion increased the concentration of somatostatin in venous plasma within the physiological range from 10 to 76 ng/I, decreased plasma concentrations of and thyroxine, but had no effect upon plasma concentrations of and . It had no effect upon digesta-free weight of the rumen and omasum but consistently decreased the weight of all post-ruminal segments of the gastro­ intestinal (GI) tract. The infusion increased the accumulation of digesta in the abomasum and caecum. Total MRT of all three markers in the entire GI tract was unaffected by somatostatin infusion, but the proportion of total MRT spent in the abomasum + small intestine + caecum increased and the proportion spent in the and rumen decreased. Somatostatin infusion decreased apparent endogenous abomasal secretion, increased water flow from the rumen and into the abomasum and decreased voluntary water consumption. It is proposed that the prime site of somatostatin action was in the abomasal to caecal region, where somatostatin-secreting D cells are found in greatest concentration, that effects observed in the large intestine and rumen may represent secondary compensatory mechanisms and that the effects observed were due to direct action of somatostatin and were not mediated by other GI .

Introduction The tetradecapeptide somatostatin (mol. wt 1639·9) was first detected in ovine hypothalamic tissue as a factor which inhibited growth secretion from the pituitary gland (Brazeau et al. 1973). Subsequently, somatostatin has been detected in the pancreatic tissue of a number of mammalian species; it has been suggested that it inhibits insulin and glucagon release from the and modifies the extraction of these hormones by the (Vale et al. 1975; Brockman 1979; Ishida et al. 1980). Schusdziarra (1979) observed that intravenous somatostatin infusion in dogs reduced plasma triglyceride concentrations following a meal, and proposed that the release of somatostatin from the gut may be involved in the homeostatic regulation of the rate of nutrient absorption. In growing sheep, Barry et al. (1982) found that abomasal infusion of casein decreased plasma somatostatin concentration, suggesting the possibility that somatostatin could be involved in the regulation of absorption rate in this species too. The objective of the present experiment was to study the effect of a continuous 0004-9417/85/040393$02.00 394 T. N. Barry et al.

intravenous infusion of somatostatin on the rate of passage of indigestible markers through the gastro-intestinal (GIl tract of sheep, on net water exchanges along the tract, on the weights of individual segments of the GI tract and on endocrine status. Materials and Methods Animals Two groups of five anoestrous Corriedale ewes aged 5-6 years were used; the mean liveweights (± s.e.) of, respectively, the control and treatment groups were 38·4 ± 0·94 and 40·0 ± 2·61. The ewes were shorn 57-58 days prior to slaughter. They were held in individual pens for 4 weeks and were then transferred to metabolism cages in a room with normal windows but with continuous artificial lighting. The mean maximum and minimum temperatures in the room were 22·2 ± O·loC and 19·6 ± 0·2°C.

Diet The diet was a ground and pelleted mixture of 60% lucerne hay and 40% oat grain. On a dry matter (DM) basis, the mean composition (glkg) of the diet was: nitrogen 22·8, cell wall organic matter 417, acid­ detergent fibre 292, acid-detergent lignin 71, crude fat 40 and ash 59. It was given daily at the rate of 791 g DM from the day of shearing and during the 4 weeks prior to slaughter it was presented continuously from a conveyor belt. Voluntary water intake was measured daily, and corrected for evaporation losses. Total water intake included that consumed in the pellets.

Experimental Methods Measurements were made first on the control then on the treatment group. In each period, 3 weeks before slaughter, each sheep was fitted with a self-retaining rumen catheter (Faichney and Colebrook 1979). In the second period, a polyvinyl catheter (I ·5 mm o.d., I· 0 mm i.d.; Dural Plastics and Engineering, Dural, N.S.W.) was placed in a jugular vein of each sheep I day prior to the commencement of a somatostatin infusion. The catheter was filled with sterile saline containing 200 i.u. heparin/m!. During each period, faecal output was collected for 7 days prior to slaughter and the markers were infused into the rumen for at least 5 days and, in the second period, the intravenous somatostatin infusion was maintained simultaneously for at least 5 days; all infusions were terminated at slaughter. Urine output was collected during the 24 h prior to slaughter.

Infusion procedures The markers used were the 51Cr complex of EDTA (51 Cr-EDTA) (Downes and McDonald 1964) and 103Ru-Iabelled tris-(l,I 0-phenanthroline)-ruthenium(II)chloride(103Ru-phen) (Tan et al. 1971). The infusate was made up to contain 37 kBq 51Cr and 7·4 kBq 103Ru per millilitre, with 5·4 /Lg inert Cr-EDTAIkBq 51Cr added as carrier. Following a priming dose of 30 ml into the rumen, the infusion was begun and maintained at 47 mllday for at least 5 days before slaughter. Synthetic cyclic somatostatin (mol. wt 1639·9; Sigma Chemical Co., Missouri, U.S.A.) was dissolved in sterile saline (9 g NaCIII) containing bovine serum albumin (2·5 gil) to act as carrier and to prevent possible binding of somatostatin to glassware and tubing. Both somatostatin concentration in the infusate and the pumping rate were adjusted for each sheep such that the somatostatin infusion rate was constant at 4·6 ng min - 1 kg - 1 liveweight. Mean somatostatin concentration in the infusate was 2083 /LgIl and the mean infusion rate was 5·35 mllh. The infusion was maintained for at least 5 days. The infusates were stored at 4°C for up to 3 days before use, and were kept on ice whilst being infused.

Sampling procedures A composite sample of faeces was prepared for each sheep by combining 20% of the daily output; this and a urine sample were stored at - IO°C. Blood samples were drawn into heparinized syringes by jugular venipuncture of all animals at 10·00 h for 3 consecutive days; the blood was transferred to tubes kept in an ice slurry and 0·33 ml aliquots of plasma prepared by centrifugation were pooled each day to give I-ml samples for individual hormone analyses. The proteinase inhibitor Trasylol (Bayer, Leverkusen, W. Germany) was added to those tubes (1000 ki.u.lml plasma) that were to be assayed for somatostatin, glucagon and , to prevent proteolysis of these hormones. In somatostatin-infused sheep, the blood samples were taken after the infusion of somatostatin and the indigestible markers had been running for 48, 72 and 96 h, and after the markers had been infused for corresponding times in control sheep. Somatostatin and Gut Function in Sheep 395

The animals were killed by the intravenous administration of concentrated sodium pentobarbitone, after which the abdomen was opened and the oesophagus, the omasal-abomasal junction and the abomasal­ duodenal junction were quickly ligated and the entire GI tract removed. The small intestine was then divided into five approximately equal sections and the large intestine into the caecum-proximal colon (caecum), the centripetal (spiral colon I), centrifugal (spiral-colon 2) and terminal colon and the rectum. Total digesta in each segment was removed and weighed and subsamples taken for the determination of radioactivity, dry matter and lignin. Visible fat was then trimmed from all gut tissues, which were then washed, blotted dry and weighed. The reticulo-rumen will be referred to in this paper as the rumen.

Analyses Samples of digesta, faeces and urine were assayed for SICr and J03Ru simultaneously in duplicate tared vials using a model 5320 Auto Gamma Spectrometer (Packard Instrument Co., Illinois). Hormones were determined by the standard radioimmunoassay procedures described by Barry et al. (1982). Total glucagon was measured using antibody K4023, which recognizes both pancreatic glucagon and enteroglucagon; pancreatic glucagon was also measured with a specific antibody and enteroglucagon estimated by difference. Gastrin was determined as described by Reynolds et al. (1984) and stimulating hormone as described by Hopkins et al. (1975). The interassay variation and assay detection limits for the hormone assays were: 8 '6%, 1·2 ",gil; prolactin 7·4%,2·4 ",gil; somatostatin 14,6%, 7·0 ng/I; insulin 4 ·0%, 1· 5 mi.u.l1; glucagon 6·3%, 15·3 ngll; gastrin 10%, I· 3 pmolll; thyroid stimulating hormone 13·8%, 0·5 ",gil; thyroxine 6%, 2·0 nmolll; tri-iodothyronine 6%, 0·04 nmolli. Plasma glucose was determined using glucose oxidase (frinder 1969) and plasma non-esterified fatty acids (NEFA) were determined as described by Patterson (1963). Feed samples were analysed as described by Faichney and White (1983). Lignin in digesta and faeces was determined as the organic matter remaining after extraction as described by Bailey (1967).

Calculations Marker concentrations were expressed as a fraction of the infusion rate, the sICr-EDTA values being corrected for absorption as described earlier (Faichney 1980) assuming that sICr-EDTA absorption from any segment of the GI tract was proportional to its retention time in that segment (Faichney 1975b). Mean SICr urinary excretion was 5·93 ± s.e. 0·82% of that infused. Lignin concentrations were expressed as a fraction of the daily faecal output. Mean retention times (MRT) of the markers and of lignin in each segment of the GI tract were calculated using the continuous infusion-total sampling procedure (equation 7, Faichney 1975a). Examination of the data confirmed that the markers did not behave independently in the small and large intestine (Faichney 1975b) and, when checked in two sheep, the MRT of lignin in these segments did not differ from the values for the markers; the MRT values reported for the segments distal to the are the mean of those determined for SJCr-EDTA and 103Ru-phen. Fractional outflow rates (FOR) of water from the rumen and abomasum were calculated as the reciprocal of the MRT for sICr-EDTA in these organs (Faichney 1975a, 1980) and, for the caecum, as the reciprocal of the mean of sICr-EDTA and 103Ru-phen MRT values. Water outflow from all three organs was calculated as the product of FOR and pool size. Water flow rate (litres per day) through other organs was calculated as the reciprocal of marker concentration, using sICr-EDTA only for the omasum, and the mean of sICr-EDTA and 103Ru-phen for all segments distal to the stomach.

Statistical analyses Treatment effects were assessed using the Students t-test.

Results Plasma Hormone and Metabolite Concentrations Somatostatin infusion markedly increased plasma concentrations of somatostatin and gastrin and depressed those of prolactin and thyroxine; concentrations of glucose did not change significantly (Table 1). The infusion had no effect upon plasma concentration of NEFA or of the other hormones measured. 396 T. N. Barry et at.

Table 1. Effect of somatostatin infusion upon plasma concentrations of hormones and metabolites Mean ± s.e. for five animals per group

Control Somatostatin­ Significance infused of difference

Growth hormone (/lg/I) 5·8±0·83 5·4±0·59 Prolactin (/lgn) 162±58·3 52± 10·6 P

Insulin (mi.uJI) 14· 9 ± 4· 27 14·2± 1·29 Pancreatic glucagon (ng/I) 104± 12·5 124 ± 11·7 Enteroglucagon (ng/I) 291 ±29·8 287 ± 35·0 Gastrin (pmolll) 13·3 ± I· 35 23·2 ± I· 88 P

Thyroid stimulating hormone {Jtg/I) I ·74 ± 0·331 1·78±0·435 Thyroxine (nmolll) 122 ± 8 . 3 90±9·3 P<0·05 Tri-iodothyronine (nmolll) I ·27 ± O· 178 1·03 ±0·092

Glucose (mg/I) 672 ± 29·7 626±6·9 Non-esterified fatty acids (/lmolll) 142 ± 24·3 157±25·3

Weight oj OJ Tract Tissues and Contents Somatostatin infusion had no effect upon the combined weight of digesta-free tissue from the rumen and omasum (Table 2), but consistently reduced the weight of all GI tract segments distal to the omasum, with the decrease being proportionately

Table 2. Effect of somatostatin infusion on the weight (g) of digesta-free organs of the GI tract of sheep Mean ± s.e. for five animals per group

Tissue Control Somatostatin- Significance infused of difference

Total GI tract 1971 ± 86·0 1878 ± 29·7 Rumen + omasum 895±28·6 942±38·4 Abomasum (A) 202±22·7 173±3·3 Small intestine (SI) 436 ±37·9 416±8·2 Caecum (CPC) 188±14·3 165± 12·2 Distal large intestine (DLI) 250± 13·8 182±4·8 P

largest for tissues of the large intestine. Ewes infused with somatostatin had consistently more total digesta and digesta DM in the abomasum and caecum, and more lignin in the abomasum, than did control ewes (Table 3). Conversely, ewes infused with somatostatin tended to accumulate less DM in the rumen and the omasum than control ewes, but this trend was rather variable for total digesta.

Marker Mean Retention Times Marker MRT's in the entire GI tract (Table 4) were unaffected by somatostatin infusion, and increased in the order slCr-EDTA < 103Ru-phen < lignin. Somatostatin Somatostatin and Gut Function in Sheep 397

Table 3. Weights (g) of total digesta, dry matter and lignin in individual segments of the GI tract of sheep Mean ± s_e_ for five animals per group

Control Somatostatin- Significance infused of difference

Total digesta Total GI tract 5820 ± 234-7 6307 ±454- 3 Rumen 3847±179-3 4100±376-4 Omasum 165±2-2 129 ± 17 -8 P=0-084 Abomasum (A) 295±55-7 455±1l1-0 Small intestine (SI) 553±45-1 555±42-1 Caecum (CPC) 630±52-4 850±92-2 P=0-071 Distal large intestine 330±26-8 218±13-4 P

Dry matter Rumen 668±33-4 616±73-1 Omasum 39 ± I-I 28 ±4- 5 P<0-05 Abomasum 40±6-2 67 ± 17-0 Caecum 113± 10-5 158± 17-6 p=o-on

Lignin Rumen 167 -0 ±9-21 147-1 ±20-37 Omasum 11-4 ±O- 34 8 -8 ± I- 57 P=0-149 Abomasum 10 -4 ± 1-48 19-7 ±4-51 P=0-086

Table 4. Effect of somatostatin infusion upon the mean retention times (h) of 51Cr-EDTA, l03Ru_phen and lignin in the rumen, omasum, abomasum and the whole GI tract of sheep Mean ± s_e_ for five animals per group

Control Somatostatin- Significance infused of difference

51Cr-EDTA Total GI tract 34-0± 1-10 35 -2 ± I- 87 Rumen 11-3±0-55 10-8±0-93 Omasum 0-7±0-04 0-5 ±0-07 P<0-05 Abomasum 0-8±0-12 1-2±0-21

103Ru-phen Total GI tract 44-0± 1-10 45 -6 ± 3 -48 Rumen 18-5±0-90 17-3± 1-91 Omasum 2-3±0-13 I- 7 ± 0- 28 P<0-05 Abomasum 1-9±0-33 3-8±0-94 P=0-093

Lignin Total GI tract 74-6±3-74 72-4±7 -52 Rumen 47-1±3-71 41-6±5-83 Omasum 3 -2 ± 0 -098 2- 5 ±0-45 Abomasum 3-0±0-49 5 -6 ± 1-26 P=O-092 398 T. N. Barry et al.

Table 5. Effect of somatostatin infusion upon the mean retention time (h) of digesta in the small intestine, caecum-proximal colon and the distal large intestine of sheep Mean ± s.e. for five animals per group. Values are the mean of those obtained for sICr-EDTA and 103Ru-phen

Control Somatostatin- Significance infused of difference

Small intestine Segment I 0·15 ± 0·038 0·17 ±0·020 Segment 2 0·28±0·056 0·37±0·051 Segment 3 0·46±0·110 0·60±0·135 Segment 4 0·70±0·189 0·82±0·On Segment 5 I· 23 ±0·080 1·42±0·295 Total 2·81 ±0·059 3·37±0·314 P=0·1l8

Caecum-proximal colon 9·8± 1·24 13·6±1·51 P=0·093

Spiral colon (SC) Segment I 1·09±0·122 0·n±0·124 P=0·098 Segment 2 1·02±0·068 0·59±0·153 P<0·05

Terminal colon (TC) 3·5±0·51 1·9 ±0·29 P<0·05

Rectum (R) 3·1 ± O· 34 2·6 ±0·35

SC+TC+R 8·6±0·81 5·8±0·50 P<0·05

Table 6. Effect of somatostatin infusion on the mean retention times of slCr-EDTA, l03Ru_phen and lignin as a percentage of the total mean retention time for each marker in sheep Mean ± s.e. for five animals per group

Control Somatostatin- Significance infused of difference

sICr-EDTA Rumen 33·2±1·87 30·7 ±2·09 Omasum 2·2±0·17 1·4±0·17 P<0·05 Abomasum (A) 2·3±0·38 3·3±0·52 Small intestine (SI) 8·4±0·28 9·6±0·88 Caecum (CPC) 28·7± 3·04 38·3 ±2· 97 P=0·054 Distal large intestine 25·3 ±2·12 16·8± 1·41 P

infusion increased marker MRT's in the abomasum and tended to reduce them in the omasum and rumen, the effect in the rumen again being the most variable and not attaining statistical significance (P > 0·05). Digesta were retained for longer time periods in all five segments of the small intestine and in the caecum of somatostatin-infused compared with control ewes (Table 5). Conversely, somatostatin infusion reduced the MRT of digesta in all four segments of the large intestine. When expressed as a proportion of the total MRT for each marker (Table 6), somatostatin infusion increased the time spent in the region of the GI tract comprising the abomasum + small intestine + caecum, with the increase occurring in all three segments for all three markers. The infusion also decreased the proportion of the total MRT spent in the large intestine and in the rumen + omasum, with the large intestine showing the greatest reduction for 5 JCr-EDTA, the rumen showing the greatest reduction for lignin and both segments showing intermediate and similar reductions for 103Ru-phen.

12

10

4

2

0·083 0·058 o ~I --~--~'~~I~~I __~' __-L __ ~I __~' ~-LI~~I 2 3, 4 5,. r 1'-..----' 2T ermma . I r f Small intestine SP~ Abomasum Caecum Colon Rectum

Fig. 1. Estimated water flow (iitres per day) through sections of the gastro­ intestinal tract from the abomasum to the rectum (mean values ± s.e.m.). 0--0 Control ewes. 0 - - - - 0 Somatostatin-infused ewes. Statistical levels of probability of the difference between treatments are given above the abscissa. Net Water Exchanges along the OJ Tract Water flow through the mid and distal segments of the small intestine was reduced by somatostatin infusion (Fig. 1), indicating greater absorption in association with the increase in MRT. Control ewes Significance of Somatostatin­ treatment difference infused ewes

.j>. o (*) o 3·1 ±0·44 2·0 ± 0·33 Total water intake

13.2 ± 0. 171 13-5±0. 311 Rumen

3·7 ± 0·57 5·8±0·58 Net water balance 6.8±0.16 (*) 7.8±0·44 Water outflow ~ ~

Omasum ---{ 2.6 ± 0·21 ....------+- -+------•. 2·9 ± 0·26 Apparent water absorption

Water flow through omasum

4·2 ± 0·21 (*) 4·9 ± 0·25

Abomasum 4·0 ± 1·40 ----If--- I 3·0 ± 0·43 Apparent endogenous secretion 10.25 ± 0.0501 rlo-."-39:--±-'-0-.0-9-'41

8.2±1~ ~±0.63 Water outflow

Small intestine { ~~ 2.7±0·09 * 2.3±0.16 Segment 5 small intestine water flow Caecum [0.52" ±o.o431*!0.74 ± 0.0701

1·4 ± 0·16 ....----1--- (*) --+----.~1·0 ± 0·13 Apparent water absorption ;-l Caecal water outflow "±~ ~O" :z t:O

~ '< ~ Fig. 2. Water flows (litres per day) into and out of the rumen, omasum, abomasum and caecum-proximal colon (mean ± s.e.) for control and somatostatin infused ,.... ewes. Rumen water balance = rumen outflow - total water intake = salivary secretion + net inflow of water across rumen wall. Apparent abomasal endogenous '" secretion = abomasal water outflow - omasal water flow. Values in boxes refer to pool sizes (litres). (*)P < 0·10. * P < 0·05. Somatostatin and Gut Function in Sheep 401

Water flows into and out of the rumen, omasum, abomasum and caecum are shown in Fig. 2. Somatostatin infusion increased water pool size in the abomasum, increased water outflow from the rumen and through the omasum by approximately 1 litre per day, and decreased apparent endogenous secretion into the abomasum by approximately 1 litre per day. The infusion decreased voluntary water consumption and, consequently, rumen net water balance was approximately 2 litres per day greater for somatostatin­ infused than for control ewes. In the caecum, somatostatin infusion increased water pool size, slightly reduced the rates of both water inflow and apparent absorption and had no effect on the rate of water outflow.

Discussion The low dose of somatostatin infused was effective in raising its concentration in plasma within the physiological range, with plasma somatostatin concentration in infused ewes (76 ng/l) being below the maximum concentration (120 ng/l) found by Barry et al. (1982) with growing lambs fed fresh forage ad libitum. Both groups of samples were assayed using the same procedures in the same laboratory. Raising circulating somatostatin concentration in this manner reduced prolactin secretion; it had no effect on thyroid stimulating hormone concentrations but depressed those of thyroxine, a finding for which no explanation can be found. The failure of somatostatin infusion to reduce plasma growth hormone concentration was unexpected in view of the known effect of somatostatin in suppressing growth hormone secretion (Brazeau et al. 1973). Growth hormone is released in a pulsatile manner and it is possible that the infusion may have altered peak frequency and peak height; such an effect would not have been detected with the sampling routine used in this study. It should be noted that acute but transient effects on hormone concentrations would not have been detected because this experiment was designed to examine chronic changes. Ishida et al. (1980) reported that somatostatin infusion inhibited pancreatic secretion and reduced plasma concentrations of insulin and glucagon. By contrast, no such effect was observed in the present experiment. However, the infusion rate used by Ishida et al. (1980) was over 50 times greater than that used here. Thus it would seem that insulin and glucagon concentrations are not affected by variations in somatostatin concentrations within the physiological range. Somatostatin infusion did not affect the wet tissue weights of the rumen and omasum. However, the weights of all GI tract segments distal to this region were reduced by the infusion and this was associated with increased accumulation of digesta in the abomasum and caecum. Using an immunoreactive staining technique, Reynolds et al. (1983) found the greatest concentration of somatostatin-secreting D cells in the abomasum and of 6-months-old sheep, with smaller concentrations in the and caecum. It therefore seems that the primary effect of the somatostatin infusion was to increase digesta content and hence MRT in those segments of the GI tract where somatostatin-secreting D cells occur. It is further proposed by us that secondary compensatory effects occurred in the rumen and the distal large intestine which tended to maintain the MRT for the whole GI tract constant. These effects include a reduction in MRT in all segments of the large intestine (Table 5) and a reduction in rumen MRT, with the latter being best indicated by the lignin MRT, which represents the particulate matter (Table 6). The nature of such compensatory mechanisms is not known. 402 T. N. Barry et at.

The differential effects of somatostatin on water flow may be explained if the primary action of somatostatin was to reduce apparent endogenous secretion into the abomasum and the animal compensated to maintain water flow from the abomasum at approximately 8 litres per day by increasing water flow from the rumen and through the omasum into the abomasum. The decrease in voluntary water intake could be seen as part of this compensatory mechanism. Thus the required increase in water flow from the rumen would be achieved as a balance between changes in intake, saliva flow and diffusion into the rumen. It is not known whether the differences in digesta MRT and GI tract water flow between control and somatostatin-infused ewes were due to a direct action of somatostatin on tissues of the GI tract, or to somatostatin affecting the concentration of other hormones that are trophic to the GI tract, or to a combination of both mechanisms. Enteroglucagon (Bloom and Polak 1981; AI-Mukhtar et al. 1981) and gastrin (Johnson 1976) have both been proposed as trophic to gut mucosa and could potentially be involved in any mechanism that increased MRT in the region from the abomasum to the caecum. As somatostatin infusion did not depress plasma concentration of either of these hormones, it is likely that effects upon MRT observed in the present study were due to direct action of somatostatin upon gut tissue. Reynolds (1982) observed an increase in plasma gastrin concentration accompanying the compensatory hypertrophy of the abomasum and small intestine (but not rumen) which occurred in response to infection with gut parasites in the sheep. The increase in plasma gastrin concentration observed in the present study may represent a similar compensatory mechanism to the effects of somatostatin upon the gut. Under normal circumstances, increases in digesta MRT in a particular organ imply increased opportunity for absorption from that organ. However, Schusdziarra et al. (1979) found that somatostatin infused intravenously at 2·3 ng min -I kg -I reduced the rate of absorption of triglycerides and xylose from the GI tract of the dog and they proposed that the postprandial rise in somatostatin concentration served to regulate the rate of nutrient absorption. On this basis, no conclusions can be drawn from the present study on the effect of somatostatin on nutrient absorption in the sheep other than that water absorption from the small intestine tended to increase in association with the longer MRT. Utilization of absorbed nutrients is likely to change if there are major changes to the . In both the present study (Table 1) and that of Schusdziarra et al. (1979), manipulation of somatostatin concentrations within the physiological range did not affect plasma concentrations of insulin or glucagon. Brockman (1979) and Brockman and Greer (1980) infused larger amounts of somatostatin (30 ng min -I kg-I) into sheep and found that, although plasma glucagon concentration was depressed, glucose concentration and irreversible loss were only marginally reduced. The present results are consistent with these findings. If compensatory mechanisms do exist within the GI tract as postulated here, it would be expected that infusion of somatostatin into sheep offered their diet to appetite would reduce voluntary feed consumption. Such a response would implicate somatostatin in the feedback control of appetite.

Acknowledgments We thank Mr J. Rawlinson for skilled technical assistance, Miss G. Caughey for performing the digesta and faecal lignin analyses, Dr G. W. Reynolds for arranging the gastrin assays and Mr A. L. Wallace for the thyroid stimulating hormone assays. ------.-----.,-----.---.------,~'"

Somatostatin and Gut Function in Sheep 403

References AI-Mukhtar, M. Y. T., et al. (1981). The relationship between endogenous gastro-intestinal hormones and cell proliferation in models of adaptation. In 'Mechanisms of Intestinal Adaptation'. (Eds J. W. L. Robinson, R. H. Dowling and E. O. Reichen.) pp. 243-55. (MTP Press: Lancaster, U.K.) Bailey, R. W. (1967). Quantitative studies on ruminant . II. Loss of ingested plant carbohydrates from the reticulo-rumen. N.Z. J. Agric. Res. 10, 15-32. Barry, T. N., Manley, T. R., Redekopp, c., Davis, S. R., Fairclough, R. J., and Lapwood, K. R. (1982). Protein metabolism in growing lambs given fresh ryegrass-clover ad libitum. 2. Endocrine changes, glucose production, and their relationship to protein deposition and to the partition of absorbed nutrients. Br. J. Nutr. 47, 319-29. Bloom, S. R., and Polak, J. M. (1981). Enteroglucagon and the gut hormone profile of intestinal adaptation. In 'Mechanisms of Intestinal Adaptation'. (Eds J. W. L. Robinson, R. H. Dowling, and E. O. Riechen.) pp. 189-99 .. (MTP Press: Lancaster, U.K.) Brazeau, P., et al. (1973). Hypothalamic polypeptide that inhibits the secretion of immunoreactive growth hormone. Science (Wash. U.S.A.) 179, 77-9. Brockman, R. P. (1979). Effect of somatostatin suppression of glucagon secretion on glucose production in sheep. Can. J. Physiol. Pharmacol. 57, 848-52. Brockman, R. P., and Greer, C. (1980). Utilisation of [2J4C]propionate on glucose production in vivo in sheep. Aust. J. BioI. Sci. 33, 457-64. Downes, A. M., and McDonald, I. W. (1964). The chromium-51 complex of ethylene-diamine tetra-acetic acid as a soluble rumen marker. Br. J. Nutr. 18, 153-62. Faichney, G. J. (1975a). The use of markers to partition digestion within the gastro-intestinal tract of ruminants. In 'Digestion and Metabolism in the Ruminant'. (Eds I. W. McDonald and A. C. I. Warner.) pp. 277-91. (University of New England Press: Armidale, N.S.W.) Faichney, G. J. (1975b). The effect of formaldehyde treatment of a concentrate diet on the passage of solute and particle markers through the gastro-intestinal tract of sheep. Aust. J. Agric. Res. 26, 319-27. Faichney, G. J. (1980). Measurement in sheep of the quantity and composition of rumen digesta and of the fractional outflow rates of digesta constituents. Aust. J. Agric. Res. 31, 1129-37. Faichney, G. J., and Colebrook, W. F. (1979). A simple technique to establish a self-retaining rumen catheter suitable for long term infusions. Res. Vet. Sci. 26, 385-6. Faichney, G. J., and White, G. A. (1983). 'Methods for the Analysis of Feeds Eaten by Ruminants.' (CSIRO: Melbourne.) Hopkins, P. S., Wallace, A. L. c., and Thorburn, G. D. (1975). Thyrotrophin concentrations in the plasma of cattle, sheep and foetal lambs as measured by radioimmunoassay. J. Endocrinol. 64, 371-87. Ishida, T., R6jdmark, S., Bloom, G., Chou, M. C. Y., and Field, J. B. (1980). The effect of somatostatin on the hepatic extraction of insulin and glucagon in the anaesthetiZed dog. Endocrinology 106, 220-30. Johnson, L. R. (1976). The trophic action of gastrointestinal hormones. Gastroenterology 70, 278-88. Patterson, D. S. P. (1963). Some observations on the estimation of non-esterified fatty acid concentrations in cow and sheep plasma. Res. Vet. Sci. 4, 230-7. Reynolds, G. W. (1982). Gastrin and gastric secretions in the sheep. Ph.D. Thesis, University of Melbourne. Reynolds, G. W., Gurnsey, M., and Birtles, M. (1983). Somatostatin immunoreactive cells in the digestive tract of the sheep. In 'Proceedings of the International Union of Physiological Sciences'. Vol. XV. (Eds D. F. Davey and R. A. L. Dampney.) p. 407. Reynolds, G. W., Hansky, J., and Titchen, D. A. (1984). Immunoreactive gastrin concentrations in gastrointestinal tissues of sheep. Res. Vet. Sci. 37, 172-4. Schusdziarra, V., Harris, V., Arimura, A., and Unger, R. H. (1979). Evidence for a role of splanchnic somatostatin in the homeostasis of ingested nutrients. Endocrinology 104, 1705-7. Tan, T. N., Weston, R. H., and Hogan, J. P. (1971). Use of J03Ru-Iabelled tris-(I,IO-phenanthroline)­ ruthenium(lI)chloride as a marker in digestion studies with sheep. Int. J. Appl. Radiat. Isotopes 22, 301-8. Trinder, P. (1969). Determination of glucose in blood using glucose oxidase with an alternative oxygen acceptor. Ann. CUn. Biochem. 6, 24-7. Vale, W., et al. (1975). Somatostatin. Recent Prog. Horm. Res. 31, 365-92.

Manuscript received 6 May 1985, accepted 27 September 1985