Effect of implantation on the seasonal variation of FSH secretion in the male blue fox (Alopex lagopus) M. Mondain-Monval, A. J. Smith, P. Simon, O. M. M\l=o/\ller,R. Scholler and A. S. McNeilly Fondation de Recherche en Hormonologie, 67-77 bd Pasteur, 94260 Fresnes, France; *Research Farm for Furbearing Animais, Rustadveien 131, 1380 Heggedal,- Norway; and fM.R.C. Unit of Reproductive Biology, Centre for Reproductive Biology, 37 Chalmers Street, Edinburgh EH3 9EW, U.K.

Summary. A heterologous radioimmunoassay system developed for the was shown to measure FSH in the plasma of the blue fox. FSH concentrations throughout the year showed a circannual rhythm with the highest values (61 \m=.\6\m=+-\14\m=.\8ng/ml) occurring shortly before or at the onset of the mating season, a pattern similar to that of LH. The concentration of FSH then declined when androgen concentrations and testicular development were maximal at the time of the mating season (March to May). Thereafter, concentrations remained low (25\m=.\2\m=+-\4\m=.\1ng/ml) in contrast to those ofLH. Implantation of melatonin in August and in February maintained high plasma values of FSH after the mating season (142\m=.\3\m=+-\16\m=.\5ng/ml) in association with a maintenance of testicular development and of the winter coat. The spring rise of prolactin was suppressed by melatonin treatment. The release of FSH after LHRH injection was also increased during this post-mating period in melatonin-treated animals, in contrast to the response of the control animals which remained low or undetectable. These results suggest that changes both in the secretions of FSH and prolactin may be involved in the prolongation of testicular activity and in the suppression of the spring moult after melatonin administration. Keywords: blue fox; FSH; melatonin; LHRH; seasonal cycle

Introduction

The male blue fox is a seasonal breeder and is only sexually active for about 6 weeks in March-April, when daylength is increasing. Testicular activity varies dramatically during the year. Testicular redevelopment begins some 5-6 months before the mating season and the testes show maximal activity in March (Smith et al., 1984, 1986). Furthermore, marked seasonal changes occur in a range of plasma , including prolactin secretion which is highest during long days (May- July) as the testes regress (Smith et al., 1985). Seasonal variations of LH are masked by the episodic nature of its release, but marked changes in basal concentrations and in the effect of LHRH stimulation on plasma testosterone have been recorded (Smith et ai, 1985, 1987a). Changes in photoperiod exert a regulatory role on the gonads via the hypothalamic-pituitary axis. In the fox, melatonin has been shown to play a role in the control of the breeding season and the moulting cycle: melatonin administration delays testicular regression and the spring moult. These effects were associated with a reduction in prolactin secretion (Smith et al., 1987a). More direct evidence for the role of prolactin in the furring cycle and testicular development has also been obtained in males treated with bromocriptine (Smith et al., 1987b). Melatonin administration did not alter LH release, but caused a prolongation of testosterone production after the mating season.

Downloaded from Bioscientifica.com at 09/28/2021 08:54:42AM via free access In addition, spermatogenesis was maintained, which might indicate an effect of melatonin on FSH secretion since FSH is known to regulate testicular growth and spermatogenesis. Melatonin admin¬ istration affects FSH secretion and hence testicular activity differently in short-day breeders such as the ram (Lincoln & Ebling, 1985) and long-day breeders such as the (Turek et al., 1975). The blue fox, which is fertile in the spring, may be considered to be a short-day breeder since both short photoperiod and melatonin administration support reproductive activity (Smith et al., 1984, 1987a). Although testicular FSH binding has been measured (Anderson et al., 1981; Smith et al., 1985), no data are available for the annual changes in plasma FSH secretion in blue foxes and the specific effect of melatonin implantation on FSH concentrations. The aims of the present study were to validate the assay for FSH and to determine whether photoperiod is involved in the control of FSH secretion. We have studied the annual variations in plasma FSH concentrations and the temporal relationship between FSH secretion and the pattern of secretion of other hormones (LH, prolactin, androgens) which we have previously described (Smith et al., 1985). In addition, we have investigated whether melatonin, in inducing the effects of short daylength, acts on the testis through modification of plasma FSH concentrations, including the FSH response to LHRH.

Materials and Methods

Animals and sampling The 15 male foxes used in this study were 1^1 years old. They were individually housed under natural conditions of daylength and temperature during the investigation on the Research Farm for Furbearing Animals, Heggedal, Norway. They were given a ration ofNorwegian wet feed and water ad libitum. The males were within visual and olfactory contact of vixens on the farm but none of them was allowed sexual contact during the study period. The mating seasons during the study were defined as the periods between the first and the last mating on the farm. To determine the annual changes in FSH concentrations, 6 intact males were bled twice a month from September until October the following year. In addition, 9 foxes were used to determine the role of melatonin on plasma FSH concentrations: 5 males served as controls and 4 received a 24 mg implant in August, a further 36 mg in February and 200 mg in March. Blood samples were taken 1-3 times each week. The two implants with a low dose of melatonin (Sigma Chemical Company, St Louis, MO, U.S.A.) consisted of Silastic cylinders (approximate length 9 mm; diameter 2 mm; surface area 65 mm2: United Veterinary Laboratories, Middleton, Wl, U.S.A.). The implants with a high dose of melatonin consisted of sealed envelopes of 0005 in Silastic sheeting (500-1 Dow Corning, Midland, MI, U.S.A.; total diffusion area approximately 4 cm2). After implantation of 24 mg and 36 mg melatonin, plasma levels rose rapidly to reach 170-308 and 685- 1248 pg/ml respectively, 4-7 days later, and then declined, while the 200 mg implants maintained plasma levels around 800 pg/ml for 5 months. Further details of the melatonin implants have been described previously (Smith et ai, 1987a). Furthermore, to test the effect of melatonin on the pituitary and testicular response to LHRH, 4 controls and the 4 foxes implanted with melatonin received an injection of 1 µg LHRH (Nialutin: Novo Industry, Oslo, Norway) on 8 occasions. Blood samples were taken 7 times at 20-min intervals. The LHRH injection was given immediately after the second blood sample. For FSH analysis, the two samples before injection were pooled. Blood samples were collected between 09:00 and 12:00 h without anaesthesia from the cephalic vein into heparinized tubes. Plasma was separated by centrifugation and was stored at 20°C until assayed.

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FSH assay Fox FSH was measured using a heterologous double-antibody radioimmunoassay as described previously for the sheep (McNeilly et al., 1976) with minor modifications. Assay procedure. Ovine FSH (LER-1976-A2) donated by Dr L. E. Reichert was radioiodinated using the lactoper- oxidase method of Holohan et al. (1973). Iodinated FSH was separated from free iodine by gel filtration and purified as described by Winter et al. (1982). The assay for fox FSH utilized a rabbit anti-human FSH antiserum (M 91/1) and a purified dog FSH preparation (LER-1685-3A) donated by Dr L. E. Reichert as reference standard. All dilutions were made in 0075 M-sodium phosphate buffer, pH 7-4, containing 015 M-NaCl and 1% BSA. The incubation mixture consisted of reference prep¬ arations (150 µ ) or samples (150 µ ) to be assayed, buffer (150 µ ) and antiserum (50 µ at an initial dilution of 1:2750). After 24 h incubation at 4°C, 125I-labelled ovine FSH (15 000c.p.m. in 50 µ ) was added. The mixture was then incubated at 4°C for a further 48 h. Donkey anti-rabbit gamma globulin (Wellcome, Beckenham, U.K.; 100µ 3 1:12 dilution) and normal rabbit serum (100 µ at 1:100 dilution) were then added and incubation continued at 4°C for 24 h

Downloaded from Bioscientifica.com at 09/28/2021 08:54:42AM via free access before separation of bound and free by centrifugation. The antibody-bound iodinated FSH in the precipitate was measured using an automatic gamma counter (Berthold, Wildbad, West Germany). Computation of potencies for the FSH assay was performed using a computer data processing program. Assay characteristics. The antiserum was as characterized by McNeilly el al. (1976) and cross-reacts with FSH from several mammalian species. Specificity was confirmed by testing the inhibition curve with dog LH (LER 1685-1). Parallelism in the displacement curves caused by dog FSH and dilutions of fox pituitary extract or plasma samples from castrated foxes was tested by comparing the slopes of the straight line (obtained by logit-log transformation) using Student's t test. The accuracy of the assay was determined by the measurement ofknown amounts ofdog FSH or diluted fox pituitary extracts added to fox plasma containing low amounts of FSH. The detection limit was defined as the minimum concentration of dog FSH capable of causing a significant displacement (P < 005) of radiolabelled FSH from the antiserum. The precision was assessed by the repeated assay of 3 pools of plasma. Presentation of results. Because of a lack of purified fox FSH, a highly purified dog FSH preparation was used as standard. The FSH values were expressed in ng LER-1685-3A equivalents/ml plasma. Plasma samples and reference preparations were measured in duplicate. Measurements of LH, prolactin and testosterone. LH, prolactin and testosterone concentrations were measured using specific radioimmunoassays previously described and validated for use in the blue fox (LH and testosterone: Meiler et ai, 1984; prolactin: Mondain-Monval et ai, 1985). The sensitivity was 0-4 ng/ml for LH, 2 ng/ml for prolactin and 20 pg/ml for testosterone. Intra- and inter-assay coefficients of variation were, respectively, 20 and 4-9% for LH, 81 and 13-9% for prolactin and 4-9 and 11 -7% for testosterone. Statistical analysis. All concentrations are reported as mean + s.e.m. For statistical evaluations, the data were analysed by the Student's / test. Comparisons between groups were made by analysis of variance in combination with Duncan's test. The data were transformed where necessary to give normal distribution.

Results

Validation of the FSH assay Specificity. The method proved to be specific for fox FSH. The binding of 125I-labelled FSH to antiserum M 91/1 was displaced in a parallel manner by crude pituitary homogenates and purified dog FSH (Fig. 1). The slopes of the straight line for the blue fox pituitary extract (b = —1-33) and for dog FSH (b = —1-38) were not significantly different. Serial dilutions of plasma from a castrated male and an ovariectomized female were parallel to the inhibition curves obtained with pituitary extract and dog FSH (Fig. 1). Binding was not affected by large doses of dog LH (10, 50, 100 ng) (Fig. 1). Furthermore, high concentrations of LH in plasma from 4 males injected with LHRH before the mating season or before puberty did not affect FSH values which remained undetectable. In contrast, all the foxes showed an increase in FSH concentration after ovariectomy or castration (Fig. 2). Accuracy. The recoveries of known amounts of dog FSH (16-2048 ng) added to plasma from foxes during anoestrus and previously assayed at <20 ng/ml were 98T ± 4-4% (n = 28). Sensitivity and precision. Under routine conditions the assay was sensitive to 20-30 ng/ml plasma. The proportion of total radioactivity bound by the antiserum in the absence of hormone ranged from 15 to 25%. The intra- and inter-assay coefficients of variation for assays run at 70, 130 or 540 ng/ml (n = 7) were, respectively, 60 and 10-6%, 5-2 and 7-7%, and 3-8 and 4-6%.

Annual pattern of plasma FSH secretion and temporal relationship with patterns of plasma LH, androgen andprolactin secretion

As shown in Fig. 3, FSH concentrations which are low from August to November (25-8 + 3-9 ng/ml) were significantly increased (P < 005) during December to March (61-6 ± 14-8 ng/ml) in association with the onset of spermatogenesis, reaching peak levels shortly before or at the onset of the mating season (range 31-5-151-3 ng/ml). They then declined (P < 0-05) (25-2 ± 4-1 ng/ml) during March when androgen concentrations reached their maximum values. The FSH profile up until March paralleled that of LH. Thereafter, FSH concentrations remained low while LH values

Downloaded from Bioscientifica.com at 09/28/2021 08:54:42AM via free access Dog LH (ng/ml) Dilutions of plasma

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1/2560 1/640 1/160 1/40 Dilutions of pituitary extract Fig. 1. Inhibition curves for dog FSH (LER 1685-3A) prepared in assay buffer with (·--·) and without (·—·) 150 µ blue fox plasma, dog LH (LER 1685-1) ( ) and dose-response curves for dilutions of pituitary extract (O) and for dilutions of plasma from a castrated blue

increased again when the androgens had returned to basal levels at the time of the spring rise in prolactin (May-June). Plasma LH concentrations on 6 April and from August to December were significantly (P < 005) lower than those observed at other times of the year (1-2 ± 0-4 vs 7-2 + 1-4 ng/ml).

Effect of melatonin implantation on the seasonal changes in FSH secretion

In melatonin-implanted foxes, as in the control animals, plasma FSH concentrations were low or undetectable from August to November (Fig. 4) (22-9 +11 and 24-4 ± 3-6 ng/ml). Concentrations of FSH increased significantly (P < 0-05) by November in the treated animals (57-2 ±111 ng/ml) and by December (89-3 ± 34-4 ng/ml) in the control group and remained high thereafter. At the end of February, when FSH concentrations began to decrease in the control group, a further implantation of melatonin on 21 February and 14 March maintained higher levels of FSH until the end of the experiment in August: from 4 March, mean concentrations of FSH were significantly (P < 001) different from those of the controls (142-3 + 16-5 ví 32-8 ± 110 ng/ml). As previously described (Smith et al., 1987c), the spring rise of prolactin was suppressed in treated foxes while testosterone production was maintained longer than in the control animals.

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— — 10 20 30 40 -20 0 20 40 60 80 100 -r— — — -10 0 10 20 30 4 Days after gonadectomy Min. after LHRH Fig. 2. Plasma FSH ( , ) and LH (·, ) concentrations in (a) a castrated male and an ovariectomized female; and (b) in 2 male blue foxes after an i.v. injection of 1 pg LHRH before the mating season and before puberty.

Effect of melatonin on the FSH response to LHRH injection The pattern of FSH release during the 100 min after LHRH injection at 8 times of the year for control and melatonin-treated animals is shown in Fig. 5. The release of FSH after LHRH remained low or even undetectable in the intact foxes on all injection dates. A significant release was observed in animals from the treated group (P < 005) (N = 4) during the period when testicular activity was recorded at the time when endogenous FSH secretion was also elevated: in 2 foxes on 11 April, in 3 foxes on 27 June and in the 4 foxes on 4 June and 8 August. The baseline level of FSH increased dramatically in treated foxes compared to control animals from April to August (153-6 ± 20-9 vs 33-7 ± 17-4 ng/ml).

Discussion

We have shown that the heterologous radioimmunoassay system developed by McNeilly etal.(\916) for the sheep and suitable for several mammalian species including the dog (Winter et ai, 1982) can also be used to measure FSH in plasma from the blue fox. Increasing quantities of fox plasma or fox pituitary tissue gave dose-response curves that were parallel to the dog FSH curve. The absence of cross-reactivity with LH was demonstrated by the fact that binding was not affected by the dosage of

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SONDJ F M A M J JASO Fig. 3. Mean ( +s.e.m.) plasma concentrations of FSH, LH, androgens and prolactin in 6 untreated male blue foxes during the annual cycle. MS = mating season. dog LH. In addition, injection of LHRH, which always stimulates LH release, did not affect FSH levels: concentrations of LH could be high when those of FSH were low or undetectable. Sensitivity, intra- and interassay variabilities and accuracy of the FSH assay were similar to those described for a similar assay in the dog (Reimers et ai, 1978; Winter et ai, 1982). Plasma FSH concentrations in the male blue fox varied during the year. Baseline levels were very low or undetectable from August onwards. From December, a rise in FSH concentrations was seen in association with testicular redevelopment, initiation of spermatogenesis and increasing levels of LH (Smith et ai, 1984). The relationship between the annual cycle of FSH, testicular activity and photoperiod varies between species. In the Soay ram (Lincoln & Davidson, 1977; Lincoln, 1978) and in the white-tailed deer (Mirarchi et ai, 1978) FSH concentrations increase with testicular redevelopment during the summer. In the roe deer (Schams & Barth, 1982), high FSH values were recorded during spring. In contrast to these seasonal breeders, FSH and LH secretion in the blue fox decrease simul¬ taneously before or at the onset of breeding season when testicular size and testosterone release are

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Aug. Sep. Oct Nov. Dec. Jan. Feb. Mar. Apr. May Fig. 4. Seasonal variations of plasma FSH in 5 controls and 4 melatonin-implanted male blue foxes. MS = mating season. The arrows indicate the dates of melatonin administration and the numbers indicate the dose of melatonin administered.

maximal. This indicates that both gonadotrophins are regulated by a similar feedback mechanism and that the high concentrations of testosterone recorded in March probably induce the rapid decline of FSH and LH seen at that time. After the mating season, as daylength increases, the testes regress and the reduced secretion of FSH is associated with an increased secretion of LH, suggesting separate modulation of FSH secretion by factors such as inhibin or steroids. In the ram, a change in the amplitude of the episodic secretion of LH has been described during the period of testicular regression (Lincoln, 1978), while FSH secretion is more stable due to the relatively slower clearance rate of FSH from the blood (Lincoln et ai, 1977). Changes in photoperiod have central effects on the , regulating the release of LHRH which can be further modified by gonadal steroids. The change in the pattern of LHRH secretion can alter the gonadotroph response and produce the differential release of LH and FSH (Lincoln & Short, 1980). This discrepancy between the profiles of the two gonadotrophins after the mating season may be related to a difference in pituitary responsiveness to LHRH. In contrast to LH, no clear-cut pattern of FSH release could be detected after the injection of LHRH at any time of the year. This has also been observed in the prepubertal male blue fox (Smith et ai, 1987b). A difference in timing of the FSH response has been observed in the ram (Lincoln, 1978) and the ferret (Donovan & ter Haar, 1977). This also suggests that the biologically active form of FSH may be different from that which is immunologically reactive in our radioimmunoassay. The pituitary is known to be able to respond to the surrounding endocrine environment by altering not only the quantity but also the type of FSH released (Kennedy & Chappel, 1985; Ulloa-Aguirre et ai, 1986). Photoperiod influences the seasonal changes in gonadotrophin secretion. Melatonin adminis¬ tration can mimic effectively short daylength in many species, resulting in profound changes in both the testicular and furring cycles in the mink (Allain et ai, 1981), weasel (Rust & Meyer, 1969), Djungarian hamster (Hoffmann, 1973), white-footed mouse (Lynch & Epstein, 1976), ram (Lincoln & Ebling, 1985) and blue fox (Smith et ai, 1987a). In the fox, implantation of melatonin in late summer induces a significant increase in the concentrations of melatonin in August and of FSH in

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18 Sep. 19 Oct. 20 Dec. 11 Apr. 4 Jun. 8 Aug. Fig. 5. Seasonal changes in FSH response to LHRH (means + s.e.m.) in 4 control and 4 melatonin-implanted foxes. The sampling dates are given below the figures. Samples were taken at 20-min intervals. Arrows indicate timing of LHRH injection.

November, but this could not be related to the presence of more advanced cell types in the testis or to a modification of the furring cycle (Smith et ai, 1987a). Implantation of melatonin in the winter (February-March), which depressed plasma prolactin concentrations and delayed the spring moult and testicular regression, also induced important changes in plasma FSH concentrations. An increased FSH secretion was correlated to the mainten¬ ance of testis size, spermatogenesis and testosterone secretion after the mating season. In contrast, as in the white-tailed deer (Bubenik et ai, 1986), no modification of the LH pattern was observed (Smith et ai, 1987a). The effect on FSH secretion agrees with results for pinealectomized sheep (Barrell et ai, 1985), for melatonin-implanted Soay rams (Lincoln & Ebling, 1985) and for melatonin- fed white-tailed deer (Bubenik et ai, 1986), which demonstrated that the effects of photoperiod mediated via the pineal directly involve FSH secretion. Although baseline values of FSH were higher during melatonin treatment from April, the response to LHRH injection was variable. Nevertheless, FSH release increased on several occasions between April and August, while that of LH remained unchanged compared to the controls (Smith et al., 1987a). This may suggest that melatonin interacts with the gonadotroph cells to increase the pituitary response to LHRH. Furthermore, the fact that plasma concentrations of FSH remained elevated during melatonin treatment while prolactin concentrations are depressed suggests that prolactin may mediate the effects of melatonin on gonadotrophins and thereby influence gonadotrophin release. High concen¬ trations of prolactin have been shown to inhibit testicular activity in the ram and a relationship was

Downloaded from Bioscientifica.com at 09/28/2021 08:54:42AM via free access established between continued depressed concentrations of prolactin and continued elevated concentrations of FSH for maintenance of testicular activity (Langford & Labrie, 1986). In the fox, there may therefore be a direct effect of melatonin on FSH secretion leading to testicular redevelopment and a simultaneous effect on prolactin concentrations leading to the effects seen on the moulting cycle. The changes in the secretion of both FSH and prolactin may be involved in the prolongation of testicular activity after the mating season observed after melatonin administration.

We thank Dr Gerald Lincoln and Fran Ebling (MRC Reproductive Biology Unit, Edinburgh, U.K.) for valuable help with the design of the melatonin implants; Professor Leo E. Reichert for the ovine and dog FSH and LH; and Professor G. D. Niswender for the LH antiserum.

References

Allaln, D., Martinet, L. & Rougeot, J. (1981) Effect cycle of rams, and the influence of photoperiod. J. of melatonin implants on changes in the coat, Reprod. Fert. 11, 337-349. plasma prolactin and testis cycle in the mink (Mustela Lincoln, G. A. & Ebling, F.J.P. (1985) Effect of constant- vison). In Pholoperiodism and Reproduction in Ver¬ release implants of melatonin on seasonal cycles in tebrates, pp. 263-271. Eds R. Ortavant, J. Pelletier reproduction, prolactin secretion and moulting in & J. P. Ravault. INRA Services Publications, rams. J. Reprod. Fert. 73, 241-253. Versailles. Lincoln, G.A. & Short, R.V. (1980) Seasonal breeding: Andersen, K., Sundby, A. & Hansson, V. (1981) Fine Nature's contraceptive. Recent Prog. Horm. Res. 36, structure and FSH binding of Sertoli cells in the blue 1-52. fox (Alopex lagopus) in different stages of reproductive Lincoln, G.A., Peet, M.J. & Cunningham, R.A. (1977) activity. Int. J. Androl. 4, 570-581. Seasonal and circadian changes in the episodic release Barrell, G.K., Lapwood, K.R. & Elgar, H.J. (1985) of follicle-stimulating hormone, FSH secretion in pinealectomized rams subjected to and testosterone in rams exposed to artificial photo- artificial photoperiods. J. Endocr. 106, 167-171. periods. J. Endocr. 11, 337-349. Bubenik, G.A., Smith, P.S. & Schams, D. (1986) The Lynch, G.R. & Epstein, A.L. (1976) Melatonin induced effect of orally administered melatonin on the season¬ changes in gonads, pelage and thermogenesis charac¬ ally of deer pelage exchange, antler development, teristics in the white-footed mouse (Peromyscus LH, FSH, prolactin, testosterone, T3, T4, cortisol leucopus). Comp. Biochem. Physiol. 53C, 67-68. and alkaline phosphatase. J. Pineal Res. 3, 331-349. McNeilly, J.R., McNeilly, A.S., Walton, J.S. & Donovan, B.T. & ter Haar, M.B. (1977) Effects of Cunningham, F.J. (1976) Development and appli¬ luteinizing hormone releasing hormone on plasma cation of a heterologous radioimmunoassay for ovine follicle-stimulating hormone and luteinizing hormone follicle-stimulating hormone. J. Endocr. 70, 69-79. levels in the ferret. J. Endocr. 73, 37-52. Mirarchi, R.E., Howland, B.E., Scanion, P.F., Hoffmann, K. (1973) The influence of photoperiod and Kirkpatrick, R.L. & Sanford, L.M. (1978) Seasonal melatonin on testis size, body weight and pelage colour variation in plasma LH, FSH, prolactin and testoster¬ in the Djungarian hamster (Phodopus sungorus). J. one concentrations in adult male white-tailed deer. comp. Physiol. 85, 267-282. Can. J. Zool. 56, 121-127. Holohan, K.N., Murphy, R.F., Buchanan, K.D. & Elmore, Meiler, O.M., Mondain-Monval, M., Smith, A.J., D.T. (1973) Enzymic iodination of polypeptide hor¬ Metzger, E. & Scholler, R. (1984) Temporal relation¬ mones for radioimmunoassay. Clin. chim. Acia 45, ships between hormonal concentrations and the 153-157. electrical resistance of the vaginal tract of blue foxes Kennedy, J. & Chappel, S. (1985) Direct pituitary effects (Alopex lagopus) at pro-oestrus. J. Reprod. Fert. 70, of testosterone and luteinizing hormone-releasing 15-24. hormone upon follicle-stimulating hormone: analysis Mondain-Monval, M., Meiler, O.M., Smith, A.J., by radioimmuno- and radioreceptor assay. Endocrin¬ McNeilly, A.S. & Scholler, R. (1985) Seasonal vari¬ ology 116, 741 -748. ations of plasma prolactin and LH concentrations in Langford, G.A. & Labrie, F. (1986) Photoperiod entrain- the female blue fox (Alopex lagopus). J. Reprod. Fert. ment of different LH, FSH and prolactin cycles in 74,439-448. ram in relation to testicular function. Biol. Reprod. Reimers, T.J., Phemister, R.D. & Niswender, G.D. 34, Suppl. l,p. 57, abstr. 16. (1978) Radioimmunological measurement of follicle- Lincoln, G.A. (1978) The temporal relationship between stimulating hormone and prolactin in the dog. Biol. plasma levels of FSH and LH in the ram. J. Reprod. Reprod. 19, 673-679. Fert. 53,31-37. Rust, CC. & Meyer, R.K. (1969) Hair color, molt and Lincoln, G.A. & Davidson, W. (1977) The relationship testis size in male, short-tailed weasels treated with between sexual and agressive behaviour and pituitary melatonin. Science, N.Y. 165, 921-922. and testicular activity during the seasonal sexual Schams, D. & Barth, D. (1982) Annual profiles of

Downloaded from Bioscientifica.com at 09/28/2021 08:54:42AM via free access reproductive hormones in peripheral plasma of the Scholler, R. (1987b) Sexual development in the imma¬ male roe deer (Capreolus capreolus). J. Reprod. Fert. ture male blue fox (Alopex lagopus), investigated by 66,463-468. testicular histology, DNA flow cytometry and Smith, A.J., Clausen, O.P.F., Kirkhus, B., Jahnsen, T., measurement of plasma LH, FSH, testosterone and Meiler, O.M. & Hansson, V. (1984) Seasonal changes soluble testicular Mn2 + -dependent adenylate cyclase in spermatogenesis in the blue fox (Alopex lagopus), activity. J. Reprod. Fert. 81, 505-515. quantified by DNA flow cytometry and measurement Smith, A.J., Mondain-Monval, \L, Simon, P., Andersen ofsoluble Mn2t -dependent adenylate cyclase activity. Berg, K., Clausen, O.P.F., Kirkhus, B., Hofmo, P.O., J. Reprod. Fert. 11, 453-461 Meiler, O.M. & Scholler, R. (1987c) Preliminary Smith, A.J., Mondain-Monval, M., Meiler, O.M., studies of the effects of bromocriptine on testicular Scholler, R. & Hansson, V. (1985) Seasonal variations regression and the spring moult in a seasonal breeder, of LH, prolactin, androstenedione, testosterone and the male blue fox (Alopex lagopus). J. Reprod. Fert. testicular FSH binding in the male blue fox (Alopex 81,517-524. lagopus). J. Reprod. Fert. 74, 449-458. Turek, F.W., Desjardins, C. & Menaker, M. (1975) Smith, A.J., Bugge, H.P., Andersen Berg, K., Meiler, O.M. Melatonin: antigonadal and progonadal effects in & Hansson, V. (1986) Seasonal changes in testicular male golden hamster. Science, N. Y. 190, 280-282. structure and function in the blue fox (Alopex lagopus), Ulloa-Aguirre, ., Mejia, J.J., Domínguez, R., Guevara- quantified by morphometrical analysis and adenylate Aguirre, J., Diaz-Sanchez, V. & Larrea, F. (1986) cyclase activity. Int. J. Androl. 9, 53-66. Microheterogeneity of anterior pituitary FSH in the Smith, A.J., Mondain-Monval, \L, Andersen Berg, K., male rat: isoelectric focusing pattern throughout Simon, P., Forsberg, M., Clausen, O.P.F., Hansen, T., sexual maturation. J. Endocr. 110, 539-549. Meiler, O.M. & Scholler, R. (1987a) Effects of mela¬ Winter, M., Pirmann, J., Falvo, R.E., Schanbacher, B.D. tonin Implantation on spermatogenesis, the moulting & Miller, J. (1982) Steroidal control of gonadotro¬ cycle and plasma concentrations of melatonin, LH, phin secretion in the orchidectomized dog. J. Reprod. prolactin and testosterone in the male blue fox Fert. 64, 449-455. (Alopex lagopus). J. Reprod. Fert. 79, 379-390. Smith, A.J., Mondain-Monval, M., Andersen Berg, K., Gordeladze, J.O., Clausen, O.P.F., Simon, P. & Received 16 September 1987

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