October, 1968] NUTRITION REVIEWS 313 cattle at the time of slaughter showed no other two stations, but the differences effect of rearing practice on protein, iron, were insignificant. For some reason, the thiamine, riboflavin, or nicotinic acid vitamin A supplement added to the content. The fat content of this muscle concentrate was not very stable. As a increased with the higher level of con- result, vitamin A was low in the livers, centrates and restricted rearing area. With especially at two of the stations. However, Downloaded from https://academic.oup.com/nutritionreviews/article/26/10/313/1832143 by guest on 27 September 2021 this went a reduction in the moisture the method of rearing had no effect on content. The most outstanding observation this level. This was also true of the pro- was that the thiamine content of this mus- tein, iron, thiamine, riboflavin, niacin, cle of the animals at one station, at which pyridoxine, vitamin BIZ. and folic acid the most intensive feeding method was concentrations in the liver. studied, was almost twice that of the ani- Results of these studies indicate that mals at the other two stations. This was the method of rearing sheep and beef also true for the superficial digital flexer cattle has no significant effect on the muscle. There were, however, no such nutrient content of the same muscles or differences for any of the other nutrients studied. of the livers. There are inherent differences Livers from the animals at the station in the amounts of certain vitamins in dif- where the muscles had a high concentra- ferent muscles within the same animal tion of thiamine had slightly more thiamine and for the same muscle from different than livers of animals from either of the breeds.

GLUCONEOGENESIS AND BOVINE KETOSIS

The concentmtion of glucogenic metabolites, including oraloacetate, in the liver of ketotic cows was found to be depressed; this is consistent with the hypothesis that an increased mte of gluconeogenesis, resulting in a decreased concentmtion of oxaloacetate, is an important cause of ketogenesis and thus of ketosis.

Bovine ketosis is an important problem, presence of glucose and insulin (J. R. Wil- particularly in lactating cows during the liamson and H. A. Krebs, Biochem. J. 80, early part of the lactation period and in 540 (1961)). cows producing large quantities of milk. Ketone bodies can be the source of as Acetoacetate and its reduction product much as one-third of the total respiratory beta-hydroxybutyrate are the two ketone :arbon dioxide in sheep (E. N. Bergman, bodies that occur in excess. Acetoacetate K. Kon, and M. L. Katz, Am. J. Physiol. arises in part as the remaining residue after 205, 658 (1963)). Although during moder- cleavage of acetyl coenzyme A units from ate ketosis an animal can utilize the ketone fatty acids during oxidation, but mostly bodies as an energy source, during severe from the acetoacetyl coenzyme A result- ketosis, (e.g. bovine or diabetic) the quan- ing from condensation of acetyl coenzyme tity of ketone bodies in the tissues becomes A units. Acetyl coenzyme A is a major pro- pathological. duct of fatty acid oxidation, but is also an It seems now that abnormal production intermediate in carbohydrate metabolism of large quantities of ketone bodies is due and in the utilization of absorbed acetate. to an increased need for oxaloacetate Ketone bodies can be important energy (Krebs, Vet. Rec. 78, 187 (1966)).Two sources, and in fact heart muscle can use important needs for oxaloacetate are per- acetoacetate preferentially even in the tinent. It is an obligatory intermediate in 314 NUTRITION REVIEWS [Vol.26, No. 10 gluconeogenesis from most precursors; different groups included L-lactate, py- bovine ketosis, of course, occurs during ruvate, and alpha-ketoglutarate. The con- those times when there is a high require- centration of glucose in blood of the ment for glucose. In ruminants most of ketotic cows tended to be lower than nor- the glucose required must usually be mal, while concentrations of free fatty synthesized, since exogenous carbohydrate acids and glycerol were higher. Downloaded from https://academic.oup.com/nutritionreviews/article/26/10/313/1832143 by guest on 27 September 2021 is largely fermented during digestion and The concentrations of metabolites in the resulting lower fatty acids absorbed. the livers of the non-lactating and normally Other forms of severe ketosis are accom- lactating cows were all similar. Those panied by an increased rate of gluconeo- from livers of the ketotic cows were strik- genesis (T. B. Van Itallie and S. S. Bergen, ingly different from those from the other Jr., Am. J. Med. 31, 909 (1961)). Acetyl cows. Beta-hydroxybutyrate and acetoace- coenzyme A, a normal end product of tate were of course much higher, 2.84 beta-oxidation of fatty acids, normally versus 0.51 mmoles per gram of wet weight reacts with oxaloacetate (the second need), of liver (p < 0.001). Concentrations of which is then carried through the tri- oxaloacetate (p < 0.001), pyruvate (p < carboxylic acid cycle. If the oxaloacetate O.O2), L-glutamate (p < 0.01), alpha- concentration in the liver is inadequate, it ketoglutarte (p < 0.011, L-alanine (p < is quite likely that acetyl coenzyme A is 0.01), and L-glutamine (p < 0.05) in the converted to ketone bodies. ketotic cows were all about one-third to G. D. Baird et al. (Biochem. J. 107, 683 one-half of those in the normal cows. Other (1968)) have studied bovine ketosis and metabolites determined, but whose con- enzymes and metabolite levels of these centrations were similar in all the cows, animals to test the hypothesis that keto- were L-malate, L-lactate, alpha-glycero- genesis is related to excessive gluconeo- phosphate, triose phosphate, L-aspartate, genesis. Three groups of dairy cows were and fructose l16-diphosphate. studied: non-ketotic lactating cows, cows The glucose content of livers of the neither lactating nor pregnant, and lac- ketotic cows was about two-thirds that of tating ketotic cows. The ketotic cows were normal (p < 0.02), while the glucose plus purchased only after they were shown to glycogen content of the ketotic cows’ livers have the clinical signs of primary spontane- was only about one-fourth that of normal ous ketosis and to be free from other cows (p < 0.02). The fat content of the pathogenic conditions that could result in livers of ketotic cows was much higher a secondary ketosis. On experimental days, than that of the normal cows (112.4 versus liver biopsies were taken from the cows 15.4 mg. per gram wet weight of liver and quickly prepared for extraction. Blood (p < 0.001). There were no differences be- samples were also prepared for analysis. tween the groups of cows in the content of The blood ketone bodies (acetoacetate protein and nitrogen. and beta-hydroxybutyrate) varied from The activity of enzymes that catalyze 0.19 to 0.44 mmolar in the non-lactating stages of the pathway of gluconeogenesis (n = 4) and the normal lactating cows was determined in liver homogenates. (n = 7), but those of the ketotic cows were Only the activity of pyruvate carboxylase much greater (p < 0.001) and varied from was significantly higher in the ketotic 2.3 to 6.0 mmolar (n = 6). Beta-hydroxy- cows (p < 0.05), while the activities of butyrate accounted for most of the ketone propionyl-CoA carboxylase, phosphopy- bodies. Other metabolites of the blood ruvate carboxylase, and fructose 1,E-di- which were measured and found not phosphatase were similar in the different significantly different from the cows of the groups of cows. October, 19681 NUTRITION REVIEWS 315

Following the liver biopsies the ketotic dicted, the oxaloacetate level of the liver COWS were each given a single daily dose was quite significantly depressed in the of 900 ml. of 20 per cent glucose solution ketotic cows. The glucogenic precursors, subcutaneously. This treatment was con- glutamate, glutamine, alanine, pyruvate, tinued until the clinical signs had disap- and alpha-ketoglutarate were also de- peared and the blood ketone body con- pressed. Therefore, it seems apparent Downloaded from https://academic.oup.com/nutritionreviews/article/26/10/313/1832143 by guest on 27 September 2021 centrations were normal (usually about that in bovine ketosis, as in other forms four days were required). Blood concen- of ketosis, gluconeogenesis increases and trations of the ketone bodies and glucose the lack of oxaloacetate is a cause of keto- returned to near normal within about 48 sis. hours after the treatment was initiated. It is not at all clear why such striking The concentrations of free fatty acids and differences occur in lactating cows in glycerol were actually below the normal their susceptibility to ketosis. It appar- concentrations within 24 hours after the ently is related to the adaptive capacity glucose was given. of the body of the animal and perhaps also As the hypothesis stated before pre- to its rate of adaptation.

PEROXIDIZED FATTY ACID ABSORPTION AND VITAMIN E

The previously held theory that vitamin E preuents peroxidation of polyumatumted fats in uiuo has been questioned by one group of inuestigators. The low peroxide leuel of tissue lipids from mts and chicks giuen supplemental uitamin E is attributed to an inhibition of absorption of oxidized fatty acids from the intestinal tmct.

Since alpha-tocopherol is an effective nated in the tissue and could not result antioxidant, it was only natural that the from an accumulation of the peroxides physiological role of this vitamin should contained in the dietary fat.” be associated with prevention of lipid per- Although considerable evidence was oxidation. The observation that the re- presented by subsequent workers to sup- quirement for vitamin E was related to port the concept of in uiuo peroxidation the level of unsaturated fatty acids in the of fats in animals deficient in vitamin E, ration added further support to this the- a number of investigators have interpreted ory (0. A. Roels, in Present Knowledge their data in a different manner. This is in Nutrition, third edition, p. 84. The especially true of J. Bunyan, E. A. Mur- Nutrition Foundation, Inc., New York, rell, J. Green, and A. T. Diplock (Brit.J. 1967). Experimental evidence which sup- Nutrition 21, 475 (1967)). To study the ex- ported this concept came from H. Dam and tent to which lipids were peroxidized in H. Granados (Acta Physiol. Scandinuu. 10, uiuo, Bunyan and co-workers took special 162 (1945)). When they fed chicks a diet precautions to reduce the oxidation of lacking vitamin E and containing 5 per lipids while tissues were being removed cent cod liver oil, they not only observed from the animals. Their rats were sacri- exudative diathesis but also noted high ficed by exposure to nitrogen in a poly- peroxide concentrations in the fat of the ethylene bag. The tissues were dissected adipose tissue. Since the depots were free under nitrogen and weighed in a bottle of peroxides when vitamin E was included filled with the same gas. in this ration, they suggested that “the When a diet free of vitamin E was fed to peroxides found in the depot fat of the vi- rats from the time they were born, the tamin E-deficient chicks must have origi- concentration of peroxides in liver lipids