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Effects of Age, Pregnancy, and Lactation on Rat, Guinea Pig, and Cow Adipose Enzyme Activities and Cow Adipose Metabolism¹

Department of Animal Science, University of California, Davis 95616

ABSTRACT

In the enzyme study, virgin, pregnant, lactating, and adult animals whose ages were comparable to lactating animals were compared. With all three species, young virgin adipose enzyme activities were higher than in older groups indicating a prominent age effect. Comparison of adipose enzyme activities of adult and lactating groups indicated that activities of only a few enzymes were increased during lactation and some differences in response exist among species. In the general study of cow adipose metabolism through tissue slices, relative rates of glucose-1-, -2-, and -6-¹⁴C oxidation and incorporation into glyceride glycerol were 1.0, .5, and .25 and .62, .92, and 1.0, indicating high hexose monophosphate shunt activity and high rates of glucose utilization for glyceride glycerol synthesis. Ratio of glucose-U-¹⁴C oxidation to use for lipogenesis was about 1.2, was increased by insulin in vitro, and was decreased in lactating as compared to nonlactating animals. Rates of glucose and acetate oxidation and use for lipogenesis were doubled approximately during lactation. Comparisons of rates of glucose oxidation with rates of fatty acid synthesis from acetate indicated that NADPH₂ yields from hexose-P oxidation via pentose cycle are not sufficient to support fatty acid synthesis. Hence, additional NADPH₂ generating reactions must occur. Rates of fatty acid esterification in adipose tissue slices exceeded rates of fatty acid synthesis by about four-fold presumably reflecting extensive fatty acid reesterification.

¹ Supported in part by USPHS grant AM07672.

² Present address: Department of Animal Nutrition, Hohenheim University, 7000 Stuttgart 70, Germany.

³ Present address: Department of Dairy Science, Cornell University, Ithaca, New York 14850.

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