Impact of nutrition on postnatal development of serine-threonine dehydratase and branched-chain keto acid dehydrogenase in the rat.

The developmental patterns of two amino acid-catabolizing enzymes, serine-threonine dehydratase (STD) and branched-chain alpha-keto acid dehydrogenase (BCKAD), were investigated in growing rats. At 10, 15, 20, 30, and 60 days of age, STD and BCKAD activities were determined in pup tissues. Hepatic STD activity increased more than 3-fold between 10 and 20 days of age; after this peak, activity decreased by 30 days of age. Threonine dosing did not affect STD activity at any age. In the liver, kidney, brain and skeletal muscle, total BCKAD activity increased 2- to 4-fold between 10 and 30 days of age. Percentages of BCKAD active in all tissues decreased between 10 and 15 days of age, associated with a large increase in total activity. The percentages of BCKAD activity were unchanged between 20 and 30 days of age but increased from 30 to 60 days of age, associated with a decrease in total activity. Leucine dosing did not affect total BCKAD activity at any age. These results demonstrate that both STD and BCKAD develop late during the suckling period and total activities are unresponsive to excess dietary amino acids.

Effects of adrenalectomy on energy balance in obese (ob/ob) mice fed high carbohydrate or high fat diets.

We reported previously that adrenalectomy reduced the energy density of body weight gain (an indicator of proportional gain in lean and fat tissue) and the efficiency of energy retention in obese (ob/ob) mice to values approximating those in lean mice, but that adrenalectomy had much less influence on these parameters in ob/ob mice fed a purified high fat diet. To determine if fat was the exclusive factor in the purified high fat diet that negated effects of adrenalectomy, ob/ob mice were fed a purified high carbohydrate (glucose) diet identical in composition to the high fat diet, except for the fat/carbohydrate ratio. Responses of adrenalectomized ob/ob mice fed the purified high glucose diet from 4 to 7 wk of age mimicked those of mice fed the purified high fat diet, not those of mice fed the high carbohydrate nonpurified diet. Plasma glucose responses to a glucose load in adrenalectomized ob/ob mice paralleled the diet-dependent changes in energy balance. These results demonstrate that diet composition interacts with adrenal secretions to influence energy and glucose metabolism in ob/ob mice; consumption of either a purified high glucose or high fat diet negates the beneficial effects of adrenalectomy on energy and glucose metabolism observed when adrenalectomized ob/ob mice consume a nonpurified diet.

Energy balance in rats with obesity-producing hypothalamic knife cuts: effects of adrenalectomy.

Rats with obesity-producing, hypothalamic knife cuts (KC) were fed a purified high fat diet for 9 wk. KC rats consumed more energy (+70-100%) and retained energy with a much higher efficiency than control rats. Adrenalectomy of KC rats 1 wk (before gross obesity was evident) or 5 wk (when KC rats were 70% overweight) after KC surgery caused a reduction in energy intake to levels approximating those of control rats. Furthermore, energy retention in adrenalectomized KC rats was depressed more than could be explained on the basis of the reduction in energy intake. Two factors associated with the reduction in energy retention, urinary excretion of norepinephrine, an indicator of sympathetic nervous system activity, and GDP binding to brown adipose tissue mitochondria, an indicator of the thermogenic capacity of the tissue, were higher in vadrenalectomized KC rats than in pair-fed KC rats. Removal of the adrenals not only suppressed hyperphagia in KC rats fed a high fat diet, but also increased energy expenditure per kilocalorie consumed.