Effects of single cortisone injections on brown adipose tissue of developing rats

An injection of a single dose of cortisone acetate (5 mg/100 g body weight) to 9-day-old rats resulted in the following changes in brown adipose tissue 24 h later: (1) the fresh weight was increased due to fat accumulation; (2) the DNA content of whole interscapular brown fat stayed unaltered, while the RNA content was increased; (3) specific activities of cytoplasmic alpha-glycerophosphate dehydrogenase and malic enzyme were increased; (4) the percentage of mitochondrial protein in the whole tissue protein was not changed, but mitochondria seemed to be more fragile, fewer were recovered by a standard isolation procedure, and more cytochrome c oxidase contaminated the microsomal fraction; (5) mitochondrial alpha-glycero-phosphate dehydrogenase and succinate dehydrogenase activities were decreased per milligram homogenate protein and (in isolated mitochondrial fraction) per milligram mitochondrial protein; (6) the endogenous respiration of brown fat mitochondria was activated much less by carnitine and CoA; and (7) CO2 formation from palmitate-14C by isolated mitochondria was considerably lower.A similar injection to 30-day-old rats had no significant effect.It is suggested that a single injection of cortisone affects the mitochondrial structure of brown adipose tissue and the ability to oxidize fatty acids and that it is effective on day 10 but not on day 30.

Development of rat liver adenylcyclase

A developmental study of rat liver adenylcyclase and of its sensitivity to stimulation by adrenalin, glucagon, and NaF was carried out. During the last days of prenatal development, basal activity and hormone or NaF stimulated activity rise. Maximal levels are reached between day 2 and 10 after birth. Thereafter, adrenalin-stimulated adenylcyclase activity decreases considerably. In relation to basal activity, glucagon (and NaF) sensitivity increases with age while adrenalin sensitivity is sharply reduced after 10 days of age. These results may be related to changes in specific enzyme inducibility and/or carbohydrate metabolism known to occur in the course of development of rat liver. Additive hormonal stimulation was only observed in preparations obtained from animals which were at least 30 days of age.

The effect of cortisone on brown adipose tissue of young rats

Rats aged 7 to 9 days were injected for 1 to 3 days with 5 mg/100 g body weight cortisone acetate per day. This led to an increase in the weight of brown adipose tissue, an increase in its fat content, and a decrease in its protein content. The content of norepinephrine in brown adipose tissue was decreased by cortisone treatment. The in vitro increase in O2 consumption following the addition of 5 μg nore-pinephrine/ml in vitro to brown adipose tissue from control animals was abolished by cortisone administration. Lipolysis due to norepinephrine was, however, not affected and was even slightly increased in cortisone-treated rats. Mitochondrial succinate–tetrazolium reductase activity was decreased after treatment with cortisone. It is concluded that cortisone alters the mitochondria of brown adipose tissue but has little effect on lipolysis as such. The content of norepinephrine in brown adipose tissue was found to decrease immediately after birth and then to return rapidly to higher levels.

Triglyceride synthesis from various precursors in adipose tissue of the rat during development

The rate of incorporation of glucose-1- and -6-14C, pyruvate-1- and -2-14C, acetate-2-14C, citrate-1,5-14C, and NaH14CO3 into pieces of brown and white adipose tissue of fetal, newborn, and weaned rats was studied in vitro. Data indicate that brown adipose tissue becomes less important with age while the opposite holds for white fat. Gluconeogenetic reactions (glyceride glycerol formation) are accentuated in both fats in the suckling period, but more so in white adipose tissue. Fatty acid formation is also more pronounced in white adipose tissue from suckling rats. Oxidation of substrates is greater in brown than in white adipose tissue.