Effect of thyroid status on glycerol metabolism in adipose tissue of fasted male rats

Effects of streptozotocin-diabetes and L-thyroxine treatment on TSH and GH, and circulating glucose and glycerol in thyroidectomized rats

The response to exogenous thyroxine in thyroidectomized rats made diabetic by treatment with streptozotocin was greatly impaired, as shown by their growth retardation and the lack of increase in plasma GH and pituitary GH and TSH concentrations. Insulin administration partially compensated for these endocrine alterations in diabetic thyroidectomized rats. When these animals received enough exogenous thyroxine to normalize their plasma PBI and TSH levels, insulin administration did not decrease their augmented glucose and glycerol concentrations. These findings show the permissive action between thyroid hormones and insulin although some effects of the former counteract those of insulin.

Triiodothyronine-dietary interrelationships in the modulation of brown adipose tissue and liver lipogenesis in the rat

The influence of diet and triiodothyronine on "in vivo" lipogenesis has been compared in liver and brown adipose tissue of the rat at weaning and in adult life. At both ages studied, hyperthyroidism increases lipogenesis only in the liver. However brown adipose tissue accumulates lipid (probably derived from white adipose tissue) thus helping to explain previous observations of low rates of lipogenesis in this tissue during the late suckling period when thermogenesis is high and plasma triiodothyronine levels rise. Suppression of lipogenesis by dietary polyunsaturated fat in both tissues at both ages studied confirms previous studies on adult animals. Malic enzyme and glucose-6-phosphate dehydrogenase activities correlate well with changes in lipogenesis in brown adipose tissue but not in liver and the hepatic enzymes exhibit a diminished response to dietary and hormonal factors with age.

The effect of glucose, insulin and adrenaline on glycerol metabolism in vitro in rat adipose tissue

The uptake and utilization of [1-14C]glycerol was determined in pieces of rat epididymal fat-pads incubated in Krebs--Ringer bicarbonate buffer containing albumin. Insulin (200 muunits/ml), adrenaline (epinephrine; 0.5 mug/ml) and glucose (0, 5, 15 and 20 mM) were added to the medium. Changes in the specific radioactivity of the tracer during the incubation were taken into account in calculating the rate of glycerol utilization. Adrenaline decreased glycerol uptake, whereas insulin plus adrenaline increased it. The rate of incorporation of glycerol into glycerides was decreased by adrenaline and insulin, singly or together. Insulin increased the rate of formation of CO2 and fatty acids from glycerol. The formation of CO2 and fatty acids was further enhanced by insulin plus adrenaline. The decrease in glycerol uptake induced by adrenaline, the decrease in incorporation of glycerol into glycerides induced by insulin and insulin plus adrenaline and the synthesis of fatty acids were dependent on the presence of glucose in the medium. Thus insulin and adrenaline act on glycerol utilization in adipose tissue and some of their effects are mediated by action on glucose metabolism, but others are independent of this.