Uptake of chylomicron triglyceride and lipoprotein lipase was studied in red and white skeletal muscles, heart, and adipose tissue of rats. Retention of triglyceride fatty acids 10 min after injection was 1.6%/g in heart and adipose tissue, 0.2-0.4%/g in red (soleus and diaphragm) muscles, and 0.1%/g in white (psoas minor) muscles of fed rats. Fasting (24 h) increased retention two- to fourfold in red skeletal muscles and heart, had no effect in white muscles, and decreased retention greater than 75% in adipose tissue. Lipoprotein lipase activity in fed rats was lowest in white muscles and in certain red (posterior belly of digastric and medial head of triceps brachii) musclws, intermediate in soleus and diaphragm muscles and adipose tissue, and highest in heart. Fasting doubled lipoprotein lipase activity in all red skeletal muscles and heart, had no effect in white muscles, and decreased activity 60% in adipose tissue. The findings indicate that triglyceride uptake is related to lipoprotein lipase activity in skeletal muscle and the changes in enzyme activity during fasting divert blood triglyceride to red skeletal muscles.

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Effects of adrenalectomy on adipose tissue and liver lipogenesis were studied in rats with acute insulin deficiency induced either by interrupting insulin administration to previously treated alloxan-diabetic rats or by almost completely removing pancreatic tissue in a convenient two-stage procedure. The adrenals were removed at the time insulin deficiency was induced and the effects of excision were determined within the next twenty-four hours. Adrenalectomy prevented the marked reduction in incorporation of 14-C from glucose and acetate into fatty acids, as well as the decrease in carbon dioxide production from hexose, in vitro, which rapidly ensue in adipose tissue from alloxan-diabetic rats following insulin withdrawal. In the same conditions, adrenal removal did not affect the metabolism of U-14-C-glucose by liver slices, but a small increase in liver fatty acid synthesis from acetate was observed during one of the experimental intervals. In similarly designed experiments, adrenalectomy increased the recovery of 14-C from acetate, administered in vivo, from fatty acids of the carcass and liver of alloxan-diabetic animals. The effects of adrenalectomy on the metabolism of U-14-C-glucose by adipose tissue from pancreatectomized rats were similar to those observed in alloxandiabetic rats although less marked. Again, adrenal removal did not affect glucose metabolism by liver slices from pancreatectomized rats, but improved liver lipogenesis from acetate. The present results, compared with others in the literature, suggest that the effects of adrenal excision are fully manifested only if the glands are removed before the metabolic changes induced by diabetes in adipose tissue are well established.

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