KOVACEV, VANCO P., AND ROBERT 0. Scow. Efect of hor-mones on jutty acid release by rat adipose tissue in uiuo. Am. J. Physiol. nm (6): I 199-1208. 1966.-A method is described for studying in vivo fatty acid release in the rat parametrial fat body. Fatty acid release was accelerated by fasting and by Yotal” pancreatectomy. Injection of insulin increased fatty acid release in fasted normal rats and decreased release in pancreatectomized rats. The lipolytic effect of insulin in normal rats occurred even when the blood glucose was maintained above 200 mg/roo ml. Glucagon infusion increased fatty acid release in insulin-treated pancreatectomized rats. The findings suggest that insulin may stimulate in normal rats secretion of glucagon or some other pancreatic factor which can cause release of fatty acids in the presence of insulin. Injection of growth hormone and dexamethasone together accelerated fatty acid release in fasted normal rats; the effect on fatty acid release occurred I hr after injection and was followed 2 hr later by an increase in blood ketone bodies. Injection of ACTI-I increased immediately fatty acid release in fed normal rats. pancreatectomy; diabetes; fasting; insulin; glucagon; growth hormone; dexamethasone; ACTH; lipid mobilization and ketosis; parametrial fat body