EFFECT OF PITRESSIN ON LIPOLYSIS AND ON PHOSPHORYLASE ACTIVITY IN RAT ADIPOSE TISSUE.

Pitressin, a mixture of arginine and lysine vasopressins, stimulates the release of glycerol and of free fatty acids from rat epididymal fat pads in vitro. This effect is inhibited by prostaglandin E 1 , which has previously been shown to interfere with the analogous effects of catecholamines, ACTH, TSH, and glucagon. Like these latter hormones, Pitressin, added for a few minutes after tissues have been incubated in the absence of hormones, significantly increases the activity of phosphorylase and of the hormone-sensitive lipase. (The activity of both of these enzymes declines during the period of incubation before the hormone is added.) No effects of synthetic oxytocin at similar concentration on glycerol release or on phosphorylase activity were demonstrated.