Mechanisms of vasopressin's anorectic effect.

The present experiments investigated the effect of vasopressin (VP) on food intake in rats under various conditions. VP (1.25-10 micrograms/kg body weight = b.wt.) injected intraperitoneally (IP) at the onset of the dark phase of the lighting cycle inhibited feeding in a dose-dependent manner. The suppression of feeding induced by VP was primarily due to a delayed onset of the first meal after injection and was reversed by a V1-receptor antagonist (7 micrograms/kg b.wt., IP), by the Ca(++)-channel blocker verapamil (5 mg/kg b.wt., IP) and by the alpha-adrenergic receptor antagonist phentolamine (500 micrograms/kg b.wt.), but not by dissection of the hepatic branch of the vagus. In further experiments VP inhibited gastric emptying. This effect was not reversed by phentolamine. VP had also an aversive effect, but this effect was weaker than that of LiCl and probably not involved in VP-induced hypophagia. The results suggest that VP reduces feeding through a V1-receptor-mediated activation of an alpha-adrenergic mechanism. The inhibition of gastric emptying or a possible stimulation of hepatic oxidative metabolism by VP seems to be not essential for VP's effect on feeding. The results are consistent with a role of VP in stress-induced anorexia in rats.