Arginine vasotocin is a nonapeptide hormone agonist of the AVT receptor (EC50 = 13 nM for eliciting membrane currents in X. laevis oocytes). Arginine vasotocin is synthesized in the pineal recess and subcommissural organ by ependymal cells and released into the cerebrospinal fluid. It inhibits the induction of sleep and release of hypothalamic releasing and inhibiting hormones. Arginine vasotocin stimulates glycogen phosphorylase α activity and incorporation of phosphate into phosphatidylinositol in rat hepatocytes (EC50s = 0.5 nM and 6.3 nM, respectively). Following a two-minute pulse of arginine vasotocin (1 μM) to neurons isolated from rat suprachiasmatic nuclei, 40.6% of neurons show an increase in firing rate with 11% of the activated neurons responding only to arginine vasotocin and not argipressin . Arginine vasotocin (0.1 μg, i.c.v.) activates sexual behavior in male newts and increases the number of clasps per male from saline control levels of 0.6 to 2.9 in an eight-hour period. In rainbow trout, arginine vasotocin (0.1 ng/g, i.c.v.) reduces food intake by over 95% and, after eight hours, increases cortisol and glucose levels by 89% and 27%, respectively.