Interaction of arginine vasotocin and norepinephrine upon pineal indoleamine synthesis in vitro

The interaction of arginine vasotocin (AVT) and norepinephrine (NE) upon pineal gland indoleamine synthesis was investigated. Rat pineal glands were incubated for 10 h in Krebs--Ringer bicarbonate plus 2 mg/ml glucose, 1 mg/ml bovine serum albumin, [14C]tryptophan, NE (10(-6) M), and log doses of AVT ranging from 100 ng to 10 microgram. Incubation media were extracted for [14C]serotonin while the other [14C]indoleamines, melatonin, hydroxyindoleacetic acid (HIAA), methoxyindoleacetic acid (MIAA), N-acetylserotonin (NAS), hydroxytryptophol (HTOL), and methoxytryptophol (MTOH) were separated by thin-layer chromatography. Serotonin metabolism was decreased by 0.1 microgram AVT and NAS decreased by 1.0 microgram AVT. Melatonin synthesis was decreased by both 0.1 and 1.0 microgram AVT. AVT also decreased the conversion of [14C]serotonin to MIAA and to HTOL. The data indicates that AVT decreased NE-stimulated pineal indoleamine synthesis in vitro and further suggests that AVT may participate in the intracellular regulation of melatonin synthesis.