The rate of serotonin synthesis in brain was determined in streptozotocin-diabetic and normal rats using two methods. Both the rate of 5-hydroxytryptophan accumulation after aromatic amino acid decarboxylase inhibition, and the decline rate of 5-hydroxyindole acetic acid after pargyline treatment were significantly reduced in diabetic rats. The reduced rate of synthesis may be a direct result of significantly lowered brain tryptophan levels in diabetic rats.

RIAs have been developed for the nonapeptide hormones arginine vasotocin (AVT), arginine vasopressin (AVP), and oxytocin (OT). The AVP RIA can detect as little as 2 pg hormone and shows essentially no cross-reactivity with AVT or OT. The OT RIA is sensitive to 7 pg and shows no significant cross-reactivity with AVP or AVT. The AVT RIA is sensitive to about 5 pg; some cross-reactivity occurs with OT and AVP, but the RIA is suitable for assaying AVT levels in biological samples containing OT and/or AVP in concentrations up to 5 times greater than that of AVT. Using these RIAs, we found large amounts of AVT (up to 1.48 microgram/gland) in the chicken pituitary but no AVP or OT. The chicken pineal also contained AVT (about 300 pg/gland) and lacked AVP and OT. Bovine pineal glands appeared to contain all three peptides in roughly similar amounts (200-400 pg/gland). Pineal glands from a variety of rodents (including the rat) contained only very small amounts of AVT-like immunoreactivity (about 10 pg/gland) and no AVP or OT. Because AVT immunoreactivity appears in the pineals of several species, the peptide may subserve some physiological function of this organ. The functional roles, if any, of AVP and OT in the bovine pineal are unknown.

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