Effect of a synthetic pineal tetrapeptide (Ala-Glu-Asp-Gly) on melatonin secretion by the pineal gland of young and old rats

The pineal gland contains many peptides known to be implicated in melatonin production. We examined the effects of a synthetic pineal tetrapeptide Ala-Glu-Asp-Gly on melatonin secretion by the pineal gland. The tetrapeptide effects on pineal gland melatonin secretion were studied in young (9 weeks) and old (27 months) male Wistar rats using a perifusion device. Pineal tetrapeptide at the concentrations used (10–4 to 10–6 M) had no significant effect upon melatonin secretion whatever the age of the animals, young or old. We also looked at the effect of the tetrapeptide on pineal melatonin stimulated by a β-adrenergic agonist, isoproterenol. We found that isoproterenol-induced melatonin increase was not modified by the tetrapeptide. Our results suggest that the pineal tetrapeptide Ala-Glu-Asp-Gly, does not seem to play a role, at least in vitro, in the control of melatonin secretion by the rat pineal gland.