CHANGES IN NOCTURNAL PINEAL INDOLEAMINE METABOLISM IN RATS TREATED WITH PARATHION ARE PREVENTED BY BETA-ADRENERGIC ANTAGONIST ADMINISTRATION

Parathion, an organophosphorous insecticide, was previously shown to e nhance the nighttime rise in pineal N-acetyltransferase (NAT) activity and serum melatonin levels. The purpose of the present study was to t est whether parathion acts on the pineal gland by means of a beta-adre nergic receptor mechanism. Whereas parathion (total dose 6.5 mg/kg bod y wt over 6 days) by itself significantly augmented nocturnal pineal N AT activity and serum melatonin levels in otherwise untreated rats, th e insecticide was ineffective in reference to this enzyme when it was given in conjunction with the beta-adrenergic receptor antagonist prop ranolol (20 mg/kg body wt, 1 h before lights off). The augmentation of NAT activity by parathion also caused significant reductions in pinea l serotonin (5-HT); again, this response was blocked by propranolol tr eatment. Neither pineal hydroxyindole-O-methyltransferase (KIOMT) acti vity nor pineal levels of 5-hydroxytryptophan or hydroxyindole acetic acid (5-HIAA) were significantly changed as a result of either parathi on or propranolol treatment. The results are consistent with the idea that parathion influences pineal 5-HT metabolism either at the level o f the beta-adrenergic receptor or via the sympathetic innervation to t he pineal gland.