Lindane may enhance nocturnal pineal N-acetyltransferase activity via beta-adrenergic receptors

Lindane, a chlorinated hydrocarbon pesticide, was previously shown to enhance the nighttime rise in pineal N-acetyltransferase (NAT) activity and melatonin as well as serum melatonin levels. The purpose of the present study was to test whether lindane acts on the pineal gland by means of a beta-adrenergic receptor mechanism. Whereas lindane (total dose 17.8 mg/kg b.wt. over 6 days) by itself significantly augmented the nocturnal levels of pineal NAT activity in otherwise untreated rats, the pesticide was ineffective in reference to this enzyme when it was given in conjunction with the beta-adrenergic receptor antagonist propranolol (20 mg/kg b.wt., one hour before lights off). The augmentation of NAT activity by lindane also caused significant reductions in pineal serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA); again, both these responses were blocked by propranolol treatment. Neither pineal 5-hydroxytryptophan nor pineal or serum melatonin levels were significantly changed as a result of either lindane or propranolol treatment. The results are consistent with the idea that lindane influences pineal 5-HT metabolism either at the level of the beta-adrenergic receptor or via the sympathetic innervation to the pineal gland.