The effect of chronic lithium treatment on rat pineal N-acetyltransferase rhythm

Lithium chloride administration to rats for 5 weeks caused a significant decrease in dark-induced activity of rat pineal N-acetyltransferase (E.C.2.3.1.5.). This effect is not observed after 3 days or 3 weeks of treatment. Furthermore, chronic lithium treatment suppressed the amplitude and may have delayed the peak of the diurnal cycle of N-acetyltransferase activity. In vitro, various concentrations of lithium chloride (2, 4 and 10 microM) did not affect N-acetyltransferase activity. Beta adrenergic receptor binding studies with [3H]dihydroalprenolol indicated a decrease in number of pineal beta adrenergic receptors in rats treated chronically with lithium. These results are consistent with a lithium-induced subsensitivity of pineal beta adrenergic receptors and may explain the effect of lithium on pineal-mediated cyclic behaviors.