Effect of estradiol on the activity of serotonin N-acetyltransferase in the rat epiphysis.

Administration of estradiol to ovariectomized females did not affect either the rhythm and basic levels of activity of the enzyme regulating the formation of melatonin in the rat epiphysis-serotonin N-acetyltransferase or the activation of this enzyme by isoproterenol in vivo. Daily administration of estradiol to young rats from birth did not alter the rhythm or activity of serotonin N-acetyltransferase in the epiphysis as estimated on the 8th day of age. The ability of estradiol to suppress noradrenaline activation of adenyl cyclase in epiphysial homogenates and its inability to suppress the same activation of serotonin N-acetyltransferase suggests either that the activation of the latter enzyme by catecholamines could occur by other mechanisms than the adenyl cyclase system or that activation of adenyl cyclase by noradrenaline is not suppressed by estradiol to the same degree in vivo as in vitro.