Neonatal steroid treatment reduces catecholamine-induced increases in pineal serotonin N-acetyltransferase activity.

Hydrocortisone acetate given to the neonatal rat diminishes subsequent elevations in pineal serotonin N-acetyltransferase (acetyl-coenzyme A:arylamine N-acetyltransferase; EC 2.3.1.5; NAT) activity produced by administration of catecholamines to the intact animal or to pineals in organ culture. The time required for development of this decrease in sensitivity varies inversely with age at treatment. A minimal dose of 200 micrograms of hydrocortisone acetate/rat is required to elicit this decreased response to agonist. Other glucocorticoids have qualitative effects similar to hydrocortisone acetate, but cholesterol and the gonadal steroids testosterone, estradiol, and progesterone are without effect. In addition to showing a smaller rise in NAT activity on stimulation, pineals from steroid-treated neonates also synthesize less N-acetylserotonin and melatonin from tryptophan. The decrease in NAT response to stimulation after steroid treatment appears due to actions beyond cyclic AMP generation and may involve inhibition of protein synthesis.