Effect of testosterone replacement on the alteration of steroid metabolism in the hypothalamic-preoptic area of male hamsters treated with melatonin.

Adult male hamsters were maintained under 14 hours of light per day and randomly assigned to groups that received daily afternoon melatonin (25 micrograms) or vehicle injections. Animals from both groups were killed following 4, 8, and 12 weeks of treatment. By 12 weeks, the melatonin-treated hamsters had significant reductions in the weights of the testes and seminal vesicles, serum testosterone levels, and activities did not differ between groups.

Effect of melatonin replacement on serum hormone rhythms in a patient lacking endogenous melatonin.

A potentially confounding variable inherent in studies designed to examine the effect of melatonin administration in humans is the presence of an endogenous melatonin rhythm in the experimental subjects. The effects of exogenous melatonin administration on serum hormone rhythms was recently examined in a male patient who lacked detectable circulating levels of endogenous melatonin. The patient's pineal gland had been destroyed five years previously in the course of treatment for a pineal astrocytoma.

Effect of a 15 minute light pulse on nocturnal serum melatonin levels in human volunteers.

Monitoring the daily melatonin rhythm during the course of phototherapy for affective disorders may be beneficial in assessing the efficacy of such treatments. It is therefore of interest to study the effects of the timing, duration, and intensity of bright light pulses on melatonin levels in normal subjects. To examine the effects of a single exposure to a brief burst of bright light on serum melatonin, groups of healthy human volunteers of both sexes were treated with a 15 minute pulse of bright light (350 cd/m2) early in the evening during the winter months.

Ontogeny of light-induced decrease of N-acetyltransferase activity in explanted chick pineal glands.

The ontogeny of chick pineal serotonin N-acetyltransferase (NAT) activity was investigated in explanted chick pineal glands at 4, 10 and 21 d of age. Nocturnal levels of the enzyme and the response of the enzyme to light exposure were determined in pineal glands maintained in short-term culture at each age. The results indicate that nocturnal NAT activity was increased in the glands from older birds.

Effects of light and an alpha-2-adrenergic agonist on serotonin N-acetyltransferase activity in chick pineal gland.

Pineal serotonin N-acetyltransferase (NAT) is the enzyme that catalyzes the production of N-acetylserotonin from serotonin and is the rate limiting step in the biosynthesis of melatonin in the chick pineal gland. Chick pineal NAT activity is decreased by light and by noradrenergic agents that act at the alpha-2-adrenergic receptor. Light-induced inhibition of nocturnal NAT activity can be demonstrated by exposing 4-day-old chicks to light, or by exposing pineal gland explants cultured in vitro either to light or to UK 14,304 (an alpha-2-adrenergic agonist).