Comparative study of the effects of melatonin-free pineal extract and melatonin on biochemical and hormonal parameters in the rats.

A melatonin-free pineal extract administered to rats in doses of 2 ml/day/animal along 12 days, induced a statistically significant drop in urinary 17 KS, cholesterolemia, hepatic, adrenal and testicular cholesterol. The dose of 1 microgram melatonin/day/animal did not alter these biochemical indices. This dose administered for 3 days did not affect the serum level and testicular concentration of testosterone, unlike the pineal extract which lowered significantly serum and testicular testosterone. Unlike the pineal extract administration of melatonin in doses of 10 micrograms/day/animal along 3 days had no effect on DNA, RNA and testicular proteins. Administration of the pineal extract lowered significantly serum LH and FSH after 3 days whereas melatonin in doses of 50 micrograms/day/animal did not have a similar effect. Furthermore, while the pineal extract inhibited the post-castration elevation of LH and FSH, melatonin in doses of 50 micrograms/day/animal had no effect. The same difference was noted with rats under GnRH stimulation: the pineal extract inhibited the pituitary response to GnRH whereas melatonin did not. The authors conclude that the effects produced by the pineal extract are not mediated by melatonin.