Neuroendocrine integrative mechanisms in mammalian pineal gland: effects of steroid and adenohypophysial hormones on melatonin synthesis in vitro.
The time course for the decrease in norepinephrine concentration of rat pineal explants in culture indicated a significant fall starting at the 4th hour and completed after 16-24 h of incubation. Significant decreases of serotonin and 5-hydroxyindoleacetic acid (HIAA) levels in tissue, an increase of HIAA/serotonin ratio, and an increase of melatonin production rate in vitro were also observed as a function of the incubation time. Estradiol (10(-7)-10(-5) M) increased rat pineal melatonin content, testosterone (10(-5) M) decreased it and progesterone was devoid of activity when incubated with explants for up to 6 h. The in vitro stimulatory effect of estradiol on rat pineal methoxyindole synthesis was blocked by propranolol but not by phentolamine; propranolol also blocked the increase of nuclear estradiol-receptor complex produced by estrogen exposure of pineal explants. TSH (1-100 ng/ml), growth hormone (10-100 ng/ml) and LH (10 ng/ml) augmented rat pineal melatonin content while 100 ng/ml of FSH decreased it significantly. Prolactin exerted a biphasic effect on rat pineal explants, the lowest concentration augmenting melatonin content while the high concentration depressed it. Deep, intermediate and superficial segments of guinea-pig pineal glands showed an increase in melatonin concentration after a 6-h incubation in the presence of 10(-7)-10(-5) M estradiol.
D000818:Animals; D012739:Gonadal Steroid Hormones / Q000494:pharmacology*; D006168:Guinea Pigs; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000096:biosynthesis*; D009638:Norepinephrine / Q000378:metabolism; D009924:Organ Culture Techniques; D010646:Phentolamine / Q000494:pharmacology; D010870:Pineal Gland / Q000187:drug effects* / Q000378:metabolism; D010908:Pituitary Hormones, Anterior / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011959:Receptors, Estradiol / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism
D012739:Gonadal Steroid Hormones; D010908:Pituitary Hormones, Anterior; D011959:Receptors, Estradiol; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D011433:Propranolol; D008550:Melatonin; D009638:Norepinephrine; D010646:Phentolamine