Nutritional status, time of day and pinealectomy: factors influencing the sensitivity of the neuroendocrine-reproductive axis of the rat to melatonin.
Afternoon but not morning injections of melatonin (Mel) resulted in significant 68, 50 and 20% reductions in seminal vesicle, ventral prostate and testicular weights, respectively, as compared with underfed controls. As in the animals injected in the morning, reproductive organ weights in underfed-pinealectomized rats were unaffected by afternoon injections of Mel. Both pituitary and serum prolactin levels were significantly depressed in underfed rats receiving Mel in the afternoon; however, Mel was ineffective when given either in the morning or to pinealectomized rats. These data indicate that there is a diurnal rhythm of sensitivity to Mel in undernourished rats which is abolished by pinealectomy.
D000818:Animals; D002940:Circadian Rhythm; D005215:Fasting; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D010870:Pineal Gland / Q000502:physiology*; D010902:Pituitary Gland / Q000032:analysis; D011388:Prolactin / Q000097:blood; D011467:Prostate / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D012669:Seminal Vesicles / Q000187:drug effects; D013737:Testis / Q000187:drug effects
D011388:Prolactin; D008550:Melatonin