title: Effects of melatonin on long-day responses in short-day housed adult Siberian hamsters.
abstract: Testis growth is stimulated when short photoperiod-regressed Siberian hamsters are exposed to a lengthening photoperiod, an effect presumably mediated by the pineal gland through a decrease in the peak nocturnal duration of secretion of its hormone melatonin (MEL)(D. S. Carter and B. D. Goldman, Endocrinology 113: 1268-1273, 1983). We examined this stimulatory or "progonadal" effect of MEL in short photoperiod-regressed, adult male Siberian hamsters that were pinealectomized (PINX) and given timed daily subcutaneous 1) injections of MEL (1 or 10 micrograms/day) or saline or 2) infusions of MEL that were "long day-like" (4 h, 10 or 100 ng/day), "short day-like" (10 h, 10 ng/day), or control saline infusions (4 h/day). Photoregressed sham PINX hamsters were transferred to long days at this time. After 5 wk of treatment, 1-microgram MEL-injected hamsters and both groups of 4-h MEL-infused hamsters had stimulatory responses that mimicked those of the long-day-exposed, sham PINX group [i.e., increased testes, body, and epididymal white adipose tissue (EPIWAT) weights, total body fat, EPIWAT lipoprotein lipase activity, and serum prolactin and follicle-stimulating hormone levels]. These effects were not observed in 10-micrograms MEL- or saline-injected and 10-h MEL- or saline-infused hamsters. Thus the peak nocturnal duration of serum MEL is the critical parameter of the MEL secretion profile for stimulating a variety of photoperiodic responses when photoregressed hamsters are exposed to lengthening daylengths.
mesh_terms: D000273:Adipose Tissue / Q000033:anatomy & histology / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000033:anatomy & histology / Q000378:metabolism; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002940:Circadian Rhythm; D006224:Cricetinae; D004822:Epididymis / Q000033:anatomy & histology; D005640:Follicle Stimulating Hormone / Q000097:blood; D008027:Light; D008071:Lipoprotein Lipase / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D009929:Organ Size / Q000187:drug effects; D010507:Periodicity; D010870:Pineal Gland / Q000502:physiology; D011388:Prolactin / Q000097:blood; D012098:Reproduction / Q000528:radiation effects; D013737:Testis / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology
chemical_list: D011388:Prolactin; D005640:Follicle Stimulating Hormone; D008071:Lipoprotein Lipase; D008550:Melatonin