title: Role of the pineal gland in diurnal endocrine secretion and rhythm regulation.
abstract: The effects of the pineal gland on diurnal endocrine function were studied in male rats. Pineal stimulation by exposure to short daily photoperiods (1L:23D) did not alter plasma levels of testosterone, thyroid-stimulating hormone (TSH) or growth hormone (GH) as compared with those of controls maintained under normal (12L:12D) lighting. Pinealectomy lowered diurnal testosterone levels and increased TSH levels in animals maintained under 1L:23D lighting. Pinealectomy also altered the TSH rhythm and shifted the peak in testosterone levels but did not abolish hormonal rhythms. Active immunization against melatonin and its precursor, N-acetylserotonin (NAS), significantly reduced diurnal androgen levels and elevated TSH levels in animals exposed to short photoperiods, but the 24-hour rhythms persisted. Plasma GH exhibited a diurnal rhythm in animals kept under short photoperiods but GH levels were not affected by any of the above treatments. These data suggest that melatonin and/or NAS may be involved in the maintenance of basal testosterone and TSH levels. The pineal may not be involved in generating hormonal rhythms; however, it may have a role in entraining TSH and testosterone rhythms to environmental lighting.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D013006:Growth Hormone / Q000097:blood*; D007109:Immunity; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood / Q000276:immunology; D010870:Pineal Gland / Q000502:physiology*; D051381:Rats; D012701:Serotonin / Q000031:analogs & derivatives / Q000097:blood; D013739:Testosterone / Q000097:blood*; D013972:Thyrotropin / Q000097:blood*; D013997:Time Factors
chemical_list: D012701:Serotonin; D013739:Testosterone; D013972:Thyrotropin; D013006:Growth Hormone; D008550:Melatonin