title: Alterations in daily rhythms of testosterone and progesterone in old male rats.
abstract: Studies were undertaken to characterize the daily patterns of secretion of testosterone (T), progesterone (P) and dihydrotestosterone (DHT) in young (3-4 months old) and old (19-20 months old) male Sprague-Dawley rats. In young rats, plasma T concentrations show dramatic daily variations with peak and nadir levels at 1130 and 2330 h, respectively. In old male rats, no such rhythmic pattern in plasma T was observed. Plasma P concentrations varied significantly in both young and old male rats, with peak levels occurring 8 h (1930 h) after the plasma T peak in young rats. Additionally, in old male rats, the daily increase in plasma P was significantly larger and was sustained for a longer period than in young rats. Plasma DHT concentrations were similar and changed little during the day in both young and old animals. In view of the known P influence on gonadal secretion, the possible significance of these age-related changes in daily patterns in plasma P and T are discussed.
mesh_terms: D000375:Aging; D000818:Animals; D002940:Circadian Rhythm; D013196:Dihydrotestosterone / Q000097:blood; D008297:Male; D011374:Progesterone / Q000097:blood*; D051381:Rats; D013739:Testosterone / Q000097:blood*
chemical_list: D013196:Dihydrotestosterone; D013739:Testosterone; D011374:Progesterone