title: Testosterone levels in the male laboratory rat: variation under experimental conditions.
abstract: This report describes the variation of testosterone (T) levels in male Wistar rats (250-300 g) bled under typical laboratory conditions. Plasma T in 114 rats ranged from 2-48 nmol/l (median 13.1; 95% confidence range, 10-15) and varied significantly (P < 0.01) during the day (07.30-16.30 h) with an acrophase between 09.00 h and 13.00 h. The distribution of plasma T levels was skewed (P < 0.05) and could be divided into basal values < 26 nmol/l and peaks > 26 nmol/l. Testosterone in testicular tissue and testis veins also varied during the day and was lower (P < 0.02) between 14.30 h and 16.30 h than from 11.30-13.30 h. It was shown that plasma T may differ significantly (P < 0.02) between groups (n = 6-7) of untreated rats bled under identical conditions and it is suggested that gonadotrophin stimulation be included in experimental designs to reduce the difficulty of differentiating between normal variability and treatment effects.
mesh_terms: D000818:Animals; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D002940:Circadian Rhythm; D008297:Male; D051381:Rats; D013737:Testis / Q000098:blood supply / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000378:metabolism*; D014680:Veins
chemical_list: D006063:Chorionic Gonadotropin; D013739:Testosterone