title: Daily variations of plasma sex hormone-binding globulin binding capacity, testosterone and luteinizing hormone concentrations in healthy rested adult males.
abstract: In this study the daily variations of plasma sex hormone-binding globulin (SHBG) binding capacity were measured together with plasma testosterone and luteinizing hormone (LH) concentrations in 7 healthy rested adult males. Plasma SHBG-binding capacity demonstrated a significant circadian rhythm (acrophase = 2.06 p.m.; mesor = 0.35 +/- 0.6 ng testosterone bound/100 ml; amplitude = 17% of the mesor). Plasma testosterone also showed a circadian rhythm (acrophase = 7.02 a.m.; mesor = 4.38 +/- 0.67 ng/ml; amplitude = 18% of the mesor). The free testosterone index (or the ratio between plasma testosterone and SHBG-binding capacity) was not correlated with plasma LH levels. In our hands this last parameter did not vary according to a circadian pattern. These data are discussed in terms of a feedback mechanism controlling the pituitary-testis axis regulation.
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013737:Testis / Q000502:physiology; D013739:Testosterone / Q000097:blood*
chemical_list: D012738:Sex Hormone-Binding Globulin; D013739:Testosterone; D007986:Luteinizing Hormone