A diurnal variation in testicular hormone production is maintained following gonadotrophin suppression in normal men

• Published in: Clinical endocrinology (Oxford) Vol. 66; no. 1; pp. 123 - 129
• Main Authors: Walton, Melanie J., Anderson, Richard A., Kicman, Andrew T., Elton, Rob A., Ossowska, Karolina, Baird, David T.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.01.2007; Blackwell
• Subjects: Adult; Analysis of Variance; Biological and medical sciences; Case-Control Studies; Circadian Rhythm; Desogestrel - pharmacology; Endocrinopathies; Epitestosterone - blood; Epitestosterone - urine; Follicle Stimulating Hormone - blood; Fundamental and applied biological sciences. Psychology; Gonadotropins - antagonists & inhibitors; Humans; Hydrocortisone - blood; Inhibins - blood; Luteinizing Hormone - blood; Male; Medical sciences; Middle Aged; Sex Hormone-Binding Globulin - analysis; Testicular Hormones - blood; Testicular Hormones - urine; Testosterone - blood; Testosterone - pharmacology; Testosterone - urine; Vertebrates: endocrinology; Human; Suppression; Adult; Male; Testicular hormone; Diurnal variation; Endocrinology
• ISSN: 0300-0664; 1365-2265
• DOI: 10.1111/j.1365-2265.2006.02696.x

Summary Objective  A diurnal variation in serum testosterone in adult men is well recognized, but whether this occurs during exogenous testosterone administration and the degree to which it is endogenous to the testis is unclear. Design  A clinical research centre investigation of testicular function in normal men. Patients  Twenty normal men were recruited, 10 of whom were investigated during administration of testosterone with etonogestrel to suppress gonadotrophin secretion. Measurements  Hourly blood samples were taken over 24 h for measurement of testosterone, inhibin B, LH, FSH and cortisol. Urinary excretion of testosterone and the testicular steroid epitestosterone was also measured. Results  In the controls, a diurnal variation in serum testosterone and LH but not FSH was detected. The treated group had similar testosterone concentrations but showed no diurnal variation. Periodicity was also detected in inhibin B concentrations in 5 of the controls and in 9 of the treated group, who also showed synchrony not seen in the controls. Both groups showed diurnal variation in cortisol. Urinary testosterone excretion did not show a diurnal variation in either group, but this was apparent for epitestosterone with a morning peak in both groups despite the markedly lower excretion in the treated men. Conclusions  The diurnal variation of testosterone in normal men is due to a change in secretion rather than in clearance and is largely LH driven. An endogenous rhythm in both testicular steroidogenesis (epitestosterone) and Sertoli cell function (inhibin B) is also present.