DECREASED SERUM TESTOSTERONE AND FREE TRIIODOTHYRONINE LEVELS IN HEALTHY MIDDLE-AGED MEN INDICATE AN AGE EFFECT AT THE PITUITARY LEVEL

In an attempt to study further the age-specific influence on the hypot halamo-pituitary-gonadal axis as well as the hypothalamo-pituitary-thy roid axis, we have now investigated young and middle-aged men, conside ring possible confounding factors, Both serum total testosterone, free testosterone and the total ratio of testosterone to sex-hormone bindi ng globulin were significantly lower among middle-aged men as compared with young men (p = 0.02, p = 0.002 and p = 0.0003, respectively). In accordance with these findings there was also a decrease in the lutei nizing hormone response to gonadotrophin-releasing hormone in the midd le-aged men (p = 0.02). Free testosterone was correlated significantly with the luteinizing hormone response (r = 0.32, p = 0.02), Serum fre e triiodothyronine was significantly higher among young men as compare d with middle-aged men (p = 0.002) and the thyrotrophin-releasing horm one-stimulated thyrotrophin response was also higher in the young grou p compared with the middle-aged group, The present results may indicat e that the age effect on serum levels of testosterone and free triidot hyronine is mediated at the pituitary level.