Endocrine Abstracts

Involutive hypoandria (late onset hypogonadism) is characterized by decline in serum testosterone and increase of gonadotropins. Changes of hypothalamo-pituitary-testicular axis sensitivity are influenced by primary testicular changes and altered neuroendocrine regulation during aging. To evaluate age-related changes in gonadotroph and Leydig cell sensitivity two groups were formed: 1) 35 men, 51.8±3.2 years old, BMI=28.2±3.1 kg/m²; 2) 32 men, 63.2±6.8 years old, BMI=27.2±3.1 kg/m². Blood samples for FSH, LH, prolactin, estradiol, testosterone, SHBG were taken at 8 am. LHRH test was then performed (100 microg LHRH i.v., FSH and LH were taken before, 20 and 60 min later). Next three days HCG test was done (Pregnyl amp. a 5000 i.j./day, testosterone, estradiol and SHBG were detected before and after test). Hormone analyses were done by RIA. Statistics: Spearman, Mann-Whitney test, area under the curve-AUC. Neither increase of LH (4.5±3.1 vs. 5.8±3.5 IU/L, P>0.05) nor decrease of testosterone (19.7±7.6 vs. 14.8±6.9 nM/L, P>0.05) reached significant difference. The maximal LH response in 20 minutes (17.6±13.2 vs.27.0±11.8 IU/L, P=0.03) and LH AUC (962.5±738.2 vs. 1428.5±658 IU/L/min) were higher in older men. Higher sensitivity of Leydig cell testosterone response was observed in older group (19.2 to 33.1 vs. 14.2 to 31 nM/L, P=0.0021). Negative correlation was found between testosterone and BMI (P=0.02). Conclusion: Older men show significantly increased gonadotrophin release due to amplified secretory burst mass, diminished gonadal hormone negative feedback or primary alterations in hypothalamo-pituitary unit with aging. Leydig cell sensitivity is preserved during aging. Secondary testicular failure in aging male is due in part to decreased GnRH gene expression rather than to decreased pituitary responsiveness to LHRH.