Hypothalamic-Pituitary-Testicular Axis Function in Endurance-Trained Males

Abstract The hypothalamic-pituitary-testicular (H-P-T) axis was evaluated in groups of endurance-trained (TRG) and untrained (UNT) males. Each group was subjected to: 1) a 4-h resting hormonal profile [testosterone (T), free-testosterone (FT), estradiol (E2), luteinizing hormone (LH), prolactin (PRL), and Cortisol (C)], 2) a dopamine antagonist (DA; 10 µg · kg -1 body weight) challenge to the pituitary-testes, and 3) a gonadotropin-releasing hormone (GnRH; 120 µg·kg -1 body weight) challenge to the pituitary-testes. Compared to UNT, the TRG resting T (4.8 ± 0.7 vs 7.1 ±1.2 ng-ml -1 ; p = 0.05) and PRL (3.3 ± 1.4 vs 7.0 ± 2.3 ng-ml -1 ; p = 0.09) were lower while LH was elevated (15.0±1.8 vs 11.8±1.5 mIU · ml -1 ; p = 0.06). The DA challenge produced a greater integrated PRL response in the TRG (2962.7±265.1 ng ± ml -1 ·min) than in the UNT (1735.3 ±282.0 ng·ml -1 ·min; p = 0.01). No significant changes were observed in T following the DA-induced PRL rise. The TRG had a blunted LH response (817.2±111.6 mIU · ml -1 · min) following the GnRH injection as compared to the UNT (1493.7 ± 213.4 mIU ·ml -1 ·min; p < 0.02). T levels were significantly (p < 0.03) increased in both groups by the LH rise after the GnRH challenge (TRG = 9.9± 5.0%; UNT = 8.6 ± 9.9%, respectively), but no significant between group differences were observed. Results suggest endurance training produces an enhanced PRL and attenuated LH release by the pituitary. Whether these alterations may have a direct effect on the functional status of the H-P-T axis, resulting in the suppressed resting levels of T in the TRG, remains uncertain.