Effects of chemotherapy-induced testicular damage on inhibin, gonadotropin, and testosterone secretion: A prospective longitudinal study

To investigate the role of inhibin in the control of follicle- stimulating hormone (FSH) secretion, we have measured levels of immunereactive inhibin (ir-inhibin), inhibin B, Pro-αC containing inhibins, FSH, luteinizing hormone (LH), and testosterone in twelve men with hematological malignancies before, during, and after chemotherapy. Inhibin B levels fell significantly by i month from a mean ± SE baseline level of 273.2 ± 32.8 pg/mL, reaching a nadir of 52.6 ± 15.3 pg/mL at 4 months (P <0.0001). FSH levels increased within the first month from a baseline level of 3.9 ± 0.6 IU/L, reaching a peak level of 22.4 ± 3.3 IU/L at 4 months (P <0.0001). FSH and inhibin B were significantly and inversely correlated (r = 0.69, P <0.0001). Pro-αC containing inhibin levels increased significantly (P <0.05) at 8 months and were significantly and positively correlated with FSH (r = 0.88, P = 0.002). LH levels increased significantly but to a much lesser extent than FSH, the increase becoming evident only 4 months after treatment commenced (P <0.03). Levels of ir-inhibin and testosterone remained unchanged throughout the study. These data provide strong support to the hypothesis that inhibin B is the physiologically important form of inhibin in men, negatively regulating FSH secretion at the pituitary. Furthermore, they suggest that FSH stimulates inhibin α-subunit secretion by the testis.