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Low Serum Bioactive Luteinizing Hormone In Nonorganic Male Impotence: Possible Relationship with Altered Gonadotropin-Releasing Hormone Pulsatility

Institute of V Clinica Medica, Chair of Andrology, University La Sapienza 00161 Rome Italy

We determined the biological activity of serum LH in 23 men, aged 25–50 yr, complaining of nonorganic impotence of at least 1-yr duration and 20 normal men. All of the impotent men had normal general physical examinations, penile Doppler tests, psychological tests, and peripheral nerve conduction. Serum PRL, FSH, LH, and thyroid hormone concentrations were normal as were the results of provocative tests of TSH, gonadotropin, and PRL secretion.

The mean serum immunoreactive LH (I-LH) levels, measured in each impotent and normal man in three samples taken at 15-min intervals, were similar [7.2 ± 0.5 (±SE) vs. 6.4 ± 0.5 mlU/mL (IU/L)]. In contrast, the mean serum bioactive LH (B-LH) level was significantly lower in the impotent men than in the normal men [15.9 ± 2.1 (±SE) vs. 33.0 ± 2.8 mlU/mL (IU/L); P < 0.05], as was the LH bio- to immunoactive (B/I) ratio (2.1 ± 0.2 vs. 5.6 ± 0.5; P < 0.02). The mean serum testosterone level in the impotent men, although all individual values were within the range of normal for our laboratory [200–900 ng/100 mL (693–3120 nmol/L)], was 25% lower than that in the normal men [347 ± 23 vs. 450 ± 26 ng/100 mL; P < 0.05 (1204 ± 81 vs. 1560 ± 91 nmol/L)]. In addition, a significant positive correlation was found between serum testosterone levels and LH B/I ratios in the impotent men (r = 0.45; P = 0.029). Pulsatile LH secretion, measured in six impotent and four normal men in blood samples collected every 15 min for 6 h, was similar in the two groups. The mean serum I-LH levels were similar [7.5 ± 1.1 (±SE) vs. 5.1 ± 1.0 mlU/mL (IU/L)], while the mean serum BLH level as well as the LH B/I ratio was significantly lower in the impotent men throughout the observation period [11.4 ± 2.0 (±SE) vs. 26.0 ± 3.2 mlU/mL (IU/L) and 1.4 ± 0.2 vs. 5.4 ± 0.6; P < 0.05 and P < 0.02, respectively]. The B-LH pulse amplitude in the impotent men was reduced [mean peak LH, 8.6 ± 0.3 vs. 25.3 ± 4.0 mlU/mL (IU/L); P < 0.05], while the LH pulse frequency was similar in the two groups. The median intrapulse LH B/I ratios were significantly higher than the median interpulse ratios in both impotent (P = 0.02) and normal men (P = 0.01). However, the increase in the intrapulse serum LH B/I ratios in the impotent men was significantly lower than that in the normal men (P = 0.008), suggesting reduced B-LH secretion in response to endogenous GnRH pulses. Exogenous GnRH administration (100 µg, iv) increased serum I-LH levels similarly in both groups [44.9 ± 5.0 vs. 34.0 ± 3.9 (±SE) mlU/mL (IU/L)], but the peak serum B-LH was lower in the impotent men [34.3 ± 4.6 vs. 153 ± 22 (±SE) mlU/mL (IU/L); P < 0.03], and therefore, the mean LH B/I ratio was significantly lower when the serum B- and I-LH levels were maximal (at 30 min) than before GnRH administration in the impotent men.

These results demonstrate that men with nonorganic impotence have reduced serum LH biological activity and LH B/I ratio, changes that may reflect pulsatile GnRH secretion of lower than normal amplitude.

^* To Whom all correspondence and requests for reprints should be addressed.

Received January 21, 1988.

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