Immunoreactive somatostatin in male reproductive system in humans.

Somatostatin-like immunoreactivity is distributed widely in humans; the highest concentration is in the central nervous system, gastrointestinal tract, and pancreas. To determine if somatostatin is present in the male reproductive system, we analyzed human testis, epididymis, prostate, and semen. Somatostatin-like immunoreactivity was detectable in acid extracts of human testis, epididymis, and prostate (n = 6 each) in concentrations of 4.0 +/- 1.4 (+/- SD), 14.7 +/- 3.2, and 27.5 +/- 5.1 pmol/g wet wt, respectively. Considerable amounts of immunoreactive somatostatin also were detectable in semen; the mean value was 3.8 +/- 1.3 nmol/L (n = 6). This value was 200-fold higher than that in peripheral plasma. The somatostatin immunoreactivity in these tissues was characterized by gel filtration chromatography. Two peaks of somatostatin immunoreactivity, one coeluting with somatostatin-14 and the other with somatostatin-28, were found in the testis, epididymis, prostate, and hypothalamus. The amounts of the two sizes were nearly equal in the testis; somatostatin-14 predominated in the epididymis, prostate, and hypothalamus; whereas only somatostatin-28 was detected in semen. The presence of somatostatin in the male reproductive system suggests that somatostatin may play a role in the regulation of reproductive function in men.