5-Hydroxytryptamine--a local regulator of testicular blood flow and vasomotion in rats.

The effects of 5-hydroxytryptamine (5-HT), 5-HT2 receptor antagonists (ritanserin and ketanserin), histamine and substance 48/80 on testicular blood flow and microcirculation were studied in adult rats. The substances were administered by topical application on the testicular surface and by intratesticular injections, and blood flow was measured by radioactive microspheres and with a laser Doppler flowmeter. Blood flow was decreased by 5-HT in a dose-dependent manner and vasomotion in the testis was inhibited, suggesting that it could be involved in the physiological regulation of the testicular vasculature. The 5-HT antagonists did not significantly influence flow or vasomotion in intact testes. Histamine did not cause any major effects on testicular blood flow. Substance 48/80 caused degranulation of testicular mast cells, and reduced testicular blood flow and vasomotion suggesting that testicular mast cells, possibly by releasing 5-HT, could be involved in the local control of the testicular vasculature.