Differential Effects of Superior and Inferior Spermatic Nerves on Testosterone Secretion and Spermatic Blood Flow in Cats*

Abstract

Abstract It has been postulated that testosterone secretion is partially regulated by signals from the spermatic nerves. To further examine this hypothesis in vivo, the superior (SSN) or the inferior (ISN) spermatic nerves were stimulated electrically (varying intensity, 25 Hz, 0.2 msec, 10 min) in anesthetized cats, determining the testosterone concentration and the blood flow in the spermatic vein. In some additional experiments arterial blood was sampled, and norepinephrine (NE) output was calculated. Stimulation of the SSN (25–35 V) increased the testosterone concentration in spermatic vein blood (P < 0.01 compared with prestimulation levels). The response varied among animals, reaching a 50–100% increase in some animals, whereas in others it ranged from almost undetectable to more than 10 ng/100 g·min. Under the same experimental conditions, the NE output increased from 135.4 ± 99 to 1614.2 ± 347 pg/ml (P < 0.01), and spermatic blood flow decreased from 24.1 ± 1.42 to 20.2 ± 1.65 ml/min·100 g (P < 0.05) during nerve stimulation. By contrast, stimulation of the ISN (25–35 V) modified neither the testosterone concentration, the NE output, nor the blood flow in the spermatic vein. High intensity stimulation (36–70 V) of each spermatic nerve evoked different vascular and hormonal effects. SSN activation induced a marked decrease in spermatic blood flow during stimulation and an increase in the testosterone response, whereas ISN activation resulted only in an enhanced spermatic blood flow. Our results suggest that testosterone secretion, although mainly dependent on gonadotropin secretion, could be further regulated by neural inputs from the SSN acting directly or alternatively through changes in blood flow. It would appear that the SSN mainly supplies the vasoconstrictor fibers to the testis, whereas the ISN provides vasodilator fibers.