Testicular blood flow : methodological and functional studies in the rat

Abstract: Different methods of measuring testicular blood flow in the rat were compared in an attempt to find an accurate method for measuring physiological testicular blood flow. It was found that both the Xenon- 133 clearance technique and the radioactive microsphere technique probably reflect true physiological blood flow in the testis.The microsphere method was used to study some functional aspects of testicular blood flow. There was a significant positive correla­tion between the testicular blood flow and the outflow of testosterone in the spermatic vein, indicating that testicular hormone secretion may be affected indirectly via a primary effect on testicular blood flow. Intra-arterial infusion of LH caused a significant decrease in the vascular resistance of the testis. However, the effect was small in comparison with the simultaneous effect of LH on plasma testosterone concentration, indicating that blood flow changes are not critically involved in the acute effect of LH on testicular endocrine function. Infusion of epinephrine or norepinephrine did not induce any absolute changes in testicular blood flow, but norepinephrine caused an in­crease in testicular vascular resistance. Both catecholamines caused significant depressions in plasma testosterone concentration. It was concluded that the catecholamine induced reductions in testosterone concentration were not due to a vascular effect on the testis.Testicular blood flow and Leydig cell function in the cryptorchid and heated testis were also studied. There was a significant increase in relative blood flow in the cryptorchid testis, probably due to an highly altered morphology consisting of a relative increase in inter­stitial tissue containing blood vessels. Furthermore, it was found that the testosterone levels, in spermatic vein blood from the cryptor­chid testis, were highly reduced in comparison to the corresponding values for the scrotal testis and the outflow of testosterone from the cryptorchid testis was estimated to be only 13% of that from the scrotal one. This result suggested that the Leydig cell function was greatly impaired in the cryptorchid testis. The vasculature of the testis is relatively insensitive to local heating since no effects on vascular resistance were observed when warming the testis to ab­dominal temperature. On the other hand, there was a significant in­crease in blood flow in the testis at 41 and 43° C, which are tempera­tures known to induce cessation of spermatogenesis in the rat. The acute response of the testis to LH stimulation was reduced when warm­ing the scrotum to 41 and 43° C. This strongly indicates an impaired Leydig cell function at these temperatures. Since blood flow was in­creased at these temperatures it was concluded that the reduced Leydig cell responsiveness to LH was unrelated to testicular perfusion.