The role of testicular fluid on blood plasma levels of FSH and LH in the ram (1)

The secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) is partly regulated by a non-steroid factor, inhibin, present in the testicular lymph and rete testis fluid (RTF). We were interested to know whether the RTF excreted into the epididymis has a regulatory role on the secretion of FSH and LH. The remaining rete testis of 6 adult rams hemicastrated 6 to 10 months earlier was cannulated. These rams were castrated either the day after the flow of RTF spontaneously stopped or 15 days after cannulation if the cannula was still functional. Two daily blood samples were taken from 7 days before cannulation to 7 days after castration and circulating levels of FSH, LH and testosterone were measured. Rete testis cannulation did not affect FSH, LH or testosterone plasma levels, although castration induced a sudden decrease in testosterone concentration and a rapid increase in FSH and LH levels. The present results suggest that the inhibin present in the RTF excreted into the epididymis does not play any role in the regulation of FSH and LH secretion. These hormones could be regulated by the inhibin present in the efferent circulation (lymph or blood) from the testis.