Hormonal Regulation of Fluid Reabsorption in Isolated Rat Cauda Epididymidis

Abstract

The hormonal dependence of fluid reabsorption was studied in isolated rat cauda epididymidis. In a group of experiments, rats were castrated by removal of the testes but leaving the epididymis with the blood supply intact. The rate of fluid reabsorption measured 3 wk after castration fell from the control value of 2.10 .+-. 0.10 .mu.l/cm2 per 30 min to 0.82 .+-. 0.12 .mu.l/cm2 per min (P < 0.001). When testosterone propionate (2 mg/kg per day) was injected into castrated rats for 7 days, the rate of fluid reabsorption was restored. This suggests that fluid reabsorption in rat cauda epididymidis is dependent on the presence of circulating androgen. Adrenalectomy in rats did not affect the rate of fluid reabsorption or did treatment of the epididymal ducts with aldosterone (10-6 M) in vitro. Both LH [luteinizing hormone] (5 .mu.g/ml) and FSH [follicle stimulating hormone] (5 .mu.g/ml) produced a small but significant increase in the rate of fluid reabsorption. Of the other hormones studied, vasopressin (10 mU[milliunits]/ml) increased the reabsorption rate by 15%. Acetylcholine (10-5 M) produced no effect on the rate of fluid reabsorption in the isolated rat cauda epididymidis. Epinephrine, 10-7 and 10-5 M, stimulated the reabsorptive rate by 52% and 101%, respectively. The effect of epinephrine (10-7 M) was completely blocked by propranolol (10-7 M). Norepinephrine (10-6 M) alone had no effect on the rate of fluid reabsorption. However, in the presence of propranolol (10-5 M) it produced an inhibition while in the presence of phenoxybenzamine (10-5 M), it produced an increase in the reabsorption rate. Both .gamma. and .beta.-receptors may be present in the epididymal epithelium. These receptors may play a physiological role in the regulation of fluid reabsorption in the rat cauda epididymidis.