Perturbation of fluid reabsorption in the efferent ducts of the rat by testosterone propionate, 17beta-oestradiol 3-benzoate, flutamide and tamoxifen.

The regulation by oestradiol and testosterone of fluid reabsorption in the efferent ducts of the rat was investigated by determining the effects of administering the hormones and their antagonists. Untreated rats were compared to animals treated for 7 days with testosterone propionate (1 mg d(-1)), oestradiol benzoate (400 microg d(-1)), flutamide (10 mg d(-1)) or tamoxifen (1 mg d(-1)). Two procedures were used to measure perturbation of transepithelial fluid fluxes in vivo. The first procedure used cannulation of the proximal epididymal duct and micropuncture of the rete testis to compare the rate at which fluid enters and leaves the efferent ducts. Oestradiol administration increased (p < 0.001) the volume of fluid entering the epididymal duct from the efferent ducts (i.e. reduced reabsorption) while flutamide and tamoxifen decreased (p < 0.05) the amount of fluid entering the epididymal duct (i.e. increased fluid reabsorption). Testosterone did not have a statistically significant effect, although it produced a small increase in fluid reabsorption. There was some perturbation of the concentration of electrolytes and the osmotic pressure of the fluid leaving the efferent ducts, but as these were not large, it is suggested that the treatments had little effect on the basic mechanisms of osmotic water transport via solute-solvent coupling. The second procedure used to test the effect of the steroids involved microperfusing individual efferent ducts, and the results were consistent with those of the first study. Oestradiol decreased fluid reabsorption by the efferent ducts (p < 0.05), and testosterone (p < 0.05, lowest perfusion rate only), flutamide (p < 0.001) and tamoxifen (p < 0.01) increased reabsorption. The similar responses to flutamide and testosterone administration suggest that flutamide acted as an androgenic agonist by elevating systemic and luminal androgen. It is concluded that fluid reabsorption in the efferent ducts is perturbed by oestrogens and androgens. Although their actions have not been completely resolved, it is proposed that they are involved in a chronic regulation, with androgens stimulating and oestrogens suppressing fluid reabsorption by the ducts.