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.

summaryIn vivo microperfusion techniques were used to investigate the role of Na¤-H¤ exchange in the efferent ducts of the rat. Individual efferent ducts were perfused with a Krebs-Ringer bicarbonate solution (KRB) containing 0, 1, 3, 5 or 7·5 mÒ amiloride. Concentrations of 1-5 mÒ amiloride inhibited fluid reabsorption from the efferent ducts in a linear dose-dependent manner with an apparent Km of 3 mÒ. Inhibition was maximal at 5 mÒ with reabsorption reduced by about 70%. The effects of amiloride were completely reversible and there was little effect of amiloride on luminal osmolality and concentrations of Na¤, Cl¦ or K¤.

Analyses of samples of luminal fluid from the rete testis, distal efferent ducts, and epididymal regions 2-5 and 8 revealed that 91% of the fluid leaving the testis is reabsorbed by the efferent ducts, 79% of the remainder is reabsorbed proximal to epididymal regions 4 and 5, and there is a net secretion of fluid into the duct caudally. There is a net reabsorption by the efferent ducts of 73% of the protein leaving the testis and then a net secretion along the epididymis. SDS-PAGE of the luminal fluids indicated that four new protein bands that were not present in blood appeared in the efferent ducts, 5 in epididymal regions 1-5, 6 in regions 6 and 7, and one in region 8. Two bands in samples from the efferent ducts were absent caudally, and one band present in region 7 was absent in region 8. The rates of incorporation of (35)S-methionine into minced duct in vitro varied among regions when expressed per milligram of wet weight of tissue (region 2-5 > region 7 > region 6 > region 1 > region 8 > ductuli efferentes), and orchidectomy had little effect on the rates. Incorporation into four proteins that were secreted in vitro (M(r) 38 000, 20 000, 15 000, and 13 000) was reduced or abolished by orchidectomy and restored by testosterone therapy. The secretion of three proteins (M(r) 52 000, 23 000, and 22 000) was reduced or abolished by orchidectomy and not restored by testosterone therapy. SDS-PAGE of detergent extracts of sperm indicated that five proteins were lost and nine were gained during epididymal transit. Seven of the proteins gained were about the same molecular weight as proteins secreted by the epididymis (M(r) 94 000, 52 000, 38 000, 36 000, 22 000, 20 000, and 13 000) and were analyzed using N-terminal amino acid microsequencing.

The role of Na(+) and Cl(-) in fluid reabsorption by the efferent ducts was examined by perfusing individual ducts in vivo with preparations of 160 mM NaCl in which the ions were replaced, together or individually, with organic solutes while maintaining the osmolality at 300 mmol/kg. Progressively replacing NaCl with mannitol reduced net reabsorption of water and the ions in a concentration-dependent manner, and caused net movement into the lumen at concentrations of NaCl less than 80 mM. The net rates of flux were lower for Na(+) than for Cl(-). In collectates, [Na(+)] was greater than [Cl(-)], indicating that Cl(-) transport is probably linked with another anion. Replacing either Na(+) or Cl(-) in perfusates (with choline and isethionate, respectively) while maintaining the other inorganic ion at 160 mM also reduced net rates of reabsorption in a concentration-dependent manner to zero when either ion was completely replaced. There were no significant differences in the osmolality of perfusate and collectate, and collectates contained a mean of 3.4 mM K(+), indicating a backflux of K(+) into the lumen. It is concluded that fluid reabsorption from the efferent ducts is dependent on the transport of both Na(+) and Cl(-) from the lumen (from a luminal concentration of at least 70-80 mM), and that Cl(-) transport is dependent on another anion. The epithelium is permeable to K(+) and has a higher permeability to a range of organic solutes (mannitol, choline, and isethionate) than epithelium in the proximal kidney tubules.

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