We have used rat cortical collecting tubules perfused in vitro to study the effects of antidiuretic hormone (ADH) and desoxycorticosterone (DOCA) on the unidirectional fluxes of sodium. We found that in the basal state, lumen-to-bath flux (Jib) and bath-to-lumen flux (JbJ) of 22Na were approximately equal, 39.5±3.9 and 41.8±11.0 pmol min-1 mm-', respectively, resulting in no net flux. Addition of 100 1U/ml ADH to the bath produced a stable increase in Jib to 583±4.7 pmol* min-' * mm-'. Addition of ADH to a tubule from a DOCA-pretreated rat caused an increase in Jib to 144.1±12.0 pmol* min-' mm-'. Neither hormone had an effect on Jbi. Thus ADH produced a greater absolute and fractional increase in Jib when the animal was pretreated with DOCA, and the ADH-induced increase over baseline was greater than the DOCA-induced increase. Both the ADHand DOCA-induced stimulation of Jib were completely abolished by 10-5 M luminal amiloride, suggesting that the route of sodium transport stimulated by both hormones involves apical sodium channels. However, ADH and DOCA have very different time courses of action; ADH acted within minutes, while aldosterone and DOCA are known to require 90-180 min. The facilitating action of ADH on DOCA-induced stimulation of sodium transport may be important for maximal sodium reabsorption and for the ability to achieve a maximally concentrated urine.

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The effect of arginine vasopressin (ADH) on water permeability and transepithelial voltage was examined in cortical collecting tubules from a specific pathogen-free line of male Sprague-Dawley rats (75-125 g body weight). Tubules were bathed in a medium resembling serum ultrafiltrate (310 mOsm/kg H2O) at 38 degrees C. Osmotic water permeability (Pf, micron/sec) was determined by the volume flow occurring with a hypo-osmotic perfusate (210-220 mOsm/kg H2O) and diffusional water permeability (Pd, micron/sec) was calculated from the lumen-to-bath flux of tritiated water using an isosmotic perfusate. In the absence of ADH, both Pf and Pd were low, 17 +/- 6 and 9.0 +/- 0.6 (SEM), respectively. ADH added to the bath at concentrations above 0.5 microunits/ml increased Pf, with a maximal response at 40 microunits/ml or greater. With 100 microunits/ml ADH, Pf and Pd were, respectively, 994 +/- 117 and 37.0 +/- 2.4. Without ADH, the transepithelial voltage was variable (range, -5.4 to +2.5 mV; mean, -1.9 +/- 0.4); however, with 100 microU/ml ADH, it hyperpolarized (lumen-negative) by 4.2 +/- 0.8 mV. In contrast to findings in the rabbit, both the hyperpolarization and the increased water permeability persisted for at least 3 hr. The higher water permeabilities are consistent with the shorter length of the cortical collecting tubule in the rat, and may reflect the importance of attaining osmotic equilibration within the cortex during maximal antidiuresis.