Modulation of the hydro-osmotic effect of vasopressin on the rabbit cortical collecting tubule by adrenergic agents

The effects of catecholamines on antidiuretic hormone ([Arg⁸]-vasopressin [AVP])-induced water absorption were evaluated in cortical collecting tubules isolated from the rabbit kidney and perfused in vitro. In the presence of AVP (100 μU/ml), net fluid volume absorption (J_v, nanoliters per minute per millimeter) was 1.14±0.12 and osmotic water permeability coefficient (P_f, X 10^-4 centimeters per second) was 217.3±39.9. The addition of the alpha-adrenergic agonist, phenylephrine (PE), in a concentration of 10^-6 M resulted in a significant decrease in J_v and P_f to 0.83±0.13 (P < 0.001) and 148.8±41.8 (P < 0.02), respectively. Increasing the concentration of PE to 10^-5 M resulted in a further decrease in J_v and P_f to 0.53±0.05 (P < 0.05 vs. PE 10^-6 M) and 88.5±9.0 (P 0.05 vs. PE 10^-6 M), respectively. In a separate group of tubules, in the presence of AVP (100 μU/ml) and PE (10^-5 M), J_v and P_f were 0.35±0.07 and 66.0±17.3, respectively. The addition of the alpha-adrenergic antagonist, phentolamine (PH), in a concentration of 10^-6 M resulted in a significant increase in J_v to 1.07±0.19 (P < 0.001) and P_f to 193.3±35.9 (P < 0.005). PH (10^-5 M) alone did not significantly affect J_v and P_f in the presence of AVP (100 μU/ml) nor in the presence of 8-bromo adenosine 3',5' cyclic monophosphate (8-BrcAMP). J_v and P_f were 1.20±0.21 and 174.0±25.8, respectively, in the presence of 8-BrcAMP (10^-4 M).

We next examined the effect of the beta-adrenergic agonist, isoproterenol (ISO), on J_v and P_f in the presence of AVP. J_v and P_f were 1.04±0.10 and 202.6±17.2, respectively, in the presence of AVP (100 μU/ml) and 1.06±0.18 and 193.4±27.7, respectively, in the presence of AVP (10μU/ml). However, in the presence of AVP in a concentration of 2.5 μU/ml, J_v was 0.60±0.07 and P_f was 100.7±24.7. ISO (10^-6 and 10^-5 M) did not have any significant effect in the presence of the above maximal and submaximal concentrations of AVP. In the absence of AVP, control J_v was 0.01±0.12 and P_f was 4.6±11.0. The addition of ISO at 25 or 37°C did not result in any significant change in J_v or P_f.

These studies indicate that alpha-adrenergic agonists directly inhibit AVP-mediated water absorption at the level of the tubule, an effect that can be blocked by a specific alpha-adrenergic antagonist. This effect appears to be exerted at the level of activation of adenylate cyclase since it is absent in the presence of cAMP. The beta-adrenergic agonists do not directly inhibit or enhance AVP-mediated water absorption at the level of the renal tubule.

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