Functional characterization the alpha adrenergic receptor modulating the hydroosmotic effect to vasopressin on the rabbit cortical collecting tubule

To characterize the type of alpha adrenergic receptor, the effects of specific alpha adrenergic agonists and antagonists 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 microU/ml), net fluid volume absorption (Jv, nanoliters per minute per millimeter) was 1.39 +/- 0.09 and osmotic water permeability coefficient (Pf, X 10(-4) centimeters per second) was 150.2 +/- 15.0. The addition of 10(-6) M phenylephrine (PE), an alpha adrenergic agonist, resulted in a significant decrease in Jv and Pf to 0.72 +/- 0.11 (P less than 0.005) and 69.9 +/- 10.9 (P less than 0.005). The addition of 10(-4) M prazosin (PZ), an alpha adrenergic antagonist, did not cause any significant change in Jv and Pf, which were 0.71 +/- 0.09 (P = NS vs. AVP + PE) and 67.8 +/- 9.5 (P = NS vs. AVP + PE), respectively. In a separate group of tubules, in the presence of AVP (100 microU/ml) and PE (10(-6) M), Jv and Pf were 0.78 +/- 0.17 and 76.1 +/- 18.0, respectively. The addition of 10(-6) M yohimbine (Y), an alpha 2 adrenergic antagonist, resulted in a significant increase in Jv to 1.46 +/- 0.14 (P less than 0.01) and Pf to 157.5 +/- 22.3 (P less than 0.005). Y (10(-4) M) or PZ (10(-4) M) alone did not significantly affect Jv and Pf in the presence of AVP )100 microU/ml). The effect of the natural endogenous catecholamine norepinephrine (NE) on Jv and Pf in the presence of AVP and propranolol (PR) was next examined. Jv and Pf were 1.53 +/- 0.07 and 176.3 +/- 5.2, respectively, in the presence of AVP (100 microU/ml) and PR (10(-4) M). The addition of NE (10(-8) M) resulted in a significant decrease in Jv to 1.19 +/- 0.11 (P less than 0.05) and Pf to 127.0 +/- 11.3 (P less than 0.02). Increasing the concentration of NE to 10(-6) M resulted in a further decrease in Jv and Pf to 0.70 +/- 0.10 (P less than 0.01 vs. NE 10(-8) M) and 68.5 +/- 10.6 (P less than 0.01 vs. NE 10(-8) M), respectively. The inhibitory effect of NE on AVP-induced water absorption was blocked by Y, but not by PZ. The effect of the alpha 2 adrenergic agonist clonidine (CD) on Jv and Pf was also examined. In the presence of AVP (10 microU/ml) Jv and Pf were 1.65 +/- 0.04 and 175.1 +/- 13.1, respectively. The addition of CD (10(-6) M) resulted in a significant decrease in Jv to 1.08 +/- 0.12 (P < 0.01) and Pf to 108.1 +/- 15.4 (P < 0.01). Increasing the concentration of C