CLONIDINE AND PGE2 HAVE DIFFERENT EFFECTS ON NA+ AND WATER TRANSPORT IN RAT AND RABBIT CCD

We examined the effects of prostaglandin E2 (PGE2) and the adrenergic agonist clonidine on osmotic water permeability (P(f)), lumen-to-bath Na-22+ flux (J1 --> b), and transepithelial voltage (V(T)) in isolated perfused cortical collecting ducts (CCD) from rats and rabbits. Although PGE2 inhibited arginine vasopressin (AVP)-dependent J1 --> b and P(f) in CCDs from deoxycorticosterone (DOC)-treated and untreated rabbits, 0.1-10-mu-M PGE2 had no inhibitory effect on any of these transport parameters in CCDs from DOC-treated rats in presence of AVP. On the other hand, clonidine (1-mu-M in bathing solution) reversibly inhibited AVP-dependent P(f), J1 --> b, and V(T) in the rat CCD by 30-40%, and 0.3-mu-M yohimbine, a specific alpha-2-adrenoceptor antagonist, reversed these effects. However, we were unable to demonstrate any inhibitory effect of 1-10-mu-M clonidine on P(f), J1 --> b, or V(T) in the rabbit CCD using a variety of protocols. These results are consistent with the pattern of inhibition of AVP-dependent adenosine 3',5'-cyclic monophosphate (cAMP) production in the rat and rabbit CCD in that PGE2 inhibits both transport and cAMP production in the rabbit but not the rat CCD, and clonidine inhibits both transport and cAMP production in the rat but not the rabbit CCD [D. Chabardes, C. Brick-Ghannam, M. Montegut, and S. Siaume-Perez, Am. J. Physiol. 255 (Renal Fluid Electrolyte Physiol. 24): F43-F48, 1988].