Dopamine Inhibits Vasopressin Action in the Rat Inner Medullary Collecting Duct via 2-Adrenoceptors

We compared the effects of dopamine and norepinephrine on vasopressin (AVP)-stimulated increases in osmotic water permeability (Pf) and cAMP accumulation in the rat inner medullary collecting duct (IMCD). Both dopamine and norepinephrine inhibited AVP-induced Pf and cAMP accumulation in a concentration-dependent manner; however, norepinephrine was approximately 100-fold more potent than dopamine. The effects of dopamine on Pf were antagonized by the selective 2-adrenoceptor antagonist, rauwolscine (10 nM–1 M). Clozapine (10 M), a dopamine D4 receptor antagonist with significant activity at adrenergic receptors, partially attenuated both dopamine and norepinephrine-induced decreases in AVP-stimulated Pf. Dopamine-induced inhibition of AVP-dependent cAMP levels was antagonized by the 2-adrenoceptor antagonists, rauwolscine, idazoxan, and yohimbine, but not by the dopamine receptor antagonists, spiperone, SCH-23390, or raclopride. Clozapine (1–10 M) inhibited the effects of both dopamine and norepinephrine on AVP-stimulated cAMP levels. We conclude that the inhibitory effects of dopamine on AVP-induced Pf and cAMP accumulation in the rat IMCD are mediated via 2adrenoceptors. It is generally accepted that dopamine is an important regulator of renal function (Lee, 1993). When administered to humans and other species, dopamine has marked natriuretic and diuretic effects (Jose et al., 1992; Lee, 1993). Although the hemodynamic actions of dopamine (increased renal blood flow and glomerular filtration rate) undoubtedly contribute to these effects on renal function, direct tubular actions of dopamine are also likely to be involved (Jose et al., 1992; Holtback et al., 2000). The proximal tubule and inner medullary collecting duct (IMCD) cells in culture synthesize dopamine (Huo et al., 1991; Jose et al., 1992), and the natriuretic effects of this catecholamine appear to be part of an intrarenal paracrine or autocrine system (Siragy et al., 1989; Jose et al., 1992; Holtback et al., 2000). Dopamine receptors have been identified in various segments of the nephron. Results from pharmacological, ligand binding, and reverse transcriptase-polymerase chain reaction studies have provided evidence for D1, D2, D3, and D4 receptors associated with various tubule segments (Meister et al., 1991; Takemoto et al., 1991; Gao et al., 1994; O’Connell et al., 1995, 1998; Sun et al., 1998). Functional effects attributed to dopamine include inhibition of Na ,K -ATPase in a number of tubule segments (Bertorello and Katz, 1993), inhibition of fluid absorption, Na /H exchange and phosphate transport in the proximal tubule (Kaneda and Bello-Reuss, 1983; Felder et al., 1990; Baum and Quigley, 1998), and inhibition of vasopressin-stimulated osmotic water permeability (Pf) and Na transport in the cortical collecting tubule (Muto et al., 1985; Sun and Schafer, 1996). Although most of the proximal tubule effects of dopamine appear to be due to activation of D1 receptors (Felder et al., 1990; Baum and Quigley, 1998; Holtback et al., 2000), a series of recent studies (Sun and Schafer, 1996; Li and Schafer, 1998; Sun et al., 1998) suggests that dopamine’s effects on vasopressin-dependent water permeability and Na transport in the rat cortical collecting tubule are mediated by a D4-like receptor. This was based on observations that D4 receptor mRNA and protein are expressed throughout the collecting duct system (Sun et al., 1998), and agonists and antagonists of D1, D2, and D3 receptors failed to mimic or attenuate the inhibitory effects of dopamine on AVP-dependent water, Na transport (Sun and Schafer, 1996), and AVP-stimulated cAMP accumulation (Li and Schafer, 1998). However, clozapine, an “atypical” neuroleptic with D4 antagonist activity (Van Tol et al., 1991), did attenuate the dopamine-mediated effects on vasopressin action (Sun and Schafer, 1996; Li and Schafer, 1998). In the present study, the effects of dopamine were examined on AVP-dependent water permeability and cAMP accumulation in the rat IMCD to determine whether a similar system is operable in this segment of the nephron. Since high concentrations of dopamine can activate 2-adrenoceptors (Phillips, 1980), which are known to inhibit AVP action in the IMCD (EdABBREVIATIONS: IMCD, inner medullary collecting duct; AVP, arginine vasopressin; Pf, osmotic water permeability; CPT-cAMP, 8-p-chlorophenylthio-cAMP. 0022-3565/01/2983-1001–1006$3.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 298, No. 3 Copyright © 2001 by The American Society for Pharmacology and Experimental Therapeutics 4062/925669 JPET 298:1001–1006, 2001 Printed in U.S.A. 1001 at A PE T Jornals on D ecem er 4, 2017 jpet.asjournals.org D ow nladed from wards and Gellai, 1988), the effects of norepinephrine were studied in parallel. Contrary to expectations, the results of the present study suggest that the effects of dopamine on AVP action in the IMCD can be attributable to activation of