BLUNTED RENAL RESPONSE TO ATRIAL-NATRIURETIC-PEPTIDE IN CONGESTIVE-HEART-FAILURE RATS IS REVERSED BY THE ALPHA-2-ADRENERGIC AGONIST CLONIDINE

We wished to determine whether pharmacologic inhibition of the exaggerated sympathetic nerve activity in congestive heart failure (CHF) could restore the renal response to exogenous atrial natriuretic peptide (ANP) administration. Left ventricular (LV) myocardial infarction was induced in Sprague-Dawley rats (n = 16) by coronary artery ligature. Four to 6 weeks postoperatively, an isotonic saline (controls) or clonidine 5 μg/h infusion was given. Four hours later, all animals received incremental doses of rat ANP (99-126) (0.25, 0.5 and 1.0 μg/kg/min). The continuous clonidine infusion transiently increased urinary volume (UV) as compared with the saline controls. Mean arterial pressure (MAP), heart rate (HR), and plasma norepinephrine (NE) were significantly decreased by clonidine. The graded ANP infusions significantly increased UV (saline 39.13 ± 12.45 and clonidine 90.25 ± 13.69 μl/min, p < 0.05) and UNaV (saline 4.26 ± 1.10 and clonidine 8.81 ± 1.59 μmol/min, p < 0.05) in clonidine-pretreated rats as compared with saline-pretreated rats. We conclude that the diuretic and natriuretic responses to ANP are significantly increased in CHF after presynaptic inhibition of NE release by low-dose clonidine.