EFFECTS OF CENTRAL ALPHA-ADRENERGIC AGONISTS ON HORMONE-INDUCED 3-PERCENT NACL AND WATER-INTAKE

Male rats received intracerebroventricular (ICV) renin (600 ng) or dai ly subcutaneous injections of deoxycorticosterone (5 mg) to induce 3% NaCl and water intake. Noradrenaline (NOR; 40-160 nmol) and clonidine (CLO; 5-20 nmol) injected ICV. induced 70 to 100% inhibition of the in takes. Phenylephrine (PHE; 40-160 nmol) injected ICV induced 60 to 95% inhibition of the intakes. NOR and PHE induced a stronger inhibition on the 3% NaCl intake induced by renin than on the intake induced by d eoxycorticosterone (DOC), and CLO did the opposite. CLO was always mor e effective than PHE to induce inhibition of the intakes. The results suggest that NOR inhibits hormone (angiotensin II, aldosterone)-induce d NaCl intake by acting mainly on alpha(2)-adrenergic receptors.