RECEPTOR-MEDIATED EFFECTS OF CLONIDINE ON NEED-INDUCED 3-PERCENT NACLAND WATER-INTAKE

Clonidine combined with adrenergic antagonists were injected in the me dial septal area in order to characterize the type of receptors involv ed with its inhibitory effect on 3% NaCl and water intake of sodium-de pleted (furosemide + 24 h of removal of ambient sodium) and 30-h water -deprived rats, respectively. The inhibitory effect of clonidine (20 n mol) on need-induced water intake was reduced 50% by an 80-nmol dose o f either idazoxan, yohimbine or prazosin. The inhibitory effect of clo nidine (30 nmol) on need-induced 3% NaCl intake was completely antagon ized by idazoxan (80, 160 nmol), not altered by yohimbine (40-160 nmol ), and partially potentiated (40 nmol) or inhibited (160 nmol) by praz osin. Propranolol did not alter the effects of clonidine on either wat er (80 nmol) or 3% NaCl (40-160 nmol) intake. The results suggest that the inhibitory effects of clonidine on 3% NaCl and water intake are m ediated by different types of alpha2-adrenergic receptors. Copyright ( C) 1997 Elsevier Science Inc.