IDAZOXAN AND THE EFFECT OF INTRACEREBROVENTRICULAR OXYTOCIN OR VASOPRESSIN ON SODIUM-INTAKE OF SODIUM-DEPLETED RATS

The alpha(2)-adrenergic agonist clonidine and the neuropeptide oxytoci n, inhibit sodium intake when injected intracerebroventricularly (i.c. v.). The present work investigates whether (1) vasopressin also inhibi ts sodium intake when injected i.c.v., and (2) the effect of oxytocin and of vasopressin on sodium intake is affected by i.c.v. injection of idazoxan, an alpha(2)-adrenergic antagonist. Clonidine (30 nmol), oxy tocin (40, 80 nmol) and vasopressin (40, 80 nmol) were injected i.c.v. 20 min prior to a 1.5% NaCl appetite test, in rats depleted of sodium for 24 h by a combination of a single s.c. injection of furosemide (1 0 mg/rat) and removal of ambient sodium. Every dose of clonidine, oxyt ocin and vasopressin inhibited the 1.5% NaCl intake. Seizures were obs erved with the higher dose of vasopressin, but not with either dose of oxytocin. The effect of i.c.v. injection of clonidine (30 nmol), oxyt ocin (80 nmol) or vasopressin (40 nmol) was partially inhibited by pri or i.c.v. injection of idazoxan (160, 320 nmol). The results suggest t hat the inhibition of 1.5% NaCl intake induced by i.c.v. injection of neuropeptides in sodium-depleted rats depends, in part, on the activat ion of central alpha(2)-adrenoceptors. (C) 1997 Elsevier Science B.V. All rights reserved.