CENTRAL OXYTOCIN AND ANP RECEPTORS MEDIATE OSMOTIC INHIBITION OF SALTAPPETITE IN RATS

These studies evaluated the involvement of central oxytocin (OT) and a trial natriuretic peptide (ANP) receptors in the osmotic inhibition of hypovolemia-induced salt appetite. Rats were pretreated centrally wit h the A chain of the cytotoxin ricin conjugated to OT (rAOT) or ANP (r AANP) to selectively inactivate cells bearing these respective recepto rs, or rats were pretreated with the unconjugated A chain (rA) as a co ntrol. Hypovolemia was induced with subcutaneous colloid injections, a nd rats then were given either 2 M mannitol, which raises plasma osmol ality but lowers plasma sodium, or 1 M NaCl, which raises both. Hypert onic mannitol inhibited saline ingestion in rA-treated control rats bu t stimulated ingestion in rAOT- and rAANP-treated rats, whereas hypert onic NaCl blunted saline ingestion in rA- and rAOT-treated rats but st imulated ingestion in rAANP-treated rats. Angiotensin II-induced salin e intake was similarly potentiated in rAOT- and rAANP-treated rats, in dicating that this treatment also activates central inhibitory OT and ANP pathways. These data suggest that central ANP receptors mediate bo th Na+- and osmolality-induced inhibition of NaCl ingestion, whereas c entral OT receptors primarily mediate osmolality-induced inhibition of NaCl ingestion in rats.