Increased levels of hypothalamic neuronal nitric oxide synthase and vasopressin in salt-loaded Dahl rat

The plasma concentration of arginine vasopression (AVP) and the expression level of the neuronal nitric oxide synthase (nNOS) gene in the paraventricu lar nucleus (PVN) and the supraoptic nucleus (SON) of Sprague-Dawley (SD), Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats on a high salt die t were examined by radioimmunoassay for AVP and in situ hybridization histo chemistry for nNOS. The high salt diet containing 8.0% NaCl was given for 4 weeks. The concentrations of AVP in hypertensive Dahl S rats were signific antly increased in comparison with those in SD rats and Dahl R rats on a hi gh salt diet. The levels of nNOS mRNA and NADPH-diaphorase activity in the PVN and SON of hypertensive Dahl S rats were greater than those in Dahl R r ats on a high salt diet. The antihypertensive drugs, either nicardipine or captopril were administered to the Dahl S rats for 2 weeks beginning 2 week s after the start of the high salt diet. The nNOS mRNA in the PVN and SON o f Dahl S rats given a high salt diet was not upregulated by treatment with nicardipine, while the nNOS mRNA in salt-loaded Dahl S rats was greater upr egulated by treatment with captopril to that greater than without the antih ypertensive drug. Our results suggest that the increased NO production in t he PVN and SON of hypertensive Dahl S rats may be ineffective in decreasing blood pressure or inhibiting AVP secretion. (C) 2001 Elsevier Science B.V. All rights reserved.