Nitric Oxide Synthase Isoform Activities in Kidney of Dahl Salt-Sensitive Rats

Abstract

Abstract An abnormal l -arginine–nitric oxide axis has been suggested to be relevant to the genesis of salt-sensitive hypertension. In the present study we investigated the activities of three isoforms of nitric oxide synthase (NOS) in the kidney of Dahl salt-sensitive and salt-resistant rats. Five-week-old Dahl Iwai salt-sensitive (n=9) and salt-resistant (n=10) rats were maintained on a high salt diet (4% sodium chloride) for 4 weeks. We measured calcium-dependent and calcium-independent NOS activities in each particulate and soluble fraction of kidney by conversion of l -[ 3 H]arginine to l -[ 3 H]citrulline. Systolic blood pressure was elevated significantly ( P <.001) in salt-sensitive but not salt-resistant rats. Calcium-dependent NOS activity in the soluble fraction was significantly lower in salt-sensitive rats than in salt-resistant rats (25.8±9.0 versus 48.2±19.2 disintegrations per microgram protein, respectively; P <.01). There were no differences in calcium-dependent NOS activity in the particulate fraction and calcium-independent NOS activity in the soluble fraction between groups. Renal norepinephrine content was lower in salt-sensitive rats than in salt-resistant rats ( P <.05) and was positively correlated with calcium-dependent NOS activity in the soluble fraction ( P <.01). Although no differences in endothelial and inducible-type NOS activity were observed a significant reduction in calcium-dependent NOS activity in the soluble fraction of the kidney of salt-sensitive rats suggests that the decreased neural-type NOS activity may in part be involved in the mechanism of salt-sensitive hypertension, possibly through alterations in renal sympathetic nervous activity and sodium handling.