NITRIC-OXIDE SYNTHASE ISOFORM ACTIVITIES IN KIDNEY OF DAHL SALT-SENSITIVE RATS

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-[H-3]arginine to L-[H-3]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 particu)ate 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.