The link between dietary salt intake and the development of hypertension in the salt-sensitive Dahl strain of rats remains elusive. There is evidence that Dahl salt-sensitive rats (DS) produce less vasodilator and natriuretic prostaglandins in response to salt loading than do control salt-resistant rats (DR), although the reason for this blunted response is unknown. We examined the effects of chronic dietary salt loading on the plasma levels of nonesterified fatty acids in DS and DR. Animals were fed the same chow containing either 0.4% or 4% NaCl (wt/wt). At 12 weeks, 75 microliters of tail capillary blood was obtained from restrained, conscious rats, and principal nonesterified fatty acids were measured by high performance liquid chromatography. Total nonesterified fatty acids rose in the 15 DR on high salt diets compared with values in 11 rats eating low salt (0.57 +/- 0.05 vs 0.35 +/- 0.01 mM; p less than 0.001). The greatest changes occurred in levels of arachidonic acid (+287%) and in the arachidonic precursors, linoleic (+89%) and linolenic (+107%) acids. In marked contrast, there was no change in levels of plasma nonesterified fatty acids in DS fed 4% NaCl compared with DS fed 0.4% NaCl. These observations suggest that defective production of natriuretic and vasodilator prostaglandins by DS may be due in part to an inability to produce or release eicosanoid precursors from phospholipid stores in response to dietary salt.