Prehypertensive Dahl Salt-Sensitive and Dahl Salt-Resistant Rats

Prehypertensive Dahl salt-sensitive rats on low sodium diet have impaired baroreceptor and cardiopulmonary receptor function as compared with Dahl salt-resistant control rats. We tested whether these abnormalities influenced the ability of conscious prehypertensive Dahl saltsensitive rats to excrete a moderate intravenous isotonic saline volume load (0.9% NaCl, 3% body weight i.v.). During control, 30-minute volume expansion, and 2-hour recovery periods, arterial blood pressure and heart rate did not change. Glomerular filtration rate and renal plasma flow remained stable throughout control and recovery. The amount of the volume load excreted as either water or sodium was the same for Dahl salt-sensitive and Dahl salt-resistant rats with either denervated or innervated kidneys. The time course of water and sodium excretion was similar in Dahl salt-sensitive and Dahl salt-resistant rats. Renal sympathetic nerve activity, however, showed different patterns. Although the initial decrease in renal sympathetic nerve activity during volume expansion was similar for both groups, Dahl salt-sensitive rats exhibited a prompt return of renal sympathetic nerve activity to control levels, whereas renal sympathetic nerve activity in Dahl salt-resistant rats remained decreased throughout the recovery period. The rapid recovery of renal sympathetic nerve activity to control levels after volume expansion in Dahl salt-sensitive rats supports the concept of impaired cardiopulmonary receptor function in these rats. The similar diuretic and natriuretic responses to moderate intravenous isotonic saline volume expansion in all four groups (Dahl salt-sensitive and Dahl salt-resistant, intact and denervated) despite markedly different renal sympathetic nerve activity responses suggest a decreased responsiveness of the kidney in both Dahl salt-sensitive and Dahl salt-resistant rats to altered neural input. (Hypertension 1989; 13:822-827)