Somatosensory regulation of renal function in the stroke-prone spontaneously hypertensive rat.

1. Chloralose-urethane-anaesthetized Wistar rats and stroke-prone spontaneously hypertensive rats (SHRSP) were prepared for measuring renal function. 2. Bilateral brachial nerve stimulation for 15 min, at 1.3 Hz (15 V, 0.2 ms), increased blood pressure from 119 +/- 2 to 151 +/- 6 mmHg (P < 0.01) in Wistar rats and from 181 +/- 6 to 203 +/- 6 mmHg (P < 0.05) in SHRSP; renal perfusion pressure was mechanically regulated at prestimulus levels but renal blood flow (4.1 +/- 0.7 ml min-1 g-1 in Wistar rats and 3.4 +/- 0.3 ml min-1 g-1 in SHRSP) and glomerular filtration rate (1.18 +/- 0.09 ml min-1 g-1 in Wistar rats and 0.88 +/- 0.01 ml min-1 g-1 in SHRSP) decreased between 5 and 30% (P < 0.05-0.001). 3. During brachial nerve stimulation, urine flow (13.8 +/- 2.2 microliters min-1 g-1) and absolute and fractional sodium excretion (3.70 +/- 0.64 mumol min-1 g-1 and 2.06 +/- 0.23%) decreased by 60-70% in the Wistar rats (P < 0.01-0.001) and the responses were unaffected by vagotomy or carotid sinus denervation. In the SHRSP, urine flow rate (9.74 +/- 2.52 microliters min-1 g-1) and absolute and fractional sodium excretion (1.98 +/- 0.59 mumol min-1 g-1 and 1.41 +/- 0.28%) decreased by 15-30% (P < 0.05-0.01), decreases which were significantly (P < 0.05) smaller than those observed in the Wistar rats. Moreover, the responses were some 40-60% larger in the vagotomized and carotid sinus-denervated SHRSP. 4. The influence of vagal and carotid sinus afferent nerves on the somatosensory-induced renal responses in the Wistar rats was small, whereas in the SHRSP they appeared to exert a marked tonic inhibitory effect. It is concluded that there is excessive baroreceptor restraint on neural regulation of renal function in the SHRSP.