Cardiac volume receptor reflex in borderline hypertensive rats.

With increased dietary NaCl intake (8% NaCl), borderline hypertensive rats (BHR) develop hypertension and exhibit an exaggerated natriuresis in response to intravenous isotonic saline volume expansion. The exaggerated natriuresis is mediated by the concurrent exaggerated withdrawal of efferent renal sympathetic nerve activity since prior renal denervation eliminates the exaggerated natriuretic response. It was the objective of the present study to examine cardiac volume receptor reflex control of efferent renal sympathetic nerve activity in BHR made hypertensive by increased dietary NaCl intake. BHR were fed either 1% or 8% NaCl from age 4 to 16 weeks. BHR fed 8% NaCl were hypertensive (148 +/- 9 mmHg) compared with BHR fed 1% NaCl (115 +/- 6 mm Hg, p < 0.05). In one protocol, measurements of right atrial pressure and efferent renal sympathetic nerve activity were made in sinoaortic-denervated BHR before and during a 10% body weight intravenous isotonic saline volume load. Compared with 1% NaCl BHR, 8% NaCl BHR showed both a greater maximal inhibition of efferent renal sympathetic nerve activity (-67 +/- 4% versus -31 +/- 3% of control, p < 0.05) and gain (-22.0 +/- 2.3 versus -9.7 +/- 1.7%/mm Hg, p < 0.05). In a second protocol, measurements of efferent renal sympathetic nerve activity were made in sinoaortic-denervated BHR before and during graded frequency stimulation of the central portion of the sectioned vagus nerve.(ABSTRACT TRUNCATED AT 250 WORDS)