Arterial baroreceptor reflex function in borderline hypertensive rats.

With increased dietary NaCl intake (8% NaCl), the borderline hypertensive rat develops hypertension, thus expressing the phenotype of the spontaneously hypertensive parent. Since arterial baroreceptor reflex function is impaired in the spontaneously hypertensive parent, it was the objective of this study to examine arterial baroreceptor reflex function in the borderline hypertensive rat made hypertensive by increased dietary NaCl intake. Borderline hypertensive rats were fed either 1% or 8% NaCl from age 4 to 16 weeks. Borderline hypertensive rats fed 8% NaCl (n = 10) were hypertensive compared with borderline hypertensive rats fed 1% NaCl (n = 11) (141 +/- 3 versus 120 +/- 4 mm Hg, p less than 0.01). They were chronically instrumented for the recording of arterial pressure, heart rate, and renal sympathetic nerve activity. The percent change from control in heart rate and renal sympathetic nerve activity resulting from increases (phenylephrine) and decreases (nitroglycerine) in arterial pressure were measured in conscious freely moving animals. With respect to arterial baroreceptor reflex control of heart rate, 8% NaCl borderline hypertensive rats had a similar range (75 +/- 4%) and maximal gain (-2.72 +/- 0.24%/mm Hg) as 1% NaCl borderline hypertensive rats (70 +/- 4%; -2.78 +/- 0.50%/mm Hg). With respect to arterial baroreceptor reflex control of renal sympathetic nerve activity, 8% NaCl borderline hypertensive rats had values for range (205 +/- 22%) and maximal gain (-3.92 +/- 0.93%/mm Hg) that were not significantly different from those for 1% NaCl borderline hypertensive rats (167 +/- 33%, -2.76 +/- 0.62%/mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)