Aberrant baroreceptor mechanotransduction in adult Dahl rats on low-salt diet

Single fiber, regularly discharging baroreceptors (n = 188) from adult Dahl salt-sensitive (DS) and salt-resistant (DR) rats on a low-salt diet were studied using an in vitro aortic arch-aortic nerve preparation. Pressure thresholds (P(th)) and suprathreshold pressure sensitivities (S(th)) were determined from responses to slow ramps of pressure. Pressure-diameter relationship measured in each rat were used to transform P(th) and S(th) values to their mechanical equivalents in terms of aortic wall strains. DS and DR ages were not different (~50 wk). Despite the low-salt diet, DS tail systolic blood pressures were significantly higher than DR by ~25 mmHg. P(th) averaged 84 mmHg in DR and 97 mmHg in DS. S(th) values were similar in DR and DS (average 1.44 and 1.39 spikes · s^-1 · mmHg^-1 in DR and DS, respectively). Increased variance of baroreceptor properties of DS over DR was a prominent finding and necessitated use of nonparametric statistics. The cumulative distribution of P(th) values of DS was significantly different from DR, but S(th) values were similar. Thus baroreceptor pressure set points are altered in adult DS, but pressure sensitivity per se is not. The differences in pressure parameters were not eliminated by conversion to their mechanical equivalents. Correlation analysis found only weak relationship between P(th) and blood pressure of DS and DR (r < 0.40). Thus in contrast to previous studies in the spontaneously hypertensive rat model, baroreceptors in adult DS on low salt are characterized by elevated variability and a weaker than expected correlation to the prevailing blood pressure in the animal. These differences may be expressions of genetic differences and might result in the less effective baroreflexes observed by others in the DS rat.