Impaired baroreflex sensitivity in the aetiology of salt hypertension in the rabbit

This study was designed to see whether normotensive rabbits with an impairment in baroreflex control of heart rate due to genetic factors are more susceptible to high salt or deoxycorticosterone acetate (DOCA)-salt hypertension. The baroreflex sensitivity of 27 conscious rabbits was assessed by both the 'steady-state' and 'ramp' methods in response to injections of phenylephrine (2.5-30 micrograms/kg). Animals with differing baroreflex sensitivities were then given 4 weeks treatment with 8% NaCl and 1.3% KCl in food (treatment A), or DOCA (25 mg pellet, subcutaneously) with 0.5% NaCl and 0.13% KCl in drinking water (treatment B). A third group were maintained on a regular diet of food and water (controls). A highly significant negative correlation (r = 0.91, P less than 0.01) was found between the increase in mean arterial pressure (MAP) produced either by treatment A or treatment B and the baroreflex sensitivity before treatment. There was no significant correlation between the increase in MAP and initial MAP; increase in body weight; serum K+ after treatment; baroreflex sensitivity before treatment, when assessed by the 'ramp' method. It is concluded that animals with low baroreflex sensitivity due to a reduced ability to suppress cardiac sympathetic activity in response to a pressor stimulus, are more likely to develop hypertension as a result of salt loading. It remains to be determined whether the susceptibility to salt of rabbits with lower baroreflex sensitivity is also associated with a difference in the renal excretion of Na+ ions.