IMPAIRED CARDIOVASCULAR REFLEXES PRECEDE DEOXYCORTICOSTERONE ACETATE SALT HYPERTENSION

We hypothesized that impaired cardiopulmonary reflexes but not altered baroreceptor reflexes precede deoxycorticosterone acetate (DOCA)-salt hypertension. Uninephrectomized rats were given either DOCA and 0.9% NaCl as drinking water, 0.9% NaCl alone, or tap water. We measured mea n blood pressure, heart rate, and renal sympathetic nerve activity. Af ter 8 days, mean blood pressure was not different in DOCA-salt and con trol rats. Volume-sensitive cardiopulmonary reflexes were tested by in travenous volume loading with saline (10% body weight in 15 minutes), which decreased renal sympathetic nerve activity without changing mean blood pressure or heart rate. This response was blunted in DOCA-salt rats. Chemosensitive cardiopulmonary reflexes were tested by 15-minute infusions of the serotonin 5-HT3 agonist phenylbiguanide, which decre ased renal sympathetic nerve activity without changing mean blood pres sure or heart rate. Sustained decreases in renal sympathetic nerve act ivity occurred during phenylbiguanide infusion in controls but were bl unted over time in DOCA-salt rats. The arterial baroreflex responses t o graded infusions of methoxamine and nitroprusside were analyzed by s igmoidal curve fitting. There were no differences in gain of renal sym pathetic nerve activity or heart rate between the groups. Thus, DOCA-s alt rats exhibit impaired cardiopulmonary reflexes before the onset of hypertension; the volume-sensitive reflexes are more severely affecte d than chemosensitive reflexes. The arterial baroreceptor reflex is un altered. The decreased sensitivity of cardiopulmonary reflexes may con tribute to DOCA-salt hypertension.