Sigmoidal curve-fitting of baroreceptor sensitivity in renovascular 2K1C hypertensive rats

The time course of changes in baroreceptor reflex sensitivity in Goldblatt two-kidney one clip (2K1C) hypertension was studied 3, 7 and 30 days after renal artery clipping by means of a sigmoidal curve-fitting analysis. Experiments were performed in 54 adult male Wistar rats (N = 9 per group) weighing 200-300 g. The reflex heart rate responses were elicited by alternate intravenous bolus injections of phenylephrine (delta +5 to +50 mmHg) and sodium nitroprusside (delta -5 to -50 mmHg). A clear upper and lower plateau (reflex tachycardia and bradycardia, respectively) was noted in both sham and hypertensive groups. Although the resting mean arterial pressure was significantly increased in all hypertensive groups (131 +/- 3, 149 +/- 7 and 168 +/- 11 mmHg, respectively, 3, 7 and 30 days after clipping), when compared to the sham group (108 +/- 2 mmHg), significant changes in baroreceptor reflex function were observed only in 7- and 30-day groups. Baroreflex sensitivity was markedly reduced in these hypertensive rats (2.3 +/- 0.3 and 1.9 +/- 0.3 bpm/mmHg, respectively) compared to the sham group (4.2 +/- 0.3 bpm/mmHg). In addition, a reduced baroreflex heart rate range was observed in these groups (117 +/- 12 and 107 +/- 10 bpm, respectively) compared to the sham group (165 +/- 11 bpm). These data indicate an impairment of baroreflex function in conscious 2K1C hypertensive rats which seems to be secondary to arterial hypertension.