Tachycardic responses during the development of renal hypertension.

Basal heart rate (HR) of conscious rats under resting conditions was measured daily by electrocardiogram (ECG) during the development of one-kidney, one clip (1K1C) hypertension. A progressive increase in HR (mean +/- SEM) was observed from Day 1 to 7: 318 +/- 11; 330 +/- 18, 338 +/- 18; 344 +/- 19; 372 +/- 14; 374 +/- 11, and 388 +/- 12 bpm, respectively. During the same period, mean arterial pressure (MAP) also increase progressively: 126 +/- 2; 129 +/- 2; 134 +/- 4; 135 +/- 7; 144 +/- 2 and 157 +/- 4 mm Hg, respectively. From Day 7 onward, the HR declined, reaching values of 336 +/- 13 bpm on Day 9, with no further alterations for the next 21 days. The MAP continued to rise, however, being 158 +/- 4 on Day 8 and 175 +/- 7 mm Hg on Day 30. Sham-operated rats showed no changes in HR or MAP. During the development of hypertension, blockade of converting enzyme with captopril (10 mg/kg, i.v.) caused a significant blood pressure fall on Day 1 (-27 +/- 1 mm Hg) and Day 3 (-18 +/- 2 mm Hg), whereas on Day 6 (-9 +/- 3 mm Hg) and Day 14 (-8 +/- 3 mm Hg) the fall was not different from that of the normotensive control rats (NCR) (-6 +/- 1 mm Hg). Reflex bradycardia, produced by increasing doses of phenylephrine which elevated the MAP by 10 to 40 mm Hg, was studied in conscious NCR and renal hypertensive rats (RHR) 3 and 7 days after surgery during the development of renal hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)