Losartan improves baroreflex control of heart rate of coarcted
hypertensive rats.
Santos, Claudia M. Dos, Vera Pontieri, Moacir Leomil Neto, and Lisete
C. Michelini.
Dept. of Physiology and Biophysics, Biomedical Sciences Institute,
University of S[angstrom]ao Paulo, S[angstrom]ao Paulo, Brazil
APStracts 2:0149H, 1995.
To assess the role of angiotensin in both the increased heart rate and
the impaired baroreceptor reflex control of heart rate that
characterize the chronic phase of coarctation hypertension, we
compared basal heart rate, pressure and baroreflex sensitivity of
coarcted hypertensive rats treated chronically with losartan,
captopril or vehicle. Baseline heart rate was recorded daily, and
pressure and reflex heart rate changes and plasma renin activity were
measured in coarcted and sham-coarcted rats on the 5th day after
coarctation. Both captopril (10 mg/kg/day p.o.) and losartan (10
mg/kg/day p.o) caused a small nonsignificant reduction of
hypertension (132+/-5 and 133+/-5, respectively vs 147+/-9 mmHg in
vehicle-treated rats), but equally inhibited the late tachycardic
phase (-37+/-13 and -29+/-12 b/min in captopril- and losartan-treated
groups, respectively, vs +79+/-19 b/min in vehicle treated rats).
Similar results were obtained for other groups of coarcted
hypertensive rats after suppression of plasma renin activity by
bilateral nephrectomy. Although hypertensive levels were the same
during both treatments, only losartan given orally or
intracerebroventricularlly (1.25 g/Kg/h) was effective in improving
the reflex bradycardia. The depressed reflex tachycardia was
corrected by chronic oral treatment with losartan. The data suggest
that the tachycardia occurring in the chronic phase of coarctation
hypertension is mediated by blood-borne angiotensin and that the
normalization of the reflex control of heart rate by losartan is
achieved by blockade of type receptors of angiotensin in central
areas accessible to oral or centrally administered losartan, but not
to oral captopril.
Received 15 December 1994; accepted in final form 4 April 1995.
APS Manuscript Number H1099-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.