Viscoelastic mechanisms of aortic baroreceptor resetting to
hemorrhagic hypotension and to phenylephrine-induced
hypertension.
Xavier-Neto, J., E. D. Moreira, and E. M. Krieger.
Unidade de Hipertensao, Instituto do Cora[cedilla]cao, Faculdade de
Medicina da Universidade de Sao Paulo, SP, Brazil. CEP 05403-000
APStracts 3:0155H, 1996.
Viscoelastic and electrophysiological mechanisms have been implicated
in the resetting of baroreceptors in hypertension, but resetting in
response to hypotension has been less studied. To evaluate the
temporal relationship between viscoelastic mechanisms and acute
resetting we examined the "in vivo" behaviour of aortic
caliber and aortic baroreceptor activity during step changes in
pressure. Fifteen minute hemorrhage in Wistar rats produced stable
hypotension (30 mmHg) and viscoelastic contraction 111 +/- 14.2 [mu]m
(systolic caliber ; p<0.01). Integrated aortic activity fell to
19.8 +/- 3.9% of control (p<0.001) after 3 seconds of
hypotension, but recovered to 64 +/- 4.1 % 15 minutes later
(p<0.01 from 3 seconds). Recovery of baroreceptor activity was
linearly correlated to viscoelastic contraction (r=0.963 ;
p<0.0001). Thirty minute phenylephrine infusion (1.0-4.0
[mu]g/min) produced stable hypertension (30 mm Hg) and viscoelastic
dilation (211 +/- 37.0 [mu]m systolic caliber). Integrated aortic
activity increased to 218.0 +/- 18 % of control values (p<0.001)
30 seconds after hypertension and was reduced to 164.0 +/- 12.0%
(p<0.001 from 3 seconds) within 30 min. Reduction of
baroreceptor activity correlated linearly with viscoelastic
relaxation (r=0.963 ; p<0.0001). The results indicate that in
the in vivo rat aorta, viscoelastic mechanisms parallel and may
contribute to the baroreceptor resetting during hypotension and
hypertension.
Received 21 July 1995; accepted in final form 5 April 1996.
APS Manuscript Number H688-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96