Chemoreflex and endocrine components of the cardiovascular
responses to acute hypoxemia in the llama fetus.
Giussani, Dino A., Raquel A. Riquelme, Fernando A. Moraga, Hugh H. G.
McGarrigle, Cristian R. Gaete, Emilia M. Sanhueza, Mark A. Hanson,
and Anibal J. Llanos.
Department of Obstetrics and Gynecology, University College London,
WC1E 6HX, Departamento de Medicina Experimental, Campus Oriente,
Facultad de Medicina, Departamento de Bioqu[acute]imica y
Biolog[acute]ia Molecular, Facultad de Ciencias Qu[acute]imicas y
Farmac[acute]euticas, Universidad de Chile
APStracts 3:0012R, 1996.
We tested the hypothesis that the llama fetus has a blunted
cardiovascular chemoreflex response to hypoxemia by investigating the
effects of acute hypoxemia on perfusion pressure, heart rate and the
distribution of the combined ventricular output in 10 chronically
-instrumented fetal llamas at 0.6-0.7 gestation. Four llama fetuses
had the carotid sinus nerves sectioned. In the intact fetuses, there
was a marked bradycardia, an increase in perfusion pressure and a
pronounced peripheral vasoconstriction during hypoxemia. These
cardiovascular responses during hypoxemia in intact fetuses were
accompanied by a pronounced increase in plasma vasopressin but not in
plasma angiotensin II concentrations. Carotid denervation prevented
the bradycardia at the onset of hypoxemia but it did not affect the
intense vasoconstriction during hypoxemia. Plasma vasopressin and
angiotensin II levels were not measured in carotid-denervated
fetuses. Our results do not support the hypothesis that the carotid
chemoreflex during hypoxemia is blunted in the llama fetus. However
they emphasize that other mechanisms, such as increased vasopressin
concentrations, operate to produce an intense vasoconstriction in
hypoxemia. This intense vasoconstriction in the llama fetus during
hypoxemia may reflect the influence of the hypoxia of high altitude
on the magnitude and gain of fetal cardiovascular responses to a
superimposed, acute episode of hypoxemia.
Received 30 January 1995; accepted in final form 14 December
1995.
APS Manuscript Number R69-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96