Development of cardiovascular responses to hypoxia in larvae of the
frog xenopus laevis.
Fritsche, Regina, and Warren Burggren.
Department of Biological Sciences, University of Nevada Las Vegas,
Las Vegas, NV 89154-4004, USA
APStracts 3:0176R, 1996.
Cardiovascular responses (blood pressure, heart rate, stroke volume,
cardiac output and peripheral vascular resistance) to acute hypoxia
(PO2=70mmHg) in developing larvae of Xenopus laevis from NF stage 45
and up to newly metamorphosed froglets were investigated. The results
revealed two distinct response patterns to acute hypoxia in
"early" (NF stage 45-48 and 49-51) and "late" (NF
stage 52-53, 54-57 and 58-62) larval Xenopus. The "early"
larvae responded to acute hypoxia with a significantly decreased
stroke volume, cardiac output and blood pressure. Peripheral
resistance increased whereas no change in heart rate occurred. In
"late" larvae, stroke volume and and blood pressure increased
during acute hypoxia, but an offsetting bradycardia prevented major
changes in cardiac output. We conclude that up to stage 51 of
development, hypoxia exerts a direct inhibitory effect on the heart
and smooth muscle of the blood vessels, with no Frank-Starling
relationship apparent. Older larvae show evidence of both intrinsic
and extrinsic regulation of the cardiovascular system in response to
acute hypoxia, suggesting that there is a specific point in larval
development when cardiovascular regulation during hypoxia is
expressed.
Received 27 December 1995; accepted in final form 26 March 1996.
APS Manuscript Number R820-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96