Aortic distensibility and compliance in conscious pregnant
rats.
Slangen, Brigitte F. M., Dorette S. Van Ingen Schenau, Ad W. Van Gorp,
Jo G. R. De Mey, and Louis L. H. Peeters.
Departments of Obstetrics and Gynecology, Physiology and
Pharmacology, University of Limburg, Maastricht, The Netherlands
APStracts 3:0429H, 1996.
In pregnancy, complex hormonal and hemodynamic changes develop. In
this study, we tested the hypothesis that these pregnancy-associated
changes are accompanied by an alteration of the compliance of central
conduit vessels. To this end, we determined in awake, restrained
pregnant rats, the distensibility (DC) and compliance (CC) of the
descending thoracic aorta. End-diastolic aortic diameter (d), and
changes in aortic diameter during the cardiac cycle (_d) were
measured noninvasively by ultrasound, simultaneously with diastolic
aortic blood pressure (Pdia) and pulse pressure (_P) through a
chronically implanted catheter. From these parameters, DC and CC (the
relative and the absolute increase in lumen cross-sectional area for
a given increase in pressure, respecti vely) were calculated. Nine
rats were studied before pregnancy, and on days 4, 8, 10 and 18 of
pregnancy, along with 8 nonpregnant rats, matched for age and days
postsurgery. On day 20, the animals were sacrificed and the thoracic
aorta was isolated for morphome tric analysis. In the pregnant group,
Pdia decreased from 109 +/- 5 mmHg on day 4 to 98 +/- 9 mmHg on day
18 (means +/- SD), while end-diastolic aortic diameter did not
change. _d increased from 242 +/- 20 [mu]m on day 4 to 271 +/- 29
[mu]m on day 18. _P did not change. Both DC and CC increased in early
pregnancy to a plateau reached by day 10. The increase in DC and CC
preceded the fall in Pdia. On day 20, neither cross-sectional area
nor thickness of the aortic media had changed significantly, when
compared with the nonpregnant group. In the nonpregnant group, none
of the variables changed consistently during the study period. On the
basis of these results we conclude that the compliance of the
thoracic aorta increases in early pregnancy. We speculate that the
increased aortic compliance and distensibility and the decreased
total peripheral resistance develop in early pregnancy in response to
the increase in stroke volume, thus preventing a concomitant rise in
arterial wall stress.
Received 16 July 1996; accepted in final form 24 September 1996.
APS Manuscript Number H632-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996