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Departments of Physiology and Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
In virgin female rats, atrial distension (an index of blood
volume expansion) causes an increase in
c-fos expression in the paraventricular nucleus of the lateral hypothalamus. During pregnancy, this response is markedly attenuated. We tested the effects of 3
-hydroxy-5
-pregnan-20-one (3
-OH-DHP) on activation of central pathways following stimulation of the atrial volume receptors. Not only
does this progesterone metabolite increase during pregnancy, but it has
already been implicated in pregnancy-induced changes in the baroreflex.
Female rats were prepared with indwelling venous cannulas and
intracardiac balloons that, when inflated, caused a discrete localized
stimulation of the atrial volume receptors in the absence of changes in
cardiac hemodynamics. Seven days later, the rats were infused with
3
-OH-DHP dissolved in cyclodextrin and the intracardiac balloons
were inflated. One hour later, the rats were killed and fixed by
perfusion and the brains were prepared for visualization of
c-fos activity. Infusion with
3
-OH-DHP significantly reduced the central response to atrial
distension, i.e., it mimicked pregnancy. These results are consistent
with the suggestion that this metabolite of progesterone may be an
important factor in cardiovascular adaptation to pregnancy.
allopregnanolone; blood volume; baroreceptors; baroreflex
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