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Department of Physiology and Biophysics and Center for Excellence in Cardiovascular-Renal Research, University of Mississippi Medical Center, Jackson, Mississippi 39216-4505
Vascular reactivity has been shown to be
reduced during pregnancy and to be enhanced during chronic inhibition
of nitric oxide (NO) synthesis in pregnant rats; however, the cellular
mechanisms involved are unclear. The purpose of this study was to
investigate whether the pregnancy-induced changes in vascular
reactivity are associated with changes in the amount and/or activity of
vascular protein kinase C (PKC). Active stress as well as the amount
and activity of PKC was measured in deendothelialized thoracic aortic strips from virgin and pregnant rats untreated or treated with the NO
synthase inhibitor
NG-nitro-L-arginine methyl
ester (L-NAME). In virgin rats, the PKC activator phorbol
12,13-dibutyrate (PDBu, 10
6 M) and the
-adrenergic agonist phenylephrine (Phe,
10
5 M) caused significant increases in
active stress and PKC activity that were inhibited by the PKC
inhibitors staurosporine and calphostin C. Western blot analysis in
aortic strips of virgin rats showed significant amount of the
-PKC
isoform. Both PDBu and Phe caused significant translocation of
-PKC
from the cytosolic to the particulate fraction. Compared with virgin
rats, the PDBu- and Phe-stimulated active stress and PKC activity as
well as the amount and the PDBu- and Phe-induced translocation of
-PKC were significantly reduced in late pregnant rats but
significantly enhanced in pregnant rats treated with
L-NAME. The PDBu- and Phe-induced changes in active stress
and the amount, distribution, and activity of
-PKC in virgin rats
treated with L-NAME were not significantly different from
that in virgin rats, whereas the changes in pregnant rats treated with
L-NAME + the NO synthase substrate L-arginine
were not significantly different from that in pregnant rats. These results provide evidence that a PKC-mediated contractile pathway in
vascular smooth muscle is reduced during pregnancy and significantly enhanced during chronic inhibition of NO synthesis. The results suggest
that one possible mechanism of the pregnancy-associated changes in
vascular reactivity may involve changes in the amount and activity of
the
-PKC isoform.
nitric oxide; vascular smooth muscle; hypertension
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