Vasodilatory effects of nifedipine, methoxyverapamil, and sodium nitroprusside on contractile responses of the ewe uterine artery at term pregnancy

Possible mechanisms underlying pregnancy-induced changes in uterine artery endothelial function

The last 10 years has seen a dramatic increase in our understanding of the mechanisms underlying the pregnancy-specific adaptation in cardiovascular function in general and the dramatic changes that occur in uterine artery endothelium in particular to support the growing fetus. The importance of these changes is clear from a number of studies linking restriction of uterine blood flow (UBF) and/or endothelial dysfunction and clinical conditions such as intrauterine growth retardation (IUGR) and/or preeclampsia in both humans and animal models; these topics are covered only briefly here. The recent developments that prompts this review are twofold. The first is advances in an understanding of the cell signaling processes that regulate endothelial nitric oxide synthase (eNOS) in particular (Govers R and Rabelink TJ. Am J Physiol Renal Physiol 280: F193-F206, 2001). The second is the emerging picture that uterine artery (UA) endothelial cell production of nitric oxide (NO) as well as prostacyclin (PGI2) may be as much a consequence of cellular reprogramming at the level of cell signaling as due to tonic stimuli inducing changes in the level of expression of eNOS or the enzymes of the PGI2 biosynthetic pathway (cPLA2, COX-1, PGIS). In reviewing just how we came to this conclusion and outlining the implications of such a finding, we draw mostly on data from ovine or human studies, with reference to other species only where directly relevant.

Pharmacological characterization of alpha 1-adrenoceptors in porcine uterine artery

This study was undertaken to ascertain if changes in the affinity to alpha 1-adrenoceptor agonists and antagonists could explain the increase in uterine artery vasoconstriction to adrenergic stimuli during the luteal phase of the estrous cycle in pigs. We also sought to determine the subtype(s) of adrenoceptor (alpha 1A and alpha 1B) in the porcine uterine artery. When phenylephrine was the agonist, uterine artery pA2 values for prazosin were 8.98, 9.04 and 9.10 in the luteal and follicular phases and in early pregnancy, respectively. The KA (dissociation constant) values for phenylephrine were 6.5, 3.7 and 4.4 (microM) in the luteal and follicular phases and in early pregnancy, respectively. The use of the putative alpha 1A-adrenoceptor WB4101 (2-[[[2-(2,6-dimethoxyphenoxy)ethyl]amino]methyl]-1,4-benzodioxane ) and the alpha 1B-adrenoceptor antagonist chloroethylclonidine indicated that both alpha 1A- and alpha 1B-adrenoceptors are present in the porcine uterine artery and that a similar magnitude of inhibition of responses to noradrenaline by each of the antagonists occurred in arteries from the luteal and follicular phases and in early pregnancy. This suggests that the alpha 1A:alpha 1B adrenoceptor ratio does not vary significantly during the estrous cycle and in early pregnancy. This study indicates that porcine uterine artery alpha 1-adrenoceptor affinity is similar in the luteal and follicular phases of the estrous cycle and in early pregnancy.