Calcitonin gene-related peptide dilates the pregnant rat uterine vascular bed via guanylate cyclase, ATP- and Ca-sensitive potassium channels and gap junctions.

We studied the mechanism of calcitonin gene-related peptide (CGRP)-induced vasorelaxation in isolated uterine vascular beds of pregnant rats. The vascular beds were perfused in situ with Krebs buffer containing dextran and indomethacin, an inhibitor of cyclooxygenase. Baseline perfusion pressure was maintained with norepinephrine. When applied as a bolus, CGRP caused a decreased perfusion pressure in uterine vascular beds that was dose-dependent and equal in both mid-pregnant and late-pregnant rats. The non-selective inhibitor of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester (L-NAME), did not significantly affect CGRP-induced vasodilatation in vascular beds of either group. CGRP-induced vasodilatation was not influenced by preincubation with the inhibitors of adenylate cyclase (SQ 22536 or MDL 12330A), but was significantly attenuated by the selective inhibitor of soluble guanylate cyclase (ODQ). The vasorelaxant effect of CGRP was not significantly influenced by the inhibitor of voltage-gated potassium (KV) channels (4-aminopyridin), but was significantly attenuated by an inhibitor of calcium-regulated potassium (KCa) channels (tetraethylammonium) and by an inhibitor of adenosine triphosphate-sensitive potassium (KATP) channels (glibenclamide). The gap junction uncoupling agent (carbenoxolone) also significantly attenuated the CGRP-induced decrease in perfusion pressure. We conclude that vasorelaxation induced by CGRP in the pregnant rat uterine vascular bed is not dependent on endothelial nitric oxide. In the uterine circulation of late-pregnant rats, the CGRP effect involves activation of soluble guanylate cyclase, but not adenylate cyclase, and does involve KCa and KATP channels and gap junctions.

The role of endothelium-derived hyperpolarizing factor in the regulation of the uterine circulation in pregnant rats.

OBJECTIVE: The purpose of this study was to determine whether endothelium-derived hyperpolarizing factor regulates rat uterine circulation in pregnant rats. STUDY DESIGN: Intact isolated uterine vascular beds from late pregnant rats were perfused in situ with Krebs buffer that contained dextran, indomethacin, N-nitro-L-arginine methyl ester, and phenylephrine. Endothelium-derived hyperpolarizing factor-induced decreases in perfusion pressure in response to acetylcholine were analyzed. RESULTS: The decrease in perfusion pressure induced by endothelium-derived hyperpolarizing factor was significantly attenuated by 4-aminopyridine and was abolished by a combination of 4-aminopyridine and tetraethylammonium. Endothelium-derived hyperpolarizing factor-induced decrease in perfusion pressure was abolished by potassium chloride and attenuated by miconazole, but not linoleyl hydroxamic acid. Endothelium-derived hyperpolarizing factor-induced decrease in perfusion pressure persisted after perfusion with solutions that contained 2 inhibitors of nitric oxide synthase and a scavenger of nitric oxide. Nitric oxide exerted negative feedback on the endothelium-derived hyperpolarizing factor effects. CONCLUSION: In the pregnant rat uterine vascular beds, endothelium-derived hyperpolarizing factor release is activated by a delayed rectifier type of voltage-sensitive potassium channel. Endothelium-derived hyperpolarizing factor does not seem to be related to nitric oxide or to products of lipoxygenase or cytochrome p450 mono-oxygenase pathways of arachidonic acid metabolism.

Responses of isolated perfused uterine vascular beds of nonpregnant and pregnant rats to endogenous and exogenous nitric oxide.

The responses to endothelial vasodilators and exogenous nitric oxide (NO) were characterized in intact isolated uterine vascular beds of nonpregnant, midpregnant and late-pregnant rats perfused with Kreb's buffer (37 degrees C, 5% CO(2) in air, pH approximately 7.4) containing 2% dextran and indomethacin. Phenylephrine increased perfusion pressure in the vascular beds equally in all three groups. In the presence of phenylephrine, N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly augmented perfusion pressure in the order: nonpregnant