Mechanisms of bradykinin-mediated dilation in newborn piglet pulmonary conducting and resistance vessels

Bradykinin (BK) is a potent dilator of the perinatal pulmonary circulation. We investigated segmental differences in BK-induced dilation in newborn pig large conducting pulmonary artery and vein rings and in pressurized pulmonary resistance arteries (PRA). In conducting pulmonary arteries and veins, BK-induced relaxation is abolished by endothelial disruption and by inhibition of nitric oxide (NO) synthase with nitro-L-arginine (L-NA). In PRA, two-thirds of the dilation response is L-NA insensitive. Charybdotoxin plus apamin and depolarization with KCl abolish the L-NA-insensitive dilations, findings that implicate the release of endothelium-derived hyperpolarizing factor (EDHF). However, endothelium-disrupted PRA retain the ability to dilate to BK but not to ACh or A-23187. In endothelium-disrupted PRA, dilation was inhibited by charybdotoxin. Thus in PRA, BK elicits dilation by multiple and duplicative signaling pathways. Release of NO and EDHF contributes to the response in endothelium-intact PRA; in endothelium-disrupted PRA, dilation occurs by direct activation of vascular smooth muscle calcium-dependent potassium channels. Redundant signaling pathways mediating pulmonary dilation to BK may be required to assure a smooth transition to extrauterine life.

Endothelial NO and prostanoid involvement in newborn and juvenile pig pial arteriolar vasomotor responses

Specific cerebrovascular dilatory responses in newborn piglets are entirely prostanoid dependent, but require both nitric oxide (NO) and prostanoids in juveniles. We examined endothelial dependency and mechanisms of NO- and prostanoid-mediated cerebrovascular responses in anesthetized newborn and juvenile pigs implanted with closed cranial windows. Light/dye endothelial injury inhibited newborn and juvenile hypercapnic and bradykinin (BK) responses and inhibited dilation to acetylcholine in juveniles. Iloprost and NO act permissively in restoring light/dye inhibited newborn and juvenile responses, respectively. Differences in sensitivity to iloprost and sodium nitroprusside were not observed. Juvenile (not newborn) hypercapnic and BK cerebrovascular responses were sensitive to soluble guanylyl cyclase inhibition. Pial arteriolar diameter and cortical production of prostacyclin, cAMP, and cGMP in response to BK were measured under control conditions, after treatment with indomethacin and/or N(omega)-nitro-L-arginine methyl ester (L-NAME). Indomethacin inhibited BK responses in newborns. Juvenile responses were inhibited by L-NAME, and mildly by indomethacin. Cortical 6-keto-PGF(1 alpha), cAMP, and cGMP increased in response to BK in both age groups. Newborn cerebrovascular responses are largely NO independent, but NO becomes more important with maturation.

Cell-to-cell communication via nitric oxide modulation of oscillatory Cl(-) currents in rat intact cerebral arterioles

1. Diffusion-mediated changes in ion channel function within blood vessels have not been demonstrated directly in a patch-clamp study. Here, we examined the hypothesis that endothelium-derived diffusible bioactive substances would modify endothelin-1 (ET-1)-evoked membrane currents in smooth muscle cells situated within intact arterioles. 2. In pieces of arterioles dissected from the rat cerebral pial membrane, patch electrodes were placed on single smooth muscle cells identified under the microscope. Under perforated patch-clamp conditions, ET-1 evoked an oscillatory inward current at negative potentials in such cells in the presence of the gap junction disrupter 18alpha-glycyrrhetinic acid. ET-1 also elicited an oscillation superimposed on a membrane depolarization in current-clamp mode. 3. The oscillatory current exhibited an outwardly rectifying current-voltage relationship, a sensitivity to niflumic acid, a requirement for inositol 1,4,5-trisphosphate (IP(3))- and caffeine-sensitive Ca(2+) stores and for external Ca(2+) and a rank order of anion permeabilities characteristic of Ca(2+)-activated Cl(-) currents (I(Ca(Cl))). 4. This oscillatory response was inhibited by bradykinin (an effect distinct from the electrical propagation of hyperpolarization) and this effect was attenuated by the NO-synthase inhibitor N(omega)-nitro-L-arginine and by the NO scavenger oxyhaemoglobin but not by the cyclo-oxygenease inhibitor indomethacin. 8-Bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP) and nitroprusside closely mimicked the effect of bradykinin. 5. The present patch-clamp study has revealed diffusion-mediated cell-to-cell interaction in an intact blood vessel: bradykinin appears to cause NO to move from endothelium to smooth muscle, there to inhibit an ET-1-evoked oscillatory I(Ca(Cl)) via the NO-cGMP pathway.