Effect of chronic perinatal hypoxia on the role of rho-kinase in pulmonary artery contraction in newborn lambs

Abstract

Exposure to chronic hypoxia during gestation predisposes infants to neonatal pulmonary hypertension, but the underlying mechanisms remain unclear. Here, we test the hypothesis that moderate continuous hypoxia during gestation causes changes in the rho-kinase pathway that persist in the newborn period, altering vessel tone and responsiveness. Lambs kept at 3,801 m above sea level during gestation and the first 2 wk of life were compared with those with gestation at low altitude. In vitro studies of isolated pulmonary arterial rings found a more forceful contraction in response to KCl and 5-HT in high-altitude compared with low-altitude lambs. There was no difference between the effects of blockers of various pathways of extracellular Ca(2+) entry in low- and high-altitude arteries. In contrast, inhibition of rho-kinase resulted in significantly greater attenuation of 5-HT constriction in high-altitude compared with low-altitude arteries. High-altitude lambs had higher baseline pulmonary artery pressures and greater elevations in pulmonary artery pressure during 15 min of acute hypoxia compared with low-altitude lambs. Despite evidence for an increased role for rho-kinase in high-altitude arteries, in vivo studies found no significant difference between the effects of rho-kinase inhibition on hypoxic pulmonary vasoconstriction in intact high-altitude and low-altitude lambs. We conclude that chronic hypoxia in utero results in increased vasopressor response to both acute hypoxia and serotonin, but that rho-kinase is involved only in the increased response to serotonin.

Developmental acceleration of bradykinin-dependent relaxation by prenatal chronic hypoxia impedes normal development after birth

“…The studies were performed within the regulations of the Animal Welfare Act, the National Institutes of Health Guide for the Care and Use of Laboratory Animals, "The Guiding Principles in the Care and Use of Animals" approved by the Council of the American Physiological Society, and the Animal Care and Use Committee of Loma Linda University (LLU). The tissue preparation, wire myography, and imaging experimental procedures and protocols are based on previously published methodology (10,35,37). Sheep were obtained from Nebeker Ranch (Lancaster, CA; 720 m altitude), and normoxic animals were brought to LLU [353 m altitude, 95 Ϯ 5 Torr arterial PO 2 (PaO 2 )] for experimental study.…”

“…This Pa O 2 was maintained until the time of the experimental study. Ewes in the normoxic and chronic hypoxic groups were allowed to give birth naturally and transported to LLU Animal Care when the lambs were 8 -17 days of age, as described previously (10). After arrival and until study, 1-2 days later, hypoxic animals were kept in a chamber supplied with 14 -16% O 2 that simulated the altitude at the Barcroft Laboratory.…”

“…As described elsewhere, fourth-to fifthbranch-order pulmonary arteries with internal diameters of ϳ500 -700 m were isolated from full-term fetal (138 -141 days) or newborn (10 -21 days old) sheep from the different experimental groups (10,35,37). The parenchyma was removed carefully from the pulmonary arteries for contractility studies.…”

“…Arteries in modified K-H solution were aerated with 95% O2-5% CO2 (pH 7.4), while unaerated HEPES-buffered BSS was used for the ProliNO studies to prevent sparge-induced loss of free NO into the atmosphere. Each ring was suspended between two tungsten wires passed through the lumen: one wire was anchored to the glass hook at the bottom of the organ chamber, while the other was connected to a tissue hook attached to a low-compliance force transducer (Radnoti Glass Instruments) that measured isometric force (10,35,37). The transducers were connected to an analog-to-digital data interface (Powerlab 16/30, A/D Instruments, Colorado Springs, CO; or MP100, Biopac, Goleta, CA) attached to a computer.…”

“…NO acts on nearby smooth muscle cells to cause downstream stimulation of soluble guanylate cyclase (sGC) pathways that leads to vasorelaxation (3,45). Previous studies have shown that regulation of vessel relaxation through various receptor signaling systems is altered during pre-and postnatal development, as well as following prenatal chronic hypoxia, which imposes a significant stress on the fetus (9,10,35). Evidence suggests that acetylcholine (ACh)-dependent endothelium-mediated relaxation of the pulmonary vasculature is reduced in the fetus relative to the adult (57).…”