Date of Award
Pulmonary vasculature tone is mediated by Acetylcholine Muscarinic Receptors (mAChR) located on the vascular smooth muscle wall which are responsible for vasoconstriction through the activation of Ca^'*’ dependant intracellular signaling pathways and by the endothelium which is responsible for vasodilation through the generation of Nitric Oxide (NO). The dismption and subsequent loss of the endothelium results in vasoconstriction of pulmonary arteries (PA). This effect is observed in several studies utilizing different animal models. Chronic Hypoxia (CH) has been shown to dismpt the endothelium which in turn alleviates the vasodilatory response associated with acetylcholine (ACh) stimulation. The interplay between smooth muscle myocytes and the endothelium allow for the hypothesis that CH reduces ACh-dependent PA contractility was tested by performing experiments using wire-myography in conjunction with endothelium-denuded PA rings from normoxic fetal and adult animals. The data indicates that ACh (100 pM) causes a decrease in tension in CH adults and completely ablated tension in CH fetuses of pre constricted arteries via 125 mM KCl. The CH adult showed contraction when stimulated with 10 pM Carbachol (CCh) which is a selective muscarinic agonist. The tension generated both from ACh and CCh were completely ablated by 1 pM Atropine which is a selective M3 muscamic receptor subtype antagonist. Muscarinic receptor activation, as stated above, generates Ca^"^ dependant intracellular signaling. Confocal imaging in situ further substantiates the finding that mAChR activation initiates intracellular signaling via dependant pathways by showing a marked increase in cytosolic Ca"'*' levels after activation of mAChRs. A notable finding is that there is no contractility in CH fetuses. The loss of the endothelium suggests that there should be vasoconstriction. However, this was not observed and the compensatory mechanism has not been elucidated. Perhaps there could be down-regulation of the mAChRs of the CH fetus in an attempt to match ventilation and perfusion rates in an attempt to maximize oxygen intake. The data garnered from this experiment could further facilitate other avenues of research in the hopes that therapeutic treatments for debilitating ailments such as Persistent Pulmonary Hypertension of Neonates (PPHN) can be discovered and or refined.
Nguyen, Dangtue Hu, "Acetylcholine Muscarinic Receptor-Mediated Contractility of Ovine Pulmonary Arteries: Changes with Maturation and Chronic Hypoxia" (2009). Honors Theses. 2242.