UVM Theses and Dissertations
Format:
Print
Author:
Celia, Gerard Francis
Dept./Program:
Molecular Physiology and Biophysics
Year:
2004
Degree:
Ph. D.
Abstract:
Mammalian pregnancy is associated with significant growth and remodeling of the uterine vasculature in order to sustain and nourish the growing conceptus, although the mechanisms that drive these adaptations remain unknown. This thesis investigates the hypothesis that a pathway of veno-arterial communication, dependent on venous permeability, exists, whereby the placenta may regulate its own perfusion through the release of specific vasoactive molecules. Veno-arterial communication was studied in vitro, using isolated, pressurized segments of the main uterine artery and vein from both Late Pregnant (LP) and nonpregnant (NP) rats. As a representative vasoconstrictor, phenylephrine (Phe) was alternately superfused around the paired vessels, and perfused into the uterine vein, in order to determine whether substances in the venous effluent could influence the tone of the adjacent artery. Intravenous Phe constricted the adjacent uterine artery in a concentration-dependent manner in both LP and NP animals. Conversely, perfusion of the uterine veins with ET-1 resulted in constriction of the uterine veins, rather than the arteries.
Superfusion of both vessels demonstrated a 6000-fold increase in sensitivity of the uterine veins to ET-1 compared to the uterine arteries, although this difference was reduced to 29-fold during pregnancy. Co-perfusion of the vein with a single dose of Phe and increasing concentrations of ET -1 effectively reduced the bioavailability of Phe to the adjacent artery in direct proportion to the degree of venous constriction to ET-1, in both LP and NP groups. These results support the hypothesis that veno-arterial communication occurs by means of molecular flux across the venous wall. To investigate the permeability of the uterine vein, as a pathway for veno-arterial communication, uterine venous segments from LP and NP rats were mounted in a vasograph and perfused with 3 and 70kDa fluorescently-labeled dextrans. Flux of each dextran through the venous wall was measured under basal conditions, in response to VEGF stimulation, and ET-1 induced constriction. Under basal conditions, veins were ~10-fold more permeable to the 3kDa dextran versus the 70kDa dextran, and pregnancy increased overall permeability by ~2.5-fold.
As venous caliber increases during gestation, the relationship between circumferential wall tension and venous permeability was also examined, and a positive correlation was discovered for molecular flux of the 3kDa, but not the 70kDa dextran. Stimulation with VEGF significantly increased venous permeability to both dextrans. Constriction to ET-1, however, resulted in a decrease in permeability, that was directly proportional to the degree of venous tone. This finding was in agreement with the results of the co-perfusion experiments. To better understand the role of VEGF in modulating uterine venous permeability, its proposed signaling cascade was investigated. Experiments using specific molecular inhibition revealed a role for a PLC/PKC mechanism dependent on Ca2+, but not NO, in VEGF induced hyperpermeability.
Collectively, the results of these experiments support the existence of a pathway for veno-arterial communication in the uterine circulation through venous permeability. Furthermore, it has been shown that this permeability is subject to modulation by the biophysical state of the vessel (ie. the amount of wall (tension and the degree of constriction), as well as by molecular signaling through the placentally-derived growth and permeability factor VEGF.
Superfusion of both vessels demonstrated a 6000-fold increase in sensitivity of the uterine veins to ET-1 compared to the uterine arteries, although this difference was reduced to 29-fold during pregnancy. Co-perfusion of the vein with a single dose of Phe and increasing concentrations of ET -1 effectively reduced the bioavailability of Phe to the adjacent artery in direct proportion to the degree of venous constriction to ET-1, in both LP and NP groups. These results support the hypothesis that veno-arterial communication occurs by means of molecular flux across the venous wall. To investigate the permeability of the uterine vein, as a pathway for veno-arterial communication, uterine venous segments from LP and NP rats were mounted in a vasograph and perfused with 3 and 70kDa fluorescently-labeled dextrans. Flux of each dextran through the venous wall was measured under basal conditions, in response to VEGF stimulation, and ET-1 induced constriction. Under basal conditions, veins were ~10-fold more permeable to the 3kDa dextran versus the 70kDa dextran, and pregnancy increased overall permeability by ~2.5-fold.
As venous caliber increases during gestation, the relationship between circumferential wall tension and venous permeability was also examined, and a positive correlation was discovered for molecular flux of the 3kDa, but not the 70kDa dextran. Stimulation with VEGF significantly increased venous permeability to both dextrans. Constriction to ET-1, however, resulted in a decrease in permeability, that was directly proportional to the degree of venous tone. This finding was in agreement with the results of the co-perfusion experiments. To better understand the role of VEGF in modulating uterine venous permeability, its proposed signaling cascade was investigated. Experiments using specific molecular inhibition revealed a role for a PLC/PKC mechanism dependent on Ca2+, but not NO, in VEGF induced hyperpermeability.
Collectively, the results of these experiments support the existence of a pathway for veno-arterial communication in the uterine circulation through venous permeability. Furthermore, it has been shown that this permeability is subject to modulation by the biophysical state of the vessel (ie. the amount of wall (tension and the degree of constriction), as well as by molecular signaling through the placentally-derived growth and permeability factor VEGF.