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1 Medicine, West Virginia University, Morgantown, West Virginia, United States
2 Medical Physiology, Texas A&M University Health Science Center, College Station, Texas, United States
3 Medical Physiology, 336 Reynolds Medical Bldg, College Station, Texas, 77843-1114, United States; Medical Physiology, Texas A&M University Health Science Center, College Station, Texas, United States
4 Medicine, The Milton S. Hershey Medical Ctr, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States
5 Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States
* To whom correspondence should be addressed. E-mail: mdelp{at}ufl.edu.
Diminished constriction of arteries and veins following exposure to microgravity or bed rest is associated with a reduced ability to augment peripheral vascular resistance (PVR) and stroke volume during orthostasis. We tested the hypothesis that small mesenteric arteries and veins, which are not exposed to large pressure shifts during simulated microgravity via head-down tail suspension (HDT), will exhibit decrements in adrenergic constriction after HDT in rats. Small mesenteric arteries and veins from control (Con; n= 41) and HDT (n= 35) male Sprague-Dawley rats were studied in vitro. Vasoactive responsiveness to norepinephrine (NE) in arteries (10-9 to 10-4 M) and veins (pressurediameter responses from 2-12 cm H2O after incubation in 10-6 or 10-4 M NE) were evaluated. Plasma concentrations of atrial (ANP) and brain (NT-proBNP) natriuretic peptides were also measured. In mesenteric arteries, sensitivity and maximal responsiveness to NE were reduced with HDT. In mesenteric veins there was a diminished venoconstriction to NE at any given pressure in HDT. Plasma concentrations of both ANP and NT-proBNP were increased with HDT, and maximal arterial and venous constrictor responses to NE after incubation with 10-7 M ANP or NT-proBNP were diminished. These data demonstrate that, in a vascular bed not subjected to large hydrodynamic differences with HDT, both small arteries and veins have a reduced responsiveness to adrenergic stimulation. Elevated levels of circulating ANP or NTproBNP could adversely affect the ability of these vascular beds to constrict in vivo, and conceivably could alter the intrinsic constrictor properties of these vessels with long-term exposure.
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