Effect of hindlimb suspension on cardiovascular responses to sympathomimetics and lower body negative pressure.
To determine whether hindlimb suspension is associated with the development of cardiovascular deconditioning, male rats were studied before and after undergoing one of three treatment conditions for 9 days: 1) cage control (n = 15, CON), 2) horizontal suspension (n = 15, HOZ), and 3) head-down suspension (n = 18, HDS). Testing included lower body negative pressure administered during chloralose-urethan anesthesia and graded doses of sympathomimetic agents (norepinephrine, phenylephrine, and tyramine) administered to conscious unrestrained animals. Both HDS and HOZ were associated with a small decrease in the hypotensive response to lower body negative pressure. The HOZ group, but not the HDS group, exhibited augmented reflex tachycardia. Furthermore, both HDS and HOZ groups manifested reduced pressor responses to phenylephrine after treatment. These reductions were associated with significantly attenuated increases in mesenteric vascular resistance. However, baroreflex control of heart rate was not altered by the treatment conditions. Collectively, these results indicate that 9 days of HDS in rats does not elicit hemodynamic response patterns generally associated with cardiovascular deconditioning induced by hypogravic conditions.
Overton
J M
JM
Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
Tipton
C M
CM
D000818:Animals; D001775:Blood Circulation / Q000187:drug effects*; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects*; D003664:Decompression; D006339:Heart Rate / Q000187:drug effects; D006614:Hindlimb / Q000098:blood supply / Q000502:physiology; D008150:Lower Body Negative Pressure; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D013566:Sympathomimetics / Q000494:pharmacology*; D014439:Tyramine / Q000494:pharmacology; D014893:Weightlessness
D013566:Sympathomimetics; D010656:Phenylephrine; D009638:Norepinephrine; D014439:Tyramine