Rat small mesenteric artery function after hindlimb suspension

To determine whether simulated microgravity in rats is associated with vasc ular dysfunction, we measured responses of isolated, pressurized mesenteric resistance artery segments (157- to 388-mu m ID) to vasoconstrictors, pres sure, and shear stress after 28-day hindlimb suspension (HS). Results indic ated no differences between HS and control (C) groups in 1) sensitivity or maximal responses to vasoconstrictors (norepinephrine, phenylephrine, serot onin, KCl; 2) ID, external diameter, or ratio of wall thickness to ID; 3) d istensibility; or 4) vasodilatory responses to shear stress. Myogenic tone was attenuated (P < 0.05) in HS arteries vs. C, as evidenced by I) decrease d magnitude of tone in larger vessels (second-order branch off superior mes enteric artery, 261- to 388-mu m ID) at pressures greater than or equal to 40 mmHg in the presence of phenylephrine (10(-7) M) and 2) decreased magnit ude of tone in smaller vessels (third-order branch off superior mesenteric artery, 157- to 277-mu m ID), which exhibited spontaneous tone, at pressure s greater than or equal to 70 mmHg. This attenuation of myogenic tone after HS could contribute to orthostatic intolerance because myogenic tone contr ibutes to the overall tone of resistance arteries.