Date of Graduation
This project's first study determined if hypertension and/or dietary salt are associated with an altered myogenic response in skeletal muscle arterioles. Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) fed low-salt (LS) or high-salt (HS) diets were enclosed in a ventilated box with the spinotrapezius muscle exteriorized for intravital microscopy. Box pressurizations caused similar increases in arterial pressure that were completely transmitted to arcade bridge arterioles, which constricted in WKY-LS, SHR-LS and SHR-HS, but not in WKY-HS. Arteriolar myogenic responsiveness was not different between WKY-LS and SHR-LS, but was greater in WKY-LS than in WKY-HS. Arteriolar myogenic responsiveness was also greater in SHR-HS than in SHR-LS. Therefore, hypertension is not associated with an altered arteriolar myogenic response in spinotrapezius muscle, and dietary salt attenuates the myogenic response in normotensive but not hypertensive rats. The second study evaluated the possible influence of nitric oxide (NO) on the arteriolar myogenic response, and determined if hypertension and/or dietary salt alter this influence. The influence of local NO on myogenic responsiveness was evaluated by repeating box pressurizations while exposing the muscle to the NO synthase (NOS) inhibitor NG-monomethyl-L-arginine. NOS inhibition augmented myogenic responsiveness in WKY-LS and SHR-LS, but not in WKY-HS and SHR-HS. Therefore, NO normally attenuates the arteriolar myogenic response in spinotrapezius muscle, and dietary salt impairs this influence. The third study explored the possibility that angiotensin II (Ang II) modulates the arteriolar myogenic response, and determined if dietary salt alters any influence of Ang II. The influence of Ang II on myogenic responsiveness was evaluated in WKY-LS and WKY-HS by repeating box pressurizations during exposure of the spinotrapezius muscle to saralasin or losartan or systemic captopril treatment. Saralasin and losartan modestly attenuated myogenic activity in WKY-LS but not in WKY-HS. Captopril attenuated myogenic responsiveness more in WKY-LS than in WKY-HS. Therefore, endogenous Ang II normally reinforces arteriolar myogenic activity in the spinotrapezius muscle, and dietary salt impairs this reinforcement.
Nurkiewicz, Timothy Robert, "Effects of hypertension and dietary salt on myogenic activity in the microcirculation: Possible roles of nitric oxide and angiotensin II." (1999). Graduate Theses, Dissertations, and Problem Reports. 9515.