Altered Vasomotion Characteristics as a Method of Investigating Vascular Phenotypic Change

Abstract

Vasomotion is the spontaneous oscillation of vascular tone, occurring due to synchronization of internal calcium fluctuations between multiple vascular smooth muscle cells by gap junction and electrical communication. Although altered vasomotion has been observed in a variety of pathological situations, characterization of these alterations has been lacking. Using a novel method of spectral quantification, and two experimental models known to have altered vascular structure, the present thesis was designed to evaluate whether vasomotion characteristics could be correlated with altered vascular structure. Rats with perinatal iron deficiency (PID) have previously been shown to possess altered vascular structure. When phenylephrine-mediated contractile and acetylcholine-mediated dilatory responses were investigated in PID animals, they both displayed blunted relaxation as compared to control vessels. When vasomotion characteristics were quantified, vessels taken from PID animals exhibited a decreased power in the very low frequency window (VLF <0.2 Hz). Changing vessel oxygenation to 10% O2 from 95% O2 did not result in significant alterations of vasomotion characteristics. The primary frequency of oscillation was investigated with a peak finder, and found to be significantly different compared to control in both the aorta and renal arteries obtained from PID animals. To investigate the effect of antihypertensive treatment (enalapril and hydrochlorothiazide) on gap junction communication, spontaneously hypertensive rats (SHR) were subject to a 2-week intensive angiotensin converting enzyme inhibitor treatment. This treatment resulted in significant vascular structural regression. All vessels (aorta, renal, mesenteric) from treated animals had greater proportions of power in the VLF window, with both the mesenteric and renal vessels exhibiting a primary peak of oscillation around 0.2 Hz; whereas the aorta had a primary peak at 0.12 Hz. Investigating altered gap junction communication with the gap junction blocker 18-α glycyrrhetinic acid, revealed that vascular bed location was the determining factor of vasomotion response. Immunoblotting did not indicate differences in connexin 43, a major gap junction protein in the vascular smooth muscle. These studies suggest that vasomotion characteristics can be used as a method of vascular phenotype investigation; vasomotion characteristics were significantly different in vessels taken from PID and hypertensive animals as compared to control and antihypertensive-treated animals, respectively.