Noninvasive assessment of vascular structure and function in conscious rats based on in vivo imaging of the albino iris

Abstract

Experimental techniques allowing longitudinal studies of vascular disease progression or treatment effects are not readily available for most animal models. Thus, most existing studies are destined to either study individual time points or use large cohorts of animals. Here we describe a noninvasive technique for studying vascular disease that is based on in vivo imaging of the long posterior ciliary artery (LPCA) in the iris of albino rats. Using a slit-lamp biomicroscope, images of the LPCA were taken weekly in conscious normotensive Wistar Kyoto rats (WKY, n = 10) and spontaneously hypertensive rats (SHR, n = 10) for 10 wk. Using imaging software, we found that lumen diameter was significantly smaller and the wall-to-lumen (W/L) ratio larger in SHR than in WKY. Wall thickness was not different. Blood pressure correlated with the W/L ratio. Histology of the abdominal aorta also revealed a smaller lumen diameter and greater W/L ratio in SHR compared with WKY. Corneal application of the muscarinic receptor agonist pilocarpine elicited a dose-dependent vasodilation of the LPCA that could be antagonized by inhibition of nitric oxide synthase, suggesting that the pilocarpine response is mainly mediated by endothelium-derived nitric oxide. Consistent with endothelial dysfunction in SHR, pilocarpine-induced vasodilation was greater in WKY rats than in SHR. These findings indicate that in vivo imaging of the LPCA allows assessment of several structural and functional vascular parameters in conscious rats and that the LPCA responds to disease insults and pharmacologic treatments in a fashion that will make it a useful model for further studies.

In vivo OCT microangiography of rodent iris

“…A single branch of a long posterior ciliary artery (LPCA) (arrows in Fig. 4(b)) traveling almost perpendicular to the radial vessels is seen in the vicinity of the iris root [16]. In order to resolve individual vessels, we performed an additional experiment by reducing the system field of view to 1.75 × 1.75 mm 2 while keeping the scanning protocol described above un-changed.…”

“…5(c) and 5(d)). This can be explained by the fact that drug-induced sympathetic stimulation causes the contraction of the dilator muscle, leading to possible compression of the radial vessels [16,17]. The iris vessel tortuosity against the increase of the pupil area is quantified and plotted in Fig.…”

Noninvasive assessment of the iridial microcirculation in rats using sidestream dark field imaging

“…The anatomical structure of iridial vascular structure in sheep was precisely described using a casting method (Olver & McCartney, 1989) and several studies evaluated iris microvascular flow in rats using laser Doppler flowmetry or other methods. However, these studies did not assess capillary density and focused mainly on iris vessel diameter changes in different disease models and treatments (Meinen et al ., 1975; Jariyapongskul, et al ., 2006; Jariyapongskul et al ., 2007; Stauss et al ., 2011). SDF imaging may, therefore, represent a novel, specific technique to examine changes in iris vascular bed, e.g.…”

Cardiovascular end-organ damage in response to increased blood pressure variability

“…All of the imaging procedures were done in conscious rats manually held in front of the slit-lamp biomicroscope by one investigator while a second investigator operated the slit-lamp and the digital camera. The methods for this procedure and some of the preliminary experiments were part of a separate study that has previously been published (Stauss, Rarick et al 2011).…”

“…The results of the pilocarpine and L-NAME experiments have been previously published (Stauss, Rarick et al 2011). All experiments were conducted in normotensive Sprague Dawley rats.…”