Red blood cell and plasma distribution in SHR cremaster muscle microvessels.

Distribution of blood in the cremaster muscle microvasculature of spontaneously hypertensive (SHR) and Wistar-Kyoto normotensive (WKY) rats was determined by fluorescence videomicroscopy and densitometry. Bolus intra-arterial injections of fluorescein isothiocyanate (FITC)-dextran or dichlorotriazenylaminofluorescein-treated red blood cells (DTAF-RBC) produced time-concentration curves in the series-coupled segments. WKY and SHR mean arterial pressure averaged 89 +/- 6 and 125 +/- 5 mmHg, respectively. Arteriolar diameters were not different between the two groups. The smallest SHR venules (V4) and larger diameters than those of WKY (P less than 0.05), whereas V3 and V2 were not different. WKY diameters for V1 were significantly greater than those of SHR. The mean transit (t) and appearance times (ta) of both indicators were equal at the largest arteriole (A1) in both groups. In A2, A3, and A4 the t for both indicators were generally lower in SHR than in WKY rats but not significantly. The venular t were significantly greater in SHR than in WKY rats with DTAF-RBC consistently less than FITC-dextran values. The greater cross-sectional area of V4 in SHR than WKY rats would reduce flow velocity and elevate t. Dispersion (ta/t = 1.0 indicates no dispersion) of both indicators was less in WKY than in SHR. The ratios for both groups increased at V4 because ta increased more than t. Shorter circuits for red blood cells than for plasma and less plasma skimming exists in WKY than in SHR.