Do red blood cell velocities and diameters of capillaries differ during the course of a day?

To study peripheral circulation without interference by anesthesia and surgical trauma, the analysis of red blood cell velocity (RBC; flying spot technique) and capillary diameters (Phi-cap; angiometer or ruler) in the depilated auricle of rats was proposed. The rats were placed in plastic tubes and the right auricle was positioned on a transparent block with electronically controlled temperature using intravital microscopic techniques (transmitted light). For recording, a video camera was mounted on top of the microscope. 8 Wistar Kyoto (WKY) and 8 spontaneously hypertensive (SHR) rats were analysed. The results were expressed as means plus/minus SEM, the t-test for dependent samples (am/pm) was used. The over-all blood pressure (tailcuff) did not differ between am/pm (WKY: 142 +- 2mm Hg; SHR: 210 +- 7mm Hg). Due to the decrease of Phi-cap in the afternoon, the resistance is increased (WKY: 12%, SHR: 7%), while RBC-Velocity is decreased (WKY: 3%, SHR: 2%). The data show that in consci ous rats there is a statistically significant decrease in capillary diameters (WKY: p smaller 0.005, SHR: p smaller 0.10) and in RBC-velocity (WKY: p smaller 0.01, SHR: p smaller 0.05) in the afternoon compared to the values measured in the morning in the same animal. (ITA)