Abstract
This study was aimed to characterize the geometric arrangement of hamster skeletal muscle arteriolar networks and to assess the in vivo rhythmic diameter changes of arterioles to clarify regulatory mechanisms of the capillary perfusion. The experimental study was carried out in male Syrian hamsters implanted with a plastic chamber in the dorsum skin under pentobarbital anesthesia. The skeletal muscle microvessels were visualized by fluorescence microscopy. The vessel diameters, lengths and the rhythmic diameter changes of arterioles were analyzed with computer-assisted techniques. The arterioles were classified according to a centripetal ordering scheme. In hamster skeletal muscle microvasculature the terminal branchings, differentiated in long and short terminal arteriolar trees (TATs), originated from anastomotic vessels, defined “arcading” arterioles. The long TATs presented different frequencies along the branching vessels; order 4 arterioles had frequencies lower than those observed in the order 3, 2, and 1 vessels. The short TAT order 3 arterioles, directly originating from “arcading” parent vessels, showed a frequency dominating all daughter arterioles. The amplitude of diameter variations in larger vessels was in the range 30–40% of mean diameter, while it was 80–100% in order 3, 2, and 1 vessels. Therefore, the complete constriction of arterioles, caused an intermittent capillary blood perfusion. L-arginine or papaverine infusion caused dilation of arterioles and transient disappearing of vasomotion waves and induced perfusion of all capillaries spreading from short and long TAT arrangements. Therefore, the capillary blood flow was modulated by changes in diameter of terminal arterioles penetrating within the skeletal muscle fibers, facilitating redistribution of blood flow according to the metabolic demands of tissues.
Highlights
Arterioles display spontaneous rhythmic diameter changes, previously called vasomotion
Eleven male Syrian Golden hamsters (Charles River, Calco, Italy) weighing 80–100 g were subjected to implantation of the chamber in the dorsal skinfold as previously reported (Colantuoni et al, 1985); seven of these animals were treated with L-arginine or papaverine (10 and 0.3 mg/100 g b.w. intravenously infused, respectively)
In short terminal arteriolar trees (TATs), we calculated blood flow of 196.8 ± 11.5 nl/s in the same 24 ± 9 capillaries above reported, with an average red blood cell velocity (RBC) of 0.30 ± 0.02 mm/s; on the other hand in long TAT capillaries we found an increase of blood flow up to 373.35 ± 12.40 nl/s with an average RBC velocity of 0.30 ± 0.02 mm/s
Summary
Arterioles display spontaneous rhythmic diameter changes, previously called vasomotion. The accompanying variations in resistance result in capillary blood flow oscillations. Vasomotion was explained as a mechanism for increasing arteriolar flow conductance (=1/resistance), which plays an important role in controlling blood pressure (Nicoll and Webb, 1955; Zweifach, 1971; Slaaf et al, 1988; Aalkjær et al, 2011) and has been demonstrated to increase oxygen supply to tissue under conditions of low oxygenation (hypoxia) (Zweifach, 1971). The contribution to the average conductance during the diameter increase phase is greater than during diameter decrease, leading to net conductance increase (Aalkjær et al, 2011).
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