title: Occurrence of the "capillary contractility" phenomenon and its significance in the distribution of microvascular flow in frog skeletal muscle.
abstract: The phenomenon of "capillary contractility" was first described more than 100 years ago. Recent reports on this phenomenon in the frog mesentery have been based on the observation of dramatic reductions of luminal diameter and blood flow during electrical stimulation of the capillary wall. The aim of this study was to establish the presence and the occurrence of this phenomenon in the frog sartorius muscle and to evaluate its contribution to the distribution of flow. Eight 1.3 X 1.7-mm areas of the muscle surface in eight anesthetized frogs were visualized by means of a microscope and also video-recorded during stimulation experiments. Microelectrodes and semitransparent surface electrodes introduced constant currents (0.1 to 1.0 microA) or pulse trains (5-msec pulse width, 1 to 64 Hz frequency, -0.2 to -5.4 V amplitude) either to individual capillaries or to whole populations of capillaries situated in these areas. Caution was exercised that stimuli did not cause muscle twitching. Red cell velocity in capillaries was measured from video recordings by the flying spot technique. Microelectrode stimulations caused flow stoppages in 4 out of 60 individual stimulated capillaries. Surface electrode stimulations had practically no effect on the mean red cell velocity in any of these populations but an appreciable effect on individual velocities in 7.5% of all capillaries in these populations. It is concluded that the phenomenon of electrically induced reductions of flow exists in the frog sartorius muscle, but it is scarce. It seems unlikely, therefore, that it represents a major mechanism of flow distribution in this tissue.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002200:Capillary Resistance; D004558:Electric Stimulation; D004566:Electrodes; D004837:Epinephrine / Q000494:pharmacology; D009132:Muscles / Q000098:blood supply*; D011893:Rana esculenta; D011896:Rana temporaria
chemical_list: D000109:Acetylcholine; D004837:Epinephrine