Microvascular myogenic reaction in the wing of the intact unanesthetized bat

Abstract

Microvascular dimension and flow responses to stepwise changes in arterial and venous pressures, ranging from zero to +100 mmHg and zero to -75 mmHg have been recorded. Observations were made in arterioles, terminal arterioles, and precapillary sphincters in the wing web of intact, unanesthetized bats. The results show for all categories of vessels that with reduced transmural pressures there is a progressive increase in mean diameter and a decrease in rhythmic vasomotion rate. Flow changes are variable. For elevated transmural pressures there is a vasoconstriction with drastic flow reduction that is inconsistent with metabolic control. However, after prolonged elevation of pressure there is a progressive increase in flow, suggesting a "metabolic escape". Computed wall tension remains reasonably constant for a wide range of transmural pressures, suggesting that wall tension may be the controlled variable. These findings support the hypothesis of a myogenic reaction as a mechanism for maintenance of basal vascular tone in the intact unanesthetized bat.

Evidence of myogenic vascular control in the rat cerebral cortex.

“…At ambient pressures of ±20 mm Hg, vessel wall tension typically remained within ±10-15% of control. At ambient pressures of ±25 mm Hg, Bouskela and Wiederhielm (1979) calculated that the wall tension remained within -32% to +28% of control, which is somewhat greater than found in the present study for a similar range of ambient pressures. Mesenteric arterioles which constricted as intravascular pressure was increased, in the study by Burrows and Johnson (1983), demonstrated only a 3.8% increase in wall tension for a 10% pressure increase.…”

“…Vessel wall tension at a nearly constant diameter would essentially be a direct function of transmural pressure and, as such, a sustained stimulus for a myogenic response. Such a situation has been observed by Bouskela and Wiederhielm (1979) for bat arterioles at ambient pressures of ±25 mm Hg and by Dacey and Duling (1982) for isolated arterioles of the rat cerebral cortex. The potential for sustained myogenic responses has been recently reviewed by Johnson (1980).…”

“…during elevations of venous pressure similar to 557 those in the present study. Bouskela and Wiederhielm (1979) have used the whole body change in ambient pressure, as originally described by Wiederhielm et al (1979), and report relatively minor changes in arteriolar diameters in the bat wing for ambient pressures of ±25 mm Hg. The vessels apparently maintained a nearly constant diameter despite whatever change in intravascular pressure occurred at ambient pressures of ±25 mm Hg.…”

Autoregulation of blood flow.

“…Bouskela and Wiederhielm 64 found that the constriction of arterioles and precapillary sphincters in the bat wing tended to maintain calculated wall tension constant during simultaneous elevation of arterial and venous pressures. Burrows and Johnson 72 found that as arterial pressure to the cat mesentery was reduced, arteriolar dilation tended to maintain wall tension.…”

Active reactions of the rabbit ear artery to distension.

“…It is not clear why increases in transmural pressure rarely enhanced constriction of these isolated blood vessels in contrast to arterioles in vivo (Bouskela & Wiederhielm, 1979; Borgstr6m, Grande & Lindbom, 1981;Burrows & Johnson, 1981;Morff & Granger, 1982). This difference between blood vessels in vivo and in vitro may, in part, reflect differences in activation of the muscle or in stress on the muscle.…”