Correlated electrical and mechanical responses of isolated rabbit pial arteries to some vasoactive drugs.

Abstract

SUMMARY Simultaneous measurements were made of spike activity and perfusion pressure (P A ) in intact segments of rabbit middle cerebral artery in vitro. The segments were mounted on a Teflon tube designed so that the perfusing solution flowed in the annular space between the tube and the artery wall, thus magnifying the P A changes occurring when the artery constricted or dilated. A widened portion of the Teflon tube immobilized 1-2 mm of the artery segment for electrical recording with fine glass microelectrodes. Spontaneous spike activity (extra-and intracellular) was regularly observed. When a steady P A and spike discharge was obtained, tests were performed by substituting for the normal perfusion liquid, solutions containing 5 ng/m\ norepinephrine, 5 Mg/ml angiotensin II or 7.5 Mg/ml isoproterenol. Norepinephrine and angiotensin each increased spike frequency (+ 293 and + 126%) and P A (+ 6.6 and + 7.9 mm Hg) whereas isoproterenol decreased spike frequency (-89%) and P A (-22.9 mm Hg). These results a) confirm the presence of receptors to these agents in pial arteries, and b) demonstrate a high degree of correlation between membrane electrical events and mechanical activity of these spontaneously-active myovascular cells. Stroke Vol 10, No 6, 1979PREVIOUS WORK in vitro on cerebral arteries has been concerned with measurements made on helical strip preparations 1 or on short whole segments in which circular tension is measured isometrically. smooth muscle are closely related to the electrical activity in many, but not necessarily all, cases, 6 and it may be that a synergistic action of several factors on the membrane potential is sufficient to elicit a mechanical change even if each factor alone is insufficient.For these reasons we have chosen to measure simultaneously mechanical and electrical activity in isolated perfused segments of rabbit cerebral arteries. This first report concerns the action of norepinephrine, isoproterenol and angiotensin II on the middle cerebral artery of the rabbit. Norepinephrine was used to allow comparison with the other (mechanical) methods for studying cerebral vessels and also with vessels from other organs, since norepinephrine has been extensively studied elsewhere. The beta-adrenergic agonist isoproterenol was used to determine whether relaxation could be obtained under the conditions of our experiment and how such action is related to the electrical activity. Our primary reason for studying angiotensin stems from its widespread use experimentally to create a

Factors involved in the physiological regulation of the cerebral circulation

“…In contrast, serotonin depolarized and contracted both vessels. Lusamvuku et al (1979) also found spike frequency in the middle cerebral artery of the rabbit correlated with tension generated by norepinephrine. Application of tetraethylammonium chloride (TEA), which suppresses K + permeability, does not change membrane potential in the basilar artery but evokes spike potentials upon application of norepinephrine (Harder et al 1981).…”

In vivo microscopy of the cerebral microcirculation using neonatal allografts in hamsters.

“…16 - 17 The cerebral arterioles were unresponsive to isoproterenol, 1415 whereas the cheek pouch arterioles responded with an intense vasodilation. Since Wahl et al 15 demonstrated that isoproterenol did not produce any significant changes in the diameters of pial arterioles in cats, this supports the present evidence that the grafted cerebral tissue and its microvasculature remained pharmacologically intact; thus, the microvessels of the cerebral allograft did not dedifferentiate to pharmacologically mimic cheek pouch arterioles.…”

Whole Mounted Pressurized in vitro Model for the Study of Cerebral Arterial Mechanics

“…The newest approach being used to study arteries in vitro entails the cannulation of whole cylindrical sections of vessel between rigid tubes which are perfused both intraluminally and extraluminally with modified Krebs solution [Lusamvuku et al, 1979;Schabert et al, 1980;Vinall and Simeone, 1981;Forstermann et al, 1984]. This method produces less cellular damage due to cutting than both the helical and ring meth ods, while duplicating levels of pressure and flow that more closely mimic in situ condi tions.…”