Effects of flumazenil during administration of midazolam on pial vessel diameter and regional cerebral blood flow in cats

Effects of topical and intravenous JM-1232(-) infusion on cerebrovascular reactivity in rats

A novel short-acting benzodiazepine receptor agonist, JM-1232(-), has been shown to have a sedative/hypnotic effect and wide safety margin. However, its effect on cerebral vessels is not well known. Therefore, we investigated the cerebrovascular reactivity to topical and intravenous JM-1232(-) and during hypotension or hypercapnia with intravenous administration of JM-1232(-). We used a closed cranial window preparation to measure the changes of cerebral pial arteriolar diameters in isoflurane-anesthetized Sprague-Dawley rats. We first measured the direct effect of topical JM-1232(-). We then determined the effect of intravenous JM-1232(-) and then we measured the response to hypercapnia before and after JM-1232(-) infusion. Finally, we measured the reaction to stepwise induction of hypotension before and after JM-1232(-) infusion. Topical infusion of JM-1232(-) dilated pial arterioles. Intravenous infusion of JM-1232(-) changed pial arterioles by 4.5 ± 2.7 %, 5.0 ± 3.9 %, and -2.8 ± 2.6 % (at 0.1, 0.3, and 1.0 mg/kg/min, respectively). Hypercapnia dilated pial arterioles before and after JM-1232(-) infusion. The diameters of pial arterioles did not change during hypotension before or after intravenous JM-1232(-) infusion. These results indicate that topical JM-1232(-) has a dilative effect on pial arterioles and that intravenous administration of JM-1232(-) may not affect cerebrovascular reactivity to hypotension or hypercapnia.

The effects of topical and intravenous JM-1232(-) on cerebral pial microvessels of rabbits

Background

JM-1232(-) is a novel anesthetic agent which acts through gamma-aminobutyric acid receptors. Cerebral pial vascular effects of JM-1232(-) are unknown. We thus evaluated topical and intravenous effects of JM-1232(-) on cerebral pial microvessels in rabbits, and the extent to which carbon dioxide (CO₂) reactivity is preserved.

Methods

Closed cranial windows were used to visualize cerebral pial circulation in 29 Japanese white rabbits. In the first experiment, the cranial window was superfused with increasing concentrations of JM-1232(-): 10^-11, 10^-9, 10^-7, 10^-5 mol/L, n = 8 per concentration. In the second experiment, we examined the effects of an intravenous bolus of 1 mg/kg bolus of JM-1232(-), followed by the continuous infusion at 0.3 mg/kg/minute on cerebral pial vascular alteration (n = 9). In the third, we examined CO₂ reactivity of cerebral pial vessels under JM-1232(-) (n = 6) or sevoflurane anesthesia (n = 6).

Results

Topical application of JM-1232(-) did not change pial venular diameter, and constricted arterials only at the highest concentration. Intravenous administration of JM-1232(-) produced cerebral pial constriction which gradually diminished over time. Under intravenous administration of JM-1232(-) and inhaled sevoflurane, diameters of vessels increased in parallel with CO₂ partial pressure. Slopes of linear regression and correlation coefficients in arterioles and venules were comparable for JM-1232(-) anesthesia and sevoflurane anesthesia.

Conclusions

Topical application of JM-1232(-) had little effect on cerebral pial vessels. Intravenous administration produced vasoconstriction of cerebral pial arterioles and venules, however those changes were clinically unimportant. In addition, JM-1232(-) did not impair CO₂ responsiveness. At least from the perspective of vascular reactivity, JM-1232(-) thus appears safe for neurosurgical patients.

Effect of mild hypothermia on inodilator-induced vasodilation of pial arterioles in cats

BACKGROUND

Mild hypothermia has been proposed as a means of providing cerebral protection after traumatic brain injury. However, hypothermia has been shown to alter not only physiologic but also pharmacologic responses. The purpose of this study was to investigate whether mild hypothermia (3-4 degrees C temperature reduction) could alter cerebral vasodilation induced by inodilators, which are characterized by having an inotropic effect in addition to a vasodilatory effect. Isoproterenol (a beta-adrenergic receptor agonist), colforsin dapropate (an adenylate cyclase stimulant), and amrinone (a phosphodiesterase inhibitor) were chosen as inodilators.

METHODS

The cranial window technique, combined with microscopic video recording, was used. Forty-eight cats were randomly assigned to either a normothermic or a hypothermic group (33 degrees C). Isoproterenol, colforsin dapropate, or amrinone was topically applied in the cranial window and the diameter of pial arterioles was measured.

RESULTS

Topical administration of isoproterenol, colforsin dapropate, and amrinone produced a significant dilation in a dose-dependent manner during normothermia. The vasodilation induced by these inodilators was not affected by mild hypothermia.

CONCLUSION

The vasodilation induced by topical administration of isoproterenol, colforsin dapropate, and amrinone was not affected by mild hypothermia.

Effect of mild hypothermia on nicorandil-induced vasodilation of pial arterioles in cats

OBJECTIVE

Nicorandil is characterized as hybrid between nitrates and potassium channel activators. Recent evidence suggested that mild hypothermia may alter cerebral vasodilation induced by a nitrate agent and potassium channel opener. However, the effect of mild hypothermia on nicorandil-induced vasodilation is not known. The present study was conducted to investigate whether mild hypothermia could alter nicorandil-induced cerebral vasodilation. In addition, the effects of mild hypothermia on cerebral vasodilation induced by nitroglycerin, a nitrate agent, and cromakalim, a selective adenosine 5'-triphosphate-sensitive potassium channel opener, were assessed in the same model.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-four cats.

INTERVENTIONS

Animals were anesthetized with pentobarbital. The cranial window technique, combined with microscopic video recording, was used to measure small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were assigned randomly to either a normothermic (37 degrees C) or a hypothermic (33 degrees C) group. Nicorandil, nitroglycerin, or cromakalim at concentrations of 10(-8), 10(-6), or 10(-4) mol/L was applied topically in the cranial window, and the diameter of pial arterioles was measured.

MEASUREMENTS AND MAIN RESULTS

Topical administration of nicorandil, nitroglycerin, and cromakalim significantly dilated both small and large pial arterioles in a dose-dependent manner during normothermia. Nicorandil-induced vasodilation of either large or small pial arterioles was not affected by hypothermia. However, hypothermia significantly attenuated nitroglycerine-induced vasodilation in both large and small pial arterioles and enhanced cromakalim-induced vasodilation in both large and small pial arterioles.

CONCLUSIONS

Nicorandil-induced vasodilation of cerebral pial arterioles was not affected by mild hypothermia. By contrast, mild hypothermia significantly attenuated nitroglycerin-induced vasodilation and enhanced cromakalim-induced vasodilation.

Response of pial vessel diameter and regional cerebral blood flow to CO2 during midazolam administration in cats

Midazolam has been demonstrated to preserve the response of cerebral blood flow to CO2. However, the responsiveness of cerebral vessels or microcirculation during midazolam administration related to alteration of cerebral blood flow has not been explored. The purpose of this study was to examine the effects of midazolam on cerebral microcirculation. Nine cats were paralyzed and mechanically ventilated under nitrous oxide/oxygen anaesthesia. Using the closed cranial window technique and laser Doppler flowmetry, diameter of pial vessels and regional cerebral blood flow (rCBF) were examined on the surface of the cerebral cortex which was perfused by the middle cerebral artery. Before midazolam administration, haemodynamic variables, blood gases, rCBF, and diameter of pial vessels were determined as a control under normocapnia, hypocapnia, and hypercapnia conditions. After midazolam administration, given initially at 0.8 mg.kg-1.min-1 for 10 min and subsequently at 0.04 mg.kg-1.min-1 (total dose 10 mg.kg-1), the same variables were again analyzed. With regard to CO2 responsiveness, an 8.85% increase in rCBF was demonstrated for a Paco2 elevation of 1 kPa before midazolam administration, compared with a 7.47% increase after midazolam administration. With regard to the correlation between CO2 response and vessel diameter, arterioles less than 50 microns in diameter were more sensitive than those more than 50 microns in diameter, although there were no significant differences before or after midazolam administration. We conclude that CO2 responsiveness is preserved in terms of rCBF and vessel diameter after high doses of midazolam (10 mg.kg-1) in cats.