Effects of thiobarbiturates on smooth muscle reactivity in isolated aortas from spontaneously hypertensive rats

Direct effects of propofol (2,6-diisopropylphenol) on canine coronary artery ring tension

1. The direct effect of the intravenous general anesthetic propofol (2,6-diisopropylphenol) on epicardial coronary artery tone was studied in unstimulated canine coronary artery rings. 2. Rings stretched to a basal tension of 5 g and exposed to increasing concentrations of propofol generated a characteristic dose-dependent biphasic change in tension-concentrations from 10(-7) to 10(-5) M resulted in constriction (+477 +/- 118 mg) while concentrations 10(-4) and 10(-3) M resulted in relaxation (-682 +/- 75 mg). 3. The response to propofol was reversible and was not modified by the presence of endothelium, alpha 1 and beta adrenoceptor blockade or TEA sensitive potassium channel blockade. 4. The propofol induced changes in tension were altered by changes in extracellular calcium concentrations as well as by blockade of the voltage dependent calcium channel by verapamil. 5. These experiments suggest that clinical concentrations (human) of propofol may have direct vasoactive effects on epicardial coronary artery smooth muscle and that these effects may be due to actions on voltage dependent calcium channels of vascular smooth muscle.

Comparison of the vasodilator effects of thiopentone and pentobarbitone

The aim of this study was to elucidate the vasodilator mechanisms of barbiturates. In helical strips of dog mesenteric artery, the effects of pretreatment with thiopentone and pentobarbitone on the contractions induced by KCl (2.0 x 10(-2) M) and norepinephrine (10(-5) M) in normal bathing fluid, and those induced by norepinephrine and caffeine (2.5 x 10(-2) M) in Ca(++)-free fluid were tested, and their effects on caffeine-induced contractions in skinned strips were also examined. Thiopentone, at concentrations over 10(-4) M, inhibited the KCl-induced contractions in normal bathing fluid and those induced by caffeine in Ca(++)-free fluid and, at concentrations over 3 x 10(-4) M, inhibited norepinephrine-induced contractions in normal and Ca(++)-free bathing fluids significantly. Pentobarbitone, at concentrations over 3 x 10(-4) M, inhibited KCl- and norepinephrine-induced contractions in normal bathing fluid significantly, whereas contractions in Ca(++)-free fluid induced by norepinephrine and caffeine were inhibited only by a high concentration (10(-3) M) of pentobarbitone. Caffeine-induced contractions of chemically skinned fibres were more susceptible to inhibition by thiopentone than by pentobarbitone. These results suggest that the vasodilator effect of thiopentone is mediated via its intracellular inhibitory effect and that, in contrast, the vasodilator effect of pentobarbitone can be attributed mainly to its Ca(++)-channel blocking action.

Age-dependent alterations in the response of isolated rat aortas to thiobarbiturates

Responses to thiamylal and thiopental were compared in helical strips of rat thoracic aortas of different ages (5-6, 10-12 and 20-22 weeks old), precontracted partially with phenylephrine or prostaglandin F(2alpha) (PGF(2alpha)). Thiamylal and thiopental, in concentrations of 3 x 10(-5) to 10(-4) M, produced a dose-dependent relaxation in aortas at 5-6 weeks of age, no significant change of tension in those at 10-12 weeks of age, and a marked constriction in those at 20-22 weeks of age. These thiobarbiturates, in a high concentration of 10(-3) M, produced a profound relaxation in aortas at any age studied. It is concluded that the responses to thiobarbiturates of thoracic aorta precontracted with phenylephrine or PGF(2alpha) alter with age.

Responses to barbiturates of isolated dog cerebral and mesenteric arteries contracted with KCl and prostaglandin F2 alpha

In helical strips of dog cerebral and mesenteric arteries previously contracted with KCl or prostaglandin F2 alpha (PGF2 alpha), the addition of pentobarbital (10(-5) to 10(-3) mol.l-1) caused dose-related relaxation, whereas thiamylal and thiopental in a low concentration (10(-5) to 10(-4) mol.l-1) caused further contraction and in a high concentration (10(-3) mol.l-1) profound relaxation. Thiobarbiturate-induced contractions were greater in mesenteric than in cerebral arteries previously contracted with PGF2 alpha. In cerebral and mesenteric arteries exposed to Ca(++)-free media for 60 min and treated with KCl or PGF2 alpha, reintroduction of Ca++ produced a transient contraction, a transient relaxation and a persistent contraction. The Ca(++)-induced persistent contraction was attenuated by pretreatment with pentobarbital (10(-4) to 10(-3) mol.l-1) and thiamylal (10(-3) mol.l-1); the attenuation was greater in arteries treated with KCl than with PGF2 alpha. The Ca(++)-induced contractions of mesenteric artery treated with PGF2 alpha were potentiated by 10(-4) mol.l-1 thiamylal. It is concluded that pentobarbital possesses only a vasodilator effect, whereas thiamylal and thiopental have both constrictor and dilator effects on vascular smooth muscle. The vasodilator effect of barbiturates is associated in part with inhibition of transmembrane influx of Ca++; the inhibition is more predominant on the influx evoked by KCl-induced depolarization than by a stimulation of PGF2 alpha receptors. Thiamylal in low concentrations appears to enhance Ca++ influx through a receptor-operated Ca++ channel for PGF2 alpha.