Phorbol ester does not mimic,but antagonizes the alpha-adrenoceptor-mediated positive inotropic effect in the rabbit papillary muscle

Summary The phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) was used to examine the hypothesis that phosphoinositide turnover is involved in the regulation of myocardial contractility mediated by stimulation of alpha-adrenoceptors in the mammalian cardiac muscle. Exposure of the isolated rabbit papillary muscle electrically driven at a rate of 1 Hz at a temperature of 37°C to TPA in concentrations of 10–1000 nmol/l for 30 min did not affect the basal force of contraction. The concentration-response curve for the positive inotropic effect of (–)-phenylephrine mediated by stimulation of alpha-adrenoceptors in the presence of (±)-bupranolol (100 nmol/1) was shifted to the right and downward by TPA in concentrations of 30–1000 nmol/l, while the effect of (–)-phenylephrine mediated by stimulation of beta-adrenoceptors in the presence of prazosin (100 nmol/l) was not decreased, but slightly enhanced by exposure of the muscle to relatively low concentrations of TPA (10–100 nmol/l). Incubation of the membrane fraction isolated from the rabbit ventricular muscle with TPA in vitro under the same condition as employed in the physiological experiments decreased the specific binding of [³H]prazosin but not that of [³H]CGP-12177, while the non-tumor promoting phorbol ester, PDD, was ineffective. These results indicate that activation of protein kinase C by TPA does not mimic the positive inotropic effect of catecholamines mediated by activation of myocardial alpha-adrenoceptors. on the other hand, the specific interaction of alpha-adrenoceptor-mediated processes with TPA in the rabbit papillary muscle is in line with the view that the facilitation of phosphoinositide turnover and subsequent activation of protein kinase C may play a certain role in the coupling of alpha-adrenoceptor occupation by agonists to the process leading to the positive inotropic action. Send offprint requests to M. Endoh     

Preponderance of β- over α-adrenoceptors in mediating the positive inotropic effect of phenylephrine in the ferret ventricular myocardium

Summary [³H]prazosin bound to the membrane fraction derived from the ferret ventricular muscle with high affinity in a saturable manner (K _d = 0.25 nmol/l and B _max = 27 fmol/mg protein in the right ventricle). [³H]CGP-12177, a -adrenoceptor ligand, bound to the membrane fraction with a _{K d} value of 0.29 nmol/l and a B _max of 42 fmol/mg protein. In the isolated ferret papillary muscle driven at 1 Hz at 37°C, phenylephrine elicited a concentration-dependent positive intropic effect. The maximal effect of phenylephrine was comparable to that of isoprenaline. Prazosin (0.3 ol/l) shifted the concentration-response curve for phenylephrine slightly but significantly to the right, the maximal response being unaffected. In contrast, bupranolol (0.3 gmol/l) shifted the curve for phenylephrine markedly downwards: the maximal response was depressed significantly to 40% and the curve became less steep. In the presence of prazosin and bupranolol the curve was shifted to the right, being essentially parallel to the control curve. These results indicate that in the ferret ventricular myocardium both - and -adrenoceptors mediate the positive inotropic effect of phenylephrine. The extent of contribution of the two classes of adrenoceptor is quite different from that in other mammalian species. In the ferret heart, -adrenoceptors predominate over -adrenoceptors in mediating the positive inotropic effect of phenylephrine, although the number of -adrenoceptors is not especially high when compared with other species. Send offprint requests to M. Endoh at the above address     

A comparison of pre- and postsynaptic α-adrenergic effects of phenylephrine and tramazoline on blood vessels of the rabbit in vivo

Summary Pre- and postsynaptic -adrenergic effects of phenylephrine and tramazoline were studied in hindlegs of rabbits. The legs were autoperfused at a constant rate of flow. Phenylephrine and tramazoline were infused intraarterially. Increases in perfusion pressure evoked by the drugs were taken to represent activation of postsynaptic -adrenoceptors. Inhibition of the pressor response to low frequency stimulation of the lumbar sympathetic chain (1 and 2 Hz) without a decrease of the response to intraarterial injection of low doses of noradrenaline (60–450 ng) was considered to reflect activation of presynaptic -adrenoceptors.Phenylephrine produced vasoconstriction at concentrations of 10^–7–3×10^–6 M. Phenylephrine 10^–7 and 3×10^–7 M did not change pressor responses to nerve stimulation or noradrenaline, whereas higher concentrations selectively inhibited the effect of nerve stimulation. The maximal inhibition amounted to about 30%. Tramazoline caused vasoconstriction at concentrations of 3×10^–8–10^–6 M. All these concentrations, and also the lower concentration of 10^–8 M, diminished the response to nerve stimulation without a change in the effect of injected noradrenaline. The inhibition maximally amounted to about 80%. The sum of the vasoconstrictor effects of phenylephrine and of nerve stimulation exceeded the effect of nerve stimulation alone, whereas the sum of the vasoconstrictor effects of low concentrations of tramazoline and of nerve stimulation was lower than the effect of nerve stimulation alone. Except for tramazoline 10^–6 M, the effects were limited to the leg that received the intraarterial infusion; there was no change in the contralateral leg.The results are compatible with the view that not only in vitro, but also in vivo pre- and postsynaptic -adrenoceptors show different pharmacological properties. In the hindleg vasculature of the rabbit as well as in some other tissues tramazoline preferentially activates the presynaptic, whereas phenylephrine preferentially activates the postsynaptic receptors. There is not sufficient evidence, however, to allow generalization of these findings and to consider all presynaptic -adrenoceptors as one pharmacologically homogeneous group and all postsynaptic -adrenoceptors as the second, distinct homogeneous group.     

Expression of c-fos-like immunoreactivity in the feline brainstem in response to isometric muscle contraction and baroreceptor reflex changes in arterial pressure

This study compared whether activation of muscle ergoreceptor afferents caused by isometric muscle contraction, activation of baroreceptor afferents induced by i.v. infusion of phenylephrine, or baroreceptor afferent inactivation, caused by carotid artery occlusion, elicit similar patterns of c-Fos induction in brainstem areas. Adult cats were anesthetized with alpha-chloralose, and in each case, the experimental intervention caused an increase in the arterial blood pressure. There were two sets of control experiments: in both, animals underwent the same surgical procedures but then either remained at rest for the entire study, or the tibial nerve was stimulated, as in the contraction group, following muscle paralysis with tubocurarine. Following the procedures, animals rested for 90 min to allow neuronal expression of c-Fos. Control cats showed very little c-Fos immunoreactivity (c-Fos-ir) in the brainstem. Muscle contraction induced c-Fos-ir expression mainly in the nucleus tractus solitarius, lateral reticular nucleus, lateral tegmental field, vestibular nucleus, subretrofacial nucleus, spinal trigeminal tract and in a lateral region of the periaqueductal grey (P 0.5-1.0). The majority of the c-Fos-ir was found in brainstem areas contralateral to the contracted muscle. In addition, muscle contraction induced c-Fos-ir in the dorsal horns of spinal segments L6-S1 on the ipsilateral side of the spinal cord. Phenylephrine infusion caused c-Fos-ir expression in the nucleus tractus solitarius, spinal trigeminal tract, solitary tract, and dorsal motor nucleus of the vagus. No c-Fos-ir was apparent in the periaqueductal grey. Carotid occlusions induced c-Fos-ir expression in the area postrema, nucleus tractus solitarius, solitary tract, and spinal trigeminal tract. Expression was bilateral. Areas that exhibited c-Fos-ir correspond to sites previously reported to release various neuropeptides in response to muscle contraction or carotid occlusions. These results indicate that the exercise pressor reflex and baroreflex activate similar, but not completely identical, sites in the brainstem.     

RESTORATION OF INVOLUNTARY TONIC CONTRACTION OF THE LEVATOR MUSCLE IN PATIENTS WITH APONEUROTIC BLEPHAROPTOSIS OR HORNER SYNDROME BY APONEUROTIC ADVANCEMENT USING THE ORBITAL SEPTUM

Müller's muscle can be thought of as a large serial type of muscle spindle of the levator muscle. Effective stretching of the mechanoreceptor in the proximal part of Müller's muscle by voluntary phasic contraction of the levator muscle for initial opening of the eye induces involuntary tonic contraction of the levator muscle as a stretch reflex via the mesencephalic trigeminal nucleus, to maintain an adequate visual field. After disinsertion of the levator aponeurosis from the tarsus by habitual rubbing, elongation of Müller's muscle secondary to thinning (aponeurotic blepharoptosis) or paralysis (Horner syndrome) desensitises the mechanoreceptor of Müller's muscle, resulting in blepharoptosis. Shortening of the elongated and thinned Müller's muscle by instillation of phenylephrine, and surgical shortening, and fixation of the disinserted, elongated, and thinned aponeurosis using the orbital septum, restored involuntary tonic contraction of the levator muscle in nearly all of 2000 patients with aponeurotic blepharoptosis and in 11 patients with Horner syndrome.     

EGCG Blocked Phenylephrin-Induced Hypertrophy in H9C2 Cardiomyocytes,by Activating AMPK-Dependent Pathway

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism. Previous studies have shown that activation of AMPK results in suppression of cardiac myocyte hypertrophy via inhibition of the p70S6 kinase (p70S6K) and eukaryotic elongation factor-2 (eEF2) signaling pathways. Epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea, possesses multiple protective effects on the cardiovascular system including cardiac hypertrophy. However, the molecular mechanisms has not been well investigated. In this study, we found that EGCG could significantly reduce natriuretic peptides type A (Nppa), brain natriuretic polypeptide (BNP) mRNA expression and decrease cell surface area in H9C2 cardiomyocytes stimulated with phenylephrine (PE). Moreover, we showed that AMPK is activated in H9C2 cardiomyocytes by EGCG, and AMPK-dependent pathway participates in the inhibitory effects of EGCG on cardiac hypertrophy. Taken together, our findings provide the first evidence that the effect of EGCG against cardiac hypertrophy may be attributed to its activation on AMPK-dependent signaling pathway, suggesting the therapeutic potential of EGCG on the prevention of cardiac remodeling in patients with pressure overload hypertrophy.     

The effects of prophylactic bolus phenylephrine on hypotension during low-dose spinal anesthesia for cesarean section

BackgroundContinuously infused phenylephrine is frequently used to reduce the incidence of hypotension in women undergoing cesarean section under spinal anesthesia, but less is known about the prophylactic bolus method. We evaluated three prophylactic bolus doses of phenylephrine during low-dose spinal anesthesia for cesarean section.MethodsOne-hundred-and-eighty-four patients were randomized to receive 0.9% saline 2 mL (Control Group) or phenylephrine 1.0 μg/kg (PHE1 Group), 1.5 μg/kg (PHE1.5 Group), or 2.0 μg/kg (PHE2 Group) immediately after induction of combined spinal-epidural anesthesia. Maternal blood pressure and heart rate were recorded at 1-min intervals until delivery. Hypotension, defined as systolic blood pressure <80% of baseline, was treated with rescue doses of phenylephrine 100 μg at 1-min intervals until hypotension resolved. The incidence of nausea, vomiting, bradycardia, and hypertension, as well as Apgar scores and umbilical blood gases, were recorded.ResultsThe incidence of hypotension was 71.7% (33/46) in the Control Group, 68.9% (31/45) in the PHE1 Group, 37.0% (17/46) in the PHE1.5 Group and 45.7% (21/46) in the PHE2 Group (P=0.001). The total rescue dose of phenylephrine was greater in the Control Group than those in the PHE1.5 Group (P <0.05) and PHE2 Group (P <0.05). The incidence of hypertension increased as the dose of prophylactic phenylephrine increased (P <0.001) and was highest in the PHE2 group (37%). Other variables did not differ among the four groups.ConclusionsUnder the conditions of this study, prophylactic bolus injection of phenylephrine 1.5 μg/kg was a suitable alternative method for reducing the incidence of hypotension during low-dose spinal anesthesia for cesarean section.     

Randomized double-blind comparison of ephedrine and phenylephrine for management of post-spinal hypotension in potential fetal compromise

BackgroundMost studies comparing phenylephrine and ephedrine have been conducted during elective caesarean sections in healthy mothers with no fetal compromise. The effect of vasopressors on fetal outcome may differ between healthy and compromised fetuses. There has been little research into the effect of phenylephrine and ephedrine, when used for management of post-spinal hypotension in the presence of potential fetal compromise.MethodsHealthy women with a singleton pregnancy undergoing emergency caesarean section for fetal compromise under spinal anaesthesia were studied. One-hundred-and-six consecutive subjects, who developed hypotension after spinal anaesthesia, were randomly allocated to two groups of 53 each, to receive either phenylephrine (Group P) or ephedrine (Group E). For every systolic blood pressure reading <100 mmHg patients received phenylephrine 100 μg or ephedrine 8 mg depending on group allocation. Umbilical blood gas parameters and Apgar scores were recorded.ResultsThere was no statistically significant difference in umbilical arterial pH (P=0.79), umbilical venous pH (P=0.98), other blood gas parameters, incidence of fetal acidosis (P=1.00) and Apgar scores. The number of hypotensive episodes, vasopressor doses for treatment of the first hypotensive episode and the total number of doses used during the study period were comparable. The median [IQR] total number of doses of phenylephrine and ephedrine used before delivery were 2 [1–2] and 2 [1–2], respectively (P=0.67). More patients receiving ephedrine (24.5%) developed tachycardia than those receiving phenylephrine (3.8%) (P=0.004). Bradycardia was more common with phenylephrine, with 39.6% of patients in Group P as compared to only 1.9% of patients in Group E developing a heart rate <60 beats/min after vasopressor administration (P=0.001).ConclusionsBoth phenylephrine 100 μg and ephedrine 8 mg boluses are equally efficacious when treating post-spinal hypotension in the presence of potential fetal compromise. However, phenylephrine may be a better choice in the presence of maternal tachycardia.     

预注不同血管活性药对重度子痫前期患者腰硬联合麻醉剖宫产母儿的影响

目的观察预注不同血管活性药对重度子痫前期患者腰硬联合麻醉剖宫产母儿的影响。方法择期拟联合阻滞麻醉下剖宫产术的重度子痫前期产妇60例,随机均分为3组,E组泵入麻黄素(2 mg/min),P组泵入去氧肾上腺素(25μg/min),C组泵注同等容量的生理盐水。调整药物输注量维持血压接近术前基础值的80%。记录三组药物的使用容量、输注血管收缩药后1、3、5、7、10、12、15 min的MAP、HR,同时记录产妇恶心、呕吐的情况。在胎儿娩出即刻,进行产妇动脉血、新生儿脐动脉和脐静脉血气分析,对新生儿进行1 min和5 min Apgar评分。结果母体术中HR变化:用药后5 min,P组与E组比较差异有统计学意义;用药后3 min,P组与C组比较差异有统计学意义;用药后3、5 min,E组与C组比较差异有统计学意义。母体术中MAP变化:用药后3、5、7 min,P组与C组、E组与C组比较差异有统计学意义。C组产妇中恶心呕吐的发生率与P组、E组比较差异有统计学意义。C组麻黄碱追加次数与P组、E组比较差异有统计学意义。结论 CSEA麻醉前预先给予去氧肾上腺素、麻黄碱等血管活性药物并维持一定的血药浓度,对维持重度子痫患者的血流动力学稳定、改善患者及胎儿的预后有一定意义。     

Visualizing the endocytosis of phenylephrine in living cells by quantum dot-based tracking

To study the intracellular receptor-drug transportation, a fluorescent probe consisting of phenylephrine–polyethylene glycol-quantum dots conjugate was employed to track endocytosis process of phenylephrine in living cells. This type of movement was studied by continuously filming fluorescent images in the same cell. We also calculated the movement parameters, and divided the endocytosis process into 6 stages. Furthermore, the movement parameters of this probe in different organelles were determined by co-localization of the probe fluorescent images and different cellular organelles. After comparing the parameters in cellular organelles with these in 6 stages, the whole endocytosis pathway was demonstrated. These results verified that this probe successfully tracked the whole intracellular dynamic endocytosis process of phenylephrine. Our method realized the visual tracking the whole receptor-mediated endocytosis, which is a new approach on investigating the molecular mechanisms and kinetic properties of intracellular receptor-drug transportation.