Effects of diltiazem, dipyridamole, and their combination on hemostasis

Calcium channel blockers and antiplatelet agents, alone and in combination, have been reported to induce bleeding in patients undergoing surgery. Since diltiazem and dipyridamole influence platelet function in vitro and in vivo, their influence on hemostasis was examined in five normal men given diltiazem, 90 mg by mouth, followed by 60 mg every 6 hr for 48 hr, or dipyridamole, 75 mg by mouth every 8 hr for 48 hr. At 24 hr, the alternate drug was added to the regimen to assess effects of the combination on hemostasis. Platelet aggregation, serum thromboxane B2 and 6-keto-PGF1 alpha concentrations (stable metabolites of thromboxane A2 and prostacyclin), bleeding time, prothrombin time, partial thromboplastin time, and serum diltiazem concentrations were measured. Diltiazem and dipyridamole alone and in combination had no significant effect on bleeding time, prothrombin time, or partial thromboplastin time. Platelet aggregation induced by threshold concentrations of adenosine diphosphate, epinephrine, and calcium ionophore A 23187 were inhibited by diltiazem and dipyridamole alone and in combination. The only change in prostaglandin concentrations was a slight increase in serum 6-keto-PGF1 alpha after diltiazem. Despite influences on platelet function, neither diltiazem nor dipyridamole alone or in combination induced clinically relevant changes in hemostasis.

Pharmacologic differences between beta blockers

All of the beta blockers act by antagonizing the actions of the endogenous adrenergic agonists epinephrine and norepinephrine at the beta-adrenergic receptors. However, a number of pharmacologic differences exist between the various agents. Some drugs, such as atenolol and metoprolol, are relatively selective for the beta-1-adrenergic receptors, requiring higher concentrations to block beta-2-adrenergic receptors than are required to block beta-1 receptors. It should be noted, however, that these selective beta blockers all block beta-2 receptors when their concentrations are high enough. When patients with asthma must receive a beta blocker, low doses of a selective drug should be used. Recent studies, however, have suggested that the use of a nonselective beta blocker may be desirable to antagonize some beta-2-mediated metabolic effects, such as hypokalemia, induced by epinephrine. Pindolol is the only beta-receptor antagonist available in the United States with intrinsic sympathomimetic, or partial agonist, activity. Such drugs, because of their partial agonist activity, cause some sympathetic stimulation under conditions of low endogenous sympathetic tone, such as while subjects are at rest in the supine position. Under conditions of higher sympathetic tone, pindolol blocks the effects of the endogenous agonists, producing the characteristic effects of a beta blocker. Membrane-stabilizing activity was first recognized with propranolol, and the value of this property has been a source of controversy ever since, but recent studies suggest that propranolol may induce electrophysiologic effects by mechanisms other than beta blockade. Pharmacokinetic differences between the drugs are also of importance.(ABSTRACT TRUNCATED AT 250 WORDS)

[How do we explain the antihypertensive effect of bromocriptine? Clinical and experimental contribution]

The mechanism of the antihypertensive properties of bromocriptine was investigated in dog and man. In anaesthetized dogs, bromocriptine induced a decrease in the pressor responses to adrenaline or phenylephrine and reduced the hypotensive properties of clonidine. In 6 hypertensive patients with Parkinson's disease, chronic treatment with bromocriptine (46.4 +/- 12.0 mg/day) elicited both a significant decrease in blood pressure and an improvement of extrapyramidal symptoms. During bromocriptine therapy, domperidone (60 mg/day during 1 month), a specific peripheral dopaminergic antagonist was introduced. The drug did not change the levels of blood pressure (before domperidone: 150.8 +/- 22.5/79.9 +/- 8.9 mmHg after domperidone: 150 +/- 17.3/87.5 +/- 12.9 mmHg). These results confirm the antihypertensive properties of bromocriptine and demonstrate that, beside their dopaminergic properties, the drug also possesses mixed alpha 1 and alpha 2 adrenolytic actions. These two properties may contribute to the mechanism of the antihypertensive effects of bromocriptine. These data also show that domperidone can be used in bromocriptine-treated hypertensive parkinsonians without side effects on blood pressure.

[Effect of adrenaline on incorporation of 125I-LDL into the aorta]

Adrenaline in concentrations of 10(-7)-10(-4) M increased the incorporation of 125I-low density lipoproteins (LDLP) into the perfused rabbit aorta, stimulating predominantly the non-specific uptake of 125I-LDLP. It was parallelled by the swelling of the endothelial lining of the aorta, expansion of the intercellular borders and an increase in the argyrophilic cell properties. The adrenoreceptor blockers phentolamine and propranolol prevented the morphological changes in the endothelium and in the incorporation of 152I-LDLP into the vascular wall. The authors feel that the catecholamine-induced damage to the endothelial lining of the aorta presents one of the mechanisms of atherogenesis stimulation following psychoemotional stress.

Repression by dexamethasone of epinephrine-induced modulation of the fatty acyl-CoA desaturase system in Tetrahymena microsomes

Epinephrine modulation of the fatty acyl-CoA desaturase activities in Tetrahymena microsomes, namely the stimulation of delta 9 desaturase activity with a decreased activity of delta 12 desaturase, was markedly inhibited by dexamethasone administered 30 min prior to epinephrine addition. This effect by dexamethasone was dose-dependent. With epinephrine or dexamethasone prior to epinephrine administration, the activities of delta 9-terminal and delta 12-terminal components were found to change in parallel with those of delta 9 and delta 12 desaturase activities respectively. Furthermore, addition of dexamethasone as early as 30 min before epinephrine repressed the epinephrine-mediated stimulation of cyclic AMP production and of adenylate cyclase activity. Therefore, it is suggested that dexamethasone may inhibit the modulation by epinephrine of the terminal component activity, which plays a crucial role in microsomal fatty acyl-CoA desaturase system, through the reduction of cyclic AMP accumulation by decreased responsiveness to epinephrine of Tetrahymena cells.

[Role of adrenergic receptors in the mechanism of action of catecholamines and DOPA on proliferative processes]

Catecholamines (adrenaline, isoproterenol) and L-DOPA decreased the mitotic index of L-cells in culture. The action of catecholamines was blocked by the beta-adrenergic antagonist propranolol, but was not abolished by the alpha-adrenoblocker phenoxybezamine. The L-DOPA-induced decrease in the mitotic index did not depend on the pretreatment with the adrenoblockers. Catecholamines inhibited the incorporation of 3H-thymidine and 3H-leucine into DNA and total protein of the cells, respectively. Preincubation of the culture with propranolol for 10-20 minutes before catecholamine administration prevented the action of catecholamines. Phenoxybenzamine, an alpha-adrenoreceptor blocker, did not produce such an effect. The data obtained point to the leading role of beta-adrenoreceptors in the mechanism of the effects of catecholamines on proliferative processes. The action of L-DOPA on cell proliferation does not seem to be linked with adrenoreceptor activation.

[Antilipolytic activity in vitro of various analogs of nicotinic acid. Structure-activity relationship]

The antilipolytic activity of a series of N aryl-nicotinamides and of alpha picolinic acid, has been tested in vitro. Lipolysis was stimulated by epinephrine (20 micrograms/ml of incubation medium) using rat's epididymal adipose tissue slices. Only N(2-carboxy methyl phenyl) nicotinamide showed antilipolytic effect comparable to that of nicotinic acid at similar concentrations (2 X 10(-5) M). Picolinic acid (10(-4) M) showed no antilipolytic effect. These results, together with those of the literature, are discussed in regard to the relations between structure and antilipolytic activity.

Reversal of adrenaline-induced contraction in the rabbit pulmonary artery by clonidine

Characterization of clonidine which reversed the adrenaline-induced contractions was assessed using the rabbit pulmonary arterial segment. Clonidine in high concentrations (10(-5)-10(-4) mol/l) contracted this vascular tissue. Nevertheless, an adrenaline (3 X 10(-6)mol/l)-induced contraction, which can be markedly depressed by phentolamine, was reversed to relaxation by pre-addition of 3 X 10(-5)mol/l clonidine. This reversal was abolished by 10(-5) mol/l propranolol, a beta-adrenoceptor antagonist. The cumulative concentration-contraction curve for adrenaline was shifted to the right by 10(-5) mol/l clonidine without further alteration at 10(-4) mol/l, suggesting a partial agonistic feature of clonidine for alpha-adrenoceptors. Contractions evoked by 5 X 10(-5) mol/l clonidine alone were effectively reduced by prazosin (IC50 = 1.7 X 10(-7) mol/l) or yohimbine, (IC50 = 3.3 X 10(-5) mol/l) and those by phenylephrine (10(-5) mol/l) were suppressed as well (prazosin, IC50 = 3.4 X 10(-8) mol/l; yohimbine, IC50 = 5.0 X 10(-6) mol/l). However, the depolarization-induced contractions with 30 mmol/l KCl were virtually unaltered by both antagonists. These results suggest that the reversal action of clonidine on the adrenaline-induced contraction is primarily mediated by a partial agonistic property for postsynaptic alpha 1-adrenoceptors.

RX781094 a potent and selective alpha 2-adrenergic antagonist. Effects in adipocytes and hepatocytes

The potency and selectivity of RX781094, 2-(2-(1,4-benzodioxanyl]-2-imidazoline HCl, as alpha 1- and alpha 2-adrenergic antagonist was studied using rat hepatocytes and hamster adipocytes. The alpha 1-adrenergic stimulation of ureogenesis produced by epinephrine in rat hepatocytes was slightly diminished by 10(-4) M RX781094. On the contrary the alpha 2-adrenergic effect of epinephrine in hamster adipocytes (inhibition of adenylate cyclase) was antagonized dose-dependently by RX781094. This agent was approximately 10-fold more potent than yohimbine. Radioligand binding studies also showed that RX781094 was more potent and selective than yohimbine at alpha 2-adrenergic sites. It is concluded that RX781094 is a potent and selective alpha 2-adrenergic antagonist.

Blockade of the release of LH induced by pharmacological suppression of adrenergic inflow into the locus coeruleus

Previous studies have indicated that stimulation of the locus coeruleus (LC) produced inhibition of the release of LH induced by stimulation of the medial preoptic area (mPOA) in ovariectomized, estrogen-primed rats. A similar response following the application of drugs into the LC was taken as an index of activation of the LC neurons. The injection of the phenylethanolamine N-methyltransferase (PNMT) blocking-agent, 2,3- dichloromethylbenzylamine ( DCMB , 0.5 micrograms) into the LC, 2 and 1 h before starting the mPOA stimulation greatly attenuated the induced release of LH. Injection of saline had no effect. The reduced release of LH in DCMB -treated rats was restored to normal by injecting clonidine (0.5 micrograms) into the LC immediately before the mPOA stimulus started, but not by injecting phenylephrine (0.5 micrograms) or saline (0.5 microliter). The release of LH induced by mPOA stimulation was also blocked in rats in which the alpha 2-antagonist, piperoxane (0.5 micrograms) was injected into the LC but not in those injected with the alpha 1-antagonist, phenoxybenzamine (0.5 micrograms) or the beta-antagonist, propranolol (0.5 micrograms). It is concluded that adrenergic afferents into the LC tonically inhibited the activity of LC neurons and that this effect is mediated by alpha 2-adrenoceptors. Interference with the synthesis of epinephrine or blockade of alpha 2-adrenoceptors resulted in activation of LC neurons and thereby in inhibition of LH release.

Inhibition of epinephrine-exacerbated coronary thrombus formation by prostacyclin in the dog

We studied the effect of intravenous prostacyclin (PGI2) infusion on epinephrine exacerbation of platelet-mediated acute coronary thrombus formation in an in vivo canine model of coronary artery stenosis. Platelet thrombi form in mechanically stenosed dog circumflex coronary arteries, producing cyclical reductions in coronary blood flow (CRF) as measured with an electromagnetic flowmeter probe. In the present study nine of 10 dogs exhibited spontaneously occurring CRF. With epinephrine (E) infusions of 10 micrograms/min CRF frequency increased 64% (p less than 0.025), CRF magnitude increased 27.1% (p less than 0.05), and the rate of flow decline increased 112.8%, indicating that the rate of thrombus formation increased with E infusion (p less than 0.005). When an identical E infusion was accompanied by simultaneous PGI2 infusion (150 ng/kg/min), CRF were abolished in nine of 10 dogs and markedly inhibited in the other. After the 10 min of simultaneous E and PGI2 infusion, E infusion alone was continued. There was a recurrence of CRF within 2.49 +/- 0.89 min after cessation of PGI2 infusion. However, CRF frequency in the subsequent 10 min was less than the frequency of CRF during the initial E infusion (p less than 0.10) and not significantly different from that of the control period (no E infusion). The rate of flow decline and magnitude during the final E infusion after cessation of PGI2 infusion were not significantly different from those of the initial E infusion. Prostacyclin infusion in the coronary care unit may be potentially beneficial in cases of acute myocardial ischemia where elevated catecholamines are a thrombogenic stimulus.

Corticosterone decreases the efficacy of adrenaline to affect passive avoidance retention of adrenalectomized rats

Short-term (48h) adrenalectomy (ADX) resulted in a deficit in the retention of a passive avoidance response. An inverted U-shaped dose-response relationship was found following immediate post-learning administration of adrenaline (A). A in a dose range of 0.005 - 5 micrograms/kg s.c. facilitated later retention. While corticosterone (CS) replacement alone had no effect, pretreatment with CS (300 micrograms/kg) was followed by a shift in the dose-response curve of A in ADX rats. Ten thousand times higher doses of A were required to improve retention behavior. Administration of the potent synthetic glucocorticoid dexamethasone failed to affect the responsiveness to A. It is concluded that corticosterone decreases the efficacy by which adrenaline affects later retention behavior of ADX rats. The specificity of corticosterone in this interaction suggests the involvement of the corticosterone receptor system which has its predominant localization in hippocampal neurons.

[Gentamycin inhibition of adrenaline auto-oxidation]

The effect of gentamicin sulfate on the rate of free radical oxidation of adrenalin was studied. Inhibition of the oxidation process at the final concentrations of gentamicin of 0.1-0.2 mg/ml was observed. The mechanism of gentamicin antiradical activity and its role in the cells are discussed.

[Effect of adrenaline on calcium transport and oxidative phosphorylation in mitochondria]

Intraperitoneal adrenaline injection induces in 15 and 30 min an increase in the phosphorylation rate, calcium capacity and Ca2+ retention time in the rat liver mitochondria. A rise of the phosphorylation rate is inhibited by inderal, a beta-adreno-blocker. Energy metabolism grows considerably with succinate exchange intensification.

Effect of ethanol on vascular prostacyclin (prostaglandin I2) synthesis, platelet aggregation, and platelet thromboxane release

A series of experiments with platelets from healthy volunteers showed a concentration related inhibitory effect of ethanol on platelet aggregation and release of thromboxane A2. This effect was observed at blood alcohol concentrations ranging between 66 and 132 mg/dl (14.3 and 28.6 mmol/l), which are commonly found in alcoholics. Investigations carried out by incubating ethanol with platelet rich plasma in vitro also showed an inverse linear correlation between ethanol concentration and platelet thromboxane synthesis. In contrast, the incubation of a wide range of concentrations of ethanol with human endothelial cells and rat aortic rings did not alter the ability of these systems to synthesise prostacyclin (prostaglandin I2). This finding of a selective inhibition of thromboxane A2 synthesis and platelet aggregation without an alteration of prostaglandin I2 synthesis may provide an explanation for the reported ethanol mediated protection against vascular disease. This effect of ethanol may also be relevant to the induction of acute gastrointestinal haemorrhage that occurs after bouts of excessive alcohol consumption.

Effects of manipulating catecholamines on the incidence of the preovulatory surge of of luteinizing hormone and ovulation in the rat: evidence for a necessary involvement of hypothalamic adrenaline in the normal or 'midnight' surge

The preovulatory surge of luteinizing hormone reaches a maximum at 18.00 h on the day of pro-oestrus in female rats maintained with regular lighting from 06.00 to 20.00 h. This surge is initiated by a discharge of luteinizing hormone-releasing hormone into hypophysial portal blood. In this study, drugs which affect catecholamine-mediated neurotransmission were administered on the day of pro-oestrus and the effects on serum concentrations of luteinizing hormone and on subsequent ovulation were observed. alpha-Methyl-p-tyrosine, diethyldithiocarbamate and SKF 64139 inhibit catecholamine synthesis at the level of tyrosine hydroxylase, dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase, respectively. Although alpha-methyl-p-tyrosine suppressed ovulation, it had a negligible effect on the incidence of the preovulatory surge. In contrast, the various treatments with diethyldithiocarbamate and SKF 64139 resulted in a minimal occurrence of the 18.00 h surge; at relatively low doses, however, these drugs frequently elicited a surge at 22.00 or 24.00 h which invariably resulted in ovulation. The failure of the surge after diethyldithiocarbamate or SKF 64139 was not associated with a loss of pituitary sensitivity to luteinizing hormone-releasing hormone. In terms of the hypothalamic concentration of dopamine, noradrenaline, adrenaline and 5-hydroxytryptamine at 18.00 h on pro-oestrus, the only common effect of diethyldithiocarbamate and SKF 64139, given in a dose which blocks the surge, was a severe depletion of adrenaline; alpha-methyl-p-tyrosine failed to produce this effect despite inducing a marked depression of dopamine and a moderate loss of noradrenaline. Neither the increase in hypothalamic dopamine after diethyldithiocarbamate, nor the alpha 2 receptor blocking properties of SKF 64139 appear to be relevant in this context since injections of L-dopa or piperoxane, an alpha 2 receptor antagonist, were without effect on the surge or ovulation. The failure of the surge after prazosin, an alpha 1 receptor antagonist, indicates that the function of adrenaline may be mediated postsynaptically by alpha 1 receptors. Clonidine, an alpha 2 receptor agonist which reduces the turnover rate of hypothalamic adrenaline, had effects of the surge and ovulation which were comparable to those of diethyldithiocarbamate and SKF 64139, the relatively low doses causing some of the surges to occur at 24.00 instead of 18.00 h and higher doses suppressing the surge at both times and thus preventing ovulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Derivatives of 1,3,3-trimethyl-6-azabicyclo[3.2.1]octane with hypotensive activity. I

The synthesis of three series of glycinamides (IV), amides (V) and diamines (VI) starting from 1,3,3-trimethyl-6-azabicyclo[3.2.1]octane is described. Some of compounds (IV), (V) and (VI) showed a moderate hypotensive activity in rats. Effects on heart rate in rats, infiltration anesthesia and antiarrhythmic activity in mice, as well as antiacetylcholine activity in vitro, are also reported.

Effective plasma concentrations of antiarrhythmic drugs against sustained halothane-adrenaline arrhythmia in dogs

We determined the minimum effective plasma concentrations of several antiarrhythmic agents against canine halothane-adrenaline arrhythmia. Sustained ventricular tachycardia was produced by continuous adrenaline infusion at rates of 1.5 to 4 micrograms/kg/min under 1.5% halothane anesthesia. Procainamide, 20 mg/kg, produced ventricular fibrillation in three of nine dogs. Disopyramide, 3 mg/kg, suppressed the arrhythmia in nine of 11 dogs at a minimum effective plasma concentration of 4.2 micrograms/ml, but produced ventricular fibrillation in the remaining two dogs. Phenytoin, 5 mg/kg, was effective at a minimum concentration of 12 micrograms/ml. Lidocaine, 10 mg/kg, suppressed the arrhythmia at a minimum concentration of 15 micrograms/ml, which is much higher than the human toxic plasma level. These drugs may have suppressed the adrenaline arrhythmia by inhibiting the sodium channel, because their effective concentrations were very close to membrane-stabilizing concentrations in vitro. Small doses of 30 micrograms/kg propranolol and 0.1 mg/kg N-696, two beta-blockers, and 0.1 mg/kg verapamil, a calcium channel blocker, yielding a concentration of 0.03 micrograms/ml, suppressed the arrhythmia, probably by indirectly or directly blocking the calcium channel.

Evidence for inhibition of sympathetic preganglionic neurons by bulbospinal epinephrine pathways

Two selective inhibitors of central epinephrine synthesis, LY 134046 and SKF 64139 (20 mg/kg, i.v.), gradually but markedly enhanced descending intraspinal transmission to sympathetic preganglionic neurons in spinal cats. Enhancement increased linearly to maximum values of 200% and 250%, respectively, at 4.5-5.5 h. Spinal sympathetic reflexes were not enhanced by either drug. The results support the proposal that bulbospinal epinephrine pathways depress the excitability of sympathetic preganglionic neurons by activating postsynaptic alpha 2-adrenergic receptors.

Prostaglandin F2 alpha inhibition of epinephrine stimulated cyclic AMP and progesterone production by rat corpora lutea of various ages

Epinephrine can mimic the stimulatory effects of LH in vitro on cyclic AMP (cAMP) and progesterone production by isolated rat corpora lutea. The aim of the present study was to test whether the effects of epinephrine in vitro on the rat corpus luteum, as with LH, can be inhibited by prostaglandin F2 alpha (PGF2 alpha). The stimulatory effect of epinephrine on tissue levels of cAMP in 1-day-old corpora lutea was not inhibited by PGF2 alpha. A dose-dependent inhibition by PGF2 alpha (0.5-50 microM) was seen for 3-day-old corpora lutea and this inhibition could not be overcome by higher concentrations of epinephrine (0.165-165 microM). The stimulation by epinephrine on progesterone production was inhibited by PGF2 alpha (5 microM) in 3- and 5-day-old, but not in 1-day-old corpora lutea. Thus, PGF2 alpha can inhibit the stimulatory effect of epinephrine in 3- and 5-day-old corpora lutea, but not in the newly formed corpora lutea (1-day-old) and PGF2 alpha shows in this respect the same age dependent inhibitory pattern as in relation to LH stimulation.

Hemorheological effects of pentoxifylline on disturbed flow behavior of blood in patients with cerebrovascular insufficiency

The influence of pentoxifylline (11-18 mg/kg orally, Trental 400) on impaired hemorheologic conditions has been investigated in a total of 73 patients with CVI. Throughout a treatment period of 4 weeks, there was a significant improvement in red cell behavior and a significant inhibition of increased platelet aggregation; moreover, a fall in plasma fibrinogen and of blood viscosity has also been observed.

Inhibitory effect of imipramine on epinephrine-dependent platelet aggregation: "in vitro" studies on platelets from healthy and depressed people

Inhibitory effect of imipramine on platelet aggregation in healthy and depressed people was studied. A different sensitivity was observed between healthy and depressed people. Two groups (D I and D II) were identified among depressed patients on the basis of sensitivity to imipramine effect. ID50 was calculated for healthy subjects (59.5 +/- 22 microM) and depressed patients (D I: 20 +/- 7 microM - D II: 117 +/- 49).

Epinephrine synthesis inhibitors block naloxone-induced LH release

Administration of the opiate receptor antagonist, naloxone, evoked rapid rises in plasma LH levels in estrogen, progesterone-primed ovariectomized rats. Pretreatment with a peripherally acting epinephrine (EPI) synthesis inhibitor, SK&F 29661, failed to influence the naloxone-induced LH release. However, two centrally acting EPI synthesis inhibitors, SK&F 64139 and LY 78335, which selectively suppressed hypothalamic EPI levels, blocked stimulation of LH release by naloxone. These results implicate brain EPI neurons in mediation of endogenous opioid peptide influence on LH release.

Effects of epinephrine on the electrophysiologic properties of Purkinje fibers surviving myocardial infarction

The electrophysiologic effects of epinephrine on canine subendocardial Purkinje fibers were examined 24 hours after two-stage ligation of the left anterior descending coronary artery. Transmembrane action potential were monitored simultaneously in noninfarcted (NZ) and infarcted (IZ) zones during epinephrine superfusion at 37 degrees C. Epinephrine (10(-8) M to 10(-5) M) induced dose-dependent increases in maximum rate of phase O depolarization (Vmax), action potential amplitude (APA), and maximum diastolic potential (MDP) in both NZ and IZ. Epinephrine consistently shortened effective refractory period (ERP) in both regions No significant change in action potential duration (APD) was noted at either 50% or 90% repolarization. Impulse conduction through the NZ and into the IZ was significantly improved, as indicated by an increased maximum follow-rate in each region at 10(-6) and 10(-5) M epinephrine. The IZ fibers showed a marked hypersensitivity to this agent, in that responses were particularly pronounced in the IZ vs the NZ in terms of both absolute and percentage changes. The effects of epinephrine on Vmax, MDP, APA, and ERP were generally reversed by propranolol, while remaining relatively unaffected by phentolamine, suggesting a beta-adrenergic mechanism. Increased stimulation of ventricular beta-adrenoceptors in the period 16 to 72 hours after myocardial infarction may influence ventricular vulnerability to "late-phase" arrhythmias through nonuniform effects in Purkinje fibers.

Lack of correlation of verapamil plasma level with cumulative protective effects against halothane--epinephrine ventricular arrhythmias

The effect of verapamil, 0.2 mg/kg i.v. over 30 s, on the amount of epinephrine required to elicit a reproducible ventricular arrhythmia during 0.9% halothane in oxygen anesthesia was investigated in two groups of dogs after three consecutive doses of verapamil given at 90 (group I) and 120 min (group II) intervals, respectively. Verapamil caused a stepwise cumulative increase in the arrhythmogenic dose of epinephrine in both groups despite plasma verapamil levels that declined to low levels (28 and 22 ng/ml, respectively) between doses. Control epinephrine arrhythmogenic doses were 2.89 +/- 0.54 and 2.74 +/- 0.19 microgram/kg/min (mean +/- SEM), respectively, for groups I and II, and rose to 4.58 +/- 0.72 and 4.55 +/- 0.30 microgram/kg/min after the first verapamil dose, to 6.20 +/- 0.74 and 6.13 +/- 0.40 microgram/kg/min after the second verapamil dose, and 8.16 +/- 0.85 and 8.09 +/- 0.95 microgram/kg/min after the third verapamil dose, respectively. All postverapamil epinephrine arrhythmogenic dose values were significantly elevated above control and above the preceding values, although there was no significant difference between the two groups. Changes in heart rate or blood pressure were similar among the three doses of verapamil in each group. These results can be interpreted to indicate that, unlike hemodynamic effects that appear to parallel plasma verapamil concentrations, the protective effects of verapamil against halothane--epinephrine ventricular arrhythmias may not be accurately reflected by plasma verapamil levels and may be significantly present when plasma levels are too low to cause measurable hemodynamic effects.

Inhibition of adrenaline-induced platelet aggregation by the alpha-adrenoceptor blocking drug benextramine

1 The activity of the irreversible alpha-adrenoceptor blocking drug, benextramine, was determined in human platelets. 2 Compared to its postsynaptic and presynaptic alpha-adrenoceptor blocking potency, benextramine had a very low potency as an antagonist of adrenaline-induced platelet aggregation. 3 The results confirm the previous observation with the irreversible alpha-adrenoceptor blocking drug, phenoxybenzamine, that platelet alpha-adrenoceptors differ from postsynaptic and presynaptic alpha-adrenoceptors.

Antiarrhythmic and hemodynamic responses to adenosine triphosphate during infusion of epinephrine in dogs anesthetized with halothane

The effects of adenosine triphosphate (ATP) on cardiovascular responses to epinephrine were evaluated in dogs anesthetized with halothane. The dose of epinephrine required to induce arrhythmias averaged 1.05 +/- 0.52 microgram/kg/min. The dose of ATP required to abolish these arrhythmias averaged 1.64 +/- 0.67 mg/kg/min. ATP had not only an antiarrhythmic effect but also antagonized epinephrine-induced increases in heart rate, systemic vascular resistance, mean arterial blood pressure, and further increased cardiac index. ATP had, however, no significant effect on epinephrine-induced increases in myocardial contractility.

The effect of carazolol on the cardiovascular responses to adrenaline in stress sensitive pigs

The effect of propranolol, carazolol and acebutolol on the heart rate and blood pressure responses to intravenous adrenaline were examined in conscious Pietrain pigs. All three drugs blocked the tachycardia and vasodilatory responses to adrenaline and induced an increase in vasopressor responsiveness. The likely complications from using non-cardioselective beta blockers for preventing stress-induced deaths in pigs are discussed.

Dose response of oral timolol combined with adrenaline

Oral timolol, a beta-adrenergic receptor blocker, was given in 5 different doses from 5 mg to 30 mg a day to 12 healthy volunteers in a double-blind cross-over trial. Adrenaline was instilled into one eye in each subject. Recording of intraocular pressure during the trial suggested the presence of a dose-response relationship between the dose of timolol and the decrease of intraocular pressure. An analysis of the interaction of timolol and adrenaline showed that the adrenaline effect diminished linearly with increasing timolol dose, which finally made the combination less effective than timolol alone.

The effect of echothiophate on the biphasic response of rabbit ocular pressure to dipivefrin

A time-course study was performed on the intraocular pressure response of pigmented rabbit eyes. Dipivefrin administration produced in initial hypertensive phase lasting less than two hours followed by a prolonged hypotensive phase. Echothiophate iodide therapy produced a more pronounced and prolonged hypertensive response; there was no hypotensive phase. Administration of echothiophate plus dipivefrin resulted in a hypertensive phase similar to that from echothiophate alone; as previously reported, this combination was not followed by a hypotensive phase. The alpha-blocker phentolamine mesylate prevented the echothiophate-induced hypertension. When dipivefrin was administered with echothiophate plus phentolamine, there was an immediate hypotensive effect. It was concluded that the hypertensive effect of echothiophate in pigmented rabbit eyes may mask the hypotensive action of dipivefrin. This, rather than an echothiophate-induced inhibition of esterases, may explain why combination therapy with these drugs seemed ineffective.

Ocular hypertensive response to beta-adrenoceptor agonists

Acute administration of non-selective and relatively selective beta-adrenoceptor agonists elicit a monophasic fall in IOP. The present study indicates that unilateral application of certain beta-agonists on consecutive days can result in marked ocular hypertension. 1-Epinephrine, reproterol and 1-isoproterenol evoked an elevation of IOP on the second and third day after topical administration of a 2% solution in normal rabbits and in rabbits with surgically transected extraocular muscles. In contrast, the same concentration of d-isoproterenol produced hypotensive responses only when administered once daily for three consecutive days. Since d-isoproterenol did not cause a rise in IOP during chronic administration, the mechanism involved in the hypertensive response appears to be more sensitive to the levorotatory form. Administration of timolol inhibited the ocular hypertensive effect of epinephrine and reproterol. Since timolol lowers IOP by depressing formation of aqueous, it is suggested that the rise in IOP following chronic administration of beta-agonists possibly involves an increase in aqueous humor production.

Synthesis and antihypertensive activity of a series of 8-substituted 1-oxa-3,8-diazaspiro[4.5]decan-2-ones

Forty-three new 1-oxa-3,8-diazaspiro[4,5]decan-2-ones optionally substituted with 2-(3-indolyl)ethyl, 3-(2-methoxyphenoxy)-2-hydroxypropyl, or 2-(1,4-benzodioxan 2-yl)-2-hydroxyethyl at the 8 position were prepared for screening as antihypertensive agents in the spontaneous hypertensive rat. For the 8-[2-(3-indolyl)ethyl] compounds the most active were those substituted in the 4 position, where activity was at maximum with the 4-ethyl compound (1). The 8-[3-(2-methoxyphenoxy)-2-hydroxypropyl] compounds were less active than their 1,4-benzodioxane counterparts, which were tested as mixtures of erythro and threo diastereoisomers. Both the 4-ethyl-8-[2-(1,4-benzodioxan-2-yl)-2-hydroxyethyl]-substituted 38 and (S)-3-methyl-8-[3-(2-methoxyphenoxy)-2-hydroxypropyl]-substituted 42 were designed as mixed alpha- and beta-adrenergic receptor blockers. Bother compounds lowered blood pressure, but they gave no evidence of working as beta-adrenergic blockers. Examination of 8-[2-(3-indolyl)ethyl]-1-oxa-3,8-diazaspiro[4.5]-decan-2-one (8) and 3 methyl-8-[2-(1,4-benzodioxan-2-yl)-2-hydroxyethyl]-1-oxa-3,8-diazaspiro[4,5]decan-2-one (29) in the dog showed them to be alpha-adrenergic blockers. Compound 29 was primarily an alpha 2-adrenoceptor antagonist, while 8 was more skewed toward alpha 1-adrenoceptor antagonism. Tilt-response studies for evaluating the potential for producing orthostatic hypotension showed that both 8 and 29 had little potential for avoiding orthostatic hypotension at therapeutically effective doses.

Effect of adrenaline synthesis inhibition on brain noradrenaline neurons in locus coeruleus

The functional significance of the morphologically identified adrenaline (A)-mediated input to the noradrenergic nucleus locus coeruleus (LC) was pharmacologically analyzed. By means of single unit recording techniques the LC neurons in the rat brain were studied following administration of SK&F 64139 and DCMB, drugs which are both potent inhibitors of the A-forming enzyme phenylethanolamine-N-methyltransferase (PNMT). SK&F 64139 (1-200 mg/kg i.v.) caused an immediate, dose-dependent and long-lasting increase in firing rate of the LC neurons. The dose-response curve for the LC inhibitory effect of the alpha 2-receptor agonist clonidine was shifted in parallel to the right by pretreatment with SK&F 64139. All the above mentioned effects of SK&F 64139 were mimicked by SK&F 72223, a structurally analogous compound which is reported to lack PNMT inhibitory activity. Consequently, the activation of LC neurons by SK&F 64139 is probably not related to its capacity to inhibit the synthesis of A but rather to some other action of the drug, such as an alpha 2-receptor blocking effect. In contrast to SK&F 64139, the other PNMT inhibitor tested, DCMB (1-60 mg/kg), produced no significant activation of the LC neurons and but little clonidine antagonistic action. Thus, judging from these experiments, DCMB is devoid of significant alpha 2-receptor blocking properties. At the time for maximal brain A depletion after DCMB administration (4-6 h) the average firing rate of randomly encountered LC neurons was unaltered when compared with controls. In contrast, pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine methylester, which causes depletion also of brain noradrenaline, significantly increased LC neuronal firing rates. These data indicate that if there exists a physiologically relevant A-mediated input to the LC, this is not of critical importance for the tonic activity of the LC neurons.

[Effect of adrenaline and thymic factor on blood coagulation and fibrinolysis in healthy and thymectomized rats]

It was discovered that adult rats develop hypercoagulation and inhibited fibrinolysis 2--4 months after thymectomy. Intramuscular injections of thymus low-molecular factor to thymectomized rats for a week made the coagulative and fibrinolytic activity of blood return to normal. After adrenaline injection, the sham-operated rats developed hypercoagulation and stimulated fibrinolysis. In thymectomized rats, fibrinolysis was stimulated far less after adrenaline injection and did not reach the levels characteristic of the sham-operated rats. The thymectomized rats given thymus factor manifested an appreciable recovery of an adequate response on the part of blood coagulation and fibrinolysis to adrenaline injection.

[Effect of insulin on cardiac contractility (author's transl)]

The effects of insulin on contractile activity of isolated heart muscle have been studied in the rat's right ventricle. The method of the isolated organ bath was used with Tyrode as perfusion liquid with constant carbogen bubbling. The addition of insulin to the bath (0.3 U/ml) increased the contractile power. Contractility increase, induced by adrenaline and CaCl2, was reduced by insulin. This decrease of adrenaline activity became clearer after partial blocking of beta-receptors with pindolol. Glucose determinations in the bath also showed an insulin-adrenaline antagonism. Insulin behaved as a partial agonist versus adrenaline at the beta-receptors site.

[Effect of lithium preparations on the toxic effects of adrenaline]

Experiments on rats have shown that intravenous injection of adrenaline in a dose of 0.3-0.4 mg/kg causes cardiac arrhythmia. In this case the primary arrhythmia developing immediately after adrenaline injection is followed by the recovery of sinusal rhythm which was replaced by the secondary arrhythmia. Apart from arrhythmias, there developed pulmonary edema. The animals died 2--3 minutes after adrenaline injections. Lithium chloride and lithium hydroxybutyrate removed the secondary arrhythmia and pulmonary edema. Lithium hydroxybutyrate has proved to be more effective.