Antihypertensive effects, plasma levels and beta-adrenergi blocking activity of racemic and dextrorotatory propranolol in man

In hypertensive patients, whose blood pressure was decreased by racemic propranolol, the dextrorotatory isomer had no antihypertensive effect. The differences in antihypertensive activity of racemic and dextrorotatory propranolol cannot be explained by different plasma levels. The data indicate that the hypotensive effect of propranolol is due to beta-receptor blockade.

Clinical experiences with prenalterol as an antidote to Beta-adrenoceptor blockade

The cases presented in this paper suggest that prenalterol is useful in the treatment of myocardial depression due to beta-blockade. According to its pharmacological properties, prenalterol might even be the drug of choice in these situations. It is wellknown that massive beta-blocker overdosage may be difficult to manage and as the therapeutic guidelines in these cases have not yet been definitely stated, it is obvious that prenalterol in this context will be of utmost importance. What remains to be solved is the dosage level. So far, experience has shown that high doses, widely exceeding the recommended initial dose of 50-100 micrograms/kg, are necessary to restore normal circulation in massive beta-blocker overdosage.

Increased tracheal responsiveness to beta-adrenergic agonist and antagonist in ovalbumin-sensitized guinea pigs

Despite the controversy of bronchial responsiveness to beta2-agonist drugs in asthma, in a previous study we have shown increased responsiveness of asthmatic tracheobronchial tree to isoprenaline. Therefore, in the present study, tracheal responsiveness to isoprenaline and also beta-adrenergic receptor blockade were studied in sensitized guinea pigs. An experimental model of asthma was induced in guinea pigs by sensitization of animals with injection and inhalation of ovalbumin (OA). The responses of tracheal chains of sensitized and control animals to cumulative concentrations of isoprenaline (I) in the absence and presence of 10 nmol/l propranolol were measured, and the effective concentration of I causing 50% of maximum response (EC50 I) was obtained. The propranolol blockade (CR - 1) was calculated by: (post-propranolol EC50 I/EC50 I) - 1. Tracheal responses of sensitized and control animals to cumulative concentrations of methacholine (M) were also measured and EC50 M were obtained. The tracheal responses of sensitized guinea pig to isoprenaline was significantly higher than that of the control animals (EC50 I for sensitized and control animals were 0.24 +/- 0.04 and 0.58 +/- 0.07 micromol/l, respectively; p < 0.001). The beta-adrenergic receptor blockade by propranolol (CR - 1) was also significantly higher in sensitized guinea pigs than that of the control animals (p < 0.001). The results of this study indicate an increased tracheal response to beta-adrenergic-stimulating drug and enhancement of beta-adrenergic blockade by propranolol in the sensitized guinea pig.

Inhibition of (–)-Propranolol Hydrochloride by Its Enantiomer in White Mice – a Placebo-Controlled Randomized Study

BACKGROUND

A previous pilot study was performed to see if toxicity of (S)-(-)-propranolol hydrochloride may be inhibited by a potentized preparation of its enantiomer. The present study is based on the hypothesis that the toxic effects of an optical isomer, may be counteracted or reversed by the administration of a potentized preparation of one of its stereoisomers, and in particular the enantiomer.

METHODS

508 ICR conventional mice were used. 254 mice were administered (R)-(+)-propranolol HCl homeopathic potency prior to and during the experiment, and the other 254 were administered indistinguishable placebo. On the day of the experiment mice were anesthetized with intraperitoneal Rometar. Once sedated the mice were administered the LD50 dose of (-)-propranolol HCl intraperitoneally.

RESULTS

The end point for statistical analysis was the difference in survival between the placebo and treatment mice. The odds ratio for survival of treatment mice relative to placebo mice was 1.52. The hypothesis of equal survival proportions gave a chi-square of 5.0429 (1 degree of freedom), which has a p-value of 0.0247. The analysis was then adjusted for mouse weight and intraperitoneal (-)-propranolol dosage using a logistic regression (LR) model. The LR treatment odds ratio was 1.51 and the LR treatment chi-square was 4.8112 (1 degree of freedom), which has a p-value of 0.0283. Consequently, we reject the null hypothesis of no treatment effect on survival. Eleven percent more treatment mice survived than placebo mice.

CONCLUSION

We conclude that the toxicity of intraperitoneal (-)-propranolol HCl, may be counteracted by administration of a potency of its enantiomer, in ICR conventional mice which have survived preceding intraperitoneal Rometar injection, and pre-dosing with (+)-propranolol HCl homeopathic potency.

Inhibition of (-)-propranolol hydrochloride by its enantiomer in white mice

BACKGROUND

This study is based on the hypothesis, that the toxic or physiological effects of an optical isomer may be counteracted or reversed by the administration of a potentized preparation of one of its stereoisomers. In the present study the enantiomer was used.

METHODS

154 ICR conventional mice were used. 77 mice were administered (R)-(+)-propranolol HCl homeopathic potency prior to and during the experiment, and the other 77 were administered indistinguishable placebo. On the day of the experiment the mice were sedated with intraperitoneal Rometar. Once sedated they were injected intraperitoneally with the LD50 dose of (S)-(-)-propranolol HCl.

RESULTS

The end point for statistical analysis was the difference in survival between the placebo and treatment mice. The odds ratio for survival of treatment mice relative to placebo mice was 1.64. The hypothesis of equal survival proportions gave a chi-square of 2.0916 (1 degree of freedom), which has a p-value of 0.1481. The analysis was then adjusted for mouse weight and intraperitoneal (-)-propranolol dosage using a logistic regression (LR) model. The LR treatment odds ratio was 2.017 and the LR treatment chi-square was 2.8864 (1 degree of freedom), which has a p-value of 0.0893. Consequently we accept the null hypothesis of no treatment effect on survival. The odds ratio estimates show that the treatment mice are 2.02 times more likely to survive than placebo mice, but this was not statistically significant with p = 0.089. Nine percent more treatment mice survived than placebo mice. The investigators accustomed to handling rodents noted that mouse recovery seemed substantially faster in the treatment mice than in the placebo mice.

Limited effect of systemic beta-blockade on sympathetic outflow

Central beta-adrenoreceptors may augment sympathetic outflow. We tested the hypothesis that beta-blockade attenuates central sympathetic outflow by inhibiting central adrenoreceptors. We studied 18 healthy controls (4 female, 14 male; age, 26+/-6 years, body mass index, 23+/-3 kg/m(2)). ECG, brachial, and finger arterial blood pressure, muscle sympathetic nerve activity, and respiration were measured continuously before and during complete beta-blockade. Subjects received a total intravenous dose of 0.21 mg/kg of propranolol in 15 minutes. Spontaneous baroreflex slopes were calculated using the sequence technique (BRSup, BRSdown). The sympathetic baroreflex slope was determined at baseline using phenylephrine and sodium nitroprusside infusions. The subjects underwent cold pressor testing before and during beta-blockade. The R-R interval increased from 861+/-119 ms at baseline to 952+/-141 ms during beta-blockade (P<0.01). Blood pressure was 117+/-9/65+/-8 mm Hg at baseline and 117+/-10/67+/-8 mm Hg during beta-Blockade (P=NS). beta-Blockade did not affect baroreflex sensitivity (BRSup: 21+/-10 versus 28+/-11 ms/mmHg, P<0.1; BRSdown: 17+/-8 versus 20+/-8 ms/mmHg, P=NS). Muscle sympathetic nerve activity increased significantly during beta-blockade (number of bursts/100 beats: 32+/-9 versus 40+/-14, P<0.05), compared with baseline. However, the operating points of the parasympathetic and sympathetic baroreflex during beta-blockade were on the baroreflex curves obtained at baseline. beta-Blockade blunted the heart rate response to cold pressor testing; blood pressure and muscle sympathetic nerve activity responses were similar. Our study demonstrates that propranolol does not cause an acute decrease in sympathetic activity in normotensive young subjects. This, observation is not consistent with an important tonic stimulatory effect of beta-adrenoreceptors in the brain.

Effect of thromboxane synthase inhibitor, CS-518, on propranolol-induced bronchoconstriction in guinea pigs

Beta-adrenoreceptor antagonists, such as propranolol, can provoke severe bronchoconstriction in asthmatic subjects. Recently we developed an animal model of propranolol-induced bronchoconstriction and investigated the involvement of chemical mediators in this reaction. The purpose of this study was to elucidate the role of thromboxane A2 in the development of propranolol-induced bronchoconstriction after allergic bronchoconstriction. Passively sensitized guinea pigs were anesthetized and treated with diphenhydramine hydrochloride and were then artificially ventilated. Propranolol at a concentration of 10 mg/ml was inhaled 20 min after an aerosolized antigen challenge. A potent and selective thromboxane A2 synthase inhibitor, CS-518, in doses of 0.01, 0.1 and 1 mg/kg and vehicle were administered intravenously 15 min after the antigen challenge. Another study was performed in naive guinea pigs; ascending doses of methacholine (12.5, 25, 50, 100 and 200 microg/ml) were inhaled for 20 sec at 5-min intervals, 10 min after intravenous administration of CS-518. Propranolol inhaled 20 min after the antigen challenge caused bronchoconstriction in sensitized guinea pigs. CS-518 administered 15 min after the antigen challenge significantly inhibited propranolol-induced bronchoconstriction in a dose-dependent manner, while CS-518 did not influence the dose-dependent response to inhaled methacholine in naive guinea pigs. We conclude that thromboxane A2 contributes to the development of propranolol-induced bronchoconstriction following allergic reaction in our guinea pig model.

Attenuation of propranolol-induced bronchoconstriction by frusemide

BACKGROUND

Inhaled propranolol causes bronchoconstriction in asthmatic subjects by an indirect mechanism which remains unclear. Inhaled frusemide has been shown to attenuate a number of indirectly acting bronchoconstrictor challenges. The aim of this study was to investigate whether frusemide could protect against propranolol-induced bronchoconstriction in patients with stable mild asthma.

METHODS

Twelve asthmatic subjects were studied on three separate days. At the first visit subjects inhaled increasing doubling concentrations of propranolol (0.25-32 mg/ml), breathing tidally from a jet nebuliser. The provocative concentration of propranolol causing a 20% reduction in FEV1 (PC20FEV1 propranolol) was determined from the log concentration-response curve for each subject. At the following visits nebulised frusemide (4 ml x 10 mg/ml) or placebo (isotonic saline) was administered in a randomised, double blind, crossover fashion. FEV1 was measured immediately before and five minutes after drug administration. Individual PC20FEV1 propranolol was then administered and FEV1 was recorded at five minute intervals for 15 minutes. Residual bronchoconstriction was reversed with nebulised salbutamol.

RESULTS

Frusemide had no acute bronchodilator effect but significantly reduced the maximum fall in FEV1 due to propranolol: mean fall 18.2% after placebo and 11.8% after frusemide. The median difference in maximum % fall in FEV1 within individuals between study days was 3.6% (95% CI 1.2 to 11.7).

CONCLUSIONS

Frusemide attenuates propranolol-induced bronchoconstriction, a property shared with sodium cromoglycate. Both drugs block other indirect challenges and the present study lends further support to the suggestion that frusemide and cromoglycate share a similar mechanism of action in the airways.

Inhibitory avoidance impairments induced by intra-amygdala propranolol are reversed by glutamate but not glucose

Both systemic and central injections of glucose can enhance memory. For example, glucose reverses impairments on inhibitory avoidance resulting from intra-amygdala injections of morphine. The present experiment investigated the ability of glucose to reverse memory impairments resulting from intra-amygdala injections of propranolol, a beta-noradrenergic antagonist. Pretraining administration of 10 microg propranolol significantly reduced inhibitory avoidance retention latencies but had no effect on performance in a spontaneous alternation task. Coadministration of glucose into the amygdala at 3 doses (1.5, 3.0, and 6.0 microg) did not reverse the propranolol-induced inhibitory avoidance deficits. However, coadministration of 2.5 microg of glutamate with the propranolol did reverse these deficits. The ability of glucose to reverse impairments following intra-amygdala injections of morphine but not propranolol may reflect the neurotransmitter system or systems through which glucose exerts its effects.

Characteristics of vagal reflex-mediated tracheal response induced by bronchoconstriction in guinea pigs

The reflex tracheal response induced by bronchoconstriction was investigated using a newly devised tracheo-bronchi preparation in anesthetized guinea pigs. Tracheal constriction and subsequent dilatation were observed in response to bronchoconstriction induced by the inhalation of 0.001-0.01% histamine and 0.003-0.03% acetylcholine. These tracheal responses were abolished by cervical vagotomy or treatment of the tracheal site with 1% tetrodotoxin. Tracheal constriction and dilatation were significantly inhibited by 0.1% atropine and 1% propranolol, respectively. When high tracheal tone was induced by 0.01% serotonin, the residual tracheal dilatation observed in the presence of propranolol was enhanced, while dilatation was completely inhibited by 1% hexamethonium. Dilatation was also suppressed by 1% N omega-nitro-L-arginine methyl ester (L-NAME) and 1% methylene blue. The tracheal constriction produced by bronchoconstriction was significantly enhanced by propranolol 2 mg/kg, i.v. and L-NAME 10 mg/kg, i.v. These results demonstrate that a vagally mediated reflex tracheal response (constriction followed by dilatation) is induced by bronchoconstriction in anesthetized guinea pigs. Cholinergic nerves may mediate the constriction, and adrenergic and nonadrenergic noncholinergic (NANC) inhibitory nerves may mediate the dilatation. Furthermore, NO may be involved in the NANC reflex tracheal dilatation.

Beta-receptor blockade by propranolol modifies the effect of the inhibitory, endogenous epidermal pentapeptide on epidermal cell flux at the G2-M transition but not at the G1-S transition

The mitosis inhibitory pentapeptide, pGlu-Glu-Asp-Ser-GlyOH (EPP), which was isolated from mouse epidermis extracts, belongs to a group of growth inhibitory peptides that all have pyroglutamyl at the N-terminal end. Earlier experiments with crude or partially purified skin extracts have shown that the inhibitory effect could be enhanced by beta-receptor agonists and by dibutyryl cAMP, and that beta-receptor blockade could neutralise it. We now show that treatment with the beta receptor blocker propranolol before or after EPP treatment of hairless mice significantly modifies the effect of EPP on mouse epidermal cell proliferation, as estimated by using a metaphase-arrest technique (Colcemid) to estimate the G2-M cell flux. The interaction between propranolol and EPP is complex; only the EPP-induced inhibition of the G2-M cell flux was modified by beta-receptor blockade, while the late (18-21 h) inhibition of the mitotic rate was unaltered. Propranolol alone was followed by a dose-related and transient increase in the epidermal mitotic rate. The phosphodiesterase inhibitor caffeine had no effect on its own on epidermal cell proliferation but counter-acted the late (18-21 h) EPP-induced inhibition.

Milrinone versus glucagon: comparative hemodynamic effects in canine propranolol poisoning

Glucagon has been reported to be one of the most effective treatments for severe beta-blocker poisoning. Recently, amrinone was suggested as an alternative therapeutic choice for beta-blocker poisoning. Milrinone, a derivative of amrinone, acts independently of beta-adrenoceptors and increases cyclic AMP. Therefore milrinone may also be effective in the treatment of beta-blocker poisoning. In the present study, we compared the effect of glucagon and milrinone in treating severe beta-blocker poisoning. Following the administration of 10 mg/kg propranolol i.v. over 10 min, heart rate, cardiac output, mean arterial pressure, stroke volume, and end tidal CO2 were depressed, while central venous pressure, and pulmonary capillary wedge pressure increased significantly (p < 0.05). Following the administration of saline (Group S, N = 3), glucagon 20 micrograms/kg (Group G, N = 5), and milrinone 300 micrograms/kg (Group M, N = 5), hemodynamic parameters were observed for 30 min. In group M, mean arterial pressure, cardiac output and stroke volume recovered to their baseline values, while central venous pressure and pulmonary capillary wedge pressure decreased. Although there were no significant differences between groups G and M, the heart rate, central venous pressure and pulmonary capillary wedge pressure, mean arterial pressure and stroke volume did not return to baseline values in group G. Milrinone administration produced a significant hemodynamic improvement without increasing the heart rate in the canine model of severe heart failure caused by propranolol. In the glucagon treatment group, central venous pressure and pulmonary capillary wedge pressure improved less than the milrinone group. Although more data are needed before a clinical recommendation, milrinone might be an effective drug to treat beta-blocker poisoning.

Substrate stereoselectivity and enantiomer/enantiomer interaction in propranolol metabolism in rat liver microsomes

The substrate stereoselectivity and enantiomer/enantiomer interaction of (S)- and (R)- propranolol for the formation of their metabolites were investigated in rat liver microsomal fractions. The enantiomers of primary metabolites of propranolol, 4-, 5-, 7-hydroxy- and N-desisopropyl-propranolol were separated and assayed by an HPLC method employing a chiral ovomucoid column. Regioselective substrate stereoselectivity (R < S for 4- and 5-hydroxylations; R > S for 7-hydroxylation; R = S for N-desisopropylation) was observed in the formation of propranolol metabolites when the individual enantiomers or a racemic mixture of propranolol were used as substrates. Concentration-dependent metabolic inhibition of propranolol enantiomers by their optical isomers was also observed. In addition, the inhibition of propranolol 4-, 5- and 7-hydroxylations between the enantiomers showed a typical competitive nature. These findings suggested that the propranolol enantiomers competed for the same enzyme, probably a cytochrome P450 isozyme in the CYP2D subfamily.

Kinetic analysis of mutual metabolic inhibition of lidocaine and propranolol in rat liver microsomes

The metabolic interaction between lidocaine (LD) and propranolol (PL) was analysed kinetically in rat liver microsomes. Employing a very short incubation time of 30 sec, we demonstrated that PL competitively inhibited liver microsomal 3-hydroxylation of LD, but did not affect either the formation of monoethylglycinexylidide or methylhydroxylidocaine from LD in PL concentrations up to 1 microM. On the other hand, LD competitively inhibited PL 4-, 5- and 7-hydroxylations, but the inhibition type of LD for PL N-desisopropylation could not be clarified. Comparison of the kinetic data for liver microsomes from Wistar and Dark Agouti rats indicated that among the primary metabolic pathways of LD, the Vmax value for 3-hydroxylation was markedly less in female Dark Agouti rats. The results suggest that LD 3-hydroxylation and PL ring hydroxylations are mediated by the same isozyme(s) belonging to the CYP2D subfamily.

Clearance by the liver in cirrhosis. I. Relationship between propranolol metabolism in vitro and its extraction by the perfused liver in the rat

To delineate the factors responsible for impaired clearance in cirrhosis, we examined propranolol disposition in rats with carbon tetrachloride-induced cirrhosis and compared it with that in control animals, rats treated with chlorpromazine (an inhibitor of propranolol metabolism) and rats with acute liver injury. We measured the extraction ratio of propranolol by the isolated perfused liver and related it to estimates of propranolol drug-metabolizing enzyme activity in homogenates of the same livers. In control animals, drug-metabolizing enzyme activity (measured as the ratio Vmax/Km) averaged 5,319 +/- 1,193 ml/min; the extraction ratio in the perfused liver was close to 1.0 (0.97 +/- 0.01). Important decreases of microsomal enzyme activity were observed in rats treated with chlorpromazine (30 +/- 27 ml/min, p < 0.001) and in rats with acute liver injury (724 +/- 401 ml/min, p < 0.001), accounting for the decrease in the hepatic extraction ratio by the perfused liver (0.33 +/- 0.09 and 0.71 +/- 0.04, respectively, p < 0.01). In cirrhotic livers, enzyme activity was not significantly different from that of controls (3,592 +/- 1,857 ml/min) and could not account for the observed decrease in extraction (0.66 +/- 0.14, p < 0.01). The extraction of antipyrine by the isolated perfused liver was also measured as an index of microsomal enzyme activity and related to propranolol extraction. Antipyrine extraction was decreased by 90% in acute liver injury, compared with 33% in cirrhosis, suggesting a much greater reduction of microsomal enzyme activity in the former group.(ABSTRACT TRUNCATED AT 250 WORDS)

Are 5-HT receptors or β-adrenoceptors involved in idazoxan-induced food and water intake?

Idazoxan (10 mg/kg, i.p.) produces an unexpected increase in food intake in freely-feeding rats which has been linked to its high affinity for non-adrenoceptor idazoxan binding sites. In this study, a dose-related antagonism of idazoxan-induced food intake by the beta-adrenoceptor antagonist (-)-propranolol (5-20 mg/kg, i.p.), which also blocks 5-HT1 (5-hydroxytryptamine1) receptors has been demonstrated. (+)-Propranolol (10, 20 mg/kg, i.p.) did not attenuate idazoxan-induced feeding. (-)-Propranolol (10 mg/kg, i.p.) but not the (+)-enantiomer (10 mg/kg, i.p.) also significantly inhibited the food intake, induced by the 5-HT1A agonist 8-OH-DPAT (0.25 mg/kg, i.p.). Idazoxan-induced feeding was not altered by the selective beta-adrenoceptor antagonists betaxolol (beta 1; 5 mg/kg, i.p.) and ICI 118,551 (beta 2; 5 mg/kg, i.p.) but was potentiated by the 5-HT receptor antagonist metergoline (5 mg/kg, i.p.). The anomalous findings with metergoline may reflect its action at different sub-types of 5-HT receptor. The water intake induced by idazoxan and the peripherally-active alpha 2-adrenoceptor antagonist L-659,066 was also blocked in a stereoselective manner by propranolol (10 mg/kg) but not significantly by either metergoline (5 mg/kg, i.p.), the beta 1-adrenoceptor antagonist betaxolol (5 mg/kg, i.p.) nor by the beta 2-adrenoceptor antagonist ICI 118,551 (5 mg/kg, i.p.). These results suggest that the food intake induced by idazoxan (and perhaps mediated by non-adrenoceptor idazoxan binding sites) may involve the 5-HT system, although further studies, using antagonists acting selectively at the different sub-types of 5-HT receptor, are required to confirm this.(ABSTRACT TRUNCATED AT 250 WORDS)

[Elimination of the atherogenic effect of beta blocker propranolol by papaverine]

Recently, the ability of beta-blockers to stimulate proliferative activity and induce lipid accumulation in cultured human aortic intimal cells has been demonstrated. Moreover, the addition of calcium antagonists completely blocked the increase in proliferative activity and abolished cholesterol accumulation caused by propranolol. In this study blood serum of rabbits treated with 20 mg of propranolol induced 2-fold cholesterol accumulation in mouse peritoneal macrophages. Papaverin did not influence this effect. In case of simultaneous administration of propranolol and papaverin rabbit serum did not exhibit the ability to accumulate intracellular lipids. Propranolol substantially stimulated the formation of myointimal thickening and neutral lipid accumulation in denuded rabbit aorta. Papaverin completely blocked the propranolol-produced atherogenic changes. The data suggest that in vitro and in vivo atherogenic effects of beta-blockers may be prevented by papaverin.

Heterogeneous interference of nicardipine, verapamil, and diltiazem with forearm arteriolar responsiveness to adrenergic stimulation in hypertensive patients

The interference of intraarterial nicardipine, verapamil, and diltiazem with the forearm vascular response to graded exogenous norepinephrine was evaluated in hypertensive patients. Nicardipine antagonized the vasoconstrictor effect of norepinephrine in a dose-dependent manner, whereas verapamil was ineffective, suggesting that functional alpha-adrenergic antagonism may participate in the vasodilatory and possibly the antihypertensive effect. Nicardipine also blunted the vasoconstriction to lower-body negative pressure and the action of angiotensin II administered intraarterially. Despite a comparable increase in basal forearm flow, verapamil was less potent than nicardipine in inhibiting vasoconstriction after both stimuli. Therefore nicardipine suppressed preferentially regional vascular reactivity, probably by blockade of the influx of extracellular calcium in response to receptor activation, because both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. At variance with both nicardipine and verapamil was potentiation of the responses to norepinephrine after the administration of diltiazem. Because intraarterial propranolol abolished that potentiating action and the local vasodilatation to isoproterenol was clearly reduced, diltiazem probably interfered also with beta-adrenergic receptor-mediated vasorelaxing mechanisms in human forearm arterioles. The data further stress the heterogeneity of calcium channel blockers in humans.

Methylprednisolone prevents propranolol-induced airway hyperreactivity in the Basenji-greyhound dog

To determine if corticosteroids would prevent beta-adrenergic-antagonist-induced increases in airway reactivity, we evaluated the ability of chronic methylprednisolone administration to prevent propranolol-induced airway hypereactivity to methacholine aerosol in the basenji-greyhound (BG) dog model of asthma. Initial studies included the measurement of lung resistance (RL) and dynamic compliance (Cdyn) with and without propranolol pretreatment in 5 BG and 5 mongrel dogs. A single dose of propranolol (2 mg/kg) did not significantly alter airway reactivity in the mongrels. The dose of methacholine needed to increase RL by 200% (ED200RL) was 0.20 +/- 0.05 mg/ml (mean +/- standard error of the mean [SEM]) in untreated and 0.18 +/- 0.04 mg/ml in propranolol-treated mongrels. In contrast, propranol significantly increased methacholine-reactivity in the BGs. The ED200RL for methacholine was 0.17 +/- 0.03 mg/ml in untreated and 0.05 +/- 0.02 mg/ml (P less than 0.05) in propranolol-treated BG dogs. Following the initial studies, the 5 BG dogs were given methylprednisolone (2 mg.kg-1.day-1) for 4 weeks, after which time propranolol no longer increased methylacholine reactivity in the BGs. The ED200RL was 0.16 +/- 0.03 mg/ml after 4 weeks of methylprednisolone and 0.22 +/- 0.06 mg/ml after propranolol administration in the BGs given 4 weeks of methylprednisolone treatment. The attenuation of propranolol-induced bronchoconstriction by corticosteroids may be a clinically useful intervention in asthmatic patients receiving beta-adrenergic antagonists in the perioperative period. However, further studies are needed to define the effective dose and duration of corticosteroid therapy that is needed.

Microinjection of propranolol into the dorsal periaqueductal gray causes an anxiolytic effect in the elevated plus-maze antagonized by ritanserin

The 5-HT1A/1B receptor antagonist propranolol was injected into the dorsal periaqueductal gray (DPAG) of rats exposed to the elevated plus-maze in order to investigate the participation in anxiety of 5-HT mechanisms operating in this brain region. Microinjection of D,L- or L-propranolol into the DPAG increased the percentage of total arm entries without affecting the total number of entries into either open or enclosed arms of the maze, an effect characteristic of anxiolytic drugs injected systemically. The doses of 5 nmol L-propranolol and 10 nmol D,L-propranolol caused anxiolytic effects of comparable magnitude, while the doses of 2.5 nmol of the former and 5 nmol of the latter were ineffective. Therefore, the L-isomer is likely to be the main one responsible for the pharmacological activity observed. In addition, the anxiolytic effect of 10 nmol D,L-propranolol was antagonized by 10 nmol of the 5-HT2/1C receptor antagonist ritanserin, previously injected into the DPAG. The present as well as previously reported results suggest that the anxiolytic effect of propranolol injected into the DPAG is due to increased release of 5-HT acting on post-synaptic 5-HT2 receptors, resultant from blockade of 5-HT1B autoreceptors that inhibit amine release from serotonergic nerve endings.

Adrenalectomy abolishes antagonism of alpha-adrenoceptor-mediated hypotension by a beta-blocker in conscious rats

1. The effects of a single bolus injection of propranolol, atenolol or ICI 118,551, non-selective beta-, selective beta 1- and selective beta 2-adrenoceptor antagonists, respectively, on mean arterial pressure (MAP) and plasma catecholamine concentrations were examined in seven groups of conscious and unrestrained adrenalectomized rats receiving a continuous infusion of the alpha-adrenoceptor antagonist phentolamine. In all rats adrenaline was undetectable in the plasma four days after adrenalectomy. 2. In the first three groups, phentolamine significantly decreased MAP and increased the plasma concentrations of noradrenaline. The injection of propranolol, atenolol or ICI 118,551 in Groups I, II and III, respectively, caused a small increase in MAP and a small, but not significant, decrease in plasma noradrenaline concentrations. 3. Groups IV, V and VI were given a continuous infusion of adrenaline for 1 h prior to the infusion of phentolamine, followed by a bolus injection of propranolol, atenolol or ICI 118,551, respectively. Group VII was treated similarly to IV, but was also given daily cortisone replacement after adrenalectomy. Adrenaline slightly, but not significantly, decreased MAP while phentolamine significantly decreased MAP and increased plasma noradrenaline concentrations in all groups. A subsequent injection of a beta-blocker caused a significant increase in MAP in each group and a slight decrease in the plasma level of noradrenaline which reached statistical significance in group VII. The pressor effect of propranolol was significantly greater in the cortisone-treated rats (Group VII) than in Group IV. 5. The results suggest that adrenaline and adrenocortical steroids are both involved in the antagonism of alpha-adrenoceptor-induced hypotension by a beta-blocker.

The effect of inhaled fenoterol and ipratropium bromide on propranolol induced bronchoconstriction in the asthmatic airways

1. The provocative dose of inhaled propranolol, (PC20P, mg/mL) needed to induce a 20% reduction in the forced expired volume in 1 s (FEV1, L) was determined for 15 adult asthmatics following randomized pre-treatment with placebo, ipratropium bromide (40, 160 micrograms) and fenoterol (200, 800 micrograms) aerosols using a double-blind protocol. 2. Fenoterol 200 micrograms, 800 micrograms increased the baseline FEV1 0.28 +/- 0.16, 0.32 +/- 0.16 L (P = 0.04, P = 0.008 respectively). Fenoterol 800 micrograms moved the PC20 P rightwards from placebo geometric mean 10.95, 95% Confidence Intervals (95% CI) 4.43-27.22 mg/mL to mean 20.41, 95% CI 10.13 to 40.64 mg/mL (P = 0.01). Fenoterol 200 micrograms was not protective; mean PC20 16.22, 95% CI 7.83-34.35 mg/mL (P = 0.08). Neither 40 or 160 micrograms ipratropium changed the FEV1 or PC20P values compared with placebo; increase in FEV1 0.15 +/- 0.27 L (P = 0.22), 0.24 +/- 0.12 L (P = 0.14) and geometric mean PC20P 16.59 +/- 0.57 mg/mL, 95% CI 8.01-34.51 mg/mL (P = 0.90), 15.58 +/- 0.66 mg/mL, 95% CI 6.72-36.05 mg/mL (P = 0.34) respectively after ipratropium treatments. 3. Bronchoconstriction induced by inhaled propranolol (P) appears to be only weakly antagonized by inhaled beta-agonist and not reduced by antimuscarinic anticholinergic aerosol. This finding argues against the activation of a cholinergic reflex to explain propranolol induced bronchoconstriction (PIB).

Antagonism of antihypertensive drug therapy in pregnancy by indomethacin?

Two women with preeclampsia treated with pindolol and propranolol became profoundly hypertensive when indomethacin was added because of premature contractions. The interaction of nonsteroidal antiinflammatory agents and beta-blockers and their role in the control of blood pressure in obstetrics are discussed. Indomethacin should not be given to pregnant patients with hypertension treated with beta-blockers.

Multiple pathways of propranolol's metabolism are inhibited by debrisoquin

We investigated the effect of debrisoquin on propranolol metabolism in six normal subjects who were extensive metabolizers of debrisoquin. Each subject was studied on two occasions. On the first occasion, each subject received oral propranolol (80 mg) alone; on the second occasion, 7 days later, each subject received a dose of propranolol (80 mg) 30 minutes after the administration of oral debrisoquin (40 mg). Oral propranolol clearance was reduced 33% +/- 16% (p less than 0.05) by the administration of debrisoquin. As predicted, the 4-hydroxypropranolol partial metabolic clearance was significantly (p less than 0.05) inhibited by debrisoquin. However, the side-chain oxidation pathway, as measured by naphthoxylactic acid, was also significantly (p less than 0.05) inhibited by debrisoquin. Debrisoquin administration did not change the renal clearance of any of the metabolites. These data support the usefulness of the in vivo inhibition model in the prediction of cosegregation of routes of metabolism. However, for propranolol, pathways of its metabolism that are not thought to cosegregate with debrisoquin was also inhibited.

Time course and extent of alpha 1-adrenoceptor density changes in rat heart after beta-adrenoceptor blockade

1. It has been suggested that impaired beta-adrenoceptor stimulation is a condition under which the functional role of cardiac alpha 1-adrenoceptors is enhanced. We therefore investigated the extent and time course of changes in alpha 1-adrenoceptor characteristics after chronic treatment with the beta-adrenoceptor blocker propranolol in rat heart. For comparison beta-adrenoceptors were also studied. The mechanism of the changes in adrenoceptor density was investigated with cycloheximide, an inhibitor of protein synthesis. The functional significance of an increased alpha 1-adrenoceptor density was tested by measuring isometric force of contraction in the presence of phenylephrine or isoprenaline in right ventricular papillary muscles. 2. Rats were treated with propranolol (9.9 mg kg-1 daily) or 0.9% NaCl, applied with osmotic minipumps for 1, 2, 3 or 7 days. Propranolol treatment resulted in a maximally 28% increase of alpha 1-adrenoceptor density after 3 days (NaCl 95.9 +/- 3.5 vs. propranolol 123.0 +/- 1.6 fmol mg-1 protein, n = 6, P less than 0.01). This up regulation reached significant levels after 2 days of treatment and was reversible after cessation of treatment within two days. KD-values were the same for NaCl- and propranolol-treated rats. Changes of Bmax and KD in beta-adrenoceptor binding assays did not reach significant levels. 3. Cycloheximide (1.5 mg kg-1 i.p. daily for 3 days) inhibited the propranolol-induced increase in Bmax of alpha 1-adrenoceptors completely. In addition, cycloheximide also decreased the density of alpha 1- and beta-adrenoceptors also under control conditions. 4. pD2-values for the positive inotropic effect of phenylephrine and isoprenaline in isolated electrically driven papillary muscle were similar in NaCl- and propranolol-treated rats (phenylephrine: 5.41 + 0.11 vs. 5.41 + 0.19, n = 7; isoprenaline: 6.31 + 0.18 vs. 6.65 + 0.19, n = 7). The observed increase in alpha-adrenoceptor density in healthy rat heart may therefore not be high enough to enhance the phenylephrine-induced increase in force of contraction. 5. In conclusion, time course and effects of cycloheximide indicate that the increase in B,,,, of myocardial alpha 1-adrenoceptors is due to de novo synthesis of receptors. However, at least for the rat heart model, a functional significance of this increase could not be demonstrated.

C1 area of the rostral ventrolateral medulla as a site for the central hypotensive action of propranolol

Previous studies suggest that the hypotensive response to centrally administered propranolol results from a drug-induced release of norepinephrine which then stimulates central alpha adrenergic receptors and, as a consequence, arterial pressure is lowered. Inasmuch as the C1 area of the rostral ventrolateral medulla is known to contain noradrenergic nerve terminals and participate in arterial pressure regulation, we determined whether this medullary region is a site mediating the hypotensive response to centrally administered propranolol. Bilateral microinjections (0.1 microliter) of dl-propranolol (0.25-2 nmol) into the C1 area of urethane-anesthetized rats resulted in a gradual reduction in mean arterial pressure which was sustained throughout the 120-min experimental period. The injection site was verified pharmacologically at the end of each experiment by bilateral microinjection of 10 nmol of tyramine and observing a further decrease in mean arterial pressure and a reduction in heart rate. Pretreatment of the C1 area bilaterally with reserpine 24 hr earlier significantly reduced the hypotensive responses to microinjections of both propranolol and tyramine whereas the hypotensive response to the direct acting agonist clonidine was unchanged. These results demonstrate that the C1 area of the rostral ventrolateral medulla is a site for a central hypotensive action of propranolol. Moreover, the data provide further evidence that the hypotensive action of centrally administered propranolol results from a drug-induced release of norepinephrine from central noradrenergic neurons.

Effects of the non-steroidal anti-inflammatory drugs, piroxicam or sulindac, on the antihypertensive actions of propranolol and verapamil

Twenty-five hypertensive patients participated in a randomized placebo-controlled study. After blood pressures were normalized with propranolol or verapamil alone over a 6-week period, patients were entered into a 4-week double-blind period where they received non-steroidal anti-inflammatory drug (NSAID) treatment (sulindac or piroxicam) or placebo treatment in addition to their antihypertensive therapy. There was a significant elevation in standing systolic blood pressure (P less than 0.05) with propranolol and sulindac, when compared with propranolol and placebo, but no significant changes were shown with propranolol and piroxicam. Systolic blood pressures on sulindac treatment were significantly lower (P less than 0.05) in both supine and standing positions during treatment of hypertension with verapamil compared with propranolol. Both supine systolic and diastolic blood pressures on piroxicam treatment were significantly lower (P less than 0.05) during treatment of hypertension with verapamil compared with propranolol. We conclude that NSAID transiently block the antihypertensive effect of propranolol, causing blood pressures to increase and side effects to improve. However, NSAID do not cause loss of antihypertensive control with verapamil.

A new method of inhalation challenge with propranolol: comparison with methacholine-induced bronchoconstriction and role of vagal nerve activity

To establish a safe procedure for examining propranolol-induced bronchoconstriction, we have developed a new method for performing inhalation challenge with propranolol. Monitoring respiratory resistance during tidal breathing with continuous inhalation of propranolol in 1.5-fold increasing concentrations from 0.78 to 30 mg/ml for 1 minute at each concentration, we tested 43 subjects with stable asthma and 10 normal subjects. We also compared bronchial responsiveness with responsiveness to inhaled methacholine on separate days. In addition, to determine the role of vagal nerve activity in propranolol-induced bronchoconstriction, we studied the effect of atropine. Inhaled propranolol caused dose-related bronchoconstriction in all subjects with asthma but not in normal subjects. None of the subjects suffered severe asthmatic attack during the test, which was performed in 15 minutes or less. The minimum cumulative dose of methacholine and of propranolol, at the point where respiratory conductance began to decrease, was not significantly correlated. Increased respiratory resistance was reversed by atropine in 70% of the subjects with asthma with marked individual differences. These data suggest that, although in most subjects with asthma, vagal nerve activity contributes in varying degree to bronchoconstriction, other constricting factors may contribute in the remaining subjects. It is also suggested that the mechanism of bronchial response to propranolol differs from that of the nonspecific airway reactivity estimated by methacholine challenge.

Tricyclohexyltin hydroxide effects on cationic and substrate activation kinetics of beta-adrenergic-stimulated cardiac Ca2+-ATPase

Previous studies from this laboratory have indicated that tricyclohexyltin hydroxide (Plictran) is a potent inhibitor of both basal- and isoproterenol-stimulated cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase, with an estimated IC-50 of 2.5 X 10(-8) M. The present studies were initiated to evaluate the mechanism of inhibition of Ca2+-ATPase by Plictran. Data on substrate and cationic activation kinetics of Ca2+-ATPase indicated alteration of Vmax and Km by Plictran (1 and 5 X 10(-8) M), suggesting a mixed type of inhibition. The beta-adrenergic agonist isoproterenol increased Vmax of both ATP- and Ca2+-dependent enzyme activities. However, the Km of enzyme was decreased only for Ca2+. Plictran inhibited isoproterenol-stimulated Ca2+-ATPase activity by altering both Vmax and Km of ATP as well as Ca2+-dependent enzyme activities, suggesting that after binding to a single independent site, Plictran inhibits enzyme catalysis by decreasing the affinity of enzyme for ATP as well as for Ca2+. Preincubation of enzyme with 15 microM cAMP or the addition of 2mM ATP to the reaction mixture resulted in slight activation of Plictran-inhibited enzyme. Pretreatment of SR with 5 X 10(-7) M propranolol and 5 X 10(-8) M Plictran resulted in inhibition of basal activity in addition to the loss of stimulated activity. Preincubation of heart SR preparation with 5 X 10(-5) M coenzyme A in combination with 5 X 10(-8) M Plictran partly restored the beta-adrenergic stimulation. These results suggest that some critical sites common to both basal- and beta-adrenergic-stimulated Ca2+-ATPase are sensitive to binding by Plictran, and the resultant conformational change may lead to inhibition of beta-adrenergic stimulation.

Direct effect of high-dose insulin on the depressed heart after beta-blockade or ischemia

The direct cardiac effects of high-dose insulin (HDI) were assessed in 13 canine hearts supported by cardiopulmonary bypass. Isovolumic peak developed pressure (PDP, mmHg), coronary blood flow (CBF, ml/beat/100 g LV) and myocardial oxygen consumption (MVO2, ml O2/beat/100 g LV) were determined during incremental left ventricular balloon inflation before and after functional depression by beta-blockade (0.2 mg/kg propranolol) or 2 hours cardioplegic ischemia at 28 degrees C. The 2 regimens gave an overall functional reduction of 46 +/- 3% and 42 +/- 2%, respectively. The hearts were then challenged with an aortic root bolus of 1000 IU insulin. A glucose clamp was maintained at physiological levels. Insulin reversed the negative inotropic effect of propranolol to 80% of control function and normalized heart rate. Despite the significant amelioration of systolic function by HDI, MVO2 indexed for cardiac effort did not change. Neither systolic function nor heart rate was changed in the ischemically depressed hearts. In conclusion, HDI reverses the negative inotropic effect of beta-adrenergic receptor blockade without augmenting oxygen utilization. Apart from effects ascribable to systemic vasodilation and metabolic shifts, no direct cardiac inotropic stimulation can be expected on the post-ischemically depressed, nondiabetic myocardium unless there is a persistent negative effect of beta-blockers.

Calcium interferes with the cardiodepressive effects of beta-blocker overdose in isolated rat hearts

Propranolol, timolol and sotalol were compared with respect to their cardiotoxic properties in isolated, spontaneously beating rat hearts. Propranolol and timolol induced a dose-dependent decrease in myocardial contractility. A high dose of sotalol had only modest negative inotropic effects. Similar reductions in myocardial contractility were observed in isolated, ventricle-stimulated rat hearts. These observations were similar to those in a previous study in which spontaneously beating and ventricle-stimulated reserpinized rat hearts were investigated. Spontaneously beating rat hearts were perfused with a high-, a normal- and a low-Ca++ medium, each with and without propranolol, timolol and sotalol. Addition of each beta-blocker to a normal-Ca++ medium induced a decrease of myocardial contractility and of heart rate and an increase of AV-conduction time when compared with the drug-free medium. In a high-Ca++ medium containing the same concentration of each beta-blocker, a less pronounced decrease of myocardial contractility was observed. Heart rate decreased and AV-conduction time increased to the same extent as after perfusion with the drug containing normal-Ca++ medium. With respect to the corresponding drug-free medium perfusion with a low-Ca++ medium with each beta-blocker enhanced the decline in myocardial contractility, most pronounced in propranolol and timolol containing media. For propranolol and sotalol the decrease in heart rate and increase in AV-conduction time were similar to the results after administration of the same beta-blocker in a high- and a normal-Ca++ perfusion media. Timolol caused an electromechanical dissociation. It was concluded that in beta-blocker intoxication the negative-inotropic phenomena cannot be explained by an action of the drugs on the beta-receptor since the results in reserpinized and non-reserpinized rat hearts were similar. Other effects have to be responsible for the observed cardiotoxic phenomena. The present results indicate that these phenomena can be influenced by Ca++ and or can be attributed to differences in lipophilicity.

The affinity of (-)-propranolol for beta 1- and beta 2-adrenoceptors of human heart. Differential antagonism of the positive inotropic effects and adenylate cyclase stimulation by (-)-noradrenaline and (-)-adrenaline

An appraisal of the affinity of (-)-propranolol was made for beta-adrenoceptors of isolated heart preparations and myocardial membrane particles from patients undergoing open heart surgery. In order to eliminate possible distorting influences of neuronal and extraneuronal uptakes of catecholamines on the affinity estimates for (-)-propranolol, isolated tissues were pretreated once with 5 or 10 mumol/l phenoxybenzamine for 2 h. Phenoxybenzamine caused potentiation of the positive inotropic effects of (-)-noradrenaline and (-)-adrenaline but not of (-)-isoprenaline; potentiation was more pronounced in atrial than in ventricular preparations. Potentiation was greater for (-)-noradrenaline than for (-)-adrenaline. It is concluded that the concentration of physiological catecholamines at the human heart beta-adrenoceptors is limited by neuronal capture but not by extraneuronal uptake. The antagonism of the positive inotropic effects of (-)-adrenaline and (-)-noradrenaline by (-)-propranolol was simple competitive in left ventricular myocardium of patients with mitral lesion. The effects of (-)-adrenaline and (-)-noradrenaline were antagonized to similar extent by (-)-propranolol. An equilibrium dissociation constant KB (-log mol/l) of 8.6 was estimated for (-)-propranolol. In atrial preparations the inotropic effects of (-)-adrenaline were antagonized significantly more by (-)-propranolol than those of (-)-noradrenaline. KB-Values (-log mol/l) of 8.9 [against (-)-adrenaline] and 8.5 [against (-)-noradrenaline] were estimated for (-)-propranolol. Concentration-effect curves for the stimulation of adenylate cyclase of both atrium and ventricle were biphasic for (-)-noradrenaline and monophasic for (-)-adrenaline. The high-sensitivity and low-sensitivity components of (-)-noradrenaline comprised 1/3 and 2/3, respectively, of maximum cyclase stimulation. As expected from beta 1-adrenoceptors, the high-sensitivity component of the curve for (-)-noradrenaline was selectively antagonized by (-)-bisoprolol; as expected from beta 2-adrenoceptors, the low-sensitivity component was selectively antagonized by ICI 118,551. (-)-Propranolol antagonized the effects of (-)-noradrenaline mediated by beta 2-adrenoceptors 2 to 3 times more potently than the effects mediated by beta 1-adrenoceptors. (-)-Propranolol competed with 3H-(-)-bupranolol for binding to left ventricular beta-adrenoceptors. An equilibrium dissociation constant (-log mol/l) of 8.6 was estimated for (-)-propranolol.(ABSTRACT TRUNCATED AT 400 WORDS)

The inhibitory effects of ranitidine and cimetidine on propranolol elimination by the rat isolated perfused liver

The effect of low (50 micrograms) and high (1 mg) doses of the histamine H2-receptor antagonists cimetidine and ranitidine on the first pass extraction of propranolol was studied in the rat isolated perfused liver. Both low and high dose cimetidine increased the area under the perfusate propranolol concentration time curve (AUC) 4 to 5-fold. Although low dose ranitidine did not alter propranolol AUC, high dose ranitidine increased it to the same extent as cimetidine. These results indicate that ranitidine has a clear propensity for microsomal inhibition, but one which is unlikely to be manifest at therapeutic dosage.

Effects of d,l-propranolol on open field behavior of rats

Rats were administered with different doses of d,l-propranolol or d,l-propranolol plus amphetamine before open-field observations. Results show that d,l-propranolol decreased locomotion and rearing frequencies and increased immobility duration in rats. An antagonism between the effects of amphetamine and d,l-propranolol on general activity of rats was also observed. Results are discussed in the light of a possible interference of the drugs with the activity of either noradrenergic neurons or mid-brain reticular formation.

Flurbiprofen interaction with single doses of atenolol and propranolol

In patients with mild hypertension, flurbiprofen in a dose of 100 mg daily for 7 days attenuated the hypotensive effect of a single dose of propranolol 80 mg but not of atenolol 100 mg. The attenuation was not due to an effect on the pharmacokinetic profile of either propranolol or atenolol. An alternative explanation is required.

Protective effect of oral oxyphenonium bromide, terbutaline and theophylline against the bronchial obstructive effects of inhaled histamine, acetylcholine and propranolol

The protective effects of oxyphenonium bromide, terbutaline and theophylline were compared in 8 asthmatic patients by determination of the degree of non-specific airway reactivity after 1 week of oral treatment according to a fixed dose scheme in a double-blind random order: oxyphenonium bromide 3 X 10 mg; terbutaline 3 X 5 mg; theophylline 2 X 300 mg and placebo. Controlled, standardized inhalation provocation tests were carried out with histamine, acetylcholine and propranolol. The study was monitored by measuring blood concentrations of the 3 drugs, and their effect on the plasma cAMP concentration was also determined. Significant protection by oxyphenonium bromide against the bronchial obstructive effects of acetylcholine and propranolol was observed, but not against the effect of inhaled histamine. The other two drugs provided no significant protection against the inhaled agents. The absence of any protective effect of terbutaline and theophylline might have resulted from too low a blood concentration. The observed differences in protection could not be explained by changes in pulmonary function. The study suggests dissociation between the bronchodilating effect of a drug and its protective effect against inhaled substances.

Pharmacologic antagonism of propranolol in dogs. III. Effects of dopamine-isoproterenol and glucagon on hemodynamics and myocardial oxygen consumption in ischemic hearts during chronic propranolol administration

In 31 dogs chronically beta blocked with oral propranolol (12 to 14 mg/kg/day), glucagon (20 micrograms/kg) and combined dopamine (10 micrograms/kg/min) and isoproterenol (0.2 micrograms/kg/min) were given intravenously and tested for hemodynamic efficacy. Dogs were divided into four groups. Basal hemodynamics were obtained In Group I (n = 8) without cardiopulmonary bypass. In Group II (n = 8), hemodynamics were studied after 15 minutes of global ischemia during cardiopulmonary bypass. In Group III (n = 8), hemodynamics were studied after regional ischemia produced by ligation of the proximal left anterior descending coronary artery. In Group IV (n = 7), myocardial oxygen consumption and left ventricular mechanics were studied before and after 1 hour of cardiopulmonary bypass. Our results indicate the following: (1) Dopamine-isoproterenol improves hemodynamics in basal, post-global ischemic, and post-regional ischemic states. Glucagon improves hemodynamics either insignificantly or to a lesser extent than dopamine-isoproterenol. Furthermore, glucagon produces a larger increase in heart rate, which is not desirable. (2) Both dopamine-isoproterenol and glucagon increase myocardial oxygen consumption in comparison with control.

Cardiovascular properties of a new cardiotonic agent, MDL 19205

The cardiovascular properties of a new cardiotonic agent, MDL 19205, were investigated in anesthetized and conscious dogs and in a dog heart-lung preparation. MDL 19205 (0.1-1 mg/kg), administered to anesthetized dogs by intravenous injection, produced a dose-related increase in cardiac contractile force lasting up to 1 h. It also produced a relatively minor increase in heart rate and a brief decrease in blood pressure. These effects did not involve beta-adrenergic receptor stimulation, as they were observed in dogs after a myocardial-depressant dose of propranolol. Given orally to conscious dogs, MDL 19205 (1 and 3 mg/kg) produced a dose-related increase in dP/dt without producing a significant alteration in heart rate or blood pressure. When administered to anesthetized dogs by constant intravenous infusion, MDL 19205 (0.1 mg/kg/min) produced a marked and sustained increase in cardiac contractile force and decreases in blood pressure and left atrial pressure, but did not produce a significant change in cardiac output or stroke volume, indicating an enhancement of cardiac pump function. Intravenous MDL 19205 reversed the hemodynamic characteristics of heart failure produced by propranolol in anesthetized dogs. In addition, it reversed the depressant effect of pentobarbital on cardiac function in a dog heart-lung preparation. These studies show that MDL 19205 is a potent, direct-acting cardiotonic agent in animals.

Cardiotonic activity of milrinone, a new and potent cardiac bipyridine, on the normal and failing heart of experimental animals

Milrinone (Win 47203) is a potent cardiac bipyridine with inotropic and vasodilator properties. Its effects were studied in anesthetized and unanesthetized dogs and in isolated cardiac tissues from guinea pigs. In the anesthetized dog, the intravenous injection of milrinone (0.01-0.1 mg/kg) increased cardiac contractile force (CF) (23 +/- 6.1 to 87 +/- 8.9%), maximum left ventricular pressure development (24 +/- 5.8 to 119 +/- 16.1%), and cardiac output (16 +/- 4.5 to 33 +/- 8.9%), with less than a 30% increase in heart rate (HR). Significant decreases in systolic and diastolic blood pressures were seen at 0.3-3 mg/kg i.v. Oral doses of milrinone (0.1-1.0 mg/kg), in unanesthetized dogs, increased cardiac CF by 35 +/- 7.0 to 99 +/- 17.0%, with a maximum increase in HR of 40 +/- 7.1% and no significant change in blood pressure. Milrinone was effective in the presence of ouabain and dopamine without enhancing their arrhythmogenic properties. It was also effective in reversing propranolol-, verapamil-, or pentobarbital-induced heart failure. The inotropic response does not seem to involve the stimulation of the autonomic receptors, the release of endogenous catecholamines, histamine, or prostaglandins, or the inhibition of Na+,K+-adenosine triphosphatase. Milrinone is an inhibitor or cardiac adenosine 3',5'-monophosphate (cAMP) phosphodiesterase, with resultant increases in cardiac cAMP levels. However, the time course for this increase does not seem to correspond to the increase in muscle developed tension, and, therefore, it is unlikely to be responsible for the initiation of the inotropic response. Milrinone is a potent cardioactive agent which should be beneficial in the treatment of acute and chronic congestive heart failure.

Reversal of propranolol and verapamil toxicity by calcium

Because of the increasing use of propranolol and verapamil in combination, a study of their interaction was conducted. In rabbits, propranolol given IV at 1 mg/kg followed by an IV infusion of verapamil at 0.1 mg/kg/min for 15 min caused profound hypotension, bradycardia, A-V block, and death in less than 1 h in each of 30 animals. In rabbits treated with propranolol and verapamil as above, calcium chloride (300 mg/kg) given IV immediately after verapamil infusion restored blood pressure and cardiac conduction to normal but the heart rate remained slow; all 12 animals survived. In miniature swine under sodium pentobarbital anesthesia, propranolol (0.5 mg/kg) and verapamil (0.5 mg/kg) IV produced the same physiological changes and death within 15 min in each of eight animals. Calcium chloride given at 150 mg/kg to miniature swine after propranolol and verapamil injections prevented death of each of the five animals; blood pressure and the electrocardiogram were restored to normal, although bradycardia persisted. In mice, the IP LD50 value of propranolol HCl, which is 80 +/- 2.7 mg/kg, was decreased to 10 mg/kg when the drug was given in combination with verapamil HCl at an IP dose of 3 mg/kg, which is less than 1/10 of its LD50. Deaths occurred within minutes and were preceded by convulsions. Pretreatment of mice with calcium chloride (600 mg/kg, IV) prevented death due to the combination of propranolol and verapamil. The data indicate that verapamil enhances the toxicity of propranolol and that calcium can antagonize this effect.

Possible role of an endogenous opioid in the antihypertensive action of propranolol in spontaneously hypertensive rats

The effect on systolic blood pressure and heart rate of the acute and chronic intraperitoneal (i.p.) administration of d- and dl-propranolol was investigated on unanesthetised spontaneously hypertensive rats. The effect of naloxone on the propranolol induced hypotension was also studied to test the hypothesis that the antihypertensive effect of propranolol involves the release of an endogenous opiate. On i.p. administration, 3 mg/kg d-propranolol was inactive; 3 and 30 mg/kg dl-propranolol decreased blood pressure and heart rate in a dose-dependent manner. When the rats were pretreated with 2 mg/kg naloxone i.p., the effect of propranolol on the blood pressure was nearly completely abolished, while that on the heart rate was only partially blocked. Chronic administration of dl-propranolol (30 mg/kg b.i.d.) to spontaneously hypertensive rats from the age of 6 weeks (prehypertensive phase) for 29 days prevented the development of hypertension while the rats treated with physiological saline for 29 days (control group) developed hypertension. Naloxone (2 mg/kg i.p.) administered on the 29th day to chronically treated rats induced a reversal of the propranolol action on systolic blood pressure and heart rate, i.e., blood pressure and heart rate increased. Naloxone had no such effect in the control group. We suggest that the release of an endogenous opioid contributes to the acute and chronic antihypertensive action of i.p. propranolol in spontaneously hypertensive rats and that the secretion of endogenous opioids participating in the control of cardiovascular functions is influenced by adrenergic mechanisms.

The behavioral effect of salbutamol (a beta-adrenergic receptor stimulant) on reserpine- and propranolol-treated rats

Reserpine- and propranolol-treated rats were given salbutamol, a beta-adrenergic stimulant, intra-peritoneally in an open control study. The results suggest that salbutamol has a therapeutic effect on the depressive behavior of reserpine- and propranolol-treated rats.

Effect of desipramine on propranolol-induced diminution of noradrenaline release by nerve stimulation

In atria from rats killed 1 h after either chronic parenteral (daily subcutaneous injections of 5 mg/kg/day for 15 days) or prolonged oral administration of (-)-propranolol (1 mg/ml ad libitum during 15 days) there was a 50% decrease in the overflow of [3H]noradrenaline ([3H]NA) elicited by cardioaccelerans nerve stimulation at 2 Hz, as previously reported for the in vitro exposure of guinea pig atria to propranolol. The chronotropic responses to nerve stimulation and to isoprenaline were also significantly reduced. On the other hand, 40 h after the last injection of propranolol, the overflow of [3H]NA induced by stimulation was still reduced to 50% of the control values, whereas no blockage to nerve stimulation or to isoprenaline was observed. Neither the basal output of [3H]NA nor the tissue levels of the endogenous transmitter were modified by any of the treatment schedules applied. In a separate set of experiments performed in isolated guinea pig atria stimulated at 4 Hz during 1 min, the in vitro exposure to 0.5 microM desipramine prevented the 30% decrease in the overflow of [3H]NA caused by 0.1 microM (-)-propranolol. Desipramine, by itself, did not modify the overflow of the transmitter. It is concluded that propranolol, both in vitro and after chronic in vivo treatments, reduces the overflow of [3H]NA in response to nerve stimulation. The fact that the in vitro effect of the beta-blocker is antagonized by desipramine suggests that propranolol may have to be taken up by the nerve terminals in order to exert its presynaptic inhibition on the release of noradrenaline.

Reversal of regional myocardial depressant effects of propranolol with nitroglycerin

Use of propranolol in acute myocardial infarction is limited by its cardiodepressant effects. The effects of nitroglycerin (0.4 mg intravenously) on regional myocardial dysfunction produced by total or partial (50 percent) coronary occlusion and intravenous administration of propranolol (1.0 mg/kg) were evaluated using pairs of ultrasonic crystals implanted subendocardially in the nonischemic and ischemic zones in 14 open chest dogs. During partial coronary occlusion, systolic shortening (% delta L) in the ischemic zone decreased from 20.9 +/- 5.3 to 7.2 +/- 6.4 (p less than 0.001). Propranolol did not change it significantly. Nitroglycerin increased % delta L from 6.7 +/- 4.5 to 11.2 +/- 5.3 (p less than 0.01). The nonischemic zone was unaffected by partial coronary occlusion but showed a decrease in % delta L from 18.6 +/- 6.2 to 15.6 +/- 5.1 (p less than 0.01) with propranolol. Nitroglycerin increased % delta L from 15.6 +/- 5.1 to 17.3 +/- 5.9 (p less than 0.02). During total coronary occlusion, nitroglycerin administration after propranolol improved % delta L in the nonischemic but not in the ischemic zone. Nitroglycerin caused a significant decrease in left ventricular systolic and end-diastolic pressures. Heart rate remained unchanged. It is concluded that nitroglycerin reversed myocardial depressant effects of propranolol in both the partially ischemic and the nonischemic zones after acute coronary occlusion.

Propranolol induces contractions of canine small and large coronary arteries

Using isolated canine small (right coronary branch, left coronary branch; o. d. 0.4-0.8 mm) and large (left coronary, circumflex; o. d. 1-2 mm) coronary arteries, the beta-adrenergic antagonist dl-propranolol (5 X 10(-7) to 5 X 10(-5) m/l) was found to produce concentration-dependent contractions. Interestingly, most of these contractile events take place with concentrations of propranolol (0.1-1 microgram/ml) found in the blood of patients who are taking this drug for various therapeutic reasons. These propranolol-induced contractions were enhanced in Krebs-Ringer solution containing slightly elevated (weak contractile) concentrations of potassium (15 mmol/l). Experiments with specific pharmacologic antagonists indicated that propranolol-induced contractions on canine coronary arteries can not be mediated by release (or inhibition) of catecholamines, histamine, serotonin or acetylcholine. Propranolol contractions could be released by low concentrations of potassium ions (4 mmol/l), suggesting that the beta receptor antagonist might inactive coronary arterial membrane Na+, K+-ATPase. Other experiments demonstrated that propranolol can enhance coronary arterial membrane permeability to calcium ions; these observations suggest that propranolol might sensitize coronary vascular smooth muscle cells to calcium ions. Removal of calcium ions from the Krebs-Ringer solution or addition of the calcium entry blocker, verapamil, prevented completely the propranolol-induced contractions. Catecholamines (i.e., epinephrine, norepinephrine, isoproterenol), which normally induce relaxation on these isolated coronary arteries, always induced contraction after use of dl-propranolol. Overall, these experiments suggest that the so-called "beta-blocker poisoning" sometimes noted with propranolol in patients might be brought about by four actions of this drug acting in concert: 1. direct coronary arterial vasospasm; 2. an unmasking of normally silent alpha-adrenergic receptors, thus allowing circulating and released catecholamines to induce potent coronary constriction; 3. attenuation of membrane Na+, K+-ATPase activity, and 4. an enhancement of coronary vascular smooth muscle membrane permeability to calcium ions.