Chronic treatment with propranolol enhances the synthesis of prostaglandins E2 and I2 by the aorta of spontaneously hypertensive rats.

The effects of treatment with dl, d- or l-propranolol (subcutaneously for 1 week) on arterial blood pressure and on 6-keto prostaglandin (PG) F1 alpha (stable metabolite of PGI2) and PGE2 production by aorta, renal medulla and renal cortex were examined in spontaneously hypertensive rats. dl-Propranolol and l-propranolol significantly (P less than .05) lowered blood pressures from 148 +/- 9/113 +/- 5 (n = 6) and 133 +/- 4/100 +/- 2 (n = 12) mm Hg to 112 +/- 3/80 +/- 3 and 121 +/- 3/81 +/- 3 mm Hg, respectively. Comparable treatment of spontaneously hypertensive rats with inactive d-propranolol was without effect. Basal immunoreactive (i) i6-keto-PGF1 alpha and iPGE2 production by isolated aorta, renal medulla and cortex was not different in vehicle compared to the dl-propranolol-treated rats. In contrast, norepinephrine (1 microM)-stimulated synthesis of i6-keto PGF1 alpha and iPGE2 by the aorta in the dl-propranolol-treated group was significantly (P less than .05) enhanced compared with the vehicle-treated group. Aortic i6-keto-PGF1 alpha and iPGE2 synthesis stimulated by norepinephrine in l-propranolol-treated rats was also significantly (P less than .05) higher than that observed in vehicle and d-propranolol-treated rats. dl-Propranolol treatment did not alter norepinephrine-stimulated renal cortical or medullary i6-keto-PGF1 alpha or iPGE2 synthesis. Indomethacin (5 mg/kg i.p.) given on the last 2 days of dl-propranolol treatment, significantly inhibited aortic i6-keto-PGF1 alpha and iPGE2 production and blunted the antihypertensive effect of dl-propranolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of nitroglycerin and perhexiline in dogs with myocardial ischemia.

Cardiovascular effects of nitroglycerin, perhexiline and the combination of these two drugs were studied in dogs with myocardial ischemia. Nitroglycerin decreased arterial blood pressure and O2 consumption (MVO2), although heart rate increased. Perhexiline decreased blood pressure, heart rate, MVO2 and modified the tachycardia and the hypotensive actions of nitroglycerin without altering the ability of nitroglycerin to reduce MVO2. These data show that the pharmacologic actions of nitroglycerin in the treatment of ischemic heart disease are enhanced when given in combination with perhexiline or similar calcium antagonists.

Inhibitors of prostaglandin synthesis reverse the effects of chronic beta-receptor blockade to attenuate adrenergic neurovascular transmission in dogs.

The effects of acute and chronic treatment with beta-adrenergic receptor blocking drugs on peripheral adrenergic neurovascular transmission were investigated. Experiments were performed using the blood perfused gracilis muscle preparation in control dogs and in animals treated with single or repeated doses of beta-receptor antagonists. After 7 days of d,l-propranolol, l-propranolol, or atenolol administration, the arterial pressor response to sympathetic nerve stimulation was significantly reduced in treated dogs (p less than 0.05) when compared with control- or d-propranolol-treated animals. In comparison, acute beta blockade produced by a single intravenous dose of propranolol had no effect on the pressor response to nerve stimulation. Inhibition of fatty acid-cyclooxygenase activity by indomethacin or piroxicam enhanced the vasoconstrictor response to sympathetic nerve stimulation in chronic d,l-propranolol-, l-propranolol-, and atenolol-treated dogs, but had no effect on vascular neurotransmission in control-, chronic d-propranolol-, or acutely d,l-propranolol-treated animals. The vasoconstrictor response to intraarterial phenylephrine was not significantly altered by chronic propranolol treatment, and measurement of norepinephrine overflow during sympathetic nerve stimulation failed to reveal any difference in neurotransmitter release between control- and propranolol-treated dogs. The results indicate that chronic but not acute beta-adrenergic receptor blockade alters signaling at the neurovascular synapse to diminish adrenergic transmission. This effect does not appear to result from a change in postsynaptic alpha 1 receptors or from a decrease in norepinephrine release.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereoselective delivery and actions of beta receptor antagonists.

These studies have revealed that the delivery and actions of beta receptor antagonist drugs are controlled by a cascade of stereoselective processes involving multiple enzymes, transport proteins and receptors. In essence, the free concentration of the pharmacologically active (-)-enantiomer species of these drugs presented to cell surface beta receptors appears to be a function of the stereoselective clearance by hepatic cytochrome P-450 isoenzymes, enantiomer selective binding to alpha 1-acid glycoprotein and albumin and perhaps predominantly by stereoselective sequestration (and release) by the vesicular amine transport protein within adrenergic neurons. Stereoselectivity in the clearance of beta blocking drugs, which can favor either the (+)- or (-)-enantiomer, only appears to be important for the lipophilic drugs which are cleared by hepatic metabolism. Such stereoselectivity is due to differential stereochemical substrate requirements of individual hepatic cytochrome P-450 isoenzymes. Interindividual variations in the stereoselectivity can occur as a result of differences in the amount and expression of cytochrome P-450 isoenzymes due to genetic predisposition or other factors. In the same context, we have observed a significant correlation between the extent and stereoselectivity of binding of beta blocking drugs to plasma proteins. This is another finding which suggests that variability in the expression of individual proteins involved in the beta blocking drug-protein cascade determines the free concentration of the pharmacologically active enantiomer. However, since most observations have been made in young normal subjects, the extent of stereoselectivity in metabolism, binding and other processes is unknown in the general population where steady-state plasma concentrations can vary widely due to multiple biological factors. The observations from neural studies support the concept that adrenergic nerve endings provide a depot for the stereoselective storage and release of the active enantiomer of beta receptor antagonists. The mechanism of this release appears to involve exocytotic secretion of drug that has been stereoselectively accumulated by the neurotransmitter storage vesicles. In terms of this idea, beta receptor antagonists released during nerve stimulation may achieve concentrations of the (-)-enantiomer within the adrenergic synapse greatly in excess of those found in plasma. Such a mechanism could significantly influence both the intensity and duration of beta receptor blockade in the heart, blood vessels, brain and other target tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis of 4'-hydroxypropranolol sulfate, a major non-beta-blocking propranolol metabolite in man.

4'-Hydroxypropranolol sulfate was recently identified as a major metabolite of propranolol (Inderal). In order to confirm the structure and to further study disposition and biological activity, we have synthesized 8 with use of 1,4-naphthoquinone as the starting material. Reduction and alkylation with benzyl iodide gave 4-(benzyloxy)naphthol. Sulfation and chlorosulfuric acid in N,N-dimethylaniline gave potassium 1-(benzyloxy)-4-naphthol sulfate. Catalytic hydrogenation, alkylation with [[[(trifluoromethyl)sulfonyl]oxy]methyl]oxirane, and amination in isopropylamine gave 8. Racemic 8 was found to be 100-1000 times less potent than racemic propranolol as a beta-adrenergic receptor blocking agent in the dog.

Effects of captopril on limiting infarct size in conscious dogs.

The effects of angiotensin-converting enzyme inhibitor captopril on infarct size and cardiovascular hemodynamics were studied in 35 conscious dogs subjected to 24 h of coronary occlusion. Following occlusion of the left anterior descending coronary artery, 10 dogs were infused with captopril 0.25 mg/kg/h i.v. (group 1), eight dogs received captopril 0.5 mg/kg/h i.v. (group 2), and 17 dogs served as saline-infused controls. All infusions were started 10 min following occlusion and continued for 15 h. Eighty-eight percent of untreated dogs and 80% of group 1 captopril dogs survived the 24-h duration of the study. No experimental deaths occurred in group 2 captopril dogs. Arterial blood pressure had decreased 10-12 mm Hg in both captopril groups by 4 h and remained relatively stable for the remainder of the study period. In untreated dogs, blood pressure was unchanged for 6 h, then began a gradual decline. There were no significant differences in infarct size among the groups. When infarct size is expressed as percent of left ventricle at risk the values were: control, 39.9 +/- 5.6; captopril group 1, 44.8 +/- 4.9; and captopril group 2, 43.8 +/- 7.8%. Creatine kinase levels were not different among the groups. Heart rate and incidence of arrhythmias also did not differ among the groups. These data show that captopril had no detrimental or beneficial effects on infarct size or on cardiovascular hemodynamics associated with myocardial infarction in conscious dogs.

Exercise-induced increments in plasma levels of propranolol and noradrenaline.

Exercise-induced changes in the plasma levels of propranolol and noradrenaline were determined in nine volunteers. Total plasma propranolol levels were increased during submaximal treadmill exercise, with exercise-induced increments of 13 +/- 4% at 4 h after the last dose, 18 +/- 7% at 9 h and 41 +/- 5% at 16 h. Exercise-induced increments in plasma propranolol were observed after single as well as repeated doses. During exercise, increments in plasma propranolol were correlated temporally with changes in plasma noradrenaline. Exercise-induced increments in plasma noradrenaline were greater during propranolol administration than during placebo periods. The changes in plasma propranolol concentration during exercise may reflect a redistribution of propranolol at its site(s) of action.

Myocardial sensitivity to isoproterenol following abrupt propranolol withdrawal in conscious dogs.

The sensitivity of the cardiovascular system to isoproterenol following abrupt cessation of propranolol administration was studied in chronically instrumented conscious dogs pretreated orally with propranolol for 14 days. The effects of intravenous isoproterenol on heart rate, blood pressure, and mean velocity of circumferential fiber shortening (Vcf) were determined before and during propranolol administration and then at 12 hr intervals following drug withdrawal. During propranolol administration, all dose-response curves to isoproterenol were predictably shifted to the right. Twenty-four hours following propranolol withdrawal, when plasma levels of drug averaged only 7 ng/ml, the chronotropic response to isoproterenol remained significantly inhibited. In contrast, the Vcf response recovered rapidly and at 24 hr equaled the pretreatment control response. Furthermore, between 36 and 60 hr, when plasma propranolol levels averaged less than 1 ng/ml, the Vcf dose-response curve to isoproterenol was shifted to the left of control prior to returning to the pretreatment level. This leftward displacement of the Vcf response curve was not accompanied by a parallel change in the heart rate response or in afterload. Plasma norepinephrine levels were measured throughout the study and were not altered during drug treatment or following withdrawal. Thus, the data indicate that abrupt cessation of propranolol administration is associated with a period of increased myocardial sensitivity to at least the inotropic effects of isoproterenol and that abrupt withdrawal does not result in acute changes in sympathetic nervous system activity.

The effects of perhexiline on the sympathetic nervous system.

The effects of perhexiline on sympathetic nervous system function were studied in vitro and in vivo. Perhexiline decreased the field stimulation-induced contractile response of the isolated vas deferens and significantly decreased the quantity of norepinephrine released during stimulation of this preparation. In vivo studies in dogs showed that perhexiline reduced the heart rate response to cardiac accelerator nerve stimulation, an effect not associated with an increase in cholinergic tone or beta adrenergic blockade. Measurements of norepinephrine released from the heart during cardiac nerve stimulation showed that perhexiline (3 mg/kg) decreased norepinephrine release by approximately 35%. These results suggest that a presynatpic effect of perhexiline, which results in a decrease in norepinephrine release, contributes significantly to the attenuated heart rate response which occurs after administration of this drug. A decrease in transmitter release during sympathetic stimulation could play an important role in the mechanism for the protective effects of perhexiline in myocardial ischemic damage.

Studies on the relationship between ST-segment elevations and extent of infarction following coronary artery occlusion in dogs.

Epicardial ST-segment alterations were determined 15 min. following acute ligation of the left anterior descending coronary artery in dogs, and the extent of the left ventricular wall infarcted at each mapping site was determined 24 hours later. A close correlation was observed between the ST-segment elevation and the percent of left ventricular wall infarcted (r = .891; P less than .001) at the same mapping site. A significant portion of the left ventricular wall remained viable at sites with less than 8 mV elevation; however, the chance of transmural infarction became high at sites with elevations greater than 10 mV. It may be that sites with less than 10 mV elevation in the epicardial ST-segment elevation are ischemic areas where pharmacologic interventions designed to limit infarct size have the greatest change of success.

Experimental spinal cord trauma, III: Therapeutic effect of immobilization and pharmacologic agents.

A wide variety of pharmacologic agents has been suggested to serve as therapeutic adjuncts in the management of acute spinal cord trauma. The present study was conducted to determine what effect, if any, these agents have when they are added to immobilization of the spinal column, the most widely used clinical measure. Rhesus monkeys were subjected to different levels of experimental spinal cord injury with and without subsequent immobilization by means of a figure of eight ligature. In the control group, five of six animals impacted at 500 gm-cm were paraplegic. In the immobilized animals, three of four animals impacted at 500 gm-cm recovered completely and the fourth was only mildly paraparetic. Paraplegia could not be uniformly produced in this group until 800 gm-cm forces were routinely employed. In the second phase of the study, only immobilized animals were used, with and without drug therapy. No change in the force-injury curve, above and beyond that from immobilization, can be demonstrated for monkeys given dextran, phenobarbital, methyldopa, phenoxybenzamine or vasopressors. The pathophysiologic concepts upon which such agents are advocated should be reassessed. Spinal immobilization can significantly improve the clinical outcome following experimental spinal cord injury, it may also serve to control some of the variability previously observed in pharmacologic experiments.

Studies of the interrelationship between plasma norepinephrine, plasma renin activity and acute myocardial infarction in dogs.

Serial determinations of plasma norepinephrine and renin activity were made in dogs following acute ligation of the left anterior descending coronary artery. Increases in both substances closely paralleled increases in creatine phosphokinase activity, heart rate and the incidence of ventricular premature contractions. Following acute myocardial infarction, significant correlations were found to exist between plasma norepinephrine and plasma renin activity and between the levels of these vasoactive substances and the measured indices of ischemic damage. These data suggest that changes in vasoactive systems associated with myocardial infarction may contribute to the extent of ischemic injury.

Nitroglycerin and propranolol on myocardial O2 consumption during myocardial ischemia.

The effects of i.v. and intracoronary (i.c.) nitroglycerin, i.v. propranolol, and the combination of propranolol and nitroglycerin on myocardial oxygen consumption (MVO2) and lactate utilization were studied in situ ischemic working dog hearts. I.v. nitroglycerin reduced MVO2 9% which was associated with the peripheral vasodilatory actions of the drug. I.c. nitroglycerin which had no detectable effects on the peripheral vasculature had no significant effect on MVO2. I.v. propranolol caused an 8% reduction in MVO2 and this action was associated with a negative chronotropic and a slight negative inotropic effect. However, the combination of propranolol and nitroglycerin which was more effective than either drug alone, reduced MVO2 18% thereby indicating that the effects of the two drugs on oxygen consumption are additive. These results support the concept that the reduction of MVO2 seen with nitroglycerin is principally due to peripheral vasodilatory actions of the drug while that seen with propranolol is due to that drug's effect on the heart and the effects of the two agents are complementary.

Effects of perhexiline on survival time and infarct size in experimental myocardial infarction.

The effects of perhexiline on survival time and infarct size were studied in three animal models. Dogs pretreated orally with perhexiline, 200 mg/day/14 days, and monitored under anesthesia for 30 hours after ligation of the left anterior descending coronary artery (LAD) had infarct weights of 9.1+/-1.9 g as compared to 15.2+/-1.0 g in paired untreated controls (P less than .02). Twelve of 15 perhexiline-pretreated dogs survived the duration of these studies while only 5 of 15 control animals survived for the same period of time (P less than .05). Serum creatine phosphokinase activity was significantly lower in the treated dogs at 9, 12 and 15 hours after ligation (P less than .05). Conscious dogs, pretreated orally with perhexiline 200 mg/day/7 days or 400 mg/day/7 days and monitored without anesthesia or analgesia for 72 hours after coronary ligation had smaller infarcts (P200=26+/-5; P400=26+/-4; C=39+/-5 g; P less than .05) lower plasma peak creatine phosphokinase activity (P less than .05) and reduced heart rate (P400=198+/-8; C=226+/-8 beats/min; P less than .05) and reduced incidence of ventricular ectopic beats (P less than .05). In pentobarbital anesthetized open-chest dogs, perhexiline (3 mg/kg i.v.) reduced the sum of S-T segment elevation after left anterior descending coronary artery occlusion from 32+/-3 to 14+/-1 mV (P less than .001); this effect was associated with and/or preceded by a reduction in arterial pressure (101+/-4 to 78+/-5 mm Hg; P less than .001) and heart rate (151+/-8 to 138+/-7 beats/min P less than .025; Circumflex flow increased from 38+/-4 to 83+/-8 ml/min (P less than .01). In noninfarcted open-chest dogs, perhexiline administration (3 mg/kg i.v.) resulted in increases in coronary blood flow, narrowing of arterial-coronary sinus O2 difference and a 14% reduction in myocardial O2 consumption. The protective effects of perhexiline on the ischemic myocardium appear to result from reductions in heart rate and associated decrease in myocardial O2 demand as well as an antiarrhythmic effect.

A positive inotropic effect of propranolol on the canine myocardium: a presynaptic effect.

Administration of propranolol directly into the anterior descending branch of the left coronary artery (LAD) resulted in a localized increase in myocardial contractile force in the area of the left ventricle perfused by the LAD. The onset of the positive inotropic response occurred within 30 seconds after drug administration with a duration of action of approximately 8 minutes and was associated with a significant increase in the coronary sinus/arterial ratio of norepinephrine. Contractile force in an area of the left ventricle perfused by the circumflex artery decreased concomitantly with the characteristic negative chronotropic action of propranolol. Pretreatment with reserpine abolished the positive inotropic effect of propranolol while ganglionic blockade with hexamethonium failed to alter the character of the response. Imipramine pretreatment not only blocked the positive inotropic effect of propranolol but resulted in an exaggerated negative inotropic effect in both areas of the left ventricle along with a significant fall in systemic arterial blood pressure. The data demonstrate that propranolol can evoke the release of norepinephrine from cardiac adrenergic nerve endings and raise the possibility that propranolol may be taken up by the amine uptake system.

Altered levels of PGF in cat spinal cord tissue following traumatic injury.

Previous studies by others indicated that PGs were present in brain, spinal cord, and c.s.f. of several mammalian species. In the present study we compared levels of PGE and PGF by R.I.A. in spinal cord tissue from traumatized cats and cats pretreated with indomethacin prior to trauma to those of baseline and sham operated controls in order to assess for the first time, to our knowledge, whether meaningful changes in levels of PGE and PGF could be detected which might shed new light on the etiology of spinal cord trauma. Levels of PGF (nanograms/gram wet wt) in the cord segment immediately adjacent to the point of trauma were 8.05 +/- 1.50, and 13.13 +/- 1.38 for baseline and sham operated cats respectively. Spinal trauma led to more than a 100% increase in PGF levels to 29.26 +/- 3.58. Although pretreatment with indomethacin 30 min prior to trauma gave the expected blockade of the PGF response to trauma, a measurable level of PGF (2.55 +/- 0.17) was found in the cord after indomethacin. Cord levels of PGF declined after 3 hr in both sham operated and traumatized animals. PGF was maximally stimulated by trauma during the first 3 hr with little effect at 72 hr. Although carefully examined, PGE levels in cat spinal cord appeared to be virtually unaffected by trauma. These findings clearly demonstrate for the first time that traumatic injury to the spinal cord is accompanied by marked increases in PG levels at the site of trauma, and that the observed elevation in PGF in response to trauma can be blocked by indomethacin in vivo. Whether PGF changes are causally related to the etiology of spinal cord trauma, or merely represent a manifestation of PG release as a result of non-specific tissue injury, remains to be seen.