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Biomedical subjects

H R Kaplan

Publications and source records attributed to H R Kaplan.

15 recordsLinked to original sources
PubMed1992

Reduction of canine myocardial infarct size by CI-959, an inhibitor of inflammatory cell activation.

CI-959, a cell-activation inhibitor that prevents the formation of oxygen-derived free radicals by inflammatory cells, was studied to determine its effects on myocardial infarct size and subsequent scar formation in dogs. The left circumflex coronary artery was occluded for 90 min, followed by 6 h of reperfusion. Drug infusion was started 15 min before reperfusion at a loading dose of 8 mg/kg i.v., followed immediately by 2 mg/kg i.v. infused over 80 min. The infarct size, assessed by TTC staining techniques, was significantly reduced in 12 dogs treated with CI-959 (23.3 +/- 3.6% of the area at risk) when compared to 11 vehicle-treated animals (35.5 +/- 4% of the area at risk, p less than 0.05). This reduction in infarct size was not attributed to changes in regional myocardial blood flow, as measured by radioactive microspheres, or to a reduction in myocardial oxygen demand, as estimated by changes in the rate-pressure product. The scar thickness, measured after a 6-week recovery period in 9 animals treated with CI-959, was not significantly reduced in comparison with 11 controls. In vitro, CI-959 effectively inhibited oxygen free radical formation by canine neutrophils. The results of this study show that CI-959 significantly reduces the myocardial infarct size without causing scar thinning, which might lead to ventricular aneurysm, and suggests the most likely mechanism for its beneficial action is the prevention of formation of toxic oxygen radicals.

Animals↗
PubMed1990

Quinapril: overview of preclinical data.

Quinapril hydrochloride, a new, orally active, nonpeptide, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor, has been studied extensively in a variety of in vitro and in vivo animal models. Quinapril inhibits the contractile and pressor effects of angiotensin I in rabbit aorta and in rats, respectively, and lowers blood pressure in both high- and normal-renin rodent and diuretic-treated dog models of hypertension. No tolerance to the antihypertensive effects of quinapril was noted in spontaneously hypertensive rats treated with quinapril for up to 14 consecutive days. As with other ACE inhibitors, quinapril had virtually no effect on the development of hypertension in the renin-independent one-kidney deoxycorticosterone (DOCA)-salt hypertensive rat. Antihypertensive activity best correlates with the inhibition of tissue (vascular) ACE, and thus the reduction in peripheral vascular resistance associated with plasma and tissue ACE most likely accounts for the therapeutic benefit of quinapril. Preliminary data from a trial of quinapril in cardiomyopathic hamsters show that the drug prevents the anticipated decline in left ventricular contractile function and retards the temporal progression of left ventricular failure. ACE inhibitors have been found to have a lipid-neutral profile, unlike some other classes of antihypertensives. Quinapril is rapidly absorbed and extensively distributed to all tissues except brain. It is rapidly hydrolyzed to quinaprilat, its pharmacologically active diacid form. Metabolism to other compounds is not extensive. Quinapril's preclinical toxicologic profile is similar to that of other ACE inhibitors. Long-term toxicology studies show that quinapril is not teratogenic, carcinogenic, or mutagenic.

Aged↗
PubMed1989

Quinapril--a preclinical review of the pharmacology, pharmacokinetics, and toxicology.

Quinapril is an orally active, non-peptide, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor that acts potently and specifically to interrupt the conversion of angiotensin I to angiotensin II in both plasma and tissue. Quinapril is enzymatically hydrolyzed to a pharmacologically active diacid form quinaprilat. Quinapril is efficacious in hypertensive models exhibiting both high (renal hypertensive rats, diuretic-treated dogs) and normal (spontaneously hypertensive rats) plasma renin activity. Quinapril does not prevent the development of hypertension when plasma renin activity (PRA) is markedly suppressed as in the deoxycorticosterone-saline treated rat. Hemodynamic studies in dogs indicate that quinapril decreases total peripheral and renal vascular resistance. Quinaprilat produces natriuresis and mild diuresis at doses that do not alter mean arterial blood pressure. Quinapril has the potential to affect plasma lipids beneficially or at least be "lipid neutral." Oral absorption of quinapril is rapid in rats, dogs, and monkeys. There is rapid and extensive distribution of radiolabel to most tissues except brain. Plasma radiolabel concentration-time profiles exhibit polyexponential decay with a prolonged terminal phase at low concentrations in all species. Metabolism to compounds other than quinaprilat is not extensive. Quinapril is excreted primarily as quinaprilat and to a lesser degree as quinapril. Quinapril is well tolerated in a variety of pharmacologic safety screens and its toxicity profile is similar to that of other ACE inhibitors. Quinapril does not adversely affect reproduction; it is not teratogenic, carcinogenic, or mutagenic.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1987

Subclasses of cyclic AMP phosphodiesterase in cardiac muscle.

Canine and guinea-pig left ventricular muscle contains multiple molecular forms of phosphodiesterase (PDE) which vary according to substrate specificity, stimulation by calmodulin and response to various selective and nonselective phosphodiesterase inhibitors. Both species possess a cyclic AMP-specific form of phosphodiesterase (PDE III). In the dog, both soluble and particulate forms of PDE III are present. The particulate form of PDE III is potently inhibited by cyclic GMP and the selective PDE III inhibitors imazodan (CI-914) and cilostamide, but is only weakly inhibited by the selective PDE III inhibitors Ro 20-1724 and rolipram. In contrast, the soluble form of PDE III in canine left ventricle is only weakly inhibited by cyclic GMP, imazodan and cilostamide, but is potently inhibited by Ro 20-1724 and rolipram. Guinea-pig left ventricle contains only one subclass of PDE III, which is potently inhibited by cyclic GMP, imazodan and cilostamide, but not by Ro 20-1724 or rolipram. However, whereas the imazodan-sensitive subclass of PDE III is a particulate enzyme in the canine left ventricle, in the guinea-pig this subclass of PDE III is a soluble enzyme. Both soluble and particulate PDE III's are (i) insensitive to calmodulin; (ii) possess comparable Km and Vmax values for hydrolysis of cyclic AMP; (iii) are equally inhibited by the nonselective PDE inhibitor theophylline, and (iv) are eluted from DEAE-cellulose anion-exchange resin by comparable concentrations of sodium acetate. The demonstration of distinct subclasses of the cyclic AMP-specific phosphodiesterase (PDE III) in canine left ventricular muscle associated with different domains of the cell suggests compartmentation of cyclic AMP. In addition, the observation that the imazodan-sensitive form of PDE III is a particulate enzyme in canine left ventricle and a soluble enzyme in guinea-pig left ventricle may explain the species differences which exist regarding the positive inotropic response to imazodan in these two species.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

Subclasses of cyclic AMP-specific phosphodiesterase in left ventricular muscle and their involvement in regulating myocardial contractility.

Ventricular muscle contains a low Km, cyclic AMP-specific form of phosphodiesterase (PDE III), which is believed to represent the site of action for several of new cardiotonic agents including imazodan (CI-914), amrinone, cilostamide, and enoximone. However, species differences in the inotropic response to these agents have raised questions about the relationship between PDE III inhibition and cardiotonic activity. The present study demonstrates that these differences can be accounted for by the presence of two subclasses of PDE III in ventricular muscle and variations in the intracellular localization of these two enzymes. For these experiments, PDE III was initially isolated from canine, guinea pig, and rat left ventricular muscle. The results demonstrate that canine left ventricular muscle contains two functional subclasses of PDE III: an imazodan-sensitive form, which is membrane bound, and an imazodan-insensitive form, which is soluble. Although only weakly inhibited by imazodan, this latter enzyme is potently inhibited by the selective PDE III inhibitors, Ro 20-1724 and rolipram. Guinea pig ventricular muscle also contains the imazodan-sensitive subclass of PDE III. Unlike canine left ventricle, however, thi enzyme is soluble in the guinea pig. No membrane-bound subclass of PDE III was observed in the guinea pig. Rat left ventricle possesses only the soluble form of PDE III, which apparently represents a mixture of the imazodan-sensitive and imazodan-insensitive subclasses of PDE III. Measurement of in vivo contractility in these three species showed that imazodan exerts a potent positive inotropic effect only in the dog, in which the imazodan-sensitive subclass of PDE III is membrane bound.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1986

Pharmacology of bevantolol hydrochloride.

Bevantolol is a cardioselective, beta-adrenoreceptor antagonist, devoid of intrinsic beta sympathomimetic activity and with weak membrane-stabilizing and local anesthetic properties. The 3,4-dimethoxyphenylethylamino moiety, substituted on the side chain amine function, confers cardioselectivity, which has been confirmed by a number of experiments. In vitro, bevantolol demonstrated greater antagonism of atrial than tracheal responses to isoproterenol. In vivo, bevantolol preferentially inhibited isoproterenol-induced tachycardias in conscious and anesthetized dogs, compared with the nonselective agent propranolol. Conversely, its effect on blood pressure after isoproterenol was minimal compared with propranolol, reflecting its muted effect on beta 2 peripheral receptors. A functional difference between bevantolol and propranolol was demonstrated in histamine-challenged guinea pigs. Bevantolol had little effect on the antiasthmatic effect of isoproterenol, whereas propranolol blocked it totally. Bevantolol's lack of intrinsic sympathomimetic activity was demonstrated in normal and reserpinized dogs, where it was devoid of intrinsic sympathomimetic activity at doses up to 10 mg/kg. Similarly, intravenous doses of 10 mg/kg had to be administered before direct myocardial depression occurred in the reserpinized animals. Metabolite 3, which is excreted in trace amounts in human urine, demonstrates intrinsic sympathomimetic activity when administered in pharmacologic doses to dogs; however, any clinical relevance remains to be established. Several laboratories have demonstrated that bevantolol interacts at alpha-adrenergic sites. These data require further investigation. The dose-related antihypertensive effect of bevantolol has been demonstrated in spontaneously hypertensive and 2 kidney, 1 clip renal hypertensive rats. Animal experiments also suggest that bevantolol may be useful in angina: It caused a favorable redistribution of blood flow in dogs in which the left circumflex artery had been stenosed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1986

Bevantolol hydrochloride--preclinical pharmacologic profile.

Bevantolol hydrochloride, a beta adrenoceptor antagonist, can be categorized using conventional schemes as being cardioselective, devoid of intrinsic sympathomimetic activity and having weak membrane-stabilizing and local anesthetic properties. The cardioselectivity of bevantolol was conferred by the incorporation of a 3,4-dimethoxyphenyl moiety into the terminal amino portion of the molecule. This portion of the molecule also appears to account for bevantolol's in vitro binding affinity at alpha-adrenoceptor sites; the in vivo significance of which remains unclear. In the various cardiovascular disease-state models, bevantolol's profile differed from that of propranolol, i.e., there was no initial pressor response in spontaneously hypertensive or renal hypertensive rats. In a myocardial ischemia model, bevantolol, unlike propranolol, increased contractile function in the ischemic myocardium. A ring hydroxylated urinary metabolite, which occurred only in trace amounts in human urine, had an interesting profile when studied in animals at pharmacologic doses. It ranked high in cardioselectivity (like bevantolol), but unlike bevantolol showed significant intrinsic beta sympathomimetic activity. The clinical significance of this metabolite, if any, remains to be established. Collectively the preclinical profile of bevantolol showed it to have an interesting profile for a beta adrenoceptor antagonist in a variety of pharmacologic test systems.

Adrenergic beta-Antagonists↗
PubMed1979

Repeat abortions: blaming the victims.

A study of 1,505 women obtaining abortions in a freestanding abortion clinic in Western New York state revealed that women having repeat abortions were more likely to be using contraception at the time of conception than women having first abortions. However, nearly one-half the non-contracepting repeaters were not contracepting at the time of the repeat pregnancy. Repeaters who were not contracepting at the time of the repeat pregnancy listed medical contraindications or lack of supplies as the major reasons for not contracepting at the time of the present conception--indicating that they had tried one or more methods since their first abortion. Repeaters were sexually more active than first timers, thus increasing their statistical risk of unwanted pregnancy even as they contracepted more than first timers. The data indicate that both first timers and repeaters overwhelmingly reject the premise that abortion is a primary or even a back-up birth control method. The essential difficulty for repeaters appears to be that they are victims of technological, organizational, and logistical inadequacies as well as statistical probabilities rather than being motivationally deficient or indifferent to the dangers of unprotected sexual intercourse.

Abortion, Legal↗
PubMed1978

l-Bunolol and propranolol: oral and intravenous beta-adrenoceptor blocking activity in rats compared to dogs and humans.

To determine the pharmacological significance of reported differences between species in l-bunolol metabolism, oral and intravenous beta-adrenoceptor blocking activity against an isoproterenol-induced tachycardia was compared in dogs, rats, and humans. Propranolol was similarly studied in rats and dogs. Species differences in intravenous potency were minimal for both compounds in contrast to oral dose studies. Oral to intravenous ratios of doses causing a comparable degree of beta-adrenoceptor blockade after l-bunolol were: rat, 212; dog 4; and human, 5. For propranolol, the oral to intravenous dose ratios were 210 and 32 for the rat and dog, respectively. These pharmacological findings show major differences in the rat compared to dogs and humans and may be explained in part by differences in the urinary excretion patterns of l-bunolol in the various species.

Administration, Oral↗
PubMed1977

Levo-bunolol and propranolol: further evaluation of oral beta-blocking activity in conscious dogs.

The oral beta-adrenoceptor blocking activity of bunolol, propanolol, and their levo-isomers was compared against isoproterenol- and treadmill exercise-induced tachycardias in normal conscious dogs. Relative potencies against isoproterenol were (ascending order): propranolol=1, levo-propranolol=2, bunolol=40, and levo-bunolol=102. Large oral doses of levo-bunolol and propranolol suppressed exercise tachycardia by only 18% (range 10 to 22%). Compared to the isoproterenol response, the tachycardia associated with severe exercise in the healthy trained dog was largely resistant to beta-receptor blockade showing factors other than beta-receptor stimulation to be involved. Differences in duration of beta-blockade were observed at equiactive doses of levo-bunolol and propranolol. The isoproterenol response had returned to greater than 50% of control by 12 hr after propranolol but was less than 10% of control at 12 hr after levo-bunolol. The time to 50% recovery of the exercise tachycardia was 24 hr after levo-bunolol and 6 to 9 hr after propranolol. The results show oral levo-bunolol to be considerably more potent and to have a longer duration of action than propranolol in inhibiting both isoproterenol and exercise-induced tachycardias in conscious dogs.

Administration, Oral↗
PubMed1976

Sympathomimetic drugs: evaluation for acute central hypotensive activity in alpha-chloralose-anesthetized dogs and cats intravertebral artery administration,.

dl-Amphetamine, phentermine and their para-chloro derivatives were tested for acute central hypotensive activity after intra-vertebral artery (iva) infusions in alpha-chloralose-anesthetized cats and intact and carotid sinus denervated dogs. Iva clonidine (reference standard) caused immediate reductions in blood pressure and heart rate and carotid sinus denervation (CSD) enhanced the clonidine response. dl-Amphetamine and phentermine did not cause acute hypotensive responses in the dog or cat whereas their para-chloro derivatives did. The vasodepressor response to para-chloramphetamine was inconsistent and transient and not modified by CSD. The magnitude and duration of the chlorphentermine vasodepressor response was minimal in the intact and CSD dog compared to clonidine. In contrast, chlorphentermine in the cat (140-300 mug/kg) caused an acute hypotensive response comparable in magnitude to clonidine (0.6-1.0 mug/kg). The bradycardias observed after iva chlorphentermine were much less pronounced than those associated with iva clonidine at comparable vasodepressor doses. By the i.v. route, each drug caused only pressor responses in the dog and cat. Suppression of the pressor response (resulting from "spill-over" of these alpha-stimulants into the systemic circulation after iva dosing) in the dog with small doses of i.v. phenoxybenzamine did not unmask or enhance the vasodepressor or bradycardic actions to iva administration of drugs. Methysergide prevented the hypotensive response to chlorphentermine in the cat and partially suppressed the response to clonidine; the reverse was true after piperoxan. Lilly 110140 and para-chlorophenylalanine reduced or abolished the effects of iva chlorphentermine. In summary, (1) iva chlorphentermine and clonidine were the only alpha-sympathomimetics tested which were effective as hypotensive substances; (2) the cat was considerably more responsive to iva chlorphentermine than the intact or CSD dog; (3) iva clonidine was more bradycardic than iva chlorphentermine; and (4) both adrenergic and serotonergic components appear to be among the mechanisms involved in the acute iva hypotensive response to chlorphentermine in the cat.

Anesthesia↗
PubMed1975

Hemoglobin solution: a potential oxygen transporting plasma volume expander.

The potential of a 6% stroma-free human hemoglobin solution (WXb8326) as a plasma volume expander with oxygen transport capabilities was evaluated in barbiturate-anesthetized spontaneously breathing dogs. WXb8326 compared favorably with dextran-70 and 5% albumin solution as a plasma volume expander. Serial phlebotomies to a blood pressure of 35 mm Hg and immediate replacement with the above colloid expanders showed that only WXb8326-exchanged dogs survived acute reductions in hematocrit to critical levels of smaller than or equal to 5%. After several exchanges with WXb8326 to levels as low as 1%, it was possible to demonstrate acute survival. With less drastic reductions in the hematocrit (between 5 and 10%) all dogs survived acutely regardless of the type of plasma volume expander used; however, subacute survival rates varied. Oxygen transport characteristics during isovolumic hemodilution (phlebotomy and simultaneous replacement with WXb8326) were studied in a separate series of spontaneously breathing dogs in which hematocrit was reduced to approximately 50% of control. Oxygen content of erythrocytic hemoglobin (EHb) and extraerythrocytic hemoglobin (EEHb) resulting from infusions of WXb8326 was studied in arterial and venous blood at different levels of hemodilution. WXb8326 did not interfere with the arterial oxygen saturation of EHb in the pulmonary vascular bed and EEHb was oxygenated as efficiently as EHb. Oxygen delivery to tissues differed between EHb and EEHb. Erythrocytic hemoglobin met oxygen demands under basal conditions while EEHb contributed oxygen to tissues during conditions of high oxygen extraction. It is concluded that WXb8326 is an attractive condidate as a plasma volume expander with the capacity to transport oxygen to tissues.

Anemia↗
PubMedDate not supplied

Multiple molecular forms of phosphodiesterase and the regulation of cardiac muscle contractility.

Two approaches were taken to examine the role which the different forms of phosphodiesterase present in cardiac muscle play in regulating contractility. In an initial study, the effect of selective inhibitors of i) the calmodulin-stimulated phosphodiesterase (M & B 22, 948), ii) the cyclic GMP-stimulated phosphodiesterase (dipyridamole), and iii) the low Km, cyclic AMP-specific phosphodiesterase (imazodan) on the contractility of isolated guinea pig left atria was examined. Of the three selective phosphodiesterase inhibitors, only imazodan increased atrial contractility. In a subsequent study, the effect of imazodan on in vivo contractility was evaluated. Imazodan was found to potently increase contractility in the dog and the Rhesus monkey, while exerting only modest-to-minimal effects of contractility in the guinea pig and the hamster. Imazodan produced no positive inotropic effect in the rat. These species differences can apparently be attributed to i) the presence of subclasses of the low Km, cyclic AMP-specific phosphodiesterase (PDE III) in cardiac muscle, one of which is potently inhibited by the selective PDE III inhibitors imazodan, cyclic GMP and cilostamide, and the other which is selectively inhibited by rolipram and Ro 20-1724, and ii) variations in the intracellular localization of imazodan-sensitive subclass of PDE III. Thus, the maximum inotropic response to imazodan was observed only in those species in which the imazodan-sensitive subclass of PDE III was present and was membrane-bound, e.g., Rhesus monkey and dog. In the dog, the imazodan-insensitive subclass PDE III does not appear to play an important role in regulating cardiac contractility. These observations provide further support for the hypothesis that the inotropic response to imazodan, amrinone and related cardiotonics is due to their inhibitory effects on the cyclic AMP-specific form of phosphodiesterase, and also provides new insight into the relationship between cyclic AMP, phosphodiesterase and myocardial contractility.

3',5'-Cyclic-AMP Phosphodiesterases↗