Suzanne Moreland

Dihydropyrimidine calcium channel blockers : 2-heterosubstituted 4-aryl-1,4-dihydro-6-methyl-5-pyrimidinecarboxylic acid esters as potent mimics of dihydropyridines

To enhance the intrinsic potency of dihydropyrimidine calcium channel blockers, we have modified the structure of previously described 2-heteroalkyl-1,4-dihydropyrimidines 2 to 3-substituted 1,4-dihydropyrimidines 3. Structure-activity studies using potassium-depolarized rabbit aorta show that ortho, meta-disubstituted aryl derivatives are more potent than either ortho- or meta-monosubstituted compounds. While vasorelaxant activity was critically dependent on the size of the C5 ester group, isopropyl ester being the best, a variety of substituents (carbamate, acyl, sulfonyl, alkyl) were tolerated at N3. Our results show dihydropyrimidines 3 are significantly more potent than corresponding 2-heteroalkyl-1,4-dihydropyrimidines 2 and only slightly less potent than similarly substituted 2-heteroalkyl-1,4-dihydropyridines 4 and 5. Whereas dihydropyridine enantiomers usually show 10-15-fold difference in activity, the enantiomers of dihydropyrimidine 3j show more than a 1000-fold difference in activity. These results strengthen the requirement of an enamino ester for binding to the dihydropyridine receptor and indicate a nonspecific role for the N3-substituent.

Pharmacologic profile of the dihydropyrimidine calcium channel blockers SQ 32,547 and SQ 32,946

SQ 32,926 and SQ 32,547, two dihydropyrimidine calcium channel blockers, were characterized as potent inhibitors of depolarization-induced contractions of isolated smooth muscle preparations. In rat aorta, the IC50 values were 5.5 nM for SQ 32,547 and 8.1 nM for SQ 32,926, values which compare favorably with that of 2.9 nM for nifedipine. The dihydropyrimidines were also tested in a model of stable angina: pacing-induced ischemia in dogs. Both SQ 32,547 and SQ 32,926 reduced the ST-segment elevation observed in vehicle-treated animals. No significant changes in hemodynamic status were detected, suggesting that a reduction in cardiac work secondary to afterload reduction was probably not a major contributor to the protective effects. Neither was increased coronary blood flow important for the antiischemic outcome because no significant effects of the dihydropyrimidines were observed on ischemic regional blood flow. SQ 32,547 was also studied in globally ischemic, isolated rat hearts. In this model, SQ 32,547 was protective because it significantly reduced contracture formation and lactate dehydrogenase (LDH) release. Washing out the effect of SQ 32,547 in isolated hearts and smooth muscles was difficult, presumably due to its lipophilicity. In the smooth muscle preparations, the effects of both nifedipine and SQ 32,926 were much more easily washed out. As with other calcium channel blockers, increasing the antiischemic effects of SQ 32,547 was associated with a higher cost in terms of cardiac function. In summary, the two novel dihydropyrimidines, SQ 32,547 and SQ 32,926, showed antiischemic properties in animal models.

Orally Active Endothelin Receptor Antagonist BMS-182874 Suppresses Neointimal Development in Balloon-Injured Rat Carotid Arteries

Vascular smooth muscle cell (SMC) proliferation is an important component in the development of restenosis. Because endothelin (ET) has been reported to act as an SMC mitogen, we postulated that the orally active ETA receptor antagonist BMS-182874 would suppress the development of the intimal lesion that develops in rat carotid arteries after balloon injury. Using cultured rat aortic SMC, we noted that ET-1-stimulated increases in [3H]thymidine incorporation were blocked by BMS-182874. To determine the effect of the drug on intimal lesion formation, we treated rats with BMS-182874 (100 mg/kg orally, p.o.) or vehicle once daily for 3 weeks, beginning 1 week before balloon injury. Two weeks after injury, drug-treated rats had a 35% decrease in lesion area and a 34% decrease in the lesion/media ratio as compared with the vehicle-treated rats. In situ hybridization (ISH) analysis of balloon-injured rat carotid arteries showed an increase in ETA receptor mRNA. These data support the concept that ETA receptor activation contributes to intimal lesion formation by promotion of SMC proliferation and suggest a potential use for ETA receptor antagonists in the amelioration of hyperproliferative vascular diseases, including restenosis.

Apparent dissociation between myosin light chain phosphorylation and maximal velocity of shortening in KCl depolarized swine carotid artery: effect of temperature and KCl concentration

Stimulation of swine carotid artery medial fibers with 110 mM KCl at 37°C results in increases in myosin light chain (MLC) phosphorylation levels and maximal shortening velocity (Vo) during the period of stress development. During the period of stress maintenance, MLC phosphorylation levels andVo are not maintained, but fall to suprabasal levels, resulting in a correlation between MLC phosphorylation andVo and suggesting that MLC phosphorylation regulatesVo. This study identifies other conditions of KCl depolarization of swine carotid medial fibers in which this relationship between MLC phosphorylation andVo is altered. A decrease in temperature from 37° to 23°C results in a similar magnitude of stress maintenance in response to 110 mM KCl and similar levels of MLC phosphorylation, but a reduction inVo by approximately 50%. This differential effect of temperature onVo and MLC phosphorylation results in a downward shift in the slope of the regression line describing the relationship between these two parameters. Decreasing [KCl] to 40 mM in the stimulating solution results again in similar magnitudes of miantained stress. MLC phosphorylation levels are not transient, but maintained at a constant value andVo is transient at levels approximately 50% of those at 110 mM KCl at 37°C. This results in a complete lack of correlation between MLC phosphorylation andVo. Thus stress can be developed to equal magnitudes under differing activation conditions with dissimilar patterns of MLC phosphorylation andVo. Therefore, there is not a strict relationship between MLC phosphorylation andVo in all cases.

Effects of neutral endopeptidase inhibition on the clearance of exogenously administered endothelin in Sprague-Dawley rats.

The effects of the selective neutral endopeptidase (EC 3.4.24.11, NEP) inhibitor SQ 28,603 on endogenous plasma endothelin (ET) concentration and on the clearance from the circulation of exogenously administered synthetic human ET-1 were examined in Sprague-Dawley rats. Inhibition of NEP by SQ 28,603 (100 mumol/kg intravenously, i.v.) affected neither basal levels of plasma ET nor the circulatory clearance of an i.v. administered bolus dose (3 nmol/kg) of ET-1. ET-1 produced marked, statistically significant increases in plasma atrial natriuretic peptide (ANP) and cyclic GMP concentrations. SQ 28,603 markedly augmented the duration of the increases in plasma concentrations of ANP and cyclic GMP induced by exogenous ET-1. SQ 28,603 alone produced modest but statistically significant increases in plasma ANP and cyclic GMP concentrations that lasted for at least 30 min. These results clearly demonstrate that NEP does not contribute to the in vivo clearance of ET and support the hypothesis that NEP plays an important role in clearance of ANP from the circulation.

The synthesis of a conformationally rigid calcium channel blocker

Abstract The preparation of (±)-3 and 4, conformationally rigi calcium channel blockers related to diltiazem, is described starting from the known bicyclic ketone 5. The synthesis include the addition of an aryl organometallic reagent to the ketones 9 and 13a respectively, which occurs with unexpected π-facial selectivity.

Pressor responses induced by Bay K 8644 involve both release of adrenal catecholamines and calcium channel activation

1 The dihydropyridine calcium channel activator, Bay K 8644, is believed to increase mean arterial blood pressure in several animal models, as a result of direct activation of vascular smooth muscle cells by increasing calcium influx through the voltage‐dependent calcium channels. The purpose of the current study was to elucidate further the mechanism of action of Bay K 8644, by examining the possibility that the pressor response to Bay K 8644 may also be the result of indirect activation of the vascular smooth muscle cells by release of adrenal catecholamines. 2 Intravenous administration of Bay K 8644 increased mean arterial pressure in a dose‐dependent manner in conscious, normotensive rats. This pressor response was blocked by calcium channel blockers (nifedipine, verapamil, and diltiazem) at doses lower than were necessary to decrease resting mean arterial pressure. 3 α‐Adrenoceptor antagonists (phentolamine, yohimbine, and prazosin) completely blocked the Bay K 8644‐induced pressor responses and converted them to depressor responses. Adrenalectomy did not alter the inhibitory effect of phentolamine on the pressor response to Bay K 8644. However, adrenalectomy or adrenal demedullectomy prevented the phentolamine‐induced reversal of the Bay K 8644 pressor response to a depressor response. In addition, adrenalectomy did not affect the ability of phentolamine to reverse the pressor response to exogenous adrenaline administration to a depressor response. 4 These data suggest that the pressor response to Bay K 8644 may involve both direct activation of vascular smooth muscle cells and indirect activation of the muscle cells by release of adrenal catecholamines.