Biomedical subjects

H C Cheng

Publications and source records attributed to H C Cheng.

131 records · Page 8Linked to original sources

PubMedDate not supplied

MR perfusion studies of brain for patients with unilateral carotid stenosis or occlusion: evaluation of maps of "time to peak" and "percentage of baseline at peak".

Maps of "time to peak" (TTP) and "percentage of baseline at peak" (PBP) were compared with maps of conventional brain perfusion parameters, namely, mean transit time (MTT) and relative cerebral blood volume (rCBV). We performed MR perfusion studies in 11 patients. All of them had occlusion or high-grade stenosis of the unilateral carotid artery. Three areas of old infarct, 4 areas of new infarct, and 10 areas of brain without infarct were evaluated specifically. In all these cases, the TTP maps appeared similar to the MTT maps. They showed increases, normal values, or decreases at the same time in all areas evaluated. Most areas of abnormally decreased CBV had increased signal in PBP maps. In conclusion, the TTP map provided the same qualitative information as MTT. PBP seemed correlated inversely to CBV and was less sensitive in demonstrating abnormality.

Aged↗

PubMedDate not supplied

Cardiovascular properties of medroxalol, a new antihypertensive drug.

Medroxalol is a new antihypertensive agent that is presently undergoing clinical trial. Its cardiovascular properties were studied using spontaneously hypertensive rats (SHR), anesthetized dogs, and isolated tissues. Medroxalol produced a long-lasting fall in blood pressure when given by the oral route to SHR. It was more potent than phentolamine in antihypertensive effectiveness. Given intravenously to dogs, medroxalol reduced the blood pressure and heart rate of doses that did not greatly reduce cardiac output. The hypotensive effect of medroxalol was reduced but not abolished following alpha- and beta-adrenergic-receptor blockade. Medroxalol inhibited heart rate and blood pressure responses to isoproterenol and phenylephrine in dogs. In vitro medroxalol resembled a competitive antagonist at alpha-adrenergic receptors in rabbit aortic strips (pA2 6.09) and beta-adrenergic receptors in guinea pig atria (pA2 7.73). It was 0.02 as potent as phentolamine at alpha-receptors and 0.09 as potent as propranolol at beta-receptors. It was concluded that the principal action of medroxalol was to produce a fall in blood pressure by decreasing peripheral vascular resistance more than cardiac output. Adrenergic alpha- and beta-receptor blockade alone does more than cardiac output. Adrenergic alpha- and beta-receptor blockade alone does not satisfactorily explain the hypotension. A contribution by an active vasodilatory component appears likely.

Animals↗

PubMedDate not supplied

Characterization of the cardiovascular activities of a new cardiotonic agent, MDL 17043 (1,3-dihydro-4-methyl-5-[4-(methylthio)-benzoyl]-2H-imidazole-2-one).

The cardiovascular actions of 1,3-dihydro-4-methyl-5[4-(methylthio)-benzoyl]-2H-imidazol-2-one (MDL 17043), a new noncatecholamine, nonglycoside cardiotonic agent, were examined in vivo in anesthetized dogs and in vitro in isolated cat atrial and papillary muscle preparations and guinea pig atria. In the anesthetized dog, intravenous administration of MDL 17043 (0.1--1 mg/kg) produced marked increases in cardiac contractile force which were accompanied by minor increases in heart rate and small decreases in blood pressure. These effects were not altered by alpha- or beta-adrenergic receptor blockade, catecholamine depletion produced by reserpine, bilateral vagotomy, or by bilateral carotid sinus denervation. MDL 17043 (10(-5)--10(-3) M) produced positive inotropic effects in isolated papillary muscle and left atrial strips of the cat that were much greater than the positive chronotropic effects seen in the spontaneously beating right atrium of the cat. The in vitro inotropic effects of MDL 17043 in guinea pig electrically driven left atrial strips were not modified by adrenergic beta-receptor or histamine H1-receptor blockade. The vasodilatory effect of MDL 17043 in the canine isolated pump-perfused hindlimb preparation was not attenuated by surgical sympathectomy, alpha- or beta-adrenergic receptor blockade, cholinergic or histaminergic receptor blockade, or by prostaglandin synthesis inhibition, indicating that MDL 17043 produces direct relaxation of vascular smooth muscle. MDL 17043 was found to be safe and effective when administered acutely in combination with ouabain, hydralazine, nitroglycerin, or furosemide, agents commonly used in the treatment of congestive heart failure.

Animals↗

PubMedDate not supplied

Studies on the mechanism of the positive inotropic effect of piroximone in cat papillary muscle.

The mechanism of the inotropic effect of piroximone HCl [MDL 19205A, 4-ethyl-1,3-dihydro-5-(4-pyridinylcarbonyl)-2H-imidozol-2-on e HCl] was studied in the cat papillary muscle paced electrically in vitro. Piroximone produced a concentration-dependent positive inotropic effect accompanied by an increase in rate of contraction and rate of relaxation, but abbreviated time to peak tension and relaxation time. The positive inotropic effect produced by piroximone was antagonized by carbachol, 3 X 10(-6) M, whereas that produced by increasing calcium concentration was not affected by carbachol. In potassium chloride (22 mM) depolarized muscle, piroximone restored contractility, which was not affected by propranolol (10(-6) M) or by tetrodotoxin (2 X 10(-5) M), but was inhibited by nifedipine (10(-7) M). Piroximine also elevated tissue cyclic AMP (cAMP) content in the papillary muscle. Although nifedipine inhibited the restoration of contractility, it did so without altering the increase of cAMP produced by piroximone. These results suggest that piroximone causes an increase in calcium influx that is mediated by an increase in cAMP, and the results are consistent with the hypothesis that specific inhibition of the high affinity cAMP phosphodiesterase (PDE III) plays a role in the positive inotropic effect of piroximone.

1-Methyl-3-isobutylxanthine↗

PubMedDate not supplied

In vitro and in vivo assessment of the cardiovascular effects of the cardiotonic drug MDL 19205.

Various in vitro and in vivo techniques were used to evaluate the cardiovascular actions of MDL 19205, a new cardiotonic agent. In the anesthetized dog, intravenous administration of MDL 19205 (0.1-1 mg/kg) produced marked increases in cardiac contractile force which were accompanied by small increases in heart rate and minor decreases in blood pressure. These effects were not altered by alpha- or beta-adrenergic receptor blockade, reserpine pretreatment, or bilateral carotid sinus denervation. In isolated cat cardiac tissues, MDL 19205 (10(-5)-10(-3) M) produced a selective inotropic effect relative to isoproterenol and, unlike isoproterenol, was nonarrhythmogenic. Adrenergic beta-receptor or histamine H1-receptor blockade did not modify the inotropic effects of MDL 19205 in guinea pig atria. The vasodilatory effect of MDL 19205 in the canine isolated pump-perfused hindlimb preparation was not significantly attenuated by surgical sympathectomy, alpha- or beta-adrenergic receptor blockade, cholinergic or histaminergic receptor blockade, or indomethacin pretreatment, indicating that MDL 19205 produced direct relaxation of vascular smooth muscle. MDL 19205 was found to be safe and effective when administered acutely in combination with ouabain, hydralazine, nitroglycerin, or furosemide, agents commonly used in the treatment of congestive heart failure. The pharmacological profile revealed by these and other studies suggests that MDL 19205 should be useful in the clinical treatment of congestive heart failure.

Adrenergic alpha-Antagonists↗