Stanley A. Rubin

Compensatory hypertrophy in the heart after myocardial infarction in the rat

Hypertrophy after myocardial infarction would be a very important process for compensation of damaged myocardium and preservation of cardiac function. Fifty-four female Sprague-Dawley rats were studied 5 weeks after randomization to infarct operation, sham operation and control groups. At sacrifice, anteroapical infarcts ranging from 1 to 51% of left ventricle were present in the infarct operated group. When classified according to infarct size, groups with the largest infarcts (greater than 15 to 30% and greater than 30%) had significant (p less than 0.001) cardiac cellular hypertrophy in the noninfarcted myocardium of the septum and anterior walls (fiber diameter 15.9 +/- 2.3 and 14.5 +/- 2.3 microns, respectively) compared with the control group (12.0 +/- 1.8 microns). Because of cardiac hypertrophy, remaining noninfarcted myocardial area, as estimated from serial histologic sections of the heart, was normal in the greater than 15 to 30% infarct group (area 1.35 cm2) compared with the control group (1.43 cm2); however, because hypertrophy plateaued in the greater than 30% infarct group, myocardial area was significantly decreased (1.06 cm2, p less than 0.001), but was still more than expected without hypertrophy. We suggest that hypertrophy accompanies large infarction in the rat and is a compensation for preserving tissue volume lost by infarction. This compensatory response appears to have limitations, such that when very large amounts of myocardium become necrotic, there is not enough hypertrophy to return myocardial volume to normal.

Arterial oxygenation and arterial oxygen transport in chronic myocardial failure at rest, during exercise and after hydralazine treatment.

Arterial oxygen transport (cardiac output x arterial oxygen content) may be decreased in heart failure. We studied the determinants of arterial oxygen transport in 15 patients with chronic, severe myocardial failure at rest and during cycle ergometry. During control therapy at rest, arterial oxygen tension was normal (81 8 mm Hg, mean ± SD) and increased slightly during exercise (90 ± 14 mm Hg). During hydralazine therapy at rest, arterial oxygen tension was slightly higher (87 9 mm Hg) and also increased during exercise (92 ± 15 mm Hg). Hydralazine did not increase arterial oxygen tension (0.10 > p > 0.05), but exercise did (p < 0.02). Arterial oxygen saturation and content were normal and did not change under any condition or treatment. During control therapy at rest, arterial oxygen transport was low (313 74 ml/min.m2) and remained abnormally low during exercise (434 ± 124 ml/min.m2). During hydralazine therapy, arterial oxygen transport was higher at rest (457 ± 100 ml/min.m2) and during exercise (577 t 131 ml/min.m2). Hydralazine increased arterial oxygen transport (p < 0.01) because it increased stroke volume at rest and during exercise, but it did not change arterial oxygenation. Arterial oxygenation is normal in chronic heart failure patients at rest and during exercise. Hydralazine increases cardiac output and arterial oxygen transport without changing arterial oxygenation.

Incremental prognostic value of exercise hemodynamic variables in chronic congestive heart failure secondary to coronary artery disease or to dilated cardiomyopathy

To determine the prognostic value of hemodynamic variables at rest and during exercise, 49 patients with chronic congestive heart failure undergoing hemodynamic evaluation at rest and during symptom-limited exercise were followed for 1 year. One-year mortality rate was 33%. On univariate analysis, nonsurvivors differed significantly from survivors in pulmonary arterial wedge pressure at rest (22 +/- 10 vs 15 +/- 10 mm Hg; p = 0.01) and during exercise (32 +/- 9 vs 24 +/- 9 mm Hg; p = 0.003), stroke work index at rest (19 +/- 6 vs 25 +/- 9 g-m/m2; p = 0.03) and during exercise (20 +/- 7 vs 32 +/- 14 g-m/m2; p = 0.001) and exercise-induced increment in stroke work index (0.5 +/- 0.4 vs 7 +/- 8 g-m/m2; p = 0.004), but not with respect to left ventricular ejection fraction, exercise duration, peak oxygen consumption or peak left ventricular hydraulic power. Patients with a peak exercise stroke work index less than 20 g-m/m2 had a 66% mortality rate compared with a mortality rate of 13% in patients with a peak exercise stroke work index greater than 20 g-m/m2 (p = 0.0001). Multiple logistic regression analysis identified pulmonary arterial wedge pressure at rest and peak exercise stroke work index as the only independent predictors of mortality. A receiver-operating characteristic curve analysis revealed that peak exercise stroke work index provided significant incremental prognostic information over the resting hemodynamic variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic assessment of exercise in chronic heart failure patients treated with short-term vasodilators.

Short–term vasodilators increase exercise cardiac output without an increase in exercise tolerance when administered to chronic heart failure patients. This study was designed to examine cardiac output, oxygen consumption, and lactate metabolism during exercise in chronic heart failure. Thirteen patients participated in 17 studies during control exercise (C) and during vasodilator exercise after short–term treatment with either hydralazine (H) or prazosin (P). Cardiac output increased during exercise both with hydralazine (C = 5.8 2.3 1/min, H = 6.9 i 2.3 1/min; p < 0.001) and with prazosin (C = 5.9 ± 2.3 1/min, P = 7.6 ± 2.7 1/min; p < 0.005). Oxygen consumption did not change during exercise either with hydralazine (C = 663 249 ml/min, H = 651 ± 200 mI/min; p > 0.10) or with prazosin (C = 696 ± 246 ml/min, P = 734 245 ml/min; p > 0.10). Peak blood lactate did not change either with hydralazine (C = 49.7 i 24.2 mg/dl, H = 44.0 ± 21.4 mg/dl; p > 0.05) or with prazosin (C = 33.8 ± 16.5 mg/dl, P = 32.1 i 12.2 mg/dl; p > 0.10). Vasodilators did not change the rate of lactate disappearance during recovery from exercise. We conclude that short–term administration of vasodilators increased cardiac output during exercise but did not improve nutritional flow to exercising muscle. However, chronic administration of vasodilators with sustained improvement in cardiac output may allow the readjustment of peripheral mechanisms that control the nutritional flow of muscle in order to take advantage of improved cardiac performance caused by vasodilators.

Biotin uptake by human colonic epithelial NCM460 cells: a carrier-mediated process shared with pantothenic acid

Previous studies showed that the normal microflora of the large intestine synthesizes biotin and that the colon is capable of absorbing intraluminally introduced free biotin. Nothing, however, is known about the mechanism of biotin absorption in the large intestine and its regulation. To address these issues, we used the human-derived, nontransformed colonic epithelial cell line NCM460. The initial rate of biotin uptake was found to be 1) temperature and energy dependent, 2) Na+ dependent (coupling ratio of 1:1), 3) saturable as a function of concentration [apparent Michaelis constant ( K m) of 19.7 μM], 4) inhibited by structural analogs with a free carboxyl group at the valeric acid moiety, and 5) competitively inhibited by the vitamin pantothenic acid (inhibition constant of 14.4 μM). Pretreatment with the protein kinase C (PKC) activators phorbol 12-myristate 13-acetate (PMA) and 1,2-dioctanoyl- sn-glycerol significantly inhibited biotin uptake. In contrast, pretreatment with the PKC inhibitors staurosporine and chelerythrine led to a slight, but significant, increase in biotin uptake. The effect of PMA was mediated via a marked decrease in maximal uptake velocity and a slight increase in apparent K m. Pretreatment of cells with modulators of the protein kinase A-mediated pathway, on the other hand, showed no significant effect on biotin uptake. These results demonstrate, for the first time, the functional existence of a Na+-dependent, specialized carrier-mediated system for biotin uptake in colonic epithelial cells. This system is shared with pantothenic acid and appears to be under the regulation of an intracellular PKC-mediated pathway.

Transport of thiamine in human intestine: mechanism and regulation in intestinal epithelial cell model Caco-2

The present study examined the intestinal uptake of thiamine (vitamin B1) using the human-derived intestinal epithelial cells Caco-2 as an in vitro model system. Thiamine uptake was found to be 1) temperature and energy dependent and occurred with minimal metabolic alteration; 2) pH sensitive; 3) Na+ independent; 4) saturable as a function of concentration with an apparent Michaelis-Menten constant of 3.18 ± 0.56 μM and maximal velocity of 13.37 ± 0.94 pmol ⋅ mg protein-1 ⋅ 3 min-1; 5) inhibited by the thiamine structural analogs amprolium and oxythiamine, but not by unrelated organic cations tetraethylammonium, N-methylnicotinamide, and choline; and 6) inhibited in a competitive manner by amiloride with an inhibition constant of 0.2 mM. The role of specific protein kinase-mediated pathways in the regulation of thiamine uptake by Caco-2 cells was also examined using specific modulators of these pathways. The results showed possible involvement of a Ca2+/calmodulin (CaM)-mediated pathway in the regulation of thiamine uptake. No role for protein kinase C- and protein tyrosine kinase-mediated pathways in the regulation of thiamine uptake was evident. These results demonstrate the involvement of a carrier-mediated system for thiamine uptake by Caco-2 intestinal epithelial cells. This system is Na+ independent and is different from the transport systems of organic cations. Furthermore, a CaM-mediated pathway appears to play a role in regulating thiamine uptake in these cells.The present study examined the intestinal uptake of thiamine (vitamin B(1)) using the human-derived intestinal epithelial cells Caco-2 as an in vitro model system. Thiamine uptake was found to be 1) temperature and energy dependent and occurred with minimal metabolic alteration; 2) pH sensitive; 3) Na(+) independent; 4) saturable as a function of concentration with an apparent Michaelis-Menten constant of 3.18 +/- 0.56 microM and maximal velocity of 13.37 +/- 0.94 pmol. mg protein(-1). 3 min(-1); 5) inhibited by the thiamine structural analogs amprolium and oxythiamine, but not by unrelated organic cations tetraethylammonium, N-methylnicotinamide, and choline; and 6) inhibited in a competitive manner by amiloride with an inhibition constant of 0.2 mM. The role of specific protein kinase-mediated pathways in the regulation of thiamine uptake by Caco-2 cells was also examined using specific modulators of these pathways. The results showed possible involvement of a Ca(2+)/calmodulin (CaM)-mediated pathway in the regulation of thiamine uptake. No role for protein kinase C- and protein tyrosine kinase-mediated pathways in the regulation of thiamine uptake was evident. These results demonstrate the involvement of a carrier-mediated system for thiamine uptake by Caco-2 intestinal epithelial cells. This system is Na(+) independent and is different from the transport systems of organic cations. Furthermore, a CaM-mediated pathway appears to play a role in regulating thiamine uptake in these cells.

Long-term outpatient vasodilator therapy of congestive heart failure: Consideration of agents at rest and during exercise

Increased left ventricular filling pressure and reduced cardiac output are two major hemodynamic deficits in pump failure. In patients with chronic heart failure, consequences of these hemodynamic deficits and diminished cardiac reserve are manifested initially during stress and eventually at rest. The purpose of therapeutic interventions include reduction of ventricular filling pressure increase in cardiac output and improvement in cardiac reserve. To achieve these goals, the hemodynamic effects of predominantly venodilators (nitrates), predominantly arteriolar dilators (hydralazine) and the combination of nitrates and hydralazine were evaluated in patients with chronic heart failure at rest: left ventricular filling pressure (mm Hg) control 28, nitrates 17, hydralazine 25, nitrates plus hydralazine 18; cardiac output (liters/min/m2) control 2.1, nitrates 2.1, hydralazine 3.2, nitrates plus hydralazine 3.3; mean blood pressure (mm Hg) control 87, nitrates 85, hydralazine 83, nitrates plus hydralazine 85. These data suggest improved left ventricular performance with a combination of nitrates and hydralazine. Exercise hemodynamics improved in some patients, suggesting that such vasodilator therapy may be beneficial in chronic heart failure.

Cardiac physiology, biochemistry and morphology in response to excess growth hormone in the rat

The cardiac effects of excess growth hormone (GH) were studied in the intact adult rat and in tissues prepared from the rat. Female Wistar-Furth rats were inoculated with a clonal cell line of pituitary cells which secrete GH. Five weeks later, heart weight had increased 37% compared to control (P less than 0.01) due to concomitant increases in left and right ventricular weight. Hemodynamic measurements in the anesthetized rat showed that GH stimulated rats had a decrease in blood pressure and heart rate and a small increase of left ventricular end-diastolic pressure (P less than 0.05). Measurement of left ventricular contractility and relaxation, and response to beta-adrenergic stimulation were decreased in GH compared to control (P less than 0.05). Contractile protein biochemistry showed an 18% reduction in Ca2(+)-myosin ATPase activity of the left ventricle (P less than 0.05) and non-denaturing pyrophosphate gels of purified myosin demonstrated a significant shift of isoforms from the exclusive V1 pattern to both V1 and V3 isomyosins in both ventricles (P less than 0.05). In contrast to the physiological and protein biochemistry adaptations, left ventricular morphology by light microscopy and ultrastructure by electron microscopy were normal in the GH stimulated heart. There were no significant changes in myofibril fraction, in the myofibril to mitochondria ratio or in the capillary numerical density of the hypertrophied left ventricle (P = N.S.). This study demonstrates that under prolonged and extreme stimulation by GH, the heart undergoes considerable growth/hypertrophy. Although cardiac morphology remains normal during this growth, there are alterations of the isomyosins such that ATPase activity is diminished and ventricular function is decreased.

MDL 17,043: Short- and long-term cardiopulmonary and clinical effects in patients with heart failure

MDL 17,043, an inotropic and vasodilator drug, is believed to have beneficial effects in patients with heart failure. Its short- and long-term hemodynamic and cardiopulmonary effects were studied in 10 patients with New York Heart Association functional class III heart failure who were maintained on digitalis and diuretic drugs. Hemodynamics at baseline study and after 24 hours of oral therapy (four doses of 6 mg/kg) showed increased cardiac output (3.9 +/- 0.7 to 6.1 +/- 1.1 liters/min, p less than 0.05), increased stroke volume (42 +/- 12 to 60 +/- 15 ml, p less than 0.05), decreased systemic vascular resistance (1,564 +/- 326 to 1,009 +/- 296 dynes X s X cm-5, p less than 0.05) but no change in pulmonary capillary wedge pressure (31 +/- 6 to 25 +/- 13 mm Hg, p = NS). Only systemic vascular resistance and arteriovenous oxygen difference were significantly decreased during exercise. When restudied after 5 weeks of therapy, neither cardiac output nor stroke volume showed a sustained increase at rest or during exercise, and effects on systemic vascular resistance and arteriovenous oxygen difference were not sustained at exercise (p = NS). Peak oxygen uptake during exercise was 8.1 +/- 2.5 ml/kg per min at baseline and was not significantly increased either acutely (9.2 +/- 2.4 ml/kg per min, p = NS) or chronically (8.9 +/- 2.2 ml/kg per min, p = NS). Problems of increased ventricular arrhythmias and diarrhea were noted after therapy was begun.(ABSTRACT TRUNCATED AT 250 WORDS)

A multicenter study of the safety and efficacy of benazepril hydrochloride, a long‐acting angiotensin‐converting enzyme inhibitor, in patients with chronic congestive heart failure

Benazepril hydrochloride is a nonsulfhydryl, long‐acting angiotensin‐converting enzyme inhibitor that is orally effective. This study was designed to determine the acute hemodynamic effects of this agent in patients with chronic congestive heart failure. Twenty‐six patients with New York Heart Association class III or IV congestive heart failure and left ventricular ejection fractions <35%, cardiac indexes <2.1 L/min/m2, and pulmonary artery wedge pressures >12 mm Hg were given 2 or 5 mg benazepril hydrochloride. All doses produced significant (p < 0.05) increases in cardiac output (26.7% to 31.6% above control) and heart rate (5.4% to 11.2% above control) and decreases in systemic (27.1% to 32.0% below control) and pulmonary (34.8% to 55.5% below control) vascular resistances, mean pulmonary (25.3% to 30.3% below control) and systemic (13.4% to 18.5% below control) arterial pressures, and pulmonary artery wedge pressure (46.9% to 51.1% below control). Twenty‐four hours after an initial dose, systemic vascular resistance and pulmonary artery wedge pressures remained below control levels. Angiotensin‐converting enzyme activity fell by 67.8% ± 6.4%, with a 15.8% ± 7.6% decline in aldosterone levels. Thus benazepril hydrochloride is an effective angiotensin‐converting enzyme inhibitor that produces hemodynamic effects that persist for 24 hours after a single oral dose.