摘要:

ABSTRACTMyocardial contractility, measured as the maximum left ventricular systolic pressure response to aortic constriction, is greater than normal in the hyperthyroid guinea pig. The effect of inotropic agents on this response was determined in anesthetized, open‐chest, euthyroid, and hyperthyroid guinea pigs. Norepinephrine and isoproterenol in single doses, 1 &mgr;g/kg, and isoproterenol infused intravenously, 1, 4 and 10 &mgr;g/kg/min, caused a smaller increase in myocardial contractile response to aortic constriction in hyperthyroid than in euthyroid animals. Hyperthyroid guinea pigs also responded to an infusion of calcium chloride, 11 mg/kg/min, with an increase in maximum systolic pressure which was less than normal. With each drug the maximum systolic pressure level attained during aortic constriction was greater in the euthyroid than in the hyperthyroid animals. Cardiac pacing of euthyroid guinea pigs at 430 beats/min, a rate similar to the spontaneous rate of the hyperthyroid guinea pig, did not alter the inotropic response to infused calcium, though single injections and intravenous infusions of isoproterenol had less of an effect than in the spontaneously beating normal heart. These results suggest that the increased myocardial contractility of the hyperthyroid guinea pig may have reached a near maximum level. As a result, the added inotropic effects of isoproterenol and calcium in these animals are less than in normal controls.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

ABSTRACTCardiac hypertrophy was induced in rats by constructing an arteriovenous fistula. Heart weights approximately doubled in 7.5 weeks. The levels of activity, expressed per gram of heart, of a variety of enzymes of the mitochondrial respiratory chain and of the citric acid cycle, as well as the concentrations of cytochrome c and of mitochondrial protein, were the same in the hypertrophied and control hearts. Similarly, the capacity of whole heart homogenate to oxidize pyruvate was unaltered in hypertrophy.There was also no change in the levels of activity of cytochrome oxidase and malate dehydrogenase, or in the concentration of cytochrome c in early hypertrophy (3 to 10 days after construction of an A‐V fistula). These results suggest that cardiac mitochondria increase in parallel with the other components of the myocardial cell.The levels of activity, per gram of heart, of creatine phosphokinase and adenylate kinase, and of the rate‐limiting enzymes of glycolysis and glycogenolysis, were the same in the hypertrophied and the control hearts.The above findings suggest that the capacity, per gram of heart, for regenerating ATP, both aerobically and anaerobically, is unchanged in the nonfailing, hypertrophied heart.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

ABSTRACTTo determine the effect of changing the P‐R interval on the intensity of the mitral component of the first heart sound (M1amplitude), fixed‐rate sequential atrioventricular pacing was used to vary the P‐R interval in a steady hemodynamic state in six anesthetized dogs. Left ventricular sound and pressure events were monitored with a catheter‐tip micromanometer, and the rate of rise of left ventricular pressure (dP/dt) was recorded using an R/C differentiator. The P‐R interval was varied from the longest interval at which continuous ventricular capture was achieved (indifferent P‐R interval) to 0.00 msec in 10‐msec increments. The mean increase in M1amplitude at the short P‐R intervals (30 to 50 msec) was 119% compared to the amplitude at the indifferent P‐R interval; there was no significant change in maximum dP/dt. No significant changes in left ventricular ejection time and left ventricular peak pressure occurred over the range of P‐R intervals. At the indifferent P‐R interval, a norepinephrine infusion increased M1amplitude 22% and maximum dP/dt 50%. At short P‐R intervals in the new inotropic state, the M1amplitude was further augmented.These data indicate that both the timing of atrial and ventricular systoles and the force of left ventricular contraction are major, independent determinants of M1amplitude. These findings are consistent with the concept that the abrupt deceleration of blood by the mitral valve shortly after the onset of ventricular systole sets the cardiohemic system into vibration producing the M1sound. The intensity of the first heart sound is proportional to the force produced in this manner.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

ABSTRACTThe responses of the paced, isovolumic atria and ventricles to cervical vagosympathetic stimulation were examined in eight normal and seven sympathectomized dogs under chloralose anesthesia. Before atropine, stimulation usually caused decreases in both atrial and ventricular contractility but with significant quantitative and qualitative variation from animal to animal. The right atrium showed the greatest average decrease (>30%), followed by the left atrium (12%), right ventricle (4% to 12%), and the left ventricle (1% to 10%). After atropine, 0.5 mg/kg, all chambers responded positively to stimulation. The right ventricle was most responsive (about 30%), and the other chambers showed increases of 10% to 20%. These positive inotropic responses were eliminated by propranolol, 0.5 mg/kg, or by pentolinium tartrate, 0.5 mg/kg. In the sympathectomized animals, negative inotropic responses were usually greater and positive responses were reduced or eliminated. The data demonstrate that fibers exist in the cervical vagosympathetic trunks which have both negative and positive inotropic effects on all chambers of the heart. The net effect of vagosympathetic stimulation on a chamber's contractility reflects the relative numbers of the two fiber types which supply it. The fibers mediating the positive effects are probably preganglionic with significant postganglionic stations in the caudal cervical and stellate ganglia and perhaps in the heart itself.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

ABSTRACTTechniques are described to study the hepatic vascular bed in the anesthetized cat without interference with the hepatic artery or portal vein. Liver volume was recorded with a plethysmograph while simultaneous recordings were made of arterial and portal pressures and total hepatic blood flow. Hepatic venous pressure could be raised to any desired level, and capillary filtration coefficients could therefore be determined. The hepatic blood volume was 27 ± 3.3 ml/100 g liver (14% of the total blood volume of the cat). Stimulation of the hepatic nerves decreased liver volume. Maximal responses were reached at frequencies of about 6/sec, and 50% of the blood in the liver was expelled. The hepatic vascular bed is thus an important blood reservoir. The capillary filtration coefficient was 0.30 ± 0.03 ml/min/mm Hg/100 g, and this value was not significantly changed during stimulation of the hepatic nerves.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

ABSTRACTThe turnover of norepinephrine and the enzymes responsible for the synthesis of catecholamines were studied in various organs of rats made hypertensive by DOCA and NaCl. After inhibition of tyrosine hydroxylase by &agr;‐methyl‐p‐tyrosine, an increase in the rate of disappearance of endogenous norepinephrine in the heart, intestine, and spleen of hypertensive rats indicated an increased norepinephrine turnover rate in these organs. Similarly, the rate of decline of3H‐norepinephrine endogenously formed from3H‐dopamine seemed to be increased in the same organs from hypertensive animals. In contrast, the salivary glands showed no change in turnover of norepinephrine.The conversion of tyrosine to catecholamines was normal in the hearts of the hypertensive rats but it was increased in the adrenal glands. The &bgr;‐hydroxylation of dopamine to norepinephrine was normal or slightly increased in the heart, spleen, intestine, and salivary glands of hypertensive animals. The phenylethanolamine N‐methyl transferase activity was normal in the adrenal glands. It thus seems that in hypertension produced by DOCA and NaCl the turnover of norepinephrine is increased in various organs without any detectable change in the synthesis rate, with the exception of the adrenal gland, in which it was increased. This might explain the reduction of the endogenous norepinephrine levels observed in many tissues of animals made hypertensive by DOCA and sodium.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID