摘要:

Reducing the sodium content of medium bathing isolated guinea pig atria produces a positive inotropic response associated with a marked decline in action potential amplitude and a decrease in relaxation velocity. The effects of sodium reduction appear to result from a decline in the rate of sodium-dependent calcium efflux across the sarcolemma. Consistent with this hypothesis, caffeine, which may inhibit calcium uptake by sarcoplasmic reticulum, produces a much more pronounced inhibition of relaxation velocity in the absence than in the presence of sodium. Cardiac glycosides also appear to inhibit sodium-dependent calcium efflux, possibly by increasing intracellular free sodium. In the presence of sodium, ouabain increased developed tension in association with a decline in the velocity of relaxation. High concentrations of ouabain (>10 JIM) increased resting tension in quiescent atria. In the complete absence of sodium, ouabain (100 JIM) had no effect on resting or developed tension. When sodium was restored to previously sodium-free medium, resting tension declined. If atria in sodium-free medium were pretreated with ouabain or deprived of potassium, sodium restoration caused an increase in resting tension. These effects can be related to inhibition of sodium-pump activity by ouabain or potassium depletion. We conclude that both sodium reduction and cardiac glycosides increase myocardial tension development by inhibiting sodium-dependent calcium efflux across the sarcolemma. The contractile effects of ouabain are dependent completely on the presence of sodium.Circ Res 46: 553-564, 1980

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We compared pump function of left and right ventricles in isolated ejecting cat hearts in which the natural series arrangement between the two sides of the heart was broken. The relationship between mean ventricular pressure and output obtained by varying the arterial load, the so-called pump function graph, and the mean external power output found at the various load levels, was taken as the basis for the comparison. The way in which pressures and flow generated by the right ventricle are changed by alterations in resistance and compliance of the loading arterial system, is qualitatively similar to what has been found in a previous study for the left side of the heart, in spite of the structural differences. The right ventricular pump function curve differs from the left ventricular curve in the absolute scale for the mean pressure axis, but if the scale is adjusted appropriately, the two curves look alike. Both ventricles appear matched to the input impedances of their respective arterial systems because both of them generate the maximum external power under the normal loading conditions. Right ventricular pump function is dependent on the left ventricular contraction mode. The presence of an isovolumic beat on the left side of the heart enhances right ventricular pump function. This is in contrast to the very small effect of the right ventricular contraction pattern on the pump function of the left side of the heart. Circ Res 46: 564-574, 1980

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Acute unilateral nephrectomy (AUN) increases electrolyte excretion by the remaining kidney and is associated with a decrease in cardiac output (CO). We studied anesthetized dogs to determine the role of the vagus nerves in these responses to AUN. In six intact animals, AUN increased sodium excretion (UNaV) from 31.7 ± 13.9 to 47.5 ± 14.3 μEq/min (P< 0.05) and potassium excretion (UKV) from 29.3 ± 5.2 to 62.0 ± 11.4 μEq/min (P< 0.02) as CO fell from 2.8 ± 0.2 to 1.9 to 0.3 liters/min (P< 0.005), and blood pressure and total peripheral resistance increased; no change in glomerular filtration rate (GFR) occurred, but renal blood flow fell significantly. In seven dogs undergoing sham nephrectomy, no signficant changes in any of these variables occurred. In 12 dogs with bilateral cervical vagotomy, AUN increased UN«V from 19.3 ± 5.3 to 39.6 ± 13.7 μEq/min (P< 0.05) and UKV from35.7 ± 5.5 to 46.8 ± 5.8 μEq/min, (P< 0.001), without changes in GFR, renal blood flow, or mean arterial pressure. However, CO and total peripheral resistance did not change in this group. In nine dogs given intravenous atropine sulfate (0.067 mg/kg), AUN again resulted in comparable increases in cation excretion, but no significant change in CO occurred. These studies demonstrate that the increased electrolyte excretion seen after AUN is not prevented by bilateral cervical vagotomy or by atropine administration. However, the decrease in CO associated with AUN does not occur under these circumstances, indicating that reflex vagal efferent activity is responsible for this hemodynamic change. Therefore, the increase in electrolyte excretion after AUN can be dissociated from the decrease in CO. Circ Res 46: 575-580, 1980

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

To study the effects of leucine, glucose, and insulin on myocardial protein degradation in fed and fasted nutritional states, we developed and validated a sensitive method for measuring rates of total protein degradation in rat isolated left atrial preparations. Fasting resulted in a progressive decrease in myocardial protein breakdown to 71% of control over a 24-hour period, with no further reduction in degradation rate between 24 and 72 hours of fasting. Insulin (100 mU/ml) suppressed atrial protein degradation by 38% in fed animals (P< 0.001) and by 51% in fasted animals (P< 0.001). Glucose alone had no effect on protein degradation in either nutritional state. At 5 times normal plasma levels, leucine suppressed protein breakdown by 21% in fed and by 15% in fasted animals. The decrease in degradation induced by fasting and the absence of an effect of glucose are in contrast to the behavior reported for skeletal muscle.Circ Res 46: 000-000, 1980

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1980

数据来源: OVID