Effect of perfusion pressure on force of contraction in thin papillary muscles and trabeculae from rat heart.

Abstract

SUMMARY1. Increased coronary perfusion leads to increased myocardial contraction and oxygen consumption (Gregg's phenomenon) even when oxygen supply is presumably sufficient. Previous studies concerned whole hearts, however, in which local hypoxia may play a role. We developed techniques for internal perfusion of thin papillary muscles from rat heart. The influence of perfusion pressure on muscle contraction was studied. We investigated whether Gregg's phenomenon is due to (a) hypoxia, (b) stretch of the muscle fibres, or (c) increased contractility.2. The effectiveness of the perfusion technique was demonstrated in four ways: (a) the diameter of the capillaries increased with perfusion pressure; (b) 14 + 4 % (mean+ S.D., n = 11) increase in muscle diameter was observed on a change of perfusion pressure from 0 to 50 cmH2O; (c) addition of India ink to the perfusate caused rapid staining of the entire muscle; (d) during internal perfusion and external superfusion peak force was mainly determined by the [Ca2+1 in the internal perfusate.3. An increase of perfusion pressure from 0 to 70 cmH2O induced 74+20 % (mean + S.D., n = 11) increase in peak force of contraction. In the absence of internal perfusion peak force was not affected by approximately 50 % reduction of the Po2 in the bathing solution (from 700 to 350 mmHg). Hence, oxygen supply was not a limiting factor, i.e. the effect of internal perfusion on force was not related to hypoxia.4. Segment length was measured with markers attached to the surface of the muscle. Perfusion-induced changes in segment length were negligible (-0-2 + 1-5 %, n = 11). Force-length relationships at different perfusion pressures show that the perfusion-induced increase in force was generally larger than the maximum increase in force that could be induced by stretch. Furthermore, the time course of stretch and perfusion effects on force was different. We conclude that Gregg's phenomenon is not related to changes in fibre length, i.e. the hypothesis of pressure-induced stretch ('garden hose' effect) does not apply to papillary muscles.5. The pressure-induced changes in the force-length relationship were similar to the changes obtained with interventions that increase contractility, such as increased [Ca21].* To whom reprint requests should be sent.MS 9434 586 V. J. A. SCHOUTEN, C. P. ALLAART AND N. WESTERHOF 6. Since hypoxia and length effects were not involved, and the effect of perfusion pressure was similar to that of inotropic interventions, we conclude that Gregg's phenomenon is a change in contractility. Possible explanations include changes in the ionic composition or volume of the interstitium, and inotropic factors produced by the endothelium or intramyocardial neurons.

The metabolic consequences of an increase in the frequency of stimulation in isolated ferret hearts.

“…Differences would then be expected depending on whether or not the vascular beds were perfused at constant flow. The differences between the contractile behaviour of isolated papillary muscles and those perfused by blood via their capillaries are well known (Kavaler, Harris, Lee & Fischer, 1971), and recent work suggests that these differences are a true consequence of perfusion and not related to the oxygencarrying capacity of blood or incomplete oxygenation of isolated muscles (Schouten, Allaart & Westerhof, 1992).…”

Coronary perfusion and muscle lengthening increase cardiac contraction: different stretch-triggered mechanisms

“…The septum was clamped on a Perspex plate, and the muscle tendon was attached to a force transducer (type KG4, Scientific Instruments; Heidelberg, Germany), which was attached to a micrometer (type 350-521-30, Mitutoyo; Veenendaal, Holland) for length adjustments. The septal artery was cannulated using a glass cannula and connected to a pressurized reservoir through a pressure difference meter (type SCX01DN, Sensym) for flow measurements (39).…”

“…Therefore, increased coronary perfusion, transversal stretch of the myocardium, and muscle lengthening, longitudinal stretch of the myocardium, increase myocardial contraction in the rat through different stretch-triggered mechanisms. myocardial stretch; papillary muscles; gadolinium; streptomycin; stretch-activated ion channels INCREASED CORONARY PERFUSION induces a slow increase of myocardial contraction, which is known as the Gregg effect (1,7,14,15,17,19,22,39). Recently, we showed in perfused rat papillary muscle that the increase in coronary perfusion, which is accompanied by an increase in muscle diameter, was initiated by activation of Gd 3ϩ -sensitive stretch-activated ion channels (SACs) (31), suggesting that transversal stretch (deformation) of the myocardium is fundamental for the Gregg effect.…”

Dual role of endothelin-1 via ETA and ETB receptors in regulation of cardiac contractile function in mice

“…It has been suggested that changes in cardiac muscle length occur because of the increased capacity of coronary vasculature (garden hose effect), thereby leading to increased force production according to the Frank-Starling law of the heart (1). However, in a more recent study (30), it was reported that in the papillary muscle preparation the magnitude of the Gregg effect is greater than that of the Frank-Starling response. On the other hand, local regulation of cardiac contractility by capillary endothelial cells has been hypothesized to account for the Gregg effect (30).…”

“…However, in a more recent study (30), it was reported that in the papillary muscle preparation the magnitude of the Gregg effect is greater than that of the Frank-Starling response. On the other hand, local regulation of cardiac contractility by capillary endothelial cells has been hypothesized to account for the Gregg effect (30). Increased coronary flow rate stimulates capillary endothelium (4), and a role for endothelial cells in the regulation of cardiac function has been demonstrated (38).…”