Selective reserpine-induced supersensitivity of the positive inotropic and chronotropic responses to isoprenaline and salbutamol in guinea-pig isolated atria.

1 Dose-response curves for the positive inotropic and chronotropic responses to isoprenaline were obtained in atria from untreated guinea-pigs and those receiving various reserpine pretreatments. 2 Tension responses were unaffected, whereas rate responses were depressed by the lowest dose of reserpine (0.05 mg/kg i.

Analysis of the inotropic: chronotropic selectivity of dobutamine and dopamine in anaethetised dogs and guinea-pig isolated atria.

The previously reported in vivo inotropic selectivity of dobutamine and dopamine compared with isoprenaline has been demonstrated in anaesthetised bivagotamised open chest dogs. Responses of heart rate, right ventricular tension, left ventricular dP/dtmax, and blood pressure were measured. Compared with isoprenaline, dobutamine and dopamine were 1.

The release of a coronary vasodilator metabolite from the guinea-pig isolated perfused heart stimulated by catecholamines, histamine and electrical pacing and by exposure to anoxia.

1 A procedure involving two guinea-pig isolated hearts perfused in series is described for detecting in the recipient heart the release of a possible coronary vasodilator metabolite from the donor heart. 2 Adrenaline and isoprenaline stimulated the rate and force of contraction and produced a multiphasic coronary vascular response, the predominant phase of which was vasodilatation. When the beta-adrenoceptors of the recipient heart were blocked, stimulation of the donor heart by the catecholamines was associated with a coronary vasodilatation of the recipient heart.

The effect of temperature upon the positive inotropic and chronotropic responses of isolated cardiac preparations to isoprenaline and its modification by experimental variables.

The effects of various experimental variables upon the optimum temperatures for positive inotropic and chronotropic responses to isoprenaline in isolated cardiac preparations were examined. Perfusion rate and animal (heart) size affected the satisfactory determination of rate and tension optima of guinea-pig and rabbit perfused hearts. Isolated spontaneous atria were assumed to have the same temperature optima as perfused hearts and these were independent of the animal size/age.

Differential blockade of guinea-pig atrial rate and force responses to (--)-noradrenaline by practolol - an uptake phenomenon.

The relative blockade of rate and force responses of guinea-pig isolated atria to catecholamines by practolol was compared. pA2 determinations revealed that with (--)-noradrenaline as the agonist, practolol was more effective in antagonizing rate (pA2, 6.99) than force (pA2, 6.

The role of H1 and H2-receptors in the coronary vascular response to histamine of isolated perfused hearts of guinea-pigs and rabbits.

1. The effects of histamine on the isolated perfused hearts of guinea-pigs and rabbits were examined. Records of contractile force, heart rate and coronary perfusion pressure were obtained.

Negative inotropic responses of the isolated heart of the rat to isoprenaline.

The isolated heart of the rat perfused at 38 degrees C responded to isoprenaline with an initial positive inotropism followed by a bi-phasic negative inotropic effect. The latter was associated with the simultaneous biphasic rate increase. On reduction of the perfusion temperature to 20 degrees C, isoprenaline no longer increased the rate but a negative inotropic response remained.

An analysis of the coronary vascular responses to catecholamines, using a modified Langendorff heart preparation.

1. A modified Langendorff heart preparation from the guinea-pig was used to analyse catecholamine responses. Contractile force, heart rate and coronary perfusion pressure were recorded.