Addition of insulin to guinea-pig left atrial strips increased the force of contraction and enhanced the uptake of noradrenaline, leading to a diminished response to noradrenaline.
1 Addition of insulin to the organ bath increased the force of contraction of guinea-pig left atrial strips driven electrically at 1 Hz. 2 The positive inotropic response to insulin remained unaltered in atria depleted of catecholamine or when beta-adrenoceptors were blocked by addition of propranolol to the organ bath. 3 The response os isolated atria to noradrenaline was significantly reduced in the presence of insulin. 4 Insulin affected neither the calcium accumulating abilities of the heart sarcolemma, mitochondria or microsomes, nor the cyclic adenosine 3',5'-monophosphate (cyclic-AMP)-protein kinase-induced stimulation of microsomal calcium uptake. 5 Addition of insulin to the organ bath enhanced significantly the ability of the cardiac tissue to take up 3H-noradrenaline as well as 3H-metaraminol. The activities of monoamine oxidase and catechol-O-methyl transferase were not changed after addition of insulin to homogenates of the heart. 6 The ability of insulin to facilitate uptake of noradrenaline would be expected to cause a decrease in the amount of the amine reaching the receptors, thus leading to a diminished response to this amine. This may explain, at least in part, insulin-induced subsensitivity to noradrenaline. 7 This view is supported by the observation that after blockade of amine uptake by destruction of nerve terminals, insulin failed to reduce the positive inotropic response to noradrenaline.
Bhagat et al. (Thu,) conducted a other in Guinea-pig left atrial strips. Insulin vs. Absence of insulin was evaluated on Force of contraction and noradrenaline uptake. Addition of insulin to guinea-pig left atrial strips increased the force of contraction and enhanced the uptake of noradrenaline, leading to a diminished response to noradrenaline.