INSULIN‐INDUCED ENHANCEMENT OF UPTAKE OF NORADRENALINE IN ATRIAL STRIPS

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Abstract
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 β-adrenoceptors were blocked by addition of propranolol to the organ bath 3 The response of 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.