No effect of atrial natriuretic factor on cardiac rate, force and transmitter release

The effects of atrial natriuretic factor (ANF, 1-300 nmol/l) on cardiac rate, force and neurotransmitter release were examined in guinea-pig isolated heart preparations. Synthetic ANF had little effect on the contractile force of electrically driven papillary muscle regardless of the presence or absence of isoprenaline. The pulse period of spontaneously beating right atria was not affected by ANF. Neither the positive nor negative chronotropic effect of isoprenaline or bethanechol respectively were changed in the presence of ANF. ANF did not affect the release of neurotransmitter from the nerve endings in the isolated atrium. ANF was confirmed to relax isolated aortic rings precontracted with either noradrenaline (ANF,IC50 = 3 nmol/l,s.e.m. = 0.2, n = 5) or potassium (ANF,IC50 = 24 nmol/l, s.e.m. = 0.2, n = 5). These results demonstrate that ANF within doses effective for vasorelaxation has no appreciable effect on myocardial function or neutrotransmitter release in the heart.