[Effect of adrenaline, noradrenaline, isoproterenol and tyramine on the isolated surviving human fetal heart].

Studies were conducted by the authors into the action of adrenergic stimulants on isolated surviving hearts of 64 foetuses obtained from termination of pregnancies. They found that under the direct impact of stimulating catecholamines (adrenaline, noradrenalinee, and isoproterenol) the adrenergic receptors caused increase in spontaneous frequency of heart contractions, as early as in the fifth to ninth weeks of development, that is before adrenergic innervation of the heart. Such tachycardic effects were increasingly pronounced between the fifth and 24th week, along with growing age. Reactions produced by early and somewhat developed hearts were different with significance. Convincing effects were not detectable until hearts were ten or eleven weeks of developmental age, when tyramine was used which acted through release of noradrenalin. The latter date was in approximate coincidence with the appearance of adrenergic nerve elements for growth into the cardiac substance. In the 17th week of development, tyramine was used with good success to produce numerous effects which were characteristic of catecholamines, such as higher irritability and contractility of the myocardium and decrease of the effective refractory phase.