RESPONSE OF EXPLANTED EMBRYONIC CARDIAC TISSUE TO EPINEPHRINE AND ACETYLCHOLINE

Abstract

A study was made of the influence of epinephrine and acetylcholine on the heart rate of chick embryos. The hearts were either excised and studied in Locke''s solution or explanted according to the methods of Carrel and Maximow. In general epinephrine and acetylcholine exerted their typical effect on embryos 6 days old or older. Many of the 5-day-old embryos showed hearts refractory to epinephrine and acetylcholine and the action of these drugs became markedly less apparent as the age of the embryo decreased. In the case of 72-hr. embryos less than 1/3 of the fragments responded. Because of the lack of definite knowledge, both in regard to the exact site of action of these drugs, and to the time of development and beginning function of the intrinsic nerve mechanism of the heart, it would seem that these results can best be explained on the basis of some intermediary substance being necessary for the action of the drugs. In explants from embryonic hearts it often happened that a fresh explant from a 2-day-old heart would be negative to epinephrine or acetylcholine whereas on cultivation for 24 hrs. these drugs would exert their typical results.