Abstract
A new photoelectric method for accurately recording contractile amplitude, tone and heart rate of the embryonic chick heart is deseribed. Under the experimental conditions employed, the preparation maintained a regular rhythm for a period of several limits. The rates of hearts isolated from 4- and 8-day-old embryos and examined utilizing this apparatus agree well with those obtained by other investigators for hearts studied in situ. The noninnervated heart of the 4-day-old embryo responded, within limits, to an increase in diastolic tension with an increase in contractile amplitude.
Embryonic hearts responded to l-epinephrine in concentrations as how as 10-10 g/ml, whether innervated or noninnervated. Dichloroisoproterenol blocked the inotropic and chronotropic effects of epinephrine and norepinephrine but not those of barium or ouabin. Acetylchohine was active in all hearts at concentrations as low as l0-8 g/ml. The negative inotropic and chronotropic actions of acetylcholine were blocked by atropine at a concentration of l0-6 g/ml. Physostigmine potentiated the effects of acetylcholine on hearts of 4-day-old and older embryos but did not alter the effects of the latter drug hearts from 3-day-old embryos. Pharmacological evidence indicates the presence of functional levels of cholinesterase in the heart prior to vagal innervation. Receptors for epinephrine, norepinephrine and acetylcholine are present and fully functional in the heart prior to innervation.
Footnotes
- Received November 13, 1959.
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