AJP - Regulatory, Integrative and Comparative Physiology, Vol 232, Issue 3 116-R123, Copyright © 1977 by American Physiological Society
Pharmacological analysis of sympathetic function in the embryonic chick heart
N. G. Culver and D. A. Fischman
Sympathetic nerve cells enter the embryonic chick heart on the fifth day in
ovo, but it is uncertain when these nerves become functional. Using
pharmacological probes known to affect the embryonic circulation,
sympathetic nerve function was examined at various stages of development.
Exogenous norepinephrine elicited cardioacceleration in the hearts of
embryos with intact extraembryonic circulation both before (stage 20-24)
and after (stage 28-32) sympathetic innervation of the heart, and this
acceleration could be inhibited by propranolol and practolol. In contrast,
ganglionic stimulation with 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP)
elicited cardioacceleration only after stages 27-28 (i.e., after
sympathetic innervation), producing a 25-30% increase in heart rate over
the predrug levels of 148.7 +/- 1.8 beats/min. DMPP-elicited positive
chronotropy was reduced by beta-receptor antagonists, hexamethonium,
guanethidine (GuE), and tetrodotoxin. In preparations of the embryonic
thorax in which the innervated heart was separated from brain and adrenal
influences, DMPP elicited a GuE-sensitive cardioacceleration. It is
concluded that during chick embryonic development, no more than a 1-day
interval exists between the appearance of sympathetic nerves in the heart
and the onset of neuronal function in that organ.
