The effect of practolol and butoxamine on aortic arch malformation in beta adrenoreceptor stimulated chick embryos.

An equimolar dose of the beta-1 adrenoreceptor antagonist practolol administered to embryonic chicks prevents the induction of aortic arch malformations by isoproterenol. Whereas 3.75 X 10(-9) mole isoproterenol in 5 microliter saline solution induced aortic arch anomalies in 39% of embryos injected at Hamburger-Hamilton developmental stage 26, pretreatment with practolol one to two minutes before catecholamine administration reduced the anomaly rate to to 4%. Practolol when injected alone did not influence survival rate nor did it cause cardiovascular malformations. Probably the most significant result of this study involves the prevention by practolol of aortic hypoplasia and interrupted aortic arch complexes, anomalies frequently induced by isoproterenol when administered at this stage of embryonic chick development. Butoxamine, a beta-2 adrenoreceptor antagonist, did not block the overall effect of isoproterenol nearly as effectively as did practolol. Results from the present study suggest that aortic arch anomalies may be induced in embryonic chicks via beta-1 adrenoreceptor stimulation. Beta-2 receptor stimulation does not appear to be as significantly involved.