Effects of diazepam on the isolated chick embryo heart.
Diazepam decreased the rate and amplitude of contraction in isolated embryonic chick hearts in a dose-dependent manner in both the noninnervated hearts obtained from 4-day-old embryos and the innervated hearts from 7-day-old embryos. The concentration of diazepam necessary to reduce the heart rate and contractile amplitude to 50% of the control values was about 1 X 10(-4) M. Concentrations less than 1.0 X 10(-5) M had no detectable depressant effects. Prior administration of atropine did not alter the depression induced by diazepam. Norepinephrine was able to stimulate the amplitude of contraction in the diazepam-depressed heart while atropine was without effect. The vehicle used in the clinical injectable preparation of diazepam had no depressant effects. The mechanism of action of the diazepam-induced depression on the isolated embryonic chick heart may be a direct depression of the myocardium.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002642:Chick Embryo; D003864:Depression, Chemical; D003975:Diazepam / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects* / Q000294:innervation; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology
D001285:Atropine; D003975:Diazepam; D009638:Norepinephrine