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Effects of diazepam on the isolated chick embryo heart
Insights
Diazepam depresses embryonic chick heart contractions in a dose-dependent manner. This effect appears to be a direct action on the heart muscle, not mediated by the nervous system.
Area of Science:
- Pharmacology
- Developmental Biology
- Cardiology
Background:
- Diazepam is a widely used anxiolytic and sedative medication.
- Its effects on cardiac function, particularly during embryonic development, require further elucidation.
Purpose of the Study:
- To investigate the impact of diazepam on the contractile properties of isolated embryonic chick hearts.
- To determine the dose-dependency and potential mechanisms of diazepam's cardiac effects in early development.
Main Methods:
- Isolated hearts from 4-day-old (non-innervated) and 7-day-old (innervated) chick embryos were utilized.
- Diazepam was administered in varying concentrations to assess its effects on heart rate and contraction amplitude.
- The influence of prior administration of atropine and norepinephrine was examined.
Main Results:
- Diazepam exhibited a dose-dependent decrease in both heart rate and contraction amplitude.
- A concentration of approximately 1 x 10(-4) M diazepam reduced these parameters by 50%.
- Lower concentrations (<1.0 x 10(-5) M) showed no significant depressant effects. Norepinephrine could still stimulate contraction amplitude in diazepam-treated hearts, while atropine had no effect.
Conclusions:
- Diazepam exerts a direct depressant effect on the embryonic chick myocardium.
- The observed cardiac depression is not mediated by the autonomic nervous system (cholinergic or adrenergic pathways).
- These findings suggest a direct pharmacological action of diazepam on cardiac muscle cells during development.
Abstract:
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.