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Noradrenaline release by nicotinic acid
Indian Journal of Physiology and Pharmacology
|July 1, 1975
Summary
Nicotinic acid (NA) acts as a positive inotropic and chronotropic agent on isolated frog hearts, likely by releasing noradrenaline. However, NA has a direct depressant effect on other organs.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Neurotransmitter Release
Background:
- Nicotinic acid (niacin) is a vitamin with known cardiovascular effects.
- Its precise mechanisms on cardiac function, particularly in lower vertebrates, require further elucidation.
Purpose of the Study:
- To investigate the effects of nicotinic acid on isolated frog heart preparations.
- To determine the mechanism of action of nicotinic acid on cardiac function.
- To compare its effects on different isolated organ preparations.
Main Methods:
- Isolated frog heart preparations were used to assess inotropic and chronotropic responses to nicotinic acid.
- Pharmacological blocking agents (pronethalol, guanethidine) and reserpine were employed to investigate the mechanism.
- Comparative studies were conducted on isolated rabbit heart, rabbit intestine, and guinea pig seminal vesicles.
Main Results:
- Nicotinic acid (100 mug to 1 mg) demonstrated positive inotropic and chronotropic effects on isolated frog hearts.
- These effects were antagonized by pronethalol and guanethidine, and absent in reserpinized frogs.
- Tachyphylaxis was observed with repeated nicotinic acid administration in frog heart preparations.
- Nicotinic acid exhibited a nonspecific direct depressant action on isolated rabbit heart, rabbit intestine, and guinea pig seminal vesicles.
Conclusions:
- Nicotinic acid-induced cardiac stimulation in frogs appears to be mediated by the release of endogenous noradrenaline.
- The findings suggest a dual mechanism of action for nicotinic acid: indirect sympathomimetic effects on the frog heart and direct depressant effects on other tissues.
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