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The action of histamine and 5-hydroxytryptamine on isolated mammalian atria.

1960; National Institutes of Health; Volume: 130; Linguagem: Inglês

U. Trendelenburg,

Receptor Mechanisms and Signaling

The action of histamine and of 5-HT on isolated atria has been analyzed by a study of the modification by various drugs of the stimulant response to these two substances. Drugs were used which are known to block ganglia (hexamethonium), to deplete the norepinephrine stores (reserpine), to interfere with the release of norepinephrine from such stores (TM 10, morphine), to depress responses mediated through nervous mechanisms (cocaine), to be specific antagonists of histamine (pyrilamine, tripelennamine), of 5-HT (LSD), and of norepinephrine (DCI). Experiments were made on atria of cats, rabbits and guinea pigs; in the first species chronotropic effects were studied, while in rabbit and guinea pig atria mainly changes of amplitude were investigated. The results suggest that histamine has a direct effect on cardiac tissue of all three species, and that this action is not antagonized by antihistaminic substances. With 5-HT species differences were striking. In cat atria 5-HT seems to have a direct effect which is blocked by LSD; in rabbit atria 5-HT seems to act on some nervous tissue and its stimulant action is the result of the liberation of norepinephrine. In guinea pig atria the direct, LSD-sensitive effect of 5-HT is prominent, but indirect (morphine- and cocaine-sensitive) effects may contribute to the stimulant response to 5-HT.