Effect of 5-hydroxytryptamine and related compounds on the isolated heart of Pila globosa (Gastropoda:Mollusca)

Abstract

5-Hydroxytryptamine produces an increase in the amplitude and frequency of the heart-beat of Pila. The threshold for the activity of 5-hydroxytryptamine is 10⁻⁸ gm./ml. However, this dose is not constant. In some cases it is 10⁻⁶ gm./ml. and in still other cases doses even upto 10⁻⁴ gm./ml. are ineffective. The action of 5-HT is not blocked by LSD. However, LSD 10⁻⁵ gm./ml. produces a positive inotropic and a very slight positive chronotropic response. The bromine derivative of LSD sometimes causes a rise in the threshold of 5-HT. Reserpine produces a positive inotropic and a negative chronotropic effect. The threshold dose for Reserpine is 10⁻⁵ gm./ml. The action of Reserpine is of long duration and both increase in amplitude and decrease in frequency go on for a long time in a progressive manner. The action of 5-HT and related compounds on the heart of Pila has been discussed in relation to that in other molluscs.