Serotonin–A Possible Transmitter for the Gastric Adaptive Relaxation

Serotonin, or 5-hydroxytryptamine (5-HT), relaxes upper guinea pig stomach, and its possible role as a transmitter in the vagally induced upper gastric adaptive relaxation has been discussed. Such a transmitter is expected to act via other mechanisms than crude muscle depression. To test whether the relaxation response to serotonin is compatible with a putative role as transmitter in gastric adaptive relaxation, we wanted to evaluate whether serotonin acts by crude muscle depression and whether it selectively inhibits histamine or prostaglandin F2α (PGF2α). The study shows that 5-HT, in addition to its relaxatory effect on fundic spontaneous activity, selectively inhibits histamine, whereas PGF2α is not inhibited. It is then concluded that the relaxatory effect of 5-HT is provided through other mechanisms than crude muscle depression and that selective inhibition of intramural agonists, like histamine, is a possible effect mechanism.