Cnidarians are the simplest metazoans to exhibit satiety after feeding
. When hydra are fed to repletion, they close their mouths and cease t
o capture prey. As feeding stops, contractions of the tentacles and bo
dy column increase. Our earlier experiments showed that a gel chromato
graphic fraction of prey substances inhibits prey capture. We now pres
ent evidence that the same fraction reduces the duration of mouth open
ing induced by reduced glutathione (GSH) and inhibits the binding of G
SH to its putative receptor. The fraction also induces column contract
ions which are similar to those normally seen in sated animals. Prey s
ubstances, of unfractionated homogenate, also induce post-feeding tent
acle contractions similar to those seen in sated animals. Cut distenti
on does not appear to induce behavior associated with satiety. Therefo
re, these experiments suggest that chemoreception of prey substances i
nduce satiety in hydra.