The effects of 5-hydroxytryptamine on glucose absorption by Hymenolepis diminuta (Cestoda) and by the mucosa of the rat small intestine

Abstract

The effect of 5-hydroxytryptamine (5-HT), over a concentration range of 0.1–2.0 mM, on in vitro regional glucose uptake by Hymenolepis diminuta, in which the incubation media contained 1–20 mM glucose, was studied in 15-day-old worms. In the anterior region of the strobila, 5-HT concentrations of 0.5 mM or greater significantly enhanced glucose uptake at all concentrations of glucose. In the posterior region of the strobila, 5-HT had no stimulatory effect on glucose uptake. In every case, glucose uptake was reduced compared with the corresponding values for the anterior region of the worm strobila. Increasing glucose concentrations significantly increased glucose utpake by the anterior and posterior regions of the strobila. Mediated (active) transport of glucose in the anterior region of the strobila was increased over the range 0.1–0.5 mM 5-HT; above 0.5 mM glucose uptake decreased. Increasing concentrations of 5-HT above 0.25 mM significantly increased the passive component of glucose uptake (Kd). Using an in vivo perfusion technique, the effect of 5-HT on glucose uptake in the jejunum, proximal ileum, and distal ileum of uninfected and parasitized rats was determined. In uninfected rats, 5-HT had no significant stimulatory effect on glucose uptake in all three regions of the intestine. In the parasitized intestine, 5-HT significantly decreased glucose uptake; in the absence of 5-HT glucose uptake was significanty enhanced in the ileum when compared with uninfected controls.