Hymenolepis diminuta: uptake of 5-hydroxytryptamine (serotonin), glucose, and changes in worm glycogen levels

Abstract

The effects of 5-hydroxytryptamine (5-HT) and its specific antagonist, methylsergide hydrogenmaleinate, on in vitro glucose uptake by Hymenolepis diminuta were followed for up to 60 min. Maximum stimulation of glucose uptake occurred with 0.5 mM 5-HT. With the addition of 10 mM methysergide (MET) glucose uptake decreased by 68%. Glucose uptake was greatest in the anterior, immature region of the worm strobila, and diminished through the middle to the posterior gravid portion of the strobila. 5-HT significantly increased glucose uptake in all three regions. The addition of 3 mM MET eliminated the stimulatory action of 5-HT on glucose uptake in the anterior and middle regions of the strobila; 10 mM MET significantly reduced glucose uptake in all three regions of the worm. The presence of 0.5 mM 5-HT both stimulated glucose uptake and decreased worm glycogen levels in all three regions of the strobila. The further addition of 0.5 mM MET did not affect the reduced glycogen levels. 5-HT uptake by H. diminuta was over 60% higher in the anterior segment of the strobila compared with uptake in the middle and posterior segments. The addition of 3 mM MET significantly decreased 5-HT uptake in the anterior and middle regions of the strobila; 10 mM MET decreased 5-HT uptake in all three regions. The regional differences in 5-HT and glucose uptake by H. diminuta suggest that the tryptaminergic receptors in the strobila are not equally distributed along the length of the worm. The effects of MET on glucose and 5-HT uptake are in part accountable through its action in blocking 5-HT receptors.