Formation of apical pseudopods by canine thyroid follicular cells: induction by thyrotropin and 5-hydroxytryptamine; antagonism by reserpine.

The role of biogenic amines in the activation of thyroid follicular cells by thyrotropin (TSH) was studied. 5-hydroxytryptamine (5-HT) was chosen as the amine to study and apical pseudopod formation, assessed by scanning electron microscopy, was used as the index of follicular cell activation. All experiments were done on dogs. TSH and 5-HT were both potent inducers of pseudopod formation. The action of TSH but not that of 5-HT was antagonized by the amine depleting drug reserpine. Reserpine depleted the thyroid of 5-HT in newborn, adolescent, and adult dogs. It is concluded that one or more biogenic amines, such as 5-HT, are probably involved in follicular cell activation by TSH.