Effects of gastrin-releasing peptide on basal and stimulated thyroid hormone secretion in the mouse

Abstract

Abstract. Recently, gastrin releasing peptide (GRP) was demonstrated to occur within normal thyroidal C cells. In the present study, the effects of GRP on basal and stimulated thyroid hormone secretion were investigated in the mouse according to the McKenzie technique. Iodine-deficient mice were pretreated with 125I and thyroxine. GRP was found dose-dependently to increase the basal radioiodine levels after iv injection, reflecting a stimulation of basal thyroid hormone secretion. The effect was maximal at a dose level of 3.0 nmol/animal, and at 2 h after injection, when GRP had increased blood radioiodine levels to 152 ± 8% compared with 96 ± 5% in controls (P< 0.001). GRP seemed to exert additive effects on thyroid hormone secretion with vasoactive intestinal peptide and with TSH at a threshold dose level. In contrast, GRP did not influence the stimulatory effects of either a half-maximal dose level of TSH or noradrenaline. Furthermore, neither L-propranolol nor methylatropine influenced the GRP-induced thyroid hormone secretion. It is concluded that GRP has the capacity to stimulate basal thyroid hormone secretion in the mouse.