gastrin-releasing-peptide and methylatropine

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 less than 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.

Topics: Animals; Atropine Derivatives; Dose-Response Relationship, Drug; Female; Gastrin-Releasing Peptide; Mice; Mice, Inbred Strains; Norepinephrine; Peptides; Propranolol; Thyroid Hormones; Thyrotropin; Vasoactive Intestinal Peptide