Hyposmolar Stimulation of Secretion of Thyrotropin,Prolactin,and Luteinizing Hormone Does not Require Extracellular Calcium and Is not Inhibited by Colchicine,Cytochalasin B,Ouabain,or Tetrodotoxin

Abstract

Hyposmolar stimulation of thyroid-stimulating hormone, prolactin, and luteinizing hormone secretion by dispersed perifused rat pituitary cells was not depressed by removal of Ca²⁺ from the perifusion medium or by 0.1 mM colchicine, 20 μM cytochalasin B, 0.1 mM ouabain, or 3 μM tetrodotoxin. The secretory response induced by medium hyposmolarity or by thyrotropin-releasing hormone was not appreciably different at 23, 37, or 43°C, but was markedly reduced or abolished when the experiments were performed at 1°C. These data indicate that microtubules or microfilaments, transport of extracellular Ca²⁺ into the cytoplasm, and plasmalemma ion transport mechanisms sensitive to ouabain or tetrodotoxin are not essential components of the mechanism by which extracellular hyposmolarity induces secretion.