This chapter provides an overview of the measurement of lipid turnover in response to thyrotropin-releasing hormone (TRH). TRH, a tripeptide, binds specifically to receptors on the plasma membrane of anterior pituitary cells and rapidly stimulates the secretion of prolactin and thyrotropin (TSH). Because the mammalian anterior pituitary gland is composed of at least six cell types, only two of which are responsive to TRH and produce prolactin (mammotropes) or TSH (thyrotropes), the heterogeneity makes the cell population isolated from normal glands less than optimal for the study of the molecular mechanisms involved in TRH action. In many cells, including these TRH-responsive pituitary cells, the interaction of stimuli with cell-surface receptors enhances the turnover of membrane phospholipids. The chapter describes the methodology that employes to study TRH stimulation of phosphoinositide metabolism in intact GH3cells and in membranes isolated from GH3cells. The observations made using a highly enriched preparation of plasma membranes appear to constitute the most convincing evidence that the turnover of plasma membrane phosphoinositides is primarily stimulated during cell activation by TRH. © 1987, Elsevier Inc.
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