The proposed research involves defining the detailed molecular mechanisms by which thyrotropin-releasing hormone (TRH, thyroliberin) stimulates the secretion (release of preformed hormone) of thyrotropin (thyroid-stimulting hormone, TSH) and prolactin (PRL) from the anterior pituitary gland. Two homogeneous populations of pituitary cells are used in these studies so that one may unambiguously assign changes in various aspects of cellular calcium homeostasis to the appropriate cell type. These are a mouse (LAF1/J) thyrotropic pituitary tumor from which cells are derived for short-term studies in culture (TtT cells) and a cloned cell line (GH3 cells) originally derived from a rat mammotropic pituitary tumor. Some comparative studies in which measurement only of TSH and PRL are made will be performed in vitro using cells derived from normal female Sprague-Dawley rats. It has recently been demonstrated that TRH causes a rapid elevation of cytoplasmic free Ca2+ concentration ([Ca2+])i and it has been proposed that this increase in [Ca2+]i serves to couple, at least in part, stimulation by TRH to secretion of TSH and PRL. In this proposal, further studies of the effects of TRH on [Ca2+]i will be made and additive, synergistic and/or antagonistic effects of other regulators of TSH and PRL secretion will be determined. The cellular pools of calcium mobilized by TRH will be determined in intact and detergent-permeabilized cells. A possible second messenger fuction if inositoltrisphosphate in TRH mobilization of cellular calcium and the mechanism of inositoltrisphosphate action will be studied in detergent-permeabilized cells and in isolated cellular organelles. Lastly, studies will be made of secretagogues, such as arachidonic acid and phorbol esters, that appear to act without causing an elevation of [Ca2+]i. The additivity or synergism of stimulation of secretion by arachidonic acid and phorbol esters with secretagogues tht act via elevating [Ca2+]i will be studied as will their effects on cellular calcium homeostasis. It is believed that a more complete understanding of how TRH acts will serve to expand our understanding of the mechanism of action of many cell-surface interacting regulators and allow us to understand better some pathologic conditions that involve abnormalities in cell regulation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases (NIADDK)
Type
Research Project (R01)
Project #
2R01AM033468-03
Application #
3152816
Study Section
Endocrinology Study Section (END)
Project Start
1983-08-01
Project End
1990-03-31
Budget Start
1985-04-01
Budget End
1986-03-31
Support Year
3
Fiscal Year
1985
Total Cost
Indirect Cost
Name
Weill Medical College of Cornell University
Department
Type
Schools of Medicine
DUNS #
201373169
City
New York
State
NY
Country
United States
Zip Code
10065
Imai, A; Gershengorn, M C (1987) Regulation by phosphatidylinositol of rat pituitary plasma membrane and endoplasmic reticulum phosphatidylinositol synthase activities. A mechanism for activation of phosphoinositide resynthesis during cell stimulation. J Biol Chem 262:6457-9
Gershengorn, M C (1986) Mechanism of thyrotropin releasing hormone stimulation of pituitary hormone secretion. Annu Rev Physiol 48:515-26
Gershengorn, M C; Paul, M E (1986) Evidence for tight coupling of receptor occupancy by thyrotropin-releasing hormone to phospholipase C-mediated phosphoinositide hydrolysis in rat pituitary cells: use of chlordiazepoxide as a competitive antagonist. Endocrinology 119:833-9
Imai, A; Gershengorn, M C (1986) Phosphatidylinositol 4,5-bisphosphate turnover is transient while phosphatidylinositol turnover is persistent in thyrotropin-releasing hormone-stimulated rat pituitary cells. Proc Natl Acad Sci U S A 83:8540-4
Kolesnick, R N; Gershengorn, M C (1986) Thyrotropin-releasing hormone stimulation of prolactin secretion is coordinately but not synergistically regulated by an elevation of cytoplasmic calcium and 1,2-diacylglycerol. Endocrinology 119:2461-6
Brenner-Gati, L; Gershengorn, M C (1986) Effects of thyrotropin-releasing hormone on phosphoinositides and cytoplasmic free calcium in thyrotropic pituitary cells. Endocrinology 118:163-9
Hinkle, P M; Hewlett, E L; Gershengorn, M C (1986) Thyroliberin action in pituitary cells is not inhibited by pertussis toxin. Biochem J 237:181-6
Kolesnick, R N; Gershengorn, M C (1985) Arachidonic acid inhibits thyrotropin-releasing hormone-induced elevation of cytoplasmic free calcium in GH3 pituitary cells. J Biol Chem 260:707-13
Kolesnick, R N; Gershengorn, M C (1985) Direct evidence that burst but not sustained secretion of prolactin stimulated by thyrotropin-releasing hormone is dependent on elevation of cytoplasmic calcium. J Biol Chem 260:5217-20
Imai, A; Gershengorn, M C (1985) Evidence for tight coupling of thyrotropin-releasing hormone receptors to stimulated inositol trisphosphate formation in rat pituitary cells. J Biol Chem 260:10536-40

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