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Title: GROWTH HORMONE RELEASING FACTOR DECREASES LONG FORM LEPTIN RECEPTOR EXPRESSION IN PORCINE ANTERIOR PITUITARY CELLS

Author
item LIN, JI - UNIVERSITY OF GEORGIA
item Barb, Claude
item Kraeling, Robert
item RAMPACEK, GEORGE - UNIVERSITY OF GEORGIA

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2002
Publication Date: 3/1/2003
Citation: Lin, J., Barb, C.R., Kraeling, R.R., Rampacek, G.B. 2003. Growth hormone releasing factor decreases long form leptin receptor expression in porcine anterior pituitary cells. Domestic Animal Endocrinology.

Interpretive Summary: Understanding the mechanisms that regulate growth hormone (GH) secretion, necessary for stimulation of growth, is of great relevance in the rapidly growing pig. Growth hormone releasing factor (GRF) stimulates GH secretion from the pituitary gland. Growth studies demonstrated that GH secretion decreases with age. These animals fail to reach their genetic potential for lean deposition. The recently discovered protein, leptin, secreted by fat cells in response to changes in body weight or energy, stimulates GH secretion. This is the first report to demonstrate that administration of GRF directly modulates leptin receptor expression at the level of the pituitary, and thereby regulates pituitary sensitivity to leptin. Therefore, understanding the leptin/GH interactions is necessary in order to develop new methods to promote maximal growth and muscle accretion.

Technical Abstract: We previously demonstrated that the Ob-Rl is expressed in the hypothalamus and anterior pituitary of the pig. Moreover, leptin stimulated basal GH secretion, but suppressed the GH response to GRF in pig anterior pituitary cells in culture. Pituitary cells from six pigs, 180 to 200 days of age, were studied in primary culture to determine if GRF affects Ob-Rl expression. On day 4 of culture, 105 cells / well were challenged with either 1000,100 or 10 nM [Ala15]-hGRF-(1-29)NH2. Secretion of GH into the media and pituitary Ob-Rl mRNA expression were determined at 4 h after treatment. Media were analyzed for GH by RIA and total RNA were isolated from cells for Ob-Rl expression by semi- quantitative RT-PCR. Basal GH secretion was 32 ± 2 ng/mL (n=6 pituitaries). Relative to control at 4 h, 1000,100 and 10 nM GRF increased GH secretion by 151%, 129% and 120% and decreased Ob-Rl expression by 32%, 50% and 38%, respectively. These results indicate that GRF directly modulates Ob-Rl expression at the level of the pituitary and may play a role in regulating pituitary sensitivity to leptin.