OREXIN-B MODULATES LUTEINIZING HORMONE AND GROWTH HORMONE SECRETION FROM PORCINE PITUITARY CELLS IN CULTURE

Authors: Barb, Claude; Matteri, Robert

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2004
Publication Date: 4/20/2005
Citation: Barb, C.R., Matteri, R.L. 2005. Orexin-b modulates luteinizing hormone and growth hormone secretion from porcine pituitary cells in culture. Domestic Animal Endocrinology 28:331-337.

Interpretive Summary: Inadequate nutrition is characterized by low blood levels of pituitary hormones, such as luteinizing hormone (LH), necessary for stimulation of the reproductive system and growth hormone (GH), necessary for growth. A lack of these hormones results in delayed puberty, irregular heat cycles and failure of animals to breed and poor growth. The brain peptide, orexin, produced by the brain in response to changes in body weight or energy, stimulates feed intake, and modultes LH secretion in rodents. Orexin may serve as a signal linking the body's energy regulating system with the reproductive and growth system. This is the first report to demonstrate that orexin administration stimulated LH secretion and suppressed GH response to GH releasing hormone (GHRH, brain hormone that stimulates GH secretion)) from pig pituitary cells in culture. Therefore, understanding the orexin- LH and GH interactions is necessary in order to develop new methods to improve reproductive efficiency and growth in the pig.

Technical Abstract: To test the hypothesis that orexin-B acts directly on the anterior pituitary to regulate LH and growth hormone (GH) secretion, anterior pituitary cells from prepuberal gilts were studied in primary culture. On d 4 of culture, 105 cells/well were challenged with 0.1, 10 or 1000 nM GnRH; 10, 100 or 1000 nM [Ala-15]-hGRF-(1-29-)NH2 or 0.1, 1, 10 or 100 nM , orexin-B individually or in combinations with 0.1 and 1000 nM GnRH or 10 and 1000 nM GRF. Secreted LH and GH were measured at 4 hr after treatment. Basal LH and GH secretion (control; n = 6 pigs) was 183 ± 18 and 108 ± 4.8 ng/well, respectively. Relative to control at 4 hr, all doses of GnRH and GRF increased LH and GH secretion. All doses of orexin-B increased LH secretion, except for the 0.1 nM dose. Basal GH secretion was unaffected by orexin-B. Addition of 1, 10 or 100 nM orexin-B in combinations with 0.1 nM GnRH increased LH secretion compared to GnRH alone. Only 100 nM orexin-B in combinations with 1000 nM GnRH increased LH secretion compared to GnRH alone. All doses of orexin-B in combination with 1000 nM GRF suppressed GH secretion compared to GRF alone, while only 0.1 nM orexin-B in combination with 10 nM GRF suppressed GH secretion compared to GRF. These results indicate that orexin may directly modulate LH and GH secretion at the level of the pituitary gland.