Title: IGF-I modulation of GH and LH secretion in the pig Authors
Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: April 15, 2008
Publication Date: July 10, 2008
Citation: Barb, C.R., Hausman, G.J. 2008. IGF-I modulation of GH and LH secretion in the pig [abstract]. Joint Abstracts of the American Dairy Science and Society of Animal Science. V:86E(Suppl.2) p. 64. Technical Abstract: Three experiments (EXP) were conducted to determine the role of IGF-I in modulating GH and LH secretion. In EXP I, prepuberal gilts, 65 ± 6 kg body weight (BW) and 140 days of age received intracerebroventricular (ICV) injections of saline (n = 4), 25µg (n = 4) or 75µg (n = 4) IGF-I and jugular blood samples were collected. In EXP II anterior pituitary cells in culture collected from 150 day old prepuberal gilts (n = 6) were challenged with 0.1, 10 or 1000 nM [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (GRF), or 0.01, 0.1, 1, 10, 30 nM IGF-I individually or in combinations with 1000 nM GRF. Secreted GH was measured at 4 and 24 h after treatment. In EXP III anterior pituitary cells in culture collected from 150 day old barrows (n = 5) were challenged with 10, 100 or 1000 nM gonadotropin releasing hormone (GnRH) or 0.01, 0.1, 1, 10, 30 nM IGF-I individually or in combinations with 100 nM GnRH. Secreted LH was measured at 4 h after treatment. In EXP I, serum GH and LH concentrations were unaffected by ICV IGF-I treatment. In EXP II, relative to control all doses of GRF increased (P < 0.01) GH secretion. Only 1, 10, 30 nM IGF-I enhanced (P < 0.02) basal GH secretion whereas by 24 h all doses except for 30 nM IGF-I suppressed (P < 0.02) GH secretion compared to control wells. All doses of IGF-I in combination with1000 nM GRF increased (P < 0.04) the GH response to GRF compared to GRF alone at 4 h. In contrast by 24 h all doses of IGF-I except for 1 nM suppressed (P < 0.4) the GH response to GRF. In EXP III, all doses of IGF-I increased (P < 0.01) basal LH levels while the LH response to GnRH was unaffected by IGF-I (P > 0.1). In conclusion, under these experimental conditions the results suggest that IGF-I may directly modulate GH secretion at the level of the pituitary gland and although IGF-I increased basal LH secretion from pituitary cultures further examination of the role IGF-I on LH secretion is needed.