PARENT SESSION
Gonadotropins and Pituitary
374
FEED RESTRICTION OF PREPUBERTAL GILTS INCREASES ANTERIOR PITUITARY GLAND (AP) RESPONSIVENESS TO GNRH BUT DOES NOT AFFECT AP CONCENTRATIONS OF IGF-I OR IGF BINDING PROTEINS (IGFBPS).
Clapper, Jeffrey1, Rempel, Lea, 1
ABSTRACT- To determine if serum and AP concentrations of IGF-I and relative amounts of serum and AP IGFBPs are reduced in response to feed restriction, 20 prepubertal gilts of similar age and weight were assigned to one of two groups, CON (n=9) or FR (n=11) on d 1. CON gilts were fed 4 kg of a corn-soy diet daily while FR gilts received 1 kg. Blood samples were collected from all gilts each day beginning on d 1 and continuing through d 13. On d 7, blood samples were collected via jugular catheters every 20 min for 4 h from 7 FR and 7 CON gilts, then each gilt was administered GnRH (0.2 mg/kg BW) and GHRH (1 mg/kg BW) i.v. and blood samples were collected every 20 min for 4 h. Gilts were killed on d 13 and AP were collected. On d 1, serum concentrations of IGF-I (ng/ml) were similar (P>.05) between FR and CON gilts. By d 3, serum concentrations of IGF-I were decreased (P<.01) in FR gilts (81.6 ± 5.2) vs CON gilts (109.5 ± 4.7), and remained less (P<.01) than in CON gilts through d 13. Serum concentrations of LH (ng/ml) were similar (P>.05) on d 7 between FR and CON gilts before administration of GnRH, but serum concentrations of LH were greater (P<.03) in FR gilts (1.28 ± .13) vs CON gilts (0.82 ± .13) after administration of GnRH. No difference was detected (P>.05) in serum concentrations of GH between FR and CON gilts before or after administration of GHRH. AP concentrations of IGF-I and GH were each similar (P>.05) in FR and CON gilts. AP concentrations of LH (ng/mg) tended to be greater (P=.06) in FR gilts (29.1 ± 2.7) than CON gilts (22.0 ± 2.5). Ligand blot analysis detected 46 and 41 kDa forms of IGFBP-3, IGFBP-2 and 28 and 24 kDa forms of IGFBP-4 in the serum, and 33 kDa IGFBP-2 and 29 kDa IGFBP-5 in the AP. Relative amounts of 41 kDa IGFBP-3 in serum were similar (P>.05) between FR and CON gilts on d 1, but relative amounts were greater (P<.01) in CON gilts (3.2 ± 0.2) than FR gilts (2.1 ± 0.2) on d 7 and continued to be greater (P<.01) on d 13. Relative amounts of 46 kDa IGFBP-3 and 24 kDa IGFBP-4 were greater (P<.05) in CON gilts than FR gilts throughout d 13. Relative amounts of AP IGFBP-2 and -5 did not differ (P>.05) between FR and CON gilts. Feed restriction of prepubertal gilts caused characteristic decreases in serum concentrations of IGF-I and IGFBPs, but increased LH secretion in response to administration of GnRH, suggesting the effects of feed restriction may be occurring within the hypothalamus.
KEY WORDS: pig, IGF-I, binding proteins, pituitary