Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 28, 1995
Publication Date: N/A
Technical Abstract: The effect of ST administration on somatotroph function has not been evaluated in neonatal pigs, which do not demonstrate a growth response to exogenous ST. Piglets received i.p. recombinant porcine ST (r-pST, 42-d implant, .5 mg/d) or vehicle implants at 3 d of age. Serum concentrations of ST and IGF-1 were evaluated in blood samples drawn at 3, 12, 21, and 42 days (10/treatment group at each time point). Mean serum ST concentration at 3, 12, 21 and 42 days were 10.14, 2.9, 4.3, and 2.2 ng/ml in the control group and 6.5, 24.5, 11.4 and 5.0 ng/ml in the r-pST group (r-pST, p < .02; Time, p < .05; r-pST x Time, p < .005). Corresponding mean serum IGF-1 concentrations were 33.6, 63.9, 51.7, and 80.4 ng/ml in the control group and 37.7, 106.1, 80.8, and 102.7 ng/ml in the r-pST group (r-pST, p < .01; Time, p < .0001; r-pST x Time, p = .05). Ten piglets were sacrificed at 21 and 42 d of age (5/treatment group). Cultured pituitary cells from each animal were challenged with vehicle; .1, 1, and 10 nM GHRH; 2 mM 8-Br-cAMP and 100 nM phorbol myristate acetate. The release of ST from cultured somatotrophs was stimulated by all secretagogues (p < .0001). Overall mean in vitro ST secretion in cultures from 21 and 42 d animals was 50.2 and 92.2 ng/250,000 cells, respectively (p < .02). Mean in vitro ST release in cultures from control and r-pST animals was 92.3 and 50.1 ng/250,000 cells, respectively (p < .02). Mean cellular ST content similarly increased with age (133.6 vs 279.8 ng/250,000 cells at 21 and 42 d; p < .02) and was reduced by r-pST treatment (269.8 vs 143.7 ng/250,000 cells in control and r-pST groups; p < .04). Piglet growth was not affected by r-pST (p > .1). These results demonstrate that r-pST induces negative feedback inhibition of somatotroph function, but does not enhance somatic growth in piglets.