Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 3/16/1998
Publication Date: N/A
Technical Abstract: Previously we have shown that treating neonatal pigs with pST inhibits somatotroph function. Reduced somatotrophic activity would result in a GH deficient animal after cessation of treatment, thus resulting in a loss of any gained performance advantage. It is important, therefore, that we understand the mechanism of suppressed pituitary GH secretion. Crossbred intact male swine (n=48) were assigned by litter and body weight to 1 of 3 treatment age groups (1, 4, or 9 wk of age; n=16/age group) at 1 d of age. Within each age group piglets were assigned to either the pST group (daily im injections of 200 ug/kg rpST; n=8) or the Control group (daily im injections of sterile water; n=8) for a 2-wk period. The 4- and 9-wk age groups were weaned at 3 wk while the 1-wk age group remained with their sows throughout the study. After 2 wk of treatment, piglets were sacrificed for blood and tissue collection. While ADG was not different (P>0.10) between pST and Control pigs, gain:feed was increased (P<0.05) fo pST treated pigs in the 9-wk age group. Serum IGF-1 at sacrifice increased with age (P<0.0001) and was greater in the pST treated pigs (P<0.008). GH mRNA was reduced (P<0.0004) in the pST treated pigs, but did not differ (P>0.10) among age groups. The reduction in GH mRNA was equivalent among age groups (P > 0.1, pST X Age). While Pit-1 mRNA increased (P<0.005) with age, pST treatment reduced (P<0.04) Pit-1 mRNA expression. GH mRNA was reduced by pST in the 1-wk age group, however, there was no concurrent change in the Pit-1 mRNA level (P > 0.10). GH-releasing hormone receptor (GHRH rec) mRNA declined with age (P<0.002) but was unaltered by pST treatment (P>0.10). Thus, down-regulation of somatotroph function does not appear to be mediated by a suppression of GHRH rec gene expression.