Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 14, 1997
Publication Date: N/A
Interpretive Summary: The beneficial effects of growth hormone (GH) on livestock growth rate, feed efficiency, and meat leanness are well known. Blood GH levels are very high at birth, but fall very rapidly in the early neonatal period in all mammals. Since the cause for this decline in GH secretion is not known, we have evaluated the controlling factors of GH production and release from its source of production, the pituitary gland, in neonatal pigs. Strong developmental regulation is revealed on several genes involved with GH control. The identification of possible mechanisms for the decline in pituitary GH production suggests novel approaches for maintaining high levels of naturally produced GH. The information produced will be of interest to neonatal biologists and to agricultural scientists in academia and industry working in the area of growth promotants.
Technical Abstract: The objective of this study was to evaluate developmental changes in somatotroph function and related gene expression in neonatal pigs. Male piglets were sacrificed at 1, 7, 14, 21, 28, 35, and 42 days of age (8/age group) for the collection of tissue and blood. Serum concentrations of GH were determined. Quantitations of mRNA were performed for pituitary Pit-1, ,GH, and GHRH receptor. Cultures of pituitary cells from each pig were stimulated with 0,.1, 1, or 10 nM GHRH; 2 mM 8-Br-cAMP; or 100 nM phorbol myristate acetate. Elevated serum concentrations of GH were observed at 1 day of age, followed by a pronounced decrease to basal levels thereafter (P < .0001). In vitro GH secretion was significantly stimulated by secretagogue treatments (P < .0001). Age-related declines in in vitro GH secretion were observed regardless of whether the cells were stimulated by GHRH or by secretagogues which bypass the GHRH receptor (P < .001). Similarly, cellular GH content varied with age (P = .01). Levels of pituitary GH mRNA (P = 0.01) and GHRH receptor mRNA (P = 0.0002) decreased with age. The quantity of GHRH receptor mRNA was correlated with GH mRNA levels (r = .55, P = .02), serum GH concentrations (r = .55, P = .02), and in vitro GH secretion (r = .66, P = .001). Pituitary Pit-1 mRNA levels at 7 and 14 days of age were significantly elevated relative to all other sampling times (P = .0002). Levels of Pit-1 and GH mRNAs were significantly correlated (r = .64, P = .003). These results demonstrate a strong developmental regulation of somatotrophic function and related gene expression during the early neonatal period of the pig. Age-related decreases in secretory function may be mediated by concurrent mechanisms relating to the expression of the GHRH receptor and of GH.