Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 1996
Publication Date: N/A
Technical Abstract: The present study evaluates potential mechanisms of developmental changes in somatotrophic axis function in the neonatal pig. Male piglets were sacrificed at 1, 7, 14, 21, 28, 35, and 42 days of age (8/age group) for blood and tissue collection. Experimental endpoints were in vitro function of somatotrophs (growth hormone (GH)-producing pituitary cells); serum GH and insulin-like growth factors (IGF) 1 and 2; pituitary GH, GHRH (GH- releasing hormone) receptor, and Pit-1 mRNA; and liver GH receptor, IGF-1 and IGF-2 mRNA. Growth increased steadily, but slowed between 14 and 28 days of age. This slower growth rate was associated with increasing GH and decreasing IGF-1 secretion. The well-characterized decline in GH secretion with age was associated with decreasing 1) intracellular GH content and GH secretion in culture and 2) GH and GHRH-receptor gene expression. Pit-1 mRNA levels were not congruent with the other developmental changes at all time points. In agreement with current theory, GH receptor gene expressio paralleled that of IGF-1, but not IGF-2. Interestingly serum concentrations of IGF-1 and IGF-2 did not reflect concurrent mRNA levels for these hormones. These results identify important mechanisms of developmental changes in somatotrophic function in the neonatal pig. In addition, new significant questions are raised relating to 1) the role of Pit-1 in regulating postnatal somatotrophic function and 2) the functional relationships between IGF-1 and -2 gene expression and circulating levels of these hormones.