RELATIONSHIP BETWEEN IN-VITRO SOMATOTROPH FUNCTION AND GROWTH IN 3-WEEK-OLD BARROWS

The relationship between in vitro somatotroph function and growth was examined in piglets demonstrating a continuous range of growth charact eristics. Twenty barrows were sacrificed at 3 weeks of age for the col lection of pituitary tissue and blood. Pituitary cells from each anima l were cultured and exposed to vehicle (culture medium);.l, 1, and 10 nM growth hormone-releasing hormone (GHRH); 2 mM 8-Br-cAMP (cAMP); 100 nM phorbol myristate acetate (PMA); and 59 mM KCl. All secretagogue t reatments stimulated growth hormone (GH) secretion p < .0001). Basal a nd stimulated GH secretion in culture, intracellular GH content (icGH) , and serum insulin-like growth factor-1 (IGF-1) concentrations were a ll positively correlated with S-week weight gain (p < .05). Concentrat ions of GH in the serum sample taken at sacrifice were not related to growth (p > .3). Intracellular GH content was correlated with in vitro GH secretion p < .01) and serum IGF-1 concentrations (p < .001). Soma totroph function was contrasted in the 7 largest and 7 smallest piglet s (large, 8.3 +/- .3 kg, n = 7; small, 4.5 +/- .2 kg, n = 7). Treatmen t with GHRH produced a dose-related increase in GH secretion in both e xperimental groups (p < .0001). No significant size x GHRH interaction was detected (p = .09). When contrasted with the small group, the lar ge group demonstrated elevated GH secretion in culture (p < .01), icGH content (p < .001), and circulating IGF-1 (p < .001). The results of this study raise the possibility of a functional relationship between porcine somatotroph secretory activity and growth, mediated by IGF-1, which may be regulated by the quantity of GH available for release.