Effects of dietary supplementation with cysteamine on growth hormone receptor and insulin-like growth factor system in finishing pigs.

The present study was conducted to test the hypothesis that chronic cysteamine (CS) supplementation may affect serum insulin-like growth factor (IGF)-I concentrations and growth hormone (GH) receptor (GHR), IGF-I, IGF-I receptor (IGF-IR), IGF binding protein (IGFBP)-3, and insulin receptor (IR) mRNA levels in different tissues of finishing pigs. A total of 24 finishing pigs (60.05 +/- 1.24 kg; 12 gilts and 12 barrows) were assigned randomly to one of the three dietary groups, with four pens/group (per pen: one gilt, one barrow). The pigs were fed a basal diet containing 0 (control), 70, or 140 mg/kg cysteamine feed additive (containing 28% cysteamine hydrochloride) for 47 days. The results indicated that CS supplementation (70 mg/kg) increased the average daily gain (ADG) and serum IGF-I level, upregulated mRNA levels of GHR and IGF-I (liver, stomach, muscle), IGF-IR (stomach, duodenum, muscle), and IGFBP-3 (liver) but downregulated IGFBP-3 (stomach, duodenum, muscle). CS supplementation (70 mg/kg) did not affect mRNA levels of GHR and IGF-I (duodenum), IGF-IR (liver), and IR (liver, stomach, duodenum, muscle). CS supplementation (140 mg/kg) downregulated GHR (duodenum), IGF-I, and IGF-IR mRNA (liver, stomach, duodenum, muscle) but upregulated IGFBP-3 and IR mRNA (liver, stomach, duodenum, muscle) and did not affect ADG and serum IGF-I concentration. Collectively, the results suggest that dietary CS supplementation modulates the growth rate, serum IGF-I concentrations, and the gene expression of GHR, IGF-I, IGF-IR, IGFBP-3, and IR in a dose-dependent manner. CS supplementation has tissue-specific regulation of GHR, IGF-I, IGF-IR, and IGFBP-3 mRNA levels. Moreover, the results also imply the possible physiologic role of the GH-IGF axis in mediating the dietary CS supplementation-supported growth of finishing pigs.