Abstract: Fifty-four, crossbred pigs (Landrace ? Large White ? Pietran) were used in a study to determine the influence of dietary tryptophan on serum IGF-I concentrations as well as IGF-I and growth hormone receptor gene expression in the liver, longissimus dorsi and duodenum of weaned pigs (9.98 + 0.31 kg BW). The pigs were assigned to one of three diets including a low tryptophan (Trp:Lys = 0.11:1.14), a medium tryptophan (Trp:Lys = 0.19:1.13) and a high tryptophan (Trp:Lys = 0.24:1.14) containing diet. Each treatment was replicated six times (3 pens of castrated males and 3 pens of females) with three pigs per pen. Consuming the low tryptophan diet for 21 d significantly decreased gain, intake and feed conversion (P<0.01) compared with the medium and high tryptophan fed groups. In addition, pigs fed the low tryptophan diet had lower serum IGF-I levels (P<0.01). The decreased serum IGF-I levels were accompanied by lower IGF-I mRNA in the liver, longissimus dorsi and duodenum, and lower growth hormone receptor mRNA in the liver of pigs fed the low tryptophan diet compared with pigs fed the other two diets (P<0.01). Hepatic IGF-I mRNA in pigs fed the medium tryptophan diet was lower than in pigs fed the high tryptophan diet (P<0.01). The low and high tryptophan fed pigs had higher growth hormone receptor mRNA (P<0.01) in muscle than the medium tryptophan group. However, in the duodenum, the low and medium tryptophan fed pigs had lower growth hormone receptor mRNA (P<0.01) compared with the high tryptophan group. The mRNA levels of IGF-I in muscle and GHR in duodenum in males were higher than in females (P=0.01). These results suggest that the growth retardation and reduction in IGF-I concentrations caused by low dietary tryptophan may be partly due to decreased IGF-I mRNA expression in liver and extra hepatic tissues and to growth hormone receptor mRNA expression in the liver. Dietary tryptophan has a distinct tissue and sex-specific effect in growth hormone receptor transcriptional events.
Yuhua Ding , Defa Li , Xiangshu Piao , Jingdong Yin and Jianjun Xing , 2004. Regulation of Insulin-Like Growth Factor-1 and Growth Hormone Receptor Gene Expression in Weaned Pigs Fed Graded Levels of Dietary Tryptophan . Journal of Animal and Veterinary Advances, 3: 490-496.