Effect of acute ammonia exposure on expression of GH/IGF axis genes GHR1, GHR2 and IGF-1 in pufferfish (Takifugu obscurus)

Waterborne ammonia has become a persistent pollutant of aquatic habitats. The exposure to ammonia stress can reduce growth in a wide range of aquatic organisms. To assess the effect of ammonia exposure on the growth hormone/insulin-like growth factors (GH/IGF) axis, we identified and characterized GHR1, GHR2 and IGF-1 from pufferfish. Comparative analysis showed that these genes shared high identity and similarity with corresponding genes in other fish species. The transcripts of these genes were widely expressed in all tested tissues. The highest level of GHR1 mRNA was found in the brain, whereas GHR2 and IGF-1 mRNA levels were the highest in the liver. Following acute ammonia exposure (100 mg/L total ammonia-nitrogen), GHR2 expression in the liver did not change at 6 h and then significantly decreased at 12, 24 and 48 h, whereas GHR1 and IGF-1 expressions were significantly down-regulated at 6, 12, 24 and 48 h, respectively. These results indicated that ammonia stress decreased the expression of GH/IGF axis genes, which might have negative effect on the growth and development of pufferfish.