EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-1) AND GROWTH HORMONE-RECEPTOR (GHR) MESSENGER-RNA IN LIVER, SKELETAL-MUSCLE AND ADIPOSE-TISSUE OF DIFFERENT BREEDS OF PIG

The work described was carried out to study the expression of insulin- like growth factor 1 (IGF-1) and growth hormone-receptor (GHR) mRNA in liver, skeletal muscle and adipose tissue from three breeds of pig wi th varying growth characteristics. The three breeds studied were the L arge White, noted for its lean tissue; the Duroc, characterized by its high intramuscular fat content; and the Meishan X Landrace (0.5 Meish an), noted for its fat, poorly conformed carcass and slower growth rat e. The probes used were designed to monitor promoter usage for IGF-1 e xpression and also expression of the extra-cellular domain of the GHR. Eighteen gilts, six of each breed, were given a barley/wheat diet (15 8 g crude protein, 10.7 g lysine and 13.9 MJ energy per kg), to appeti te, for 1 to 2 weeks until they reached about 85 kg. Samples of liver, longissimus dorsi (LD) muscle and three adipose tissue depots (subcut aneous (SC), perirenal (PR) and omental (OM)) were collected immediate ly after slaughter and frozen in liquid nitrogen (total time of sample collection to plunging of sample into liquid nitrogen was <3 min), pr ior to extraction of total RNA and ribonuclease protection assays. Ind ividual serum samples collected at exsanguination were frozen prior to IGF-1 radioimmunoassay. There were no breed differences in the serum IGF-1 concentrations (range 49 to 134 mu g/l), or in expression of the GHR gene or either class of IGF-1 transcript in the liver. However, t here was a significant difference between the breeds in expression of IGF-1 mRNA in the LD muscle (P < 0.001), the order being Duroc > White > Meishan, with only class 1 transcripts of IGF-1 being found. GHR ex pression in LD muscle was lower in White than in the other two breeds (P = 0.022). There was a significant difference between the breeds in expression of IGF-1 mRNA (only class 1 transcripts present) in the adi pose tissue (P = 0.006), the order being White > Duroc > Meishan, and also a significant depot difference, with expression being highest in the SC depot (P < 0.001). There were no differences between the breeds or depots in expression of GHR mRNA in adipose tissue. The observed d ifferences in muscle and adipose tissue IGF-1 expression may relate to the overall growth of the animal.