Developmental Regulation Of Splenic Expression Of Growth-related Genes In The Pig

Slowly-growing Erhualian(EHL) pigs and fast-growing Large White(LW) pigs were used as experimental animal models to analyse the relationship of spleen development and somatotropic axis hormones in the present study. Body weight(BW), spleen weight(SW) and spleen index(SW/BW) in different breeds and sexes were compared.Splenic IL-2 and IL-6 concentrations in pigs at 0, 3. 20, 45 , 90 ,120 and 180 days of age were measured via RIA method respectively.. Further studies on developmental changes of splenic GHU GHR, IGF-1 and IGF-1R mRNA expression levels were detected by PT-PCR. In order to furtherinvestigate the effect of somatotropic hormones on spleen development, 15-day-old pre-weaning piglets was treated with dietary cysteamine and the changes of splenic GHR and IGF-1R mRNA expression were studied.The present study includes four series as follows:1. Developmental changes of body weight gain, spleen weight gain and the contents of IL-2 and IL-6 in the spleen of EHL and LW pigs.From day 0 to day 180, the body weight (BW) of EHL was significantly lower than that of LW,and the spleen weight increased from day 0 to day 180 both in EHL and LW.The spleen indexreached a peak at day 20 in EHL, while in LW, the peak was observed at day 30, this indicates that the patterns of the spleen development were different between EHL and LW pigs, LW lagged behindEHL in terms of spleen development..The pattern of developmental changes of IL-2 level hi spleen were similar in male EHL and male LW pigs. The spleen contents of IL-2 were significantly higher at birth compared with all the other age groups investigated (p<0.05). The concentration of IL-2 in EHL were higher than those hi LW at day 90 and day 120(p<0.05). The concentration of IL-6 in the spleen was much lower than that of IL-2 and no significant differences were found between age groups, breeds and sexes. 2. Developmental changes of splenic GH mRNA and GHR mRNA expression in EHL and LW pigs.GH mRNA was detected by RT-PCR in the spleen of EHL and LW pigs throughout the whole period of investigation from day 0 to day 180, however, the quantitative analysis was not possible due to the low ratio of abundance. Splenic GHR mRNA followed a similar developmental pattern both in EHL and LW pigs. The highest expression of splenic GHR mRNA was observed at birth in both breeds of pigs which was followed by a decline that occured earlier in EHL pigs at D3 compared with LW pigs at D20. The nadir of splenic GHR mRNA level was observed at D20 in EHL pigs and at D30 in LW pigs. The timing of the nadirs for splenic GHR mRNA was in accord with the timing of the peaks for spleen index in both breeds.3. Developmental changes of splenic IGF-1 and IGF-1R mRNA abundance in EHL and LW pigsThe abundance of IGF-1 mRNA in the spleen waslow at birth both in EHL and LW pigs and peaked at D20 for males and D30 for females. The pattern of developmental changes in splenic IGF-1 mRNA abundance was basically in accordance with spleen index hi EHL and LW pigs. The results implied that the autocrine and paracrine IGF-1 may play an important role in pig spleen growth and development. IGF-1R mRNA abundance hi spleens was higher at birth, subsequently, remained relatively stable levels in both EHL and LW pigs. On the whole, the developmental trends of IGF-1 R mRNA abundance hi spleens were similar with that of splenic IL-2 concentrations.4. Effects of cysteamine treatment on splenic CHR mRNA and IGF-1R mRNA expression hi LW pigs15-day-old piglets were fed with the diet supplemented with 400 ppm of CT2000(contains 30% of cysteamine). . Spleen samples were taken at 25 and 35 days of age, respectively. The results showed that body weight and spleen weight in the treatment group were not significantly different in comparison with the control group. GHR mRNA abundance in spleen at day 35 was slightly lower than that at day 25 in both groups, but no statistically significant differences were observed between treatment and control group in splenic expression of GHR mRNA and IGF-1R mRNA...