Poly(d, l-lactide-co-glycolide) microsphere-mediated expression of growth hormone-releasing hormone in skeletal muscle of pregnant pigs enhances offspring weight gain

Somatostatin (SS) and growth hormone-releasing hormone (GHRH) are synthesized and secreted by the hypothalamus, which mediates the synthesis and secretion of the growth hormone (GH) from the hypophysis, as well as regulates the GH concentrations in animals and humans. In this paper, we describe the regulation of animal growth using plasmid DNA-encoding GHRH gene. In this study, we introduce a gene transfer technique mediated by PLGA microspheres. The eukaryon expression vectors based on the RNA replicon, namely, pCMV-Rep-GHRH, were constructed; further, poly(d, l-lactide-co-glycolide) (PLGA) microsphere-encapsulating plasmids were prepared. Gilts were intramuscularly injected at day 85 of gestation with 1 or 5 mg of pCMV-Rep-GHRH microspheres. Piglets were weighed following birth and at days 20 and 50 postbirth. Blood samples were collected at day 50 to evaluate serum IGF-1 and GHRH concentrations. The result showed that the birth weight of the piglets at 20 d and 50 d were significantly higher (by 20.32-110.76%; P < 0.01) than that in the group injected with saline-MP. After 50 days, the concentrations of serum IGF-I in the treatment groups injected with plasmid were observed to be significantly higher (2.5 times; P < 0.01) than that in the group injected with saline-MP; the concentration of serum GHRH was higher than 21% in 1 case (P < 0.01). The lymphocyte stimulation indices detected confirmed that GHRH gene transfer could improve immunity in first-generation progeny pigs. The results of this study confirmed that PLGA microsphere-mediated GHRH expression in pregnant pig skeletal muscle enhanced the body weight of piglets prior to and following birth.