Evaluation of Plasmid Delivery by Electroporation as a Means of Increasing Gonadotropin-Releasing Hormone Production in Stallions

A comparison of the growth responses following intramuscular GHRH plasmid administration versus daily growth hormone injections in young pigs

The efficacy of daily porcine growth hormone (GH) injections versus plasmid-driven porcine GH-releasing hormone (pGHRH) production to promote growth was assessed. Ten-day-old piglets were injected intramuscularly with 0.1, 1, or 3 mg pGHRH, or a control plasmid followed by electroporation. Plasmid constructs were driven by a synthetic muscle-specific promoter. A fifth group received daily injections of GH [0.15 mg/(kg.day)]. Control and pGHRH-treated pigs were pair-fed to GH-treated pigs. Body composition was assessed by dual-energy X-ray absorptiometry (DXA). Weight gains of GH- and pGHRH-treated pigs were greater than of controls (P < 0.001) due to greater lean mass accretion; fat accretion was similar across all treatments. Weight gain of pGHRH- and GH-treated pigs was similar for 6 weeks, but over the final 10 days, only pigs administered the highest plasmid dose maintained higher growth rates. Serum insulin-like growth factor-I (IGF-I) levels were two- to threefold higher in GH- and pGHRH-treated pigs than in controls after 4 weeks (P = 0.05), but subsequently decreased to control levels in the pGHRH-treated group. Organ weights were greater in GH- than pGHRH-treated and control piglets (P < 0.02). These results demonstrate that pGHRH transfer is effective for promoting growth and avoids the need for the frequent injections necessitated with peptide hormone use.