Evaluation of a plasmid delivery system for production of GnRH and GHRH in the horse and goat
The efficacy of a novel plasmid delivery system was assessed for long-term expression of gonadotropin releasing hormone (GnRH) and growth hormone releasing hormone (GHRH) in horses and goats. The efficacy of the technology was demonstrated using 3 novel plasmids: pSEAP [expressing secreted embryonic alkaline phosphatase (SEAP)], pGHRH (expressing GHRH), and pGnRH (expressing GnRH). Geldings were electroporated with a reporter plasmid expressing SEAP in 3 muscle sites. Expression of SEAP, measured from jugular plasma samples, indicated muscle specificity for uptake and expression of the plasmid. Concentrations of SEAP were greatest (P < 0.05) after pectoralis injection, which was chosen as the site for electroporation in subsequent studies. In a second experiment, stallions were electroporated with pGHRH or pSEAP to evaluate the effect of long-term GHRH treatment on the growth hormone (GH) axis and testicular function. Stallions treated with pGHRH had increased (P < 0.05) plasma concentrations of IGF-I, increased (P < 0.05) volume of accessory sex gland fluid, and increased (P < 0.05) number of normal spermatozoa in the ejaculate relative to controls. In the third experiment, stallions were electroporated with pGnRH or pSEAP to test the effects of GnRH on the reproductive axis. Treatment with pGnRH increased (P < 0.05) plasma testosterone concentrations to d 56 and increased (P < 0.01) the LH response to GnRH on d 21, but did not alter (P > 0.1) seminal characteristics evaluated after 36 d of treatment. In a final experiment, goat does were treated with pGnRH or pSEAP to assess the effects of GnRH treatment on the reproductive axis during seasonal anestrus. Plasma concentrations of LH and FSH were not affected (P > 0.1) by treatment through d 56. Plasma progesterone measurements indicated that ovulation did not occur in does treated with pGnRH or pSEAP. Does treated with pSEAP had increased (P < 0.05) plasma SEAP concentrations. In conclusion, electroporatic plasmid delivery of peptide hormones may serve as an effective technique for expression of protein hormones in the horse and goat.
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Animal Science (Animal, Dairy, and Poultry Sciences)