Ex Vivo Evaluation of Buserelin Permeation Across Porcine Endometrial Tissue: A Pilot Study

Buserelin, a gonadotropin-releasing hormone (GnRH) analog, is commonly used in swine to induce ovulation and facilitate fixed-time artificial insemination (FTAI). Supplementation of diluted semen with buserelin has been developed as a less invasive approach to synchronize ovulation and potentially enhance litter size in gilts. This study evaluated the diffusion of buserelin across porcine endometrial tissue using an ex vivo Franz diffusion cell system. The primary objective was to determine whether buserelin, either alone or in combination with extended boar semen, could penetrate sow uterine tissue. Endometrial tissues were collected post-mortem from six sows confirmed to be in the follicular phase by macroscopic examination of the reproductive tract. Each uterine sample was divided into two portions and assigned to either a buserelin group or a buserelin plus diluted semen group. Boar semen used for the diluted semen group was prepared using a commercial extender, and the pH of all test samples was measured prior to analysis. Diffusion studies were performed using vertical Franz diffusion cells maintained at 37 °C, with phosphate-buffered saline (pH 7.4) serving as the receptor medium. To standardize the total drug dose applied (rather than the concentration or application volume), tissue samples were treated either with 4 µg of buserelin acetate in 1 mL of solution or with 4 µg of buserelin acetate in 1 mL of solution mixed with 1 mL of diluted semen. Receptor fluid was collected over an 8-h period for quantification of permeated and absorbed buserelin using high-performance liquid chromatography (HPLC). The overall percentage of buserelin permeation through porcine endometrial tissue was similar between the buserelin group (61.3 ± 7.8%; range 54.0-73.7%) and the buserelin plus diluted semen group (62.2 ± 4.6%; range 48.6-68.9%), with no significant difference (p = 0.840). During the first 0.75 h (0-45 min), the cumulative permeation did not differ between treatments (10.2 ± 2.4% vs. 11.8 ± 2.4%, p = 1.000). However, at 1.5 h, the permeation rate was lower in the buserelin group than in the buserelin plus diluted semen group (18.0 ± 2.4% vs. 29.2 ± 2.4%, p = 0.032). From this point onward, the buserelin plus diluted semen group maintained higher permeation until approximately 6 h, after which permeation values became comparable (p = 0.174). The steady-state fluxes (J_ss) were 0.21 and 0.28 µg/cm²·h, with corresponding apparent permeability coefficients (P_app) of 0.052 and 0.069 cm/h, respectively. In conclusion, this ex vivo pilot study showed that more than 61% of the administered buserelin permeated porcine endometrial tissue within 8 h, irrespective of semen supplementation. The addition of diluted semen enhanced permeation during the early phase but did not affect the overall cumulative diffusion.