PREPARATION AND EVALUATION OF POLYANHYDRIDE MICROSPHERES CONTAINING GONADOTROPIN-RELEASING-HORMONE (GNRH), FOR INDUCING OVULATION AND SPERMIATION IN FISH

We developed a microspheric delivery system for a synthetic analog of gonadotropin-releasing hormone (GnRHa) for inducing ovulation and enhancing spermiation in broodfish which, relative to mammals, are maintained at low temperatures (10-22 degrees C). The microspheres were based on a biodegradable copolymer of fatty acid dimer and sebacic acid (p[FAD-SA]) of a 25:75 molar ratio, and were prepared by a solvent evaporation method, using double emulsion. The GnRH analog [D-Ala(6),Pro(9)NEt]-GnRH was entrapped into the microspheres at 3% loading with 86% (+/-5.4) efficiency. The prepared microspheres had a spherical shape, with diameters from 10 to 240 mu m. In vitro, GnRHa was released for at least 90 days at 15 degrees C, following an initial release of 8.8% of the total amount, The release during the first 30 days followed first-order kinetics described by the equation GnRHa (mu g) = 1.7[day](0.33) (R(2) = 0.99), and zero-order kinetics thereafter, described by the equation GnRHa (mu g) = 0.027 [day] + 4.5 (R(2) = 0.98). Plasma GnRHa levels of microsphere-injected striped bass (Morone saxatilis) remained elevated for at least 8 weeks at 16 degrees C, although the levels dropped dramatically after day 28. Microsphere injection of postvitellogenic striped bass females and Atlantic salmon (Salmo salar) induced 100% ovulation by day 11 and 15 after treatment, respectively. Similar treatment induced a 4-10-fold increase in sperm production of striped bass males for at least 14 days after treatment and resulted in a 2.5-fold increase of expressible sperm volume of male Atlantic salmon 10 days after treatment.