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 enha ncing spermiation in broodfish which, relative to mammals, are maintai ned 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 evapor ation method, using double emulsion. The GnRH analog [D-Ala(6),Pro(9)N Et]-GnRH was entrapped into the microspheres at 3% loading with 86% (/-5.4) efficiency. The prepared microspheres had a spherical shape, wi th 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) remaine d elevated for at least 8 weeks at 16 degrees C, although the levels d ropped dramatically after day 28. Microsphere injection of postvitello genic striped bass females and Atlantic salmon (Salmo salar) induced 1 00% 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 d ays after treatment.