A new animal model for evaluation of long-term growth rate over one month by rhGH/PLGA microcapsule formulations.

A new animal model to evaluate the long-term growth rate produced by a sustained-release formulation of recombinant human growth hormone (rhGH) over one month was developed and the usefulness of our microcapsule formulations was demonstrated in this model. Long-term pharmacological effects by subcutaneous injection of microcapsules for sustained release of rhGH were evaluated in hypophysectomized (Hpx) rats treated with immunosuppressive agent along with hormone supplement. Copoly(DL-lactic/glycolic)acid (PLGA) microcapsules for sustained release of rhGH, a two-week sustained-release formulation (rhGH-SR-2W) and a one-month sustained-release formulation (rhGH-SR-1M), were prepared by a solid-in-oil-in-water emulsion solvent evaporation technique. Body-weight gain, body-length gain and serum levels of rat insulin-like growth factor-I (rIGF-I) induced by subcutaneous injection of rhGH-SR were compared with those by daily injections of rhGH solution in Hpx rats for 35 days. Serum IGF-I levels in Hpx rats after the injection of rhGH-SR2W microcapsules were higher than those after daily injections of rhGH solution. Body-length gain, a new parameter, after single injection of rhGH-SR-1M microcapsules demonstrated the higher growth rate than that after daily injections of rhGH solution for 35 days. Thus, single injection of rhGH-SR microcapsules demonstrated long-term pharmacological effects greater than those by daily injections of rhGH solution in a newly developed model, immunosuppressed Hpx rats.