Effect of dextran on the release of gonadotropin-releasing hormone (GnRH) injected into rats: plasma GnRH and gonadotropin response.

Prolonged release of the peptide gonadotropin-releasing hormone (GnRH) from its aqueous solution was achieved by addition of the polymer dextran (Mw ∼ 500,000). This effect observed in an in vitro system was caused by a decrease of the diffusion coefficient of the peptide. When GnRH was intramuscularly injected into male rats, the addition of dextran to the injected peptide solution led to a prolongation of the GnRH plasma level at the expense of its peak value. This change can be explained by a decrease of the absorption rate of GnRH into blood, which parallels the in vitro observation. As a result, the gonadotropin response to GnRH was stronly increased.