Conclusion
Performed studies indicate that GnRH analogs in the form of suspension have higher bioavailability than their solution counterparts. It influences the effects of their action, especially in relation to LH and FSH.
Methods
Two sets of experiments were performed. In the first one, buserelin and dalarelin were injected into mature female rats in two forms: suspension, in which the analogs are bounded by Zn2+ ions and solution. The pharmacokinetic parameters and bioavailability of the analogs were calculated, based on their concentration in the plasma measured by high-performance liquid chromatography method (HPLC). In the second experiment, the hormones in two different forms were injected into superovulated immature female rats and then the concentration of Luteinizing hormone (LH), Follicle-stimulating hormone (FSH) and 17β-estradiol in the serum was measured by radioimmunological method.
Results
The Extent of Biological Availability (EBA), calculated on the base of AUC0-∞, showed that in the form of solution buserelin and dalarelin display, respectively, only 13 and 8 % of biological availability of their suspension counterparts. Comparing both analogs, the EBA of dalarelin was half (53 %) that of buserelin delivered in the form of solution and 83 % when they were delivered in the form of suspension. The injection of buserelin or dalarelin, in the form of solution or suspension, into superovulated female rats increased LH, FSH and estradiol concentration in the serum. However, after injection of the analogs in the form of suspension, the high concentration of LH and FSH in the serum persisted longer.