Kinetic Model of the Action of 17 alpha-Ethynylestradiol on the Capacitation of Mouse Sperm, Monitored by HPLC-MS/MS
Abstrakt
17 alpha-Ethynylestradiol (EE2), a synthetic estrogen used in contraceptive pills, is resistant to hepatic degradation and is excreted in the urine. It is chemically stable and has a negative impact on the endocrine system.
The aim of this work was to mathematically describe the possible interaction of EE2 (200, 20, and 2 mu g/L) with sperm estrogen receptors during sperm maturation, which is called capacitation. The concentrations of the unbound EE2 remaining in capacitating medium during 180 min of sperm capacitation were determined at 30 min intervals by high performance liquid chromatography with tandem mass spectrometric detection (HPLC-MS/MS) and the data obtained (relative concentrations B-t) were subjected to kinetic analysis.
The suggested kinetic schema was described by the system of differential equations with the optimization of rate constants used to calculate the theoretical B-t values. Optimal parameters (overall rate constants K-1-K-5 and molar ratio n) were determined by searching the minimum of absolute values of the difference between theoretical and experimental B-t values.
These values were used for the design of the theoretical B(t) curves which fit to experimental points. The proposed kinetic model assumes the formation of an unstable adduct between EE2 and the receptor in cytoplasm, which acts as an autocatalytic agent and gradually decomposes.