Kinetics of gonadotropin binding by receptors by the rat testis. Analysis by a nonlinear curve-fitting method

Abstract

The kinetics of the reaction between human chorionic gonadotropin (hCG) and specific gonadotropin receptors in the rat testis were determined at 24 and 37 degrees, over a wide range of hormone concentrations. Hormone concentrations were corrected for the binding activity of the (-125I)hCG tracer preparations. Analysis of the experimental data was performed with an interactive nonlinear curve fitting program, based upon the second-order chemical kinetic differential equation. The mean values for the association rate constant (k1) were 4.7 x 10-7 M-1 min-1 at 24 degrees, and 11.0 x 10-7 M-1 min-1 at 37 degrees. At both temperatures, the values of kl were independent of hormone concentration. Initial dissociation rates were consistent with first order kinetics, with dissociation rate constant (k2) of 1.7 x 10 minus -3 and 4.6 x 10 minus -3 min minus -1 at 24 and 37 degrees, respectively. When studied over longer periods at 24 degrees, the dissociation process appeared to be multiexponential. The kinetics of degradation of (-125I)hCG and receptors were determined at both temperatures, and a mathematical model was developed by modification of the second-order chemical kinetic differential equation to take these factors into account. The application of such a model to hCG kinetic binding data demonstrated that reactant degradation had little significant effect on the derivation of the association rate constant (k1), but caused significant overestimation of the dissociation rate constant (k2) values derived from association experiments. The model was also applied by computer simulation to a theoretical analysis of the effects of degradation of free hormone and receptor sites upon kinetic and steadystate binding data. By this method, the initial velocities of hormone binding were shown to be less affected by degradation than the steady-state levels of hormone-receptor complex. Also, reactant degradation in simulated steady-state experiments caused an underestimate of the apparent equilibrium association constant, but had relatively less effect on the determination of binding site concentration.

Study of Follitropin Receptors in Testis Using a Homologous System

“…Such an approach has been used successfully for the analysis of the binding of choriogonadotropin to rat testis receptors [38].…”

Luteinising hormone receptor kinetic and LH-induced prostaglandin production throughout the oestrous cycle in porcine endometrium

“…These parameters were the basis for the classification of the uterine tissues into four major groups (n = 4-6): 1) pro-oestrus (days [18][19][20]; 2) early luteal phase (days 6-7); 3) pre-luteolysis (days [12][13][14]; and 4) luteolysis (days [15][16] figure 3).…”

Kinetic and autoradiographic studies on binding of hCG to the testicular LH receptors of neonatal rats

“…The specific activity of each batch of labelled hormone was determined by self-displacement analysis in the homologous radioligand-receptor assay, using rat testis homogenate (Catt, Ketelslegers & Dufau, 1976). A correction was also made for the fraction of radioactivity associated with biologically active hormone, as measured in each labelled preparation by determining the maximum specific binding of a sample ofthe tracer to an excess of rat testis receptors (Catt et al, 1976 (Rodbard & Hutt, 1974;Ketelslegers, Knott & Catt, 1975) was used to perform all curve fittings and calculations. This program, using a PDP-10 time sharing computer, also pro¬ vided the original graphic output of the illustrations presented in this report.…”