Hormone Binding Assays Research Articles

Studies on Receptor-mediated Activation of Adenylyl Cyclases: V. TRANSIENT KINETICS OF THE ACTIVATION OF BEEF RENAL MEDULLARY ADENYLYL CYCLASE BY NEUROHYPOPHYSEAL HORMONES: ESTIMATION OF APPARENT RATE CONSTANTS OF THE RECEPTOR-HORMONE INTERACTION

Abstract Activation of the beef renal medullary adenylyl cyclase system by submaximally stimulating concentrations of neurohypophyseal hormones (NHH) is a time-dependent process that requires several minutes to reach completion. This time dependency expresses itself in the appearance of lag periods in progress curves describing the time courses of hormone-induced cyclic adenosine 3':5'-monophosphate accumulation. Analysis of the extent (duration) and form (function describing the curvature) of these lags as a function of varying concentrations of the NHH [Arg8]vasopressin, indicated that the experimental data fit a model of adenylyl cyclase activation in which (a) the rate-limiting step of the hormone-dependent activation is the formation of the hormone-receptor complex, (b) the hormone reacts with receptor on a one to one basis, and (c) the function coupling receptor occupation to adenylyl cyclase activation is linear. Simulation of progress curves obtained with the NHH oxytocin using the same model agreed well with experimental data obtained at submaximally stimulating concentrations of hormone but predicted a maximally stimulated adenylyl cyclase activity that was 20 to 25% lower than found experimentally, suggesting the existence of a small degree of negative cooperativity between receptor sites. Apparent rate constants of association (k1) and dissociation (k2) of [Arg8]vasopressin and oxytocin to and from the NHH receptor were estimated using the above assumptions and led to the following values for [Arg8]vasopressin: k1 = 3.22 x 106 m-1 s-1, k2 = 703 x 10-3 s-1; for oxytocin: k1 = 8.69 x 104 m-1 s-1, k2 = 11.5 x 10-3 s-1. Thus, the main kinetic difference between the receptor-[Arg8]vasopressin interaction (apparent Ka = 1 to 2 x 10-9 m) and the receptor-oxytocin interaction (apparent Ka = 0.8 to 1.2 x 10-7 m) appears to lie in the rate at which these hormones associate to their receptor. GTP was found at 10-5 m to accelerate the rate at which the beef renal medullary adenylyl cyclase is stimulated by submaximally stimulating concentrations of [Arg8]vasopressin or oxytocin, presumably by accelerating the rates at which these hormones interact with the NHH receptor. The potential usefulness of the approach used here to study kinetic parameters of hormone-receptor interactions as a tool for validating a hormone binding assay as a receptor assay is discussed.

Serum follicle-stimulating and luteinizing hormone and progesterone in single and multiple gestations following induction of ovulation

Radioimmunoassays for serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), and competitive binding assays for serum progesterone were performed upon normal women and in 5 patients during 7 treatment cycles with human menopausal gonadotropin (HMG)/human chorionic gonadotropin (HCG) therapy. The FSH and LH determinations in the patients with induced ovulation differ considerably from those of the normal menstrual cycle and suggest that efforts to mimic a normal menstrual cycle are probably unnecessary in the treatment of anovulatory women. Induced multiple ovulation with resultant multiple corpora lutea produced serum progesterone levels approximately 2 to 3 times those found in normal singleton gestations. Evidence is given for the endogenous trophoblastic elaboration of HCG at approximately Days 8 to 9 of gestation following induced ovulation and for apparent suppression of FSH during the gestational period. Those patients who have higher pretreatment LH levels initially exhibit moderate suppression of serum LH followed by an elevation during the latter half of HMG administration. Those with low initial values do not.