Showing papers by "Michel Bouvier published in 1994"

Inverse agonist activity of beta-adrenergic antagonists.

Abstract: Agonist-independent properties of the human beta 2-adrenergic receptor (beta 2AR) were studied using the baculovirus expression system in Sf9 cells. In the absence of agonist but in the presence of GTP, membranes from cells expressing the beta 2AR exhibited higher levels of cAMP production than did membranes from uninfected cells or from cells infected with wild-type baculovirus. The increase in cAMP production was proportional to the number of beta 2AR expressed, up to 40 pmol/mg of membrane protein, and it could be inhibited in a dose-dependent manner by beta AR antagonists. The increase and its reversal both were independent of the possible presence of contaminating catecholamines in the culture medium and thus appear to reflect spontaneous beta 2AR activity and direct antagonist-receptor interactions, respectively. The maximal level of inhibition varied among the beta AR ligands tested, to yield the following rank order of "inverse efficacy"; timolol > or = propranolol > alprenolol > or = pindolol > labetalol > dichloroisoproterenol. The same rank order was observed using membranes prepared from Chinese hamster fibroblasts expressing beta 2AR. The effect of timolol was partly blocked by labetalol and dichloroisoproterenol, in an apparently competitive manner. The intracellular cAMP content of Sf9 cells cultured in serum-free medium was also increased by the expression of beta 2AR, and that increase was reversed by timolol and propranolol, consistent with observations in membrane preparations. The properties revealed by the expression of the beta 2AR in Sf9 cells suggest two agonist-independent traits of G protein-linked receptors, i.e., 1) that unliganded receptors are able to activate G proteins both in membrane preparations and in whole cells and 2) that antagonists may mediate their effects not only by preventing the binding of agonists but also by decreasing the propensity of the receptor to assume an active state.

Characterization, expression, and hormonal control of a thymic beta 2-adrenergic receptor.

Abstract: In the present study, we have characterized the beta 2-adrenergic receptor (beta 2-AR)-adenosine 3',5'-cyclic monophosphate (cAMP) system of the rat thymus gland and examined the hormonal regulation of the thymic beta 2-AR gene expression under physiological or pharmacological conditions accompanied by marked alterations of the sex steroid hormone milieu. We report here that membrane preparations of female rat thymic tissue contain iodocyanopindolol binding sites that exhibit pharmacological properties typical of a beta-AR. Detailed analysis by computer modeling of the binding potencies of a large series of beta 1- and beta 2-adrenergic agonists and antagonists revealed predominantly the beta 2-AR subtype (78%) in rat thymus. This inference from radioligand binding studies was corroborated functionally by the rank order of potencies of a series of adrenergic agonists to stimulate the production of cAMP. Northern blot analysis, using a human beta 2-AR cDNA as a probe, revealed the presence of a mRNA of 2.3 kb, which is consistent with the size of the beta 2-AR mRNA found in other rat tissues. Physiological regulation of specific beta 2-AR in the rat thymus was indicated by significant increases in both receptor concentration and steady-state levels of beta 2-AR mRNA during the diestrous 2 and proestrous phases of the rat estrous cycle and pregnancy, whereas castration sharply reduced beta 2-AR numbers and transcript levels within the thymus. The modulation of the thymic beta 2-AR-cAMP signaling system by the preexisting sex steroid milieu, coupled with the sex-dependent adrenergic modulation of thymic cell-mediated immune response, may contribute to the various sex-related alterations in immune responsiveness and could play a role in sexually related immune disorders.

Compound screening based on a window of chemical-messenger-independent activity

Abstract: A method of testing chemical compounds for their abilities to inhibit chemical-messenger-independent activity of G protein-coupled receptors involving; expressing DNA encoding a G protein-coupled receptor in a cell expression system in such a manner as to generate a reproducible "window of chemical-messenger-independent activity" that allows for discrimination of chemical compounds based on relative ability to inhibit chemical-messenger-independent activity of said G protein-coupled receptor; measuring a quantifiable parameter using biochemical or other assay procedures that indicate the agonist-independent activity of said receptor in said system comprising whole cells or membrane fragments containing G protein, an appropriate effector, and cloned G protein-linked receptor; contacting a test-compound with the system under conditions permitting interaction of the test-compound with said receptor; and measuring the change, if any, of the quantifiable parameter which reflects the ability of the test compound to inhibit the chemical-messenger-independent activity of the G protein-coupled receptor.

Effects of trandolapril on the sympathetic tone and reactivity in systemic hypertension.

Abstract: Hemodynamic and autonomic evaluations were carried out after 2–3 weeks of treatment with placebo and at the end of 4 weeks of treatment with an anglotensin converting enzyme (ACE) inhibitor, trandolapril, 2 mg/day in 18 hypertensive patients (average age, 48 ± 2 years) of either sex. This treatment lowered the mean arterial pressure in the whole group from 112 to 105 mm Hg (p

β-Adrenergic receptor desensitization in the early stage of hereditary cardiomyopathy in hamsters

Abstract: The β-adrenergic receptor (βAR)/adenylyl cyclase signalling pathway was examined in cardiac membranes from cardiomyopathic Syrian hamsters. Three stages were examined during the progression of this...