Affinities of full agonists for cardiac ?-adrenoceptors calculated by use of in vitro desensitization

Abstract

Positive chronotropic and inotropic responses of guinea-pig isolated spontaneously beating right atria and paced left atria to beta-adrenoceptor agonists were recorded. Cumulative concentration-response curves for the rate and tension responses to isoprenaline, orciprenaline, terbutaline and fenoterol were obtained before incubation of the tissues with isoprenaline (10(-6) M), the tissues were then washed during 1 h to remove isoprenaline before constructing a post-incubation curve to the same agonist. Incubation with isoprenaline for 4 h caused parallel rightwards shifts to the curves, but extending the incubation to 8 h caused additional depression of the rate (85.2 +/- 5.4%) and tension (68.9 +/- 2.3%) maxima. Incubation with isoprenaline for 4 h only shifted the curves for orciprenaline to the right but depressed the post-incubation maximum rate and tension responses to terbutaline (74.8 +/- 1.5 and 33.8 +/- 2.5%) and fenoterol (85.6 +/- 5.5 and 76.0 +/- 5.1%). Thus incubation with isoprenaline for 4 h induced desensitization of the cardiac beta-adrenoceptor which was revealed as a loss in sensitivity to both isoprenaline and other beta-adrenoceptor agonists. The reduced maxima were attributed to a loss of beta-adrenoceptors and exhaustion of the receptor reserve. Those experiments displaying the reduced maxima were used for calculation of dissociation constants (KA) values by the method of Furchgott (1966) for irreversible antagonism. The values for the right atria were 57 (19-170)nM, 29 (8.4-100)microM and 13 (1.9-8.4)microM and for the left atria, 89 (15-510)nM, 25 (9.9-64)microM and 18 (7.7-42)microM for isoprenaline (8 h incubation), terbutaline and fenoterol respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin-induced reduction of β-adrenergic binding sites on splenic lymphocytes and : Its modulation by anterior hypothalamic lesions

“…The plasma and splenic catecholamine data in the present study are comparable with previous findings (38). The plasma cortisol levels are intermediate to those reported in literature (15,17,28) and are much lower than the reported value of '1990 nmol/l in stressed guinea pigs (12). Thyroid hormone levels which are insensitive to stress-effects, are alike the values from other groups (7, 15,26).…”

Functional analysis of desensitization of the β‐adrenoceptor signalling pathway in rat cardiac tissues following chronic isoprenaline infusion

“…Differences in the pattern of β‐AR desensitization for inotropic and chronotropic responses of atria have previously been reported. Isoprenaline, both in vitro ( Kaumann & Birnbaumer, 1976 ; Herepath & Broadley, 1990 ) and in vivo ( Butterfield & Chess‐Williams, 1993 ; Russell et al ., 1994 ), induced a more marked desensitization of inotropic responses to β‐AR stimulation than chronotropic responses. The reasons for this are unclear.…”

“…We therefore examined β‐AR signalling in the heart following infusion of rats with isoprenaline (400 μg kg −1 h −1 ) or vehicle for 2 weeks. Since the extent of β‐AR desensitization differs between atrial and ventricular preparations ( Chess‐Williams, 1993 ; Butterfield & Chess‐Williams, 1993 ) and between inotropic and chronotropic responses ( Kaumann & Birnbaumer, 1976 ; Ball et al ., 1982 ; Herepath & Broadley, 1990 ; Butterfield & Chess‐Williams, 1993 ; Russell et al ., 1994 ), we examined chronotropic responses of spontaneously beating right atria and the inotropic responses of electrically driven left atria and left and right ventricular papillary muscles to agents acting at several points of the β‐AR‐cyclic AMP signalling pathway.…”

Phenoxybenzamine and Benextramine, but Not 4-Diphenylacetoxy-N-[2-chloroethyl]piperidine Hydrochloride, Display Irreversible Noncompetitive Antagonism at G Protein-Coupled Receptors

“…tor complexes (Herepath and Broadley, 1990;Adham et al, 1993;Agneter et al, 1993;Zhu, 1993;Tian et al, 1996;Kenakin, 1997;Morey et al, 1998;Koek et al, 2000). Irreversible antagonists have also been used to label and count receptor subtypes, to investigate drug and receptor specificity and receptor structure (Jenkinson, 2003), to investigate receptor trafficking (Taouis et al, 1987;McKernan et al, 1988), and to unravel drug action mechanisms (Timmermans et al, 1985).…”