Pharmacologic Receptor Activity of Rabbit Aorta

Abstract

IV-ethylmaleimide (NEM), an alkylating agent that covalently binds sulfhydryl groups, and dithiothreitol (DTT, Cleland's reagent), which reduces disulfide bridges to sulfhydryl groups, affected drug-induced contractions of rabbit aorta. NEM depressed aortic responses to potassium chloride (KC1), norepinephrine, serotonin, histamine, and angiotensin II. This action was attributed to an interaction of NEM with sulfhydryl groups vital to either the membrane function or the contractile apparatus. DTT had minimal effects on responses to KC1, norepinephrine, and serotonin; it potentiated aortic contractions produced by histamine and abolished responses to angiotensin II. Enhancement of the histamine response by DTT was not accompanied by an effect on the histamine-metabolizing enzymes or by an alteration in the K B and pA 2 values for pyrilamine. The results suggest that a disulfide bridge plays a prominent role in both histamine and angiotensin receptor activity of rabbit aorta. With regard to the histamine receptor system, two possibilities exist: (1) reduction of a disulfide bridge at some vital point increases receptor activity or (2) the histamine receptor system, normally in a reduced state, is oxidized in the artificial environment of the tissue bath and needs to be reduced to regain full activity.KEY WORDS histamine angiotensin norepinephrine serotonin sulfhydryl group disulfide bridge vascular smooth muscle drug receptors• Drug receptor systems can be modified in situ by various procedures including changes in temperature or pH, exposure to enzymes, lipid solvents, protein denaturants, or chelating agents, and chemical reaction with site-directed reagents (1). As these procedures become more selective for one or another receptor, it becomes increasingly likely that an altered macromolecule can be identified and associated with receptor function. Especially with the site-directed drugs, greater selectivity gives greater insight into the nature of a particular receptor system. Among the more group-specific reagents are those which cause oxidation of sulfhydryl groups or reduction of disulfide bridges. Sulfhydryl groups and disulfide bridges have been implicated in the oxytocin and vasopressin (2, 3),

The effect of group selective reagentsN-ethylmaleimide and dithiothreitol on histamine H1-receptor binding sites in the vascular smooth muscle membranes

“…When we compared the effect of DTT and NEM on the histamine H~-receptor binding site in beef aortic membranes with the effects of the two reagents on the histamine-induced contractions of isolated rabbit aorta [1,2], we obtained a good correlation between the radioligand binding and pharmacological data. DTT, similarly to the results of the binding experiments (Fig.…”

“…In our previous experiments, we showed that DTT and NEM altered the contractile responses, induced by histamine, in the rabbit aortic tissue [1,2]. This alteration in the receptor activity lead us to investigate, at the molecular level, the influence of the same reagents on the histamine Hi-receptor binding sites.…”

“…In several membrane-receptor systems, group selective protein modifying reagents have been shown to affect selectively or non-selectively the receptor function when receptor still in situ or modulate the agonist or antagonist binding to the receptor, in the radioligand binding assay [1][2][3][4]. These observations have lead to investigations, where the chemical alteration of the receptor induced by the group selective reagents, was used as a tool to obtain better insight into the receptor structure, to differentiate the functional groups essential for the function of the receptor-effector system, to elucidate the differences between the agonist and antagonist binding, particularly the proposed conformational changes of the receptor induced by agonist binding, and to find chemical differences between the receptor subtypes, etc.…”

Proceedings of the Physiological Society, 18‐19 April 1986, Sheffield Meeting: Poster Communications

“…That lignocaine relaxes or modifies vascular responses of rat aorta and sheep carotid artery has been reported (Fleisch & Titus, 1973;Jacobs & Keatinge, 1974) Passive leg raising causes a reflex vasodilatation of forearm vasculature owing to stimulation of low-pressure receptors in the intrathoracic vascular bed (Roddie, Shepherd & Whelan, 1957). The anti-gravity suit (G suit) also causes redistribution of blood volume to the thorax by the application of pneumatic pressure to the legs and lower abdomen.…”

Communications

“…After perfusion of isolated vascular smooth muscles with this agent there is a potentiation of the vasoconstrictor responses to histamine (Fleisch, Krzan & Titus, 1973;Carroll & Glover, 1977). If this potentiation of histamine by dithiothreitol is due to reduction of a disulphide linkage in a histamine receptor (Fleisch et al 1973) it is possible that such a change in a receptor-linked protein would activate that receptor. In isolated rabbit-ear arteries a large and prolonged contraction follows perfusion with dithiothreitol (Allen & Deering, 1976).…”