Robert A. D. Hull

Combined dose-ratio analysis of cholecystokinin receptor antagonists, devazepide, lorglumide and loxiglumide in the guinea-pig gall bladder.

1 Interactions between cholecystokinin octapeptide (CCK‐8) and CCKA‐receptor antagonists derived from benzodiazepines (devazepide) and glutamic acid (lorglumide and loxiglumide) have been examined in an improved bioassay using the guinea‐pig, isolated, gall bladder preparation. 2 The presence of CCKB‐receptors in the assay was provisionally‐ruled out on the basis of the low potency of pentagastrin in the assay. By applying analyses of both agonism and antagonism, pentagastrin was shown to behave as a partial agonist at the CCKA‐receptor. 3 Devazepide, lorglumide and loxiglumide behaved as simple competitive antagonists of CCKA‐receptors and pKB values of 9.98, 7.59 and 7.07 were estimated, respectively. 4 Application of a combined dose‐ratio analysis to the interactions between CCK‐8 and combinations of devazepide/lorglumide and devazepide/loxiglumide indicated that these molecules behave as syntopic, competitive, antagonists at the CCKA‐receptor. 5 We conclude that the guinea‐pig gall bladder assay contains a homogeneous population of CCKA‐receptors and offer an explanation for the differences between our results and those obtained recently by Maubach et al. (1991) which were taken as preliminary evidence for CCKA‐receptor heterogeneity.

Analysis of the variation in the action of L‐365,260 at CCKB/gastrin receptors in rat, guinea‐pig and mouse isolated gastric tissue assays

1 . Since L‐365,260 was first described as a selective antagonist at cholecystokinin (CCK)B/gastrin receptors, we have used it periodically as a reference compound in isolated tissue assays of guinea‐pig gastric muscle and lumen‐perfused stomachs from mouse and immature rat. L‐365,260 behaved as a surmountable antagonist and produced parallel rightward shifts of pentagastrin con***ćentration‐effect curves in each of the replicate experiments. The experiments were performed by several different experimenters in the same laboratories over a five year period. 2 . In the isolated, lumen‐perfused, immature rat stomach assay, L‐365,260 behaved as a simple competitive antagonist (Schild plot slope = 1.00 ± 0.10, pKB = 7.54 ± 0.03 from a global analysis of the data) acting at a homogeneous population of receptors in five separate, highly‐reproducible, experiments. In contrast, the replicate data sets obtained from the interaction in the isolated, lumen‐perfused mouse stomach and guinea‐pig gastric muscle assays, over the same period, were not consistent with the presence of a single receptor population. The guinea‐pig gastric muscle data were relatively reproducible between experiments but some individual Schild plot slopes and the slope estimated from a global analysis of all the data were significantly less than unity (slope = 0.80 ± 0.07, pA2 = 8.56 ± 0.05 from the global analysis). The data obtained in the mouse stomach were significantly more variable than that obtained in the same assay, during the same period, from the interaction between histamine and the H2‐receptor antagonist, famotidine. The individual Schild plot slopes ranged from being very flat (0.20) to being not significantly different from unity (1.23) and the pA2 values ranged from 7.68 to 8.70. 3 . Overall, the data could be accounted for by assuming the variable expression of two receptor subtypes across the assays. The rat stomach appeared to express a single receptor characterized by a low affinity constant for L‐365,260 (pKB ∼ 7.5). The guinea‐pig gastric muscle and mouse stomach data could be explained by the presence of this receptor and a second one characterized by a high affinity constant for L‐365,260 (pKB ∼ 8.6). The activity of the two proposed receptor subtypes was consistent between experiments in the guinea‐pig and the high affinity receptor appeared to be predominant. In contrast, the mouse stomach data could only be simulated by assuming that the proportion and absolute number of each subtype varied significantly between the replicate experiments. 4 . The L‐365,260 affinity estimates at the inferred receptor subtypes were indistinguishable from those obtained in a corresponding analysis of the behaviour of L‐365,260 in CCKB/gastrin receptor radioligand binding experiments in guinea‐pig gastric gland and mouse and rat cerebral cortex preparations.

Kallikrein rK10‐induced kinin‐independent, direct activation of NO‐formation and relaxation of rat isolated aortic rings

1 rK10, a weak T‐kininogenase isolated from the rat submandibular gland, is a protein belonging to the rat kallikrein family. In the present work, we have studied the biological effects of rK10 with respect to its ability to alter vascular resistance, either directly like rK9, i.e., another kallikrein‐like protein, trypsin and thrombin, or through the release of kinins like tissue kallikrein (rK1). The direct effect was studied by its vasomotor activity on rat isolated aortic rings since this preparation was insensitive to the action of kinins. Its ability to induce altered vascular resistance through kinin‐generation was investigated by blood pressure studies in whole animals. The studies were performed in comparison to rK1. 2 Unlike rK1, which induces hypotension when administered intravenously to rats (ΔBP = − 56 ± 5 mmHg, 5 μg kg−1), rK10 did not have any: effect on systemic blood pressure (ΔBP= −3 ± 1, 5 μg kg−1, i.v.) 3 rK10 was without effect on uncontracted aortic rings, but showed a concentration‐dependent (10−8−10−6 m) relaxant effect on tissue precontracted with phenylephrine (10−6m). After removal of endothelial cells, no relaxation was observed. The relaxant response to rK10 was transient. rK1 (with and without endothelium), bradykinin and T‐kinin (with endothelium) had no effect on contracted or uncontracted aortic rings. 4 The relaxant effect of rK10 was dependent on its enzymatic activity since preincubation with aprotinin (1.02 mm) significantly reduced vasorelaxation from 74 ± 4% to 24 ±3%. 5 The relaxant effect was not inhibited by the kinin antagonist Hoe 140 (10−7 m; 34 ± 4% without, versus 30 ± 2% with Hoe 140), but was totally inhibited by the NO‐synthase inhibitor N.nitro‐L‐arginine methyl ester (l‐NAME) (2.5 × 10−4m; 27 ± 3% without and 2± 1% with l‐NAME). 6 These results show that rK10 has the ability to induce vascular relaxation by a specific, direct effect on endothelial cell NO‐synthesis, dependent on rK10 proteolytic activity, but independent of its ability to generate kinin. This effect, or its T‐kininogenase activity in blood, was not sufficient for rK10 to have an effect on peripheral vascular resistance since intravenous injections of rK10, unlike rK1, did not induce hypotension. Thus, rK10 does not seem to play a role in blood pressure homeostasis but may have a local effect on vascular resistance.

Synthesis and pharmacological properties of BW315c and other inotropic 2-arylimidazo[1,2-a]pyrazines

A series of 2-aryl imidazo[1,2-a]pyrazines has been prepared and evaluated for inotropic activity. Sulphoxide 12, BW315C, displayed potent inotropic effects having comparable in vitro and vivo inotropic potencies to those of isomazole. Structure-activity relationships are discussed.

Nobel prize recognizes industrial scientists' contribution to pharmacology and medicine.

Abstract The award of the 1988 Nobel Prize for Physiology or Medicine to three industrial scientists is a long overdue recognition of the major contributions of drug development to modern medicine. It is no longer necessary for patients to suffer the pain of angina, stomach ulcers and gout; new drugs that have been developed by Nobel laureates Sir James Black, Gertrude Elion and George Hitchings have allowed these very common conditions to be alleviated or cured. Zidovudine (AZT) was the first drug to offer hope to AIDS victims. The following tributes to these scientists are not confined to the retrospective — Jim Black continues to actively research new pharmacological targets; Trudy Elion is presidential appointee on the National Cancer Advisory Board and chairs the Chemotherapy of Malaria Steering Committee of the WHO/World Bank/UNPP special programme in tropical diseases; George Hitchings continues to work as a Consultant at Burroughs Wellcome.