P. N. C. Elliott

Substituted benzamides as cerebral dopamine antagonists in rodents

Abstract The substituted benzamides metoclopramide, sulpiride, tigan and clebopride and its debenzylated metabolite (DP) were compared for their ability to act as dopamine antagonists in rodents. All compounds inhibited apomorphine-induced circling in animals with unilateral nigro-striatal lesions; all except tigan inhibited the apomorphine-induced reversal of reserpine akinesia; and all induced some degree of catalepsy. The potency of the compounds in these behavioural experiments ranked in the order : clebopride > metoclopramide > sulpiride > tigan and DP. Striatal and mesolimbic HVA levels were elevated to a variable degree by all compounds. Their potency in elevating striatal HVA ranked in the order : clebopride > metoclopramide > sulpiride > tigan and DP. The benzamides, in general, elevated both striatal and mesolimbic HVA to the same degree. Metoclopramide and clebopride produced an increase in striatal and mesolimbic DOPAC only at high dosage levels; sulpiride, however, elevated the levels of both dopamine metabolites concommittantly. This data suggests that such substituted benzamides produce a functional blockade of cerebral dopamine receptors. However, metoclopramide, sulpiride, tigan and DP were without effect on the in vitro dopamine sensitive adenylate cyclase system from rat striatum. Clebopride in high concentrations caused a small reduction in dopamine stimulation of cyclic AMP production. All compounds induced ipsilateral circling in apomorphine-treated rats when injected directly into one striatum, which makes the possibility that their actions are due to active metabolites unlikely. This data suggests that substituted benzamides form a pharmacologically-distinct group of dopamine antagonists, whose mechanism of action differs from that of classical neuroleptics. Also, there may be differences in the modes of action of various benzamides, to explain their varying clinical potencies.

A comparison of in vitro and in vivo dopamine receptor antagonism produced by substituted benzamide drugs

Cerebral dopamine receptor antagonism in vivo is associated with the ability to interact with two in vitro models of these receptors. Thus the ability to inhibit dopamine stimulation of the adenylate cyclase from rat striatum has been suggested as a model of post-synaptic dopamine receptor activity and of neuroleptic potential (Clement-Cormier, Kebabian & others, 1974; Miller, Horn & Iversen, 1974). Similarly, the ability to displace radioactive ligands from their binding sites in rat striatal preparations is also used as an index of an interaction with post-synaptic dopamine receptors and of neuroleptic activity (Seeman, Chau-Wong & others, 1975; Creese, Burt & Snyder, 1976). This latter model is believed to provide a better correlation between in vivo clinical neuroleptic activity and in vitro activity than the adenylate cyclase system. We have previously reported that some substituted benzamide drugs, such as metoclopramide and sulpiride, exhibit behavioural and biochemical properties associated with a blockade of cerebral dopamine receptors (Dolphin, Jenner & others, 1975; Peringer, Jenner & Marsden, 1975; Peringer, Jenner & others, 1976; Elliott, Jenner & others, 1977). Such compounds to a variable degree block apomorphine-induced locomotor activity, inhibit apomorphine-induced circling in rodents with unilateral nigrostriatal lesions, and elevate striatal and mesolimbic concentrations of the dopamine metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC). We have, however, been unable to demonstrate a significant effect of these compounds on the dopamine stimulation of the adenylate cyclase from rat striatum. This, and other data, has led us to conclude that these compounds act on the cerebral dopamine pathways in a manner which differs from that of classical neuroleptics. The present study is a comparison of the activity of five substituted benzamide drugs in the in vitro models of dopamine receptor activity with their ability to induce catalepsy and to inhibit apomorphine-induced stereotyped behaviour, these behavioural tests being chosen since they are often used to screen neuroleptic activity. These data are then compared with the

Prostaglandins and the anti‐inflammatory activities of aspirin and sodium salicylate

Acetylsalicylic acid (aspirin) and sodium salicylate are equally effective in reducing the swelling in the carrageenan‐induced paw test and the accumulation of leucocytes into the inflammatory exudate produced by the subcutaneous implantation of polyvinyl sponges in the rat. Aspirin but not sodium salicylate caused a significant reduction in the potentiation of paw oedema found after the concurrent administration of carrageenan and arachidonic acid. Some implications of these findings are discussed.

Prostaglandins and the anti‐inflammatory activity of a human plasma fraction in carrageenan‐induced paw oedema in the rat

A fraction prepared from normal human plasma inhibits the swelling of the acute carrageenan‐induced paw oedema in the rat. Treatment of the animals with prostaglandin E1, arachidonic acid or with substances which either block the formation of prostaglandins or antagonize their action showed that these mediators are concerned in the development of the paw oedema. The anti‐inflammatory effect of the plasma fraction in the carrageenan reaction does not involve a specific interference with the prostaglandin system. The plasma fraction is not an inhibitor of the action of SRS‐A on the guinea‐pig ileum.

Effects of a human plasma fraction on leucocyte migration into inflammatory exudates.

A fraction prepared from normal human plasma inhibits the migration of polymorphonuclear and mononuclear leucocytes into inflammatory exudates produced by the intrapleural injection of carrageenan or turpentine and by the subcutaneous implantation of polyvinyl sponges in the rat. The mechanism of the effect does not involve complement depletion.

Histamine, 5-hydroxytryptamine, kinins and the anti-inflammatory activity of human plasma fraction in carrageenan-induced paw oedema in the rat.

In the carrageenan‐induced paw oedema reaction in the rat, the swelling and accumulation of [131I]albumin showed a similar time course over 4 h. Both aspects of the oedema were inhibited by a fraction prepared from human plasma. Treatment of the animals with substances which either deplete the levels or antagonize the actions of either histamine, 5‐hydroxytryptamine or kinins showed that these mediators are concerned in the development of rat paw oedema after the injection of either carrageenan or yeast but not with the anti‐inflammatory action of the plasma fraction.

The effects of a human plasma fraction on adjuvant arthritis and granuloma pellet reactions in the rat

A fraction prepared from normal human plasma has been shown to inhibit acute paw oedemas in the rat induced by either carrageenan (Ford-Hutchinson, Insley & others, 1973), dextran (Elliott, Ford-Hutchinson & Smith, 1974) or yeast (Bolam, Elliott & others, 1974). When injected intravenously the fraction (1 ml of the combined fractions I1 and IV, Ford-Hutchinson & others, 1973) has now been found to inhibit the development of the secondary lesions in adjuvant arthritis but not to affect the deposition of granulation tissue around implanted cotton wool pellets in the rat. The results in the adjuvant arthritis test for the development of all the secondary lesions are given in Table 1 and for the swelling of the contralateral uninjected hind paw in Fig. 1 .

Atropine manipulation of elevated cerebral dopamine turnover caused by haloperidol or substituted benzamide drugs.

High concentrations of acetylcholine, choline acetyltransferase and cholinesterase are found in the striatum, probably within a system of cholinergic interneurons (McGeer & others, 1975; Butcher, 1977). These cholinergic interneurons appear to be inhibited, functionally, by the dopaminergic nigrostriatal pathway. Thus, neuroleptic drugs, which are dopamine antagonists, have been shown to decrease striatal acetylcholine concentrations and increase acetylcholine release (Stadler, Lloyd & others, 1973; Consolo, Ladinsky & Garattini, 1974; Consolo, Ladinsky & Bianchi, 1975; Consolo, Ladinsky & others, 1977). The reverse is also true in that the dopamine nigrostriatal pathway appears t o be inhibited functionally by a cholinergic input. Thus, neuroleptic-induced increases in striatal dopamine turnover can be reversed, a t least partially, by the administration of antiacetylcholine drugs (O’Keefe, Sharman & Vogt, 1970; AndCn, 1972; Corrodi, Fuxe & Lidbrink, 1972; Bartholini, Keller & Pletscher, 1975). In another dopamine containing area, the mesolimbic system, high concentrations of acetylcholine also are present. However, in contrast to the striatum, the relation between dopaminergic and cholinergic pathways within the mesolimbic area is unclear. Thus, while administration of oxotremorine or physostigmine results in an increase in limbic (and striatal) homovanillic acid (HVA) concentrations, effects reversible by trihexiphenidyl (AndCn, 1974), dopamine agonists and antagonists failed to alter acetylcholine concentrations or release in the tuberculum olfactorium and nucleus accumbens in doses effective in the striatum (Stadler, Gadea-Ciria & Bartholini, 1975; Consolo & others, 1977). Further, neuroleptic-induced increases in mesolimbic HVA concentrations have been reported not to be reversed by antiacetylcholine drugs (Anden, 1972). Substituted benzamide drugs such as sulpiride and metoclopramide represent an unusual group of dopamine receptor antagonists. Thus, while blocking locomotor activity induced by apomorphine, inhibiting apomorphineand amphetamine-induced circling behaviour and increasing both striatal and mesolimbic dopamine turnover, these compounds have little cataleptic activity, do not inhibit dopamine stimulated adenylate cyclase in rat striatal preparations, and only

Anti-inflammatory and irritant effects of a fraction from normal human plasma

1 By the use of carrageenan‐induced rat paw oedema assay the anti‐inflammatory activity of a fraction isolated from normal human plasma has been measured after its intravenous, intraperitoneal and oral administration. Its effects in the dextran‐induced rat paw oedema and the systemic dextran anaphylactoid reaction in the rat were also studied. 2 The fraction showed marked anti‐inflammatory activity in the carrageenan test after intravenous administration and a smaller but still significant activity when given intraperitoneally, but was inactive orally after the administration of a larger dose. It was active in the dextran‐induced paw oedema test but not against the anaphylactoid reaction. 3 A comparison between its anti‐inflammatory and irritant properties revealed no correlation when each parameter was determined in relation to dose. The fraction did not affect the blood pressure of the anaesthetized rat. 4 These findings are discussed in relation to the existence of a natural anti‐inflammatory substance or substances in human plasma.

The effects of a human plasma fraction on carrageenan-induced paw oedema in the rat

A fraction isolated from normal human plasma inhibits the swelling of carrageenan‐induced paw oedema in the rat when given as a single intravenous injection at time intervals up to 24 h before and up to 3 h after the administration of the carrageenan. Repeated doses of the fraction cause a delay in the development of the paw oedema.