H]phosphatydilinositol). All drugs stimulated h5-HT 1A receptors with efficacies (compared with 5-HT, 100%) ranging from modest (apomorphine, 35%) to high (cabergoline, 93%). At h5-HT 1B receptors, efficacies varied from mild (terguride, 37%) to marked (cabergoline, 102%) and potencies were modest (pEC 50 values of 5.8 -7.6): h5-HT 1D sites were activated with a similar range of efficacies and greater potency (7.1-8.5). Piribedil and apomorphine were inactive at h5-HT 1B and h5-HT 1D receptors. At h5-HT 2A receptors, terguride, lisuride, bromocriptine, cabergoline, and pergolide displayed potent (7.6 -8.8) agonist properties (49 -103%), whereas apomorphine and roxindole were antagonists and piribedil was inactive. Only pergolide (113%/8.2) and cabergoline (123%/8.6) displayed pronounced agonist properties at h5-HT 2B receptors. At 5-HT 2C receptors, lisuride, bromocriptine, pergolide, and cabergoline were efficacious (75-96%) agonists, apomorphine and terguride were antagonists, and piribedil was inactive. MDL100,907 and SB242,084, selective antagonists at 5-HT 2A and 5-HT 2C receptors, respectively, abolished these actions of pergolide, cabergoline, and bromocriptine. In conclusion, antiparkinson agents display markedly different patterns of agonist and antagonist properties at multiple 5-HT receptor subtypes. Although all show modest (agonist) activity at 5-HT 1A sites, their contrasting actions at 5-HT 2A and 5-HT 2C sites may be of particular significance to their functional profiles in vivo.

Employing a novel, rapid and sensitive method for evaluation of phospholipase C (PLC) activity, the present study characterized the actions of diverse agonists and antagonists at human (h)5-HT2C receptors expressed in Chinese Hamster Ovary (CHO) cells. In addition, affinities and efficacies at these sites were compared with those obtained at h5-HT2B receptors.5-HT elicited a robust and rapid reduction in levels of the pre-labelled, membrane-bound substrate of PLC, [3H]phosphatidylinositols ([3H]PI). The time-course of [3H]PI depletion paralleled that of [3H]inositol phosphate ([3H]IP) accumulation, as determined by conventional anion exchange chromatography. Inactivation of h5-HT2C receptors with the alkylating agent, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), revealed a large receptor reserve, with half-maximal PLC activation induced by a concentration of 5-HT occupying only 5% of sites. In analogy to 5-HT ( Emax=100%), DOI, MK212 and mCPP, as well as the novel ligands, Ro600332, Ro600175 and BW723C86, showed "full" efficacy at h5-HT2C sites. Their efficacies were similar at h5-HT2B sites, with the exception of mCPP and MK212, which acted as partial agonists. Further, lisuride and Ro600869 behaved as partial agonists and antagonists at h5-HT2C and h5-HT2B receptors, respectively. As concerns functional selectivity (potency for induction of [3H]PI depletion), only Ro600175 preferentially activated h5-HT2B sites. In contrast, Ro600332 preferentially activated h5-HT2C receptors. Amongst antagonists, RS102221 and SB242084 displayed a marked preference for h5-HT2C sites, whereas LY266097, S33526 and SB204741 behaved as selective antagonists at h5-HT2B receptors. At both h5-HT2C and h5-HT2B receptors, antagonist potency (p Kb) and binding affinity (p Ki) were highly correlated. In conclusion, this rapid and innovative method for determination of PLC activity permitted characterization of an extensive range of novel ligands at h5-HT2C receptors. Although several antagonists clearly differentiated h5-HT2C from h5-HT2B receptors under these conditions, highly selective agonists remain to be identified.

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The markers of the bioavailability of NO (endothelium-dependent relaxation to acetylcholine and cyclic GMP content) in the thoracic aorta of apolipoprotein-E-deficient (ApoE KO) mice, 20 weeks old with enriched cholesterol diet or 35 weeks old on regular chow, are not decreased, in contrast with other models of atherosclerosis. However, severe hypercholesterolemia, the presence of atherosclerotic lesions and increased NADPH oxidase activity have been reported as early as at 20 weeks of age. The present experiments were designed to test if an increased capacity of NO production in these mice explains this paradox. The expressions of the 3 isoforms of NO synthase (NOS) were compared in ApoE KO and C57Bl/6J mice using Western blot and localized by immunohistochemistry. No adaptive increase in the expression of NOS was detected in ApoE KO mice. NO bioavailability could also be preserved by upregulation of enzymes involved in redox status such as CuZn or Mn superoxide dismutase and catalase. However, these enzymes were less expressed in ApoE KO mice than in control mice. These results highlight that ApoE KO mice represent an atypical model of atherosclerosis.

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