Relating protein pharmacology by ligand chemistry.

The identification of protein function based on biological information is an area of intense research. Here we consider a complementary technique that quantitatively groups and relates proteins based on the chemical similarity of their ligands. We began with 65,000 ligands annotated into sets for hundreds of drug targets. The similarity score between each set was calculated using ligand topology. A statistical model was developed to rank the significance of the resulting similarity scores, which are expressed as a minimum spanning tree to map the sets together. Although these maps are connected solely by chemical similarity, biologically sensible clusters nevertheless emerged. Links among unexpected targets also emerged, among them that methadone, emetine and loperamide (Imodium) may antagonize muscarinic M3, alpha2 adrenergic and neurokinin NK2 receptors, respectively. These predictions were subsequently confirmed experimentally. Relating receptors by ligand chemistry organizes biology to reveal unexpected relationships that may be assayed using the ligands themselves.

High-sugar diets increase cardiac dysfunction and mortality in hypertension compared to low-carbohydrate or high-starch diets.

OBJECTIVE: Sugar consumption affects insulin release and, in hypertension, may stimulate cardiac signaling mechanisms that accelerate left ventricular hypertrophy and the development of heart failure. We investigated the effects of high-fructose or sucrose diets on ventricular function and mortality in hypertensive Dahl salt-sensitive rats. METHODS: Rats were fed chows that were either high starch (70% starch, 10% fat by energy), high fat (20% carbohydrates, 60% fat), high fructose (61% fructose, 9% starch, 10% fat), or high sucrose (61% sucrose, 9% starch, 10% fat). Hypertension was induced by adding 6% salt to the chow (n = 8-11/group). RESULTS: After 8 weeks of treatment, systolic blood pressure and left ventricular mass were similarly increased in all rats that were fed high-salt diets. Hypertension caused a switch in mRNA myosin heavy chain isoform from alpha to beta, and this effect was greater in the high-salt sucrose and fructose groups than in starch and fat groups. The cardiac mRNA for atrial natriuretic factor was also increased in all high-salt groups compared to respective controls, with the increase being significantly greater in the hypertensive sucrose fed group. Mortality was greater in the sucrose group (44%) compared to all the other hypertensive groups (12-18%), as was cardiomyocyte apoptosis. Left ventricular ejection fraction was lower in the high-salt sucrose group, which was due to an increase in end-systolic volume, and not increased end-diastolic volume. CONCLUSION: Diets high in sugar accelerated cardiac systolic dysfunction and mortality in hypertension compared to either a low-carbohydrate/high-fat or high-starch diet.

Metabolic dysregulation in the SHROB rat reflects abnormal expression of transcription factors and enzymes that regulate carbohydrate metabolism.

The Koletsky (SHROB) strain of rats is spontaneously hypertensive and displays insulin resistance, hyperglucagonemia and hypertriglyceridemia but is normoglycemic under fasting conditions. The aim of this study was to unravel the pattern of expression of genes encoding key regulatory enzymes involved in carbohydrate metabolism in the liver and kidney that may be impacted in this strain. We found that SHROB animals have decreased beta-adrenergic receptor density and, consequently, blunted increases in cAMP levels in response to beta-adrenergic agonists. They also have lower levels of hepatic as well as renal phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) mRNA and protein than their lean littermates. Expression of the genes for glycogen phosphorylase and glycogen synthase was also decreased. Hepatocytes from the SHROB animals exhibited glycogen depletion of only 50% compared to 86% by hepatocytes from lean littermates when challenged with either glucagon or forskolin to stimulate adenylyl cyclase. The expression of C/EBPalpha and C/EBPbeta, two key transcription factors that are essential for the coordinated expression of genes involved in glucose homeostasis, was depressed in livers of the SHROB rats, as were levels of HNF-4alpha, PPARalpha and PGC-1alpha. We conclude that overproduction of glucose is prevented in the SHROB rats by decreased expression of the genes for glycogen phosphorylase and the gluconeogenic enzymes PEPCK and G6Pase, which may prevent progression to diabetes in this model.

Metabolic actions of angiotensin receptor antagonists: PPAR-gamma agonist actions or a class effect?

Accumulating basic and clinical data support the hypothesis that angiotensin receptor blockers have beneficial effects on glucose and lipid metabolism that are not shared by other classes of antihypertensive agents. These metabolic actions might only partially be shared by angiotensin-converting enzyme inhibitors. Specific benefits beyond those of other angiotensin receptor blockers have been claimed for telemesartan and, to a lesser extent, irbesartan based on a partial agonist action on PPAR-gamma receptors. Although the evidence is strong in vitro, specific actions not shared by other angiotensin receptor blockers have not yet been convincingly demonstrated in vivo or in clinical trials. In many cases, a full range of doses has not been compared, and the apparent superiority of telmesartan could be an artifact of its higher receptor binding affinity, greater tissue penetration owing to lipophilicity, and longer half life.

Therapeutic actions of allylmercaptocaptopril and captopril in a rat model of metabolic syndrome.

BACKGROUND: Hypertension often coexists with hyperlipidemia, insulin resistance, and glucose intolerance in metabolic syndrome. Allylmercaptocaptopril is a conjugate of the angiotensin-converting enzyme inhibitor captopril with allicin, an active principle in garlic with multiple beneficial actions on metabolic-syndrome abnormalities. We sought to test the hypothesis that the conjugation of allicin to captopril may confer additional therapeutic actions in metabolic disease. METHODS: We compared allylmercaptocaptopril (53.5 mg/kg/day orally for 60 days) to an equimolar dose of captopril (40 mg/kg/day) in the spontaneously hypertensive, obese rat (SHROB) model. RESULTS: Allylmercaptocaptopril prevented progressive weight gain, without a detectable effect on food intake. Both captopril and allylmercaptocaptopril lowered blood pressure, but allylmercaptocaptopril was more effective. Allylmercaptocaptopril, but not captopril, improved cardiac hypertrophy, as indicated by heart weight and ventricular-wall thickness. Allylmercaptocaptopril improved, whereas captopril impaired, oral glucose tolerance after a fast. Triglycerides were decreased by both captopril and allylmercaptocaptopril. Total cholesterol and non-HDL cholesterol were reduced by captopril but not by allylmercaptocaptopril. The SHROB rats developed severe glomerulosclerosis and renal failure. Allylmercaptocaptopril showed significant nephro-protection, as indicated by reductions in urinary protein loss, urinary protein-to-creatinine ratio, and plasma creatinine. Captopril showed the same trends and also prevented the decline of creatinine clearance. Finally, both allylmercaptocaptopril and captopril reduced the basal level of lipolysis in isolated abdominal adipocytes, and restored the response to catecholamine stimulation. CONCLUSIONS: Both captopril and allylmercaptocaptopril are effective in attenuating multiple abnormalities of metabolic syndrome. Allylmercaptocaptopril may have additional effectiveness on improving glucose tolerance, further lowering blood pressure, reducing cardiac hypertrophy, preventing weight gain, and protecting against renal disease.

High fructose diet increases mortality in hypertensive rats compared to a complex carbohydrate or high fat diet.

BACKGROUND: Chronic hypertension leads to cardiac hypertrophy, heart failure, and premature death. Little is known about the impact of dietary macronutrient composition on hypertension-induced cardiac hypertrophy and mortality. We investigated the effects of consuming either a high complex carbohydrate diet, a high simple sugar diet, or a high fat diet on cardiac hypertrophy and mortality in hypertensive Dahl salt-sensitive (DSS) rats. METHODS: Rats were assigned to four diets: complex carbohydrate (CC; 70% starch, 10% fat, 20% protein by energy), high fat (FAT; 20% carbohydrates, 60% fat, 20% protein), high fructose (FRU; 70% fructose, 10% fat, 20% protein), and "western" (WES; 35% fructose, 45% fat, 20% protein). Hypertension was initiated by adding 6% NaCl (+S) to the chow of half the animals within each diet (n = 10 to 13/group). Tail cuff blood pressure measurements were assessed after 5 and 11 weeks of treatment, and echocardiography were assessed after 12 weeks of treatment. RESULTS: All rats fed a high salt diet had similar levels of hypertension (CC+S 220 +/-2 mm Hg, FAT+S 221 +/- 3 mm Hg, FRU+S 221 +/- 1 mm Hg, WES+S 226 +/- 3 mm Hg). Echocardiography results show that the addition of salt to FRU resulted in increased regional wall thickness that was not observed in other dietary groups. All rats fed a low salt diet (CC, FAT, FRU, WES) and the FAT+S group survived 90 days. On the other hand, there was 90-day mortality in the WES+S group (18% mortality) and the CC+S group (30% mortality). In addition, FRU+S rats started dying after 45 days of salt feeding, and only 15% survived the full 90 days. CONCLUSIONS: These results demonstrate that a high fructose diet consumed during hypertension increases mortality and left ventricular (LV) wall thickness compared to either a high fat, high starch, or a "western" diet.

Allergic lung inflammation affects central noradrenergic control of cholinergic outflow to the airways in ferrets.

Brain stem noradrenergic cell groups mediating autonomic responses to stress project to airway-related vagal preganglionic neurons (AVPNs). In ferrets, their activation produces withdrawal of cholinergic outflow to the airways via release of norepinephrine and activation of alpha(2A)-adrenergic receptors (alpha(2A)-AR) expressed by AVPNs. In these studies, we examined the effects of allergen exposure of the airway (AE) with ovalbumin on noradrenergic transmission regulating the activity of AVPNs and, consequently, airway smooth muscle tone. Experiments were performed in vehicle control (Con) and AE ferrets. Microperfusion of an alpha(2A)-AR agonist (guanabenz) in close proximity to AVPNs elicited more pronounced effects in Con than AE ferrets, including a decrease in unit activity and reflexly evoked responses of putative AVPN neurons with a corresponding decrease in cholinergic outflow to the airways. Although no differences were found in the extent of noradrenergic innervation of the AVPNs, RT-PCR and Western blot studies demonstrated that AE and repeated exposure to antigen significantly reduced expression of alpha(2A)-ARs at message and protein levels. These findings indicate that, in an animal model of allergic asthma, sensitization and repeated challenges with a specific allergen diminish central inhibitory noradrenergic modulation of AVPNs, possibly via downregulation of alpha(2A)-AR expression by these neurons.

Robust experiment design for estimating myocardial beta adrenergic receptor concentration using PET.

Myocardial beta adrenergic receptor (beta-AR) concentration can substantially decrease in congestive heart failure and significantly increase in chronic volume overload, such as in severe aortic valve regurgitation. Positron emission tomography (PET) with an appropriate ligand-receptor model can be used for noninvasive estimation of myocardial beta-AR concentration in vivo. An optimal design of the experiment protocol, however, is needed for sufficiently precise estimates of beta-AR concentration in a heterogeneous population. Standard methods of optimal design do not account for a heterogeneous population with a wide range of beta-AR concentrations and other physiological parameters and consequently are inadequate. To address this, we have developed a methodology to design a robust two-injection protocol that provides reliable estimates of myocardial beta-AR concentration in normal and pathologic states. A two-injection protocol of the high affinity beta-AR antagonist [18F]-(S)-fluorocarazolol was designed based on a computer-generated (or synthetic) population incorporating a wide range of beta-AR concentrations. Timing and dosage of the ligand injections were optimally designed with minimax criterion to provide the least bad beta-AR estimates for the worst case in the synthetic population. This robust experiment design for PET was applied to experiments with pigs before and after beta-AR upregulation by chemical sympathectomy. Estimates of beta-AR concentration were found by minimizing the difference between the model-predicted and experimental PET data. With this robust protocol, estimates of beta-AR concentration showed high precision in both normal and pathologic states. The increase in beta-AR concentration after sympathectomy predicted noninvasively with PET is consistent with the increase shown by in vitro assays in pig myocardium. A robust experiment protocol was designed for PET that yields reliable estimates of beta-AR concentration in a population with normal and pathologic states. This methodology is applicable in general to optimal estimation of parameters in heterogeneous populations.

Novel oxotremorine-related heterocyclic derivatives: Synthesis and in vitro pharmacology at the muscarinic receptor subtypes.

A set of novel heterocyclic ligands (6-27) structurally related to Oxotremorine 2 was designed, synthesized and tested at muscarinic receptor subtypes (mAChRs). In the binding experiments at cloned human receptors (hm1-5), compounds 7 and 15 evidenced a remarkable affinity and selectivity for the hm2 subtype. The in vitro functional assays, performed on a selected group of derivatives at M(1), M(2), and M(3) tissue preparations, singled out the 3-butynyloxy-5-methylisoxazole trimethylammonium salt 7 as a potent unselective muscarinic agonist [pEC(50): 7.40 (M(1)), 8.18 (M(2)), and 8.14 (M(3))], whereas its 5-phenyl analogue 12 behaved as a muscarinic antagonist, slightly selective for the M(1) subtype [pK(B): 6.88 (M(1)), 5.95 (M(2)), 5.53 (M(3))]. Moreover, the functional data put in evidence that the presence of the piperidine ring may generate a functional selectivity, e.g., an M(1) antagonist/M(2) partial agonist/M(3) full agonist profile (compound 21), at variance with the corresponding quaternary ammonium salt (compound 22) which behaved as a muscarinic agonist at all M(1-3) receptors, with an appreciable selectivity for the cardiac M(2) receptors.

Metabolic effects of antihypertensive agents: role of sympathoadrenal and renin-angiotensin systems.

Reports of beneficial, neutral and adverse impacts of antihypertensive drug classes on glucose and lipid metabolism can be found in human data. Furthermore, mechanisms for these diverse effects are often speculative and controversial. Clinical trial data on the metabolic effects of antihypertensive agents are highly contradictory. Comparisons of clinical trials involving different agents are complicated by differences in the spectrum of metabolic disturbances that accompany hypertension in different groups of patients. Two physiological systems are predominant at the interface between metabolic and cardiovascular regulation: the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). These two systems are major targets of antihypertensive drug actions, and also mediate many of the beneficial and adverse effects of antihypertensive agents on glucose and lipid metabolism. Thiazides and beta-adrenergic antagonists can adversely affect glucose and lipid metabolism, which are frequently compromised in human essential hypertension, and increase the incidence of new cases of diabetes. Laboratory studies confirm these effects, and suggest that compensatory activation of the SNS and RAS may be one mechanism. Other antihypertensives directly targeting the SNS and RAS may have beneficial effects on glucose and lipid metabolism, and may prevent diabetes. Resolution of the controversies surrounding the metabolic effects of antihypertensive agents can only be resolved by further laboratory studies, in addition to controlled clinical trials.

Lipid-lowering actions of imidazoline antihypertensive agents in metabolic syndrome X.

Agonists active at I1-imidazoline receptors (I1R) not only lower blood pressure but also ameliorate glucose intolerance, insulin resistance, and hyperlipidemia with long-term treatment. We sought to determine the possible mechanism for the lipid-lowering actions of imidazolines in a model of metabolic Syndrome X, the spontaneously-hypertensive obese (SHROB) rat. The acute actions of moxonidine and rilmenidine, selective I1R agonists, were compared to a specific alpha2-adrenergic receptor agonist, guanabenz, with and without selective receptor blockers. Moxonidine and rilmenidine rapidly reduced plasma triglyceride (20+/-4% and 21+/-5%, respectively) and cholesterol (29+/-9% and 27+/-9%). In contrast, the specific alpha2-adrenergic receptor agonist guanabenz failed to reduce plasma lipids. Blocking experiments showed that moxonidine's actions were mediated by I1R and not alpha2-adrenergic receptors. To evaluate a hepatic site of action, radioligand binding studies with liver plasma membranes confirmed the presence of I1R. Intraportal moxonidine reduced plasma triglycerides by 23+/-3% within 10 min. Moxonidine inhibited hepatic triglyceride secretion by 75% compared to vehicle treatment. Tracer studies with 2H2O suggested that moxonidine inhibits de novo fatty acid synthesis. Thus, activation of I1R lowers plasma lipids, with the main site of action probably within the liver to reduce synthesis and secretion of triglycerides. More selective I1R agonists might provide monotherapy for hyperlipidemic hypertension.

The National Weight Control Registry: a critique.

This article is a critique of the claim that the National Weight Control Registry provides data showing that a significant number of adults in the United States have achieved permanent weight loss. We believe that promoting calorie-restricted dieting for the purpose of weight loss is misleading and futile. We advocate the adoption of a health-at-every-size (HAES) approach to weight management, focusing on the achievement and maintenance of lifestyle changes that improve metabolic indicators of health.

H1-histamine receptor affinity predicts short-term weight gain for typical and atypical antipsychotic drugs.

As a result of superior efficacy and overall tolerability, atypical antipsychotic drugs have become the treatment of choice for schizophrenia and related disorders, despite their side effects. Weight gain is a common and potentially serious complication of some antipsychotic drug therapy, and may be accompanied by hyperlipidemia, hypertension and hyperglycemia and, in some extreme cases, diabetic ketoacidosis. The molecular mechanism(s) responsible for antipsychotic drug-induced weight gain are unknown, but have been hypothesized to be because of interactions of antipsychotic drugs with several neurotransmitter receptors, including 5-HT(2A) and 5-HT(2C) serotonin receptors, H(1)-histamine receptors, alpha(1)- and alpha(2)-adrenergic receptors, and m3-muscarinic receptors. To determine the receptor(s) likely to be responsible for antipsychotic-drug-induced weight gain, we screened 17 typical and atypical antipsychotic drugs for binding to 12 neurotransmitter receptors. H(1)-histamine receptor affinities for this group of typical and atypical antipsychotic drugs were significantly correlated with weight gain (Spearman rho=-0.72; p<0.01), as were affinities for alpha(1A) adrenergic (rho=-0.54; p<0.05), 5-HT(2C) (rho=-0.49; p<0.05) and 5-HT(6) receptors (rho=-0.54; p<0.05), whereas eight other receptors' affinities were not. A principal components analysis showed that affinities at the H(1), alpha(2A), alpha(2B), 5-HT(2A), 5-HT(2C), and 5-HT(6) receptors were most highly correlated with the first principal component, and affinities for the D(2), 5-HT(1A), and 5-HT(7) receptors were most highly correlated with the second principal component. A discriminant functions analysis showed that affinities for the H(1) and alpha(1A) receptors were most highly correlated with the discriminant function axis. The discriminant function analysis, as well as the affinity for the H(1)-histamine receptor alone, correctly classified 15 of the 17 drugs into two groups; those that induce weight gain and those that do not. Because centrally acting H(1)-histamine receptor antagonists are known to induce weight gain with chronic use, and because H(1)-histamine receptor affinities are positively correlated with weight gain among typical and atypical antipsychotic drugs, it is recommended that the next generation of atypical antipsychotic drugs be screened to avoid H(1)-histamine receptors.

In vitro receptor screening of pure constituents of St. John's wort reveals novel interactions with a number of GPCRs.

RATIONALE: Hypericum perforatum L. (St. John's wort; SJW) is one of the leading psychotherapeutic phytomedicines and great effort has been devoted to clarifying its mechanism of action. OBJECTIVE: We have undertaken a comprehensive analysis of several pure compounds isolated from the crude extract to gain further insight into the molecular actions of various substituents of SJW. METHODS: We characterized the in vitro pharmacology of the naphthodianthrones hypericin and pseudohypericin, the phloroglucinol derivative hyperforin, and several flavonoids at 42 biogenic amine receptors and transporters using the resources of the National Institute of Mental Health Psychoactive Drug Screening Program. RESULTS: The biflavonoid amentoflavone significantly inhibited binding at serotonin (5-HT(1D), 5-HT(2C)), D(3)-dopamine, delta-opiate, and benzodiazepine receptors. The naphthodianthrone hypericin had significant activity at D(3)- and D(4)-dopamine receptors and beta-adrenergic receptors. With the exception of the D(1)-dopamine receptor, the phloroglucinol derivative hyperforin was less active than other SJW constituents tested on all screened receptors. CONCLUSION: Our present in vitro data clearly show that several pure substances in SJW are potential CNS psychoactive agents and may contribute to the antidepressant efficacy of the plant in a complex manner. Our data also reveal novel and heretofore unexpected interactions of pure compounds in SJW at a number of GPCRs, transporters, and ion channels. We hypothesize that additive or synergistic actions of different single compounds may be responsible for the antidepressant efficacy of SJW. These results and this general approach may impact our understanding of phytomedicines in general and H. perforatum specifically.

The role of I(1)-imidazoline receptors and alpha(2)-adrenergic receptors in the modulation of glucose and lipid metabolism in the SHROB model of metabolic syndrome X.

Hypertension is commonly accompanied by obesity, hyperlipidemia, and insulin resistance in humans, a cluster of abnormalities known as metabolic syndrome X. With the notable exception of inhibitors of the renin-angiotensin system, which have mildly beneficial effects on insulin resistance, most antihypertensive agents worsen one or more components of metabolic syndrome X. Second-generation centrally acting antihypertensive agents such as rilmenidine and moxonidine have mixed effects on components of metabolic syndrome X, which might reflect in part actions on two different receptors: I(1)-imidazoline and alpha(2)-adrenergic. Using a rat model of metabolic syndrome X, we sought to separate the influence of these two receptors on glucose and lipid metabolism by using selective antagonists. Rilmenidine and moxonidine acutely raised glucose and lowered insulin, thereby further worsening glucose tolerance. These effects were entirely mediated by alpha(2)-adrenergic receptors. Rilmenidine and moxonidine also lowered glucagon, an effect that was mediated solely by I(1)-imidazoline receptors since it was potentiated by alpha(2)-blockade, but eliminated in the presence of I(1)-antagonists. Lowering of triglyceride and cholesterol levels followed the same pattern as glucagon, implicating I(1)-imidazoline receptors in lipid-lowering actions. Chronic treatment with moxonidine reproduced the beneficial effects on glucagon and lipids while the acute hyperglycemic response did not persist. Thus, alpha(2)-adrenergic receptors mediate an acute deterioration of glucose tolerance, whereas in contrast I(1)-imidazoline receptors appear to mediate the persistent long-term improvements in glucose tolerance. The therapeutic action of I(1)-imidazoline agonists may be primarily mediated through reduced glucagon secretion.

The I(1)-imidazoline receptor in PC12 pheochromocytoma cells reverses NGF-induced ERK activation and induces MKP-2 phosphatase.

We sought to further elucidate signal transduction pathways for the I(1)-imidazoline receptor in PC12 cells and their interaction with the well-characterized signaling events triggered by nerve growth factor (NGF) in these cells. Stimulation of the I(1)-imidazoline receptor with moxonidine, a centrally acting antihypertensive, increased by greater than two-fold the proportion of ERK-1 and ERK-2 in the phosphorylated active form. Similarly, NGF elicited a five-fold increase in activated ERKs. Surprisingly, treatment of NGF-treated cells with moxonidine completely reversed activation of ERK. Moxonidine-induced inhibition of ERK activation in NGF-treated cells was dose-dependent, followed a limited time course and could be blocked by the I(1)-antagonist efaroxan. These data suggested possible deactivation of ERK by specific phosphatases. Therefore, we assayed levels of MKP-2, a dual specificity phosphatase whose substrates include ERK. Moxonidine and NGF both increased levels of MKP-2 by three-fold. These effects were additive, as both agents together increased MKP-2 by a total of six-fold. Moxonidine-induced induction of MKP-2 was time- and dose-dependent and could be blocked by the I(1)-antagonist efaroxan or by D609, an inhibitor of phosphatidylcholine-selective phospholipase C known to block downstream signaling events coupled to I(1)-receptors. Thus, I(1)-receptors can abrogate the primary signaling cascade activated by NGF, most likely by increasing levels of a specific phosphatase to return dually phosphorylated ERK to its unphosphorylated state.

Plasma glucagon and free fatty acid responses to a glucose load in the obese spontaneous hypertensive rat (SHROB) model of metabolic syndrome X.

Metabolic Syndrome X is a cluster of abnormalities including insulin resistance, hyperlipidemia, hypertension, and obesity. We sought to determine if excess plasma glucagon and free fatty acids (FFA) might contribute to the insulin resistance in the obese spontaneous hypertensive rat (SHROB), a unique animal model of leptin resistance and metabolic Syndrome X. SHROB were extremely hyperinsulinemic and mildly glucose intolerant compared with lean SHR. SHROB had elevated fasting plasma glucagon and FFA, and showed paradoxical responses to an oral glucose challenge, with increased glucagon at 30 and 60 min postchallenge (200% plus minus 45% and 91% plus minus 13%, respectively; n = 9). In lean SHR, glucagon was nearly unchanged by glucose loading (<30% increase, P > 0.05; n = 5). Plasma FFA were not affected by a glucose load in SHROB, whereas SHR showed a decrease of 40% plus minus 6% (n = 5--9). The I/G molar ratio changed in opposite directions in the two genotypes, with a decrease in SHROB at 30 and 60 min, in contrast to the appropriate increase at 30 and 60 min postchallenge in the lean SHR (P < 0.01; n = 5--9). Administration of 500 ng/kg exogenous glucagon to SHR raised glucagon 56% plus minus 5% to a level that was similar to fasting SHROB. This level of circulating glucagon was sufficient to elevate glucose and insulin during the 7 hr of observation (n = 9). Based on these results, we suggest that fasting hyperglucagonemia and impaired suppression of glucagon secretion and FFA in response to an oral glucose load may contribute to insulin resistance and glucose intolerance in the SHROB model of metabolic Syndrome X.

Synthesis and in vitro pharmacology of novel heterocyclic muscarinic ligands.

A set of novel heterocyclic ligands (7a-9a, 7b-9b, and 9c) structurally related to oxotremorine 2 was designed, synthesized, and tested at muscarinic receptor subtypes. In the binding experiments at cloned hm1-5, the presence of the 2-methylimidazole/2-methyl-3-alkylimidazolium moiety in place of the pyrrolidine ring revealed, in derivatives 8a, 8b, and 9c, a moderate selectivity for some receptor subtypes. The functional in vitro assays yielded results that correlated closely to binding data. In general, on passing from agonists bearing the pyrrolidine moiety to their analogues carrying the 2-methylimidazole function, the overall pharmacological efficacy profile is shifted from agonism toward partial agonism. The insertion of the 2-methyl-3-alkylimidazolium moiety advances the effect such that the compounds are pure antagonists. Quite similarly, chiral 3-oxo-Delta(2)-isoxazoline (+/-)-10 behaved as a weak antagonist unable to discriminate the different muscarinic receptor subtypes.

Pharmacological properties of the central antihypertensive agent, moxonidine.

The sympathetic nervous system plays a central role in the pathophysiology not only of hypertension and other cardiovascular diseases but also metabolic disorders including disturbances of glucose and lipid homeostasis. A centrally acting sympathetic agent is therefore attractive not only for lowering blood pressure, but also intervening with multiple disease processes. Older agents such as clonidine and guanabenz have numerous side effects, including sedation and dry mouth that limit their acceptability to patients. Moxonidine and the related agent rilmenidine have greatly reduced side effects, because they have reduced activity at the α(2) -adrenergic receptors that mediate these undesirable actions. Instead, moxonidine and rilmenidine act primarily through a novel cellular site, termed the I(1) -imidazoline receptor. The molecular biology of the I(1) -imidazoline receptor protein has recently been described, and the cell signaling pathways linked to this protein have been characterized. Moxonidine has unique effects on a number of cell types through this unusual cellular site of action. There are multiple therapeutic implications of these cellular actions, especially for metabolic syndrome and its associated derangements in glucose and lipid metabolism. Finally, the clinical trials that seemed to identify an unfavorable outcome in severe heart failure are dissected and critiqued. We conclude that moxonidine and future successors to this agent could be of great value in treating multiple chronic diseases.