Efficacy and safety of preprandial human insulin inhalation powder versus injectable insulin in patients with type 1 diabetes.

AIMS/HYPOTHESIS: The efficacy and safety of human insulin inhalation powder (HIIP) plus insulin glargine were compared to subcutaneously injected insulin (SC insulin) plus insulin glargine in patients with type 1 diabetes. METHODS: This was a randomised, open-label crossover study in which one group of patients received preprandial HIIP plus insulin glargine for 12 weeks, followed by the same duration with preprandial SC insulin (lispro or regular) plus insulin glargine. Another group of patients received the reverse treatment sequence. The trial was designed as a non-inferiority comparison of the two treatments for effect on HbA(1c); blood glucose levels were also monitored. Safety assessments included adverse event reporting and hypoglycaemic events. RESULTS: HbA(1c) at endpoint was 7.95+/-0.12% for the HIIP treatment and 8.06+/-0.12% for the SC insulin treatment; mean changes from baseline to endpoint were -0.08 and 0.00%, respectively, (p=NS). The upper limit of the 95% CI of mean difference in HbA(1c) between the two treatments was 0.02%, indicating that HIIP was not inferior relative to SC insulin, as measured against the pre-defined margin of 0.3%. Fasting blood glucose was significantly lower for HIIP treatment (8.09+/-0.33 mmol/l; n=117) than for SC insulin treatment (9.05+/-0.33 mmol/l; n=111) (p=0.01). Safety profiles were comparable between the two treatments. The rate of any hypoglycaemia (least-squares mean adjusted for 30 days+/-SE) was 8.9+/-0.7 and 8.2+/-0.8 for HIIP and SC insulin treatments, respectively, (p=0.29). The rate of nocturnal hypoglycaemia was greater for HIIP (4.2+/-0.4) than for SC insulin (2.7+/-0.4; p<0.001). CONCLUSIONS/INTERPRETATION: HIIP was similar in efficacy to SC insulin for glycaemic control in type 1 diabetes mellitus. The two treatments had comparable safety profiles.

Sustained effects of pioglitazone vs. glibenclamide on insulin sensitivity, glycaemic control, and lipid profiles in patients with Type 2 diabetes.

AIMS: This study compared the effects of 52 weeks' treatment with pioglitazone, a thiazolidinedione that reduces insulin resistance, and glibenclamide, on insulin sensitivity, glycaemic control, and lipids in patients with Type 2 diabetes. METHODS: Patients with Type 2 diabetes were randomized to receive either pioglitazone (initially 30 mg QD, n = 91) or micronized glibenclamide (initially 1.75 mg QD, n = 109) as monotherapy. Doses were titrated (to 45 mg for pioglitazone and 10.5 mg for glibenclamide) to achieve glycaemic targets during the next 12 weeks: fasting blood glucose of < or = 7 mmol/l and 1-h postprandial blood glucose of < or = 10 mmol/l. Patients were maintained on the titrated dose for 40 weeks. RESULTS: Pioglitazone significantly increased insulin sensitivity compared with glibenclamide, as assessed by homeostasis model assessment (17.0% vs. -13.0%; P < 0.001), quantitative insulin sensitivity check index (0.011 vs. -0.007; P < 0.001) and fasting serum insulin (-1.3 pmol/l vs. 23.8 pmol/l; P = 0.007). The glibenclamide group had significantly lower HbA1c than the pioglitazone group after 12 weeks of therapy (7.8% vs. 8.3%, P = 0.015), but significantly higher HbA1c after 52 weeks of therapy (7.8% vs. 7.2%, P = 0.001). Pioglitazone significantly (vs. glibenclamide) increased mean HDL-C (P < 0.001), decreased mean triglycerides (P = 0.019), and decreased mean atherogenic index of plasma (AIP; P = 0.001) and mean total cholesterol/HDL-C (P = 0.004), without significantly elevating mean total cholesterol or mean LDL-C compared with glibenclamide. CONCLUSIONS These data suggest that the effects of pioglitazone are more sustained than those of glibenclamide for improving insulin sensitivity in patients with Type 2 diabetes, and that 52 weeks' treatment with pioglitazone has favourable effects on glycaemic control and lipoprotein profile.

Subtype-selective N-methyl-D-aspartate receptor antagonists: synthesis and biological evaluation of 1-(heteroarylalkynyl)-4-benzylpiperidines.

4-[4-(4-Benzylpiperidin-1-yl)but-1-ynyl]phenol (8) and 4-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]phenol (9) are potent NR1A/2B receptor antagonists (IC(50) values 0.17 and 0.10 microM, respectively). Administered intraperitoneally, they both potentiated the activity of L-DOPA in the unilaterally 6-hydroxydopamine-lesioned (6-OHDA) rat, a model of Parkinson's disease. However, compound 9 was not active orally, likely due to rapid first-pass metabolism of the phenol moiety. The phenol was replaced by several bicyclic heterocyclic systems containing an NH group to function as a H-bond donor in the hope that these would be less likely to undergo rapid metabolism. In general, indoles, indazoles, benzotriazoles, indolones, and isatins gave analogues with weaker NR1A/2B activity than the parent phenols, while benzimidazolones and benzimidazolinones gave equipotent or more potent analogues. The preference for a para arrangement between the H-bond donor and the linking acetylene moiety was confirmed, and a propyne link was preferred over a butyne link. Substitution on the benzyl group or a 4-hydroxyl group on the piperidine had little effect on NR1A/2B potency; however, 4-hydroxypiperidines demonstrated slightly improved selectivity for NR1A/2B receptors versus alpha-1 adrenergic and dopamine D2 receptor affinity. From this study, 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1, 3-dihydrobenzoimidazol-2-one (46b) was identified as a very potent, selective NR1A/2B receptor antagonist (IC(50) value 0.0053 microM). After oral administration at 10 and 30 mg/kg, 46b potentiated the effects of L-DOPA in the 6-OHDA-lesioned rat and seemed to have improved oral bioavailability but lower brain penetration compared to phenol 9.

Parallel synthesis of a series of subtype-selective NMDA receptor antagonists.

A series of 1-(heteroarylthioalkyl)-4-benzylpiperidines was rapidly synthesized through the use of parallel synthesis to investigate the binding affinity for the NR1A/2B receptor subtype.

4-Hydroxy-1-[2-(4-hydroxyphenoxy)ethyl]-4-(4-methylbenzyl)piperidine: a novel, potent, and selective NR1/2B NMDA receptor antagonist.

A structure-based search and screen of our compound library identified N-(2-phenoxyethyl)-4-benzylpiperidine (8) as a novel N-methyl-D-aspartate (NMDA) receptor antagonist that has high selectivity for the NR1/2B subunit combination (IC(50) = 0.63 microM). We report on the optimization of this lead compound in terms of potency, side effect liability, and in vivo activity. Potency was assayed by electrical recordings in Xenopus oocytes expressing cloned rat NMDA receptors. Side effect liability was assessed by measuring affinity for alpha(1)-adrenergic receptors and inhibition of neuronal K(+) channels. Central bioavailability was gauged indirectly by determining anticonvulsant activity in a mouse maximal electroshock (MES) assay. Making progressive modifications to 8, a hydroxyl substituent on the phenyl ring para to the oxyethyl tether (10a) resulted in a approximately 25-fold increase in NR1A/2B potency (IC(50) = 0.025 microM). p-Methyl substitution on the benzyl ring (10b) produced a approximately 3-fold increase in MES activity (ED(50) = 0.7 mg/kg iv). Introduction of a second hydroxyl group into the C-4 position on the piperidine ring (10e) resulted in a substantial decrease in affinity for alpha(1) receptors and reduction in inhibition of K(+) channels with only a modest decrease in NR1A/2B and MES potencies. Among the compounds described, 10e (4-hydroxy-N-[2-(4-hydroxyphenoxy)ethyl]-4-(4-methylbenzyl)piperid ine, Co 101244/PD 174494) had the optimum pharmacological profile and was selected for further biological evaluation.

Subtype-selective N-methyl-D-aspartate receptor antagonists: synthesis and biological evaluation of 1-(arylalkynyl)-4-benzylpiperidines.

A search of our compound library for compounds with structural similarity to ifenprodil (5) and haloperidol (7) followed by in vitro screening revealed that 4-benzyl-1-(4-phenyl-3-butynyl)piperidine (8) was a moderately potent and selective antagonist of the NR1A/2B subtype of NMDA receptors. Substitution on the benzyl group of 8 did not significantly affect NR1A/2B potency, while addition of hydrogen bond donors in the para position of the phenyl group enhanced NR1A/2B potency. Addition of a hydroxyl moiety to the 4-position of the piperidine group slightly reduced NR1A/2B potency while reducing alpha-1 adrenergic and dopamine D2 receptor binding affinities substantially, resulting in improved overall selectivity for NR1A/2B receptors. Finally, the butynyl linker was replaced with propynyl or pentynyl. When the phenyl was para substituted with amine or acetamide groups, the NR1A/2B potency order was butynyl > pentynyl >> propynyl. For the para methanesulfonamide or hydroxyl groups, the order was butynyl approximately propynyl > pentynyl. The hydroxyl propyne (48) and butyne (23) were among the most potent NR1A/2B antagonists from this study. They both potentiated the effects of L-DOPA in the 6-hydroxydopamine-lesioned rat, a model of Parkinson's disease, dosed at 10 mg/kg ip, but 48 was not active at 30 mg/kg po.

Synthesis of 7,8-(methylenedioxy)-1-phenyl-3,5-dihydro-4H-2, 3-benzodiazepin-4-ones as novel and potent noncompetitive AMPA receptor antagonists.

A group of 7,8-(methylenedioxy)-1-phenyl-3,5-dihydro-4H-2, 3-benzodiazepin-4-ones was synthesized and assayed for antagonism of rat brain alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors expressed in Xenopus oocytes. The benzodiazepinones inhibited AMPA-activated membrane current responses in a manner consistent with noncompetitive, allosteric inhibition of the receptor-channel complex. The most potent compound in the series was 1-(4-aminophenyl)-7,8-(methylenedioxy)-3,5-dihydro-4H-2, 3-benzodiazepin-4-one (6), which had an IC50 of 2.7 microM. For comparison, the reference compound GYKI 52466 (2) had an IC50 of 6.9 microM. Compound 6 also had potent anticonvulsant activity in a mouse maximum electroshock-induced seizure (MES) assay: the ED50 was 2.8 mg/kg iv, whereas the ED50 for GYKI 52466 was 4.6 mg/kg iv. In contrast to a previous report, the 7,8-dimethoxy analogue of 6 was a low-potency AMPA antagonist (IC50 >100 microM) and weak anticonvulsant (ED50 >10 mg/kg iv). The benzodiazepinones described herein are potent noncompetitive AMPA receptor antagonists that could have therapeutic potential as anticonvulsants and neuroprotectants.

3 alpha-Hydroxy-3 beta-(phenylethynyl)-5 beta-pregnan-20-ones: synthesis and pharmacological activity of neuroactive steroids with high affinity for GABAA receptors.

Neuroactive steroids that allosterically modulate GABAA receptors have potential uses as anticonvulsants, anxiolytics, and sedative-hypnotic agents. Recently, a series of pregnanes substituted with simple alkyl groups at the 3 beta-position were synthesized and found to be active in vitro. The present report describes the synthesis of a series of substituted 3 alpha-hydroxy-3 beta-(phenylethynyl)pregnan-20-ones and their in vitro structure-activity relationship determined by their potency for inhibition of [35S]TBPS binding in rat brain membranes. Appropriate substitution of the phenyl group results in ligands with particularly high affinity for the neuroactive steroid site on GABAA receptors (e.g., 4-acetyl 28, IC50 10 nM). The potency of selected steroids was confirmed electrophysiologically in oocytes expressing cloned human GABAA alpha 1 beta 2 gamma 2L receptors (e.g., compound 28, EC50 6.6 nM). Consistent with their in vitro activity, some of the 3 beta-(phenylethynyl)-substituted steroids displayed anticonvulsant activity in the pentylenetetrazol (PTZ) and maximal electroshock (MES) tests following ip administration in mice. Notably, the 3 beta-[(4-acetylphenyl)ethynyl]-19-nor derivative 36 demonstrated an attractive anticonvulsant profile (PTZ and MES ED50 values of 2.8 and 9.2 mg/kg, respectively). A new pharmacophore for the neuroactive steroid site of GABAA receptors is proposed based upon the high affinity of certain substituted 3 beta-(phenylethynyl) steroids.

Subtype-selective antagonism of NMDA receptors by nylidrin.

The 1,4-di-substituted piperidines ifenprodil, eliprodil, CP 101,606 ((1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol ) and Ro 25-6981 ((R-(R*,S*))-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenyl-methyl)-1- piperidinepropanol) are allosteric antagonists of NMDA receptors. Inhibition of diheteromeric NMDA receptors by this class of antagonist is characterized by pronounced selectivity for NR1/2B subunit combinations. In the current study, we assayed effects of nylidrin, a structurally-related non-piperidine, on recombinant and neuronal NMDA receptors. Nylidrin was a potent (IC50 = 0.18 microM) antagonist of NR1A/2B receptors expressed in Xenopus oocytes and was at least 150-fold weaker against NR1A/2A and NR1A/2C receptors. The blockade of NR1A/2B responses by nylidrin was not surmounted by increasing the concentrations of glutamate or glycine and was not voltage-dependent. Potency of inhibition increased approximately 3-fold upon lowering extracellular pH from 8 to 6.8. Nylidrin inhibited NMDA responses in cultured rat cortical neurons with similar potency and apparent mechanism of action as the NR1A/2B receptors. Our results suggest that nylidrin interacts with the same allosteric inhibitory site previously described for the related piperidine antagonists, and should serve as a structural lead for designing novel subtype-selective inhibitors of NMDA receptors.

Ectoenzymes as sites of peptide regulation.

The ectoenzyme-mediated metabolism of neuropeptides may be an important regulatory site of peptide-mediated activity. These membrane-bound, extracellularly oriented peptidases are not only responsible for inactivating peptide substrates, but also lead to the formation of metabolic fragments. Peptide fragments formed after enzymatic proteolysis have been shown to display novel bioactivity as a consequence of a shift in receptor selectivity. This example of nervous system plasticity through peptide biotransformation can have multiple consequences. Centrally acting drugs have been shown to have profound effects on peptide-mediated systems throughout the brain and spinal cord including a differential alteration in ectoenzyme activity and ectoenzyme-mediated metabolism of neuropeptides. In this review, Tom Davis and Chris Konkoy suggest that the modulation of ectoenzyme-mediated peptide metabolism represents an additional level at which the concentration of extracellular neuropeptides, and thus peptide-mediated transmission, can be regulated.

Haloperidol and apomorphine differentially affect neuropeptidase activity.

In addition to their well characterized effects at dopamine receptors, neuroleptic drugs have been shown to affect the level and in vitro metabolism of neuropeptides. In the present study, the effect of acute and subchronic administration of the neuroleptic haloperidol and the nonselective, dopamine agonist apomorphine on neuropeptidase activity was determined in regional, rat brain P2 membranes. Subchronic administration of haloperidol decreased the activity of aminopeptidase N in the frontal cortex and caudate-putamen. In contrast, subchronic administration of apomorphine increased aminopeptidase N activity in the frontal cortex and caudate-putamen. Neutral endopeptidase 24.11 also was affected differentially in the caudate-putamen, but both subchronic haloperidol and apomorphine decreased neutral endopeptidase 24.11 activity in the frontal cortex. Metalloendopeptidase 24.15 activity was decreased in the caudate-putamen after acute haloperidol and increased in the frontal cortex after acute apomorphine administration; however, no effect was noted after subchronic administration of either drug. Angiotensin converting enzyme was not affected by any treatment. Therefore, neuroleptic-induced alterations in aminopeptidase N, neutral endopeptidase 24.11 and metalloendopeptidase 24.15 activity may account for previously reported alterations in neuropeptide degradation. In view of the interaction between mesocorticolimbic dopamine neurons and neuropeptides, e.g., substance P, neurotensin and enkephalins, neuroleptic-induced alterations in the activities of neuropeptidases, and thus neuropeptide metabolism can, in turn, play a role in modulating midbrain dopaminergic activity.

Subchronic haloperidol administration decreases aminopeptidase N activity and [Met5]enkephalin metabolism in rat striatum and cortex.

Previously we have shown that subchronic intraperitoneal (i.p.) administration of haloperidol decreases the degradation of [Met5]enkephalin by regional brain slices (Waters et al., 1995, J. Pharmacol. Exp. Ther. 274, 783). In the present study, subchronic (7-day i.p.) administration of haloperidol (1 mg/kg) decreased the accumulation of aminopeptidase-derived fragments Tyr and Gly-Gly-Phe-Met on cortical and striatal slices. The accumulation of Tyr-Gly-Gly, however, was not altered by haloperidol treatment on slices from either region. Further, aminopeptidase N activity was decreased in P2 membranes isolated from either the cortex or striatum of haloperidol-treated animals. These data suggest that the haloperidol-induced decrease in [Met5]enkephalin metabolism results, at least in part, from a reduction in the activity of aminopeptidase N.

Regional metabolism of Met-enkephalin and cholecystokinin on intact ratbrain slices: characterization of specific peptidases.

The metabolism of Met-enkephalin and cholecystokinin (CCK) 8-(sulfated) by intact microslices was studied in rat brain regions. Incubation of brain slices with Met-enkephalin (400 microM) resulted in a linear rate of disappearance of parent peptide and appearance of metabolic fragments whose rate of accumulation was specific to brain region. The degradative rate (pmol/min/mg of protein) of Met-enkephalin was high in caudate-putamen (5,160 +/- 120) and lower in nucleus accumbens (3,630 +/- 110) and frontal cortex (3,180 +/- 120). Inhibition of aminopeptidases decreased Met-enkephalin degradation (50-97% vs. control) in frontal cortex but was less effective in caudate-putamen (20-34%). Tyr-Gly-Gly and Phe-Met were recovered in caudate-putamen and nucleus accumbens, whereas negligible quantities of these fragments were recovered from frontal cortex. Phosphoramidon, an inhibitor of neutral endopeptidase 24.11, decreased Met-enkephalin degradation in caudate-putamen (14%) but had no effect on that in frontal cortex. A cocktail of bestatin or leuhistin (inhibitors of aminopeptidases), phosphoramidon, and captopril (an inhibitor of angiotensin converting enzyme) protected Met-enkephalin from degradation (recovery > 95%) in caudate-putamen. CCK 8-(sulfated) degradation on slices from caudate-putamen, nucleus accumbens, and frontal cortex was not altered by inhibitors of neutral endopeptidase 24.11, metalloendopeptidase 24.15, angiotensin converting enzyme, or thiol proteases. Inhibitors of either aminopeptidases or serine proteases produced small reductions (13-30%) in CCK degradation in each region. These data provide evidence for regional and structural specificity in terminating the actions of neuropeptides.

Neuropeptide metabolism on intact, regional brain slices: effect of dopaminergic agents on substance P, cholecystokinin and Met-enkephalin degradation.

Neuroleptic drugs have been shown to affect the level and messenger ribonucleic acid of specific neuropeptides. The effect of subchronically administered neuroleptics on neuropeptide metabolism, however, has not been systematically characterized. In the present study, the effect of neuroleptics and other dopaminergic compounds on substance P (SP), cholecystokinin and met-enkephalin degradation was determined on intact, regional, rat brain slices. After 7-day administration of haloperidol (1 mg/kg) or chlorpromazine (20 mg/kg), SP degradation was decreased in caudate-putamen and nucleus accumbens. After administration of the dopaminergic agonist apomorphine (5 mg/kg, b.i.d.), SP degradation was increased in the nucleus accumbens. The dopamine D2-receptor antagonist sulpiride (100 mg/kg, b.i.d.) produced no effect on SP degradation. Met-enkephalin degradation was decreased after haloperidol administration in both frontal cortex and caudate-putamen and unaffected by apomorphine administration. The metabolism of cholecystokinin was not affected by neuroleptic treatment. Studies performed with specific peptidase inhibitors suggested that neutral endopeptidase 24.11, metalloendopeptidase 24.15 and aminopeptidases degrade SP on caudate-putamen and nucleus accumbens slices. Therefore, alterations in these peptidases may be responsible for the change noted in SP degradation after dopaminergic compound administration. These metabolic changes noted after neuroleptic administration may therefore contribute to neuroleptic-induced alterations in regional peptide levels.

Acute administration of neuroleptics decreases neurotensin metabolism on intact, regional rat brain slices.

Treatment with antipsychotic agents has been shown to affect both neurotensin (NT) levels and the activities of enzymes implicated in the metabolism of NT. In the present study the effects of i.p. administered antipsychotics and dopaminergic agents on NT metabolism were examined in the microslice preparation from discrete regions of rat brain. Significant degradation of NT 1-13 with the concomitant production of NT fragments, including NT 1-8, 1-10, 1-11 and 9-13, occurred after incubating for 2 hr regionally dissected microslices with 100 microM NT 1-13. Acute administration (i.p.) of haloperidol (3 mg/kg) 1 hr before slice preparation had no effect on NT metabolism in any of the regions studied. Acute administration of either haloperidol (3 mg/kg) or chlorpromazine (20 mg/kg) 24 hr before slice preparation decreased NT metabolism significantly, as indicated by decreases in both NT degradation and formation of NT 1-8 in both the nucleus accumbens and caudate-putamen. Furthermore, a decrease in the formation of biologically active NT 9-13 was detected in the nucleus accumbens after neuroleptic administration 24 hr before slice preparation. Assay of crude membrane homogenates revealed a significant reduction in the NT-degrading enzyme metalloendopeptidase 24.15 (E.C. 3.4.24.15) activity in the caudate-putamen of haloperidol-treated rats. The level of NT metabolism remained significantly reduced at 48 hr after haloperidol administration, but returned to that of the control level by 96 hr. Acute administration of apomorphine (2 i.p. injections of 20 mg/kg) increased NT degradation on slices from the nucleus accumbens, but not on slices from the caudate-putamen.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic treatment with neuroleptics alters neutral endopeptidase 24.11 activity in rat brain regions.

Chronic administration of neuroleptics has been shown to affect the endogenous levels, mRNA, posttranslational processing, and metabolism of neuropeptides in specific regions of rat brain. Neutral endopeptidase 24.11 (NEP) is known to metabolize a variety of neuropeptide substrates, including the enkephalins and neurotensin, thus modifying or terminating the bioactivity of such peptides. In the present study, chronic treatment with haloperidol (1 mg/kg/day, 12 days) increased NEP activity in nucleus accumbens, and chronic treatment with chlorpromazine (4 mg/kg/day, 12 days) increased NEP activity in caudate putamen. Higher dosages with either compound did not significantly alter NEP activity, and none of the treatments altered NEP activity in the hypothalamus. Chronic treatment with apomorphine (5 mg/kg/day, 12 days) decreased NEP activity in both nucleus accumbens and caudate putamen. These data suggest that chronic treatment with neuroleptic drugs may lead to regionally specific alterations in the metabolism of neuropeptides.

Relationship between kappa 1 opioid receptor binding and inhibition of adenylyl cyclase in guinea pig brain membranes.

Previously, we showed that kappa-selective ligands inhibit adenylyl cyclase in guinea pig cerebellar membranes. The present studies explore the relationship between kappa 1 binding sites (as determined with [3H]U-69,593 binding) and kappa 1-inhibition of adenylyl cyclase (using U-50,488H) in guinea pig brain membranes. Various kappa opioids displaced [3H]U-69,593 binding at a single site with subnanomolar affinities. These agonists were several hundred-fold weaker in inhibiting adenylyl cyclase, but for most agonists the rank order of adenylyl cyclase inhibition paralleled the displacement of kappa 1 binding. The correlation of IC50 values for both adenylyl cyclase and binding was significant except for alpha-neo endorphin, which was relatively weak at inhibiting adenylyl cyclase despite a Ki value of 0.08 nM versus kappa 1 binding. Comparison between kappa 1 binding and kappa 1-inhibited adenylyl cyclase across eleven guinea pig brain regions revealed that kappa 1-inhibited adenylyl cyclase was highest in the cerebellum, absent in thalamus and superior colliculus, and moderate in other regions. In most regions, kappa 1 binding correlated with the efficacy of kappa 1-inhibited adenylyl cyclase. However, the hippocampus had high levels of kappa 1-inhibited adenylyl cyclase despite low levels of kappa 1 binding, while cortex exhibited a high density of kappa 1 sites but a relatively low level of kappa 1-inhibited adenylyl cyclase. Reaction of cerebellar kappa receptors with beta-chlornaltrexamine (beta-CNA) blocked both kappa 1 binding and kappa 1-inhibited adenylyl cyclase. The effect of beta-CNA on kappa 1-inhibited adenylyl cyclase was to inhibit efficacy with little decrease in agonist potency, thus suggesting no significant level of kappa receptor reserve for this effector system.

Dynorphin-selective inhibition of adenylyl cyclase in guinea pig cerebellum membranes.

Guinea pig cerebellum, which contains kappa opioid receptors uncontaminated by other opioid receptor types, was chosen to examine whether kappa receptors are coupled to adenylyl cyclase. Membranes were prepared from guinea pig cerebellum and pretreated at pH 4.5 to increase inhibitory activity, and adenylyl cyclase was assayed in the presence of dynorphin analogs as prototypical kappa agonists. Results showed that several dynorphin analogs inhibited adenylyl cyclase by 30-50%, whereas mu- and delta-preferring agonists had no effect. Dynorphin A and the kappa-selective compounds D-Pro10-dynorphin(1-11) and U-50,488H were the most potent agonists, with IC50 values of 0.03-0.05 microM, whereas other dynorphin gene products like dynorphin B and alpha-neo-endorphin were approximately 10-fold less potent. Like other Gi-coupled responses, dynorphin-inhibited adenylyl cyclase required GTP and sodium. Naloxone was a competitive antagonist for dynorphin-inhibited adenylyl cyclase, with 1 microM naloxone shifting the IC50 value of dynorphin A by 20-fold. The kappa-selective antagonist nor-binaltorphimine was even more potent, with 0.1 microM nor-binaltorphimine shifting the dynorphin IC50 value by 50-fold. These results suggest that dynorphin A and its analogs inhibit adenylyl cyclase by binding to a guanine nucleotide-binding protein-coupled opioid receptor whose pharmacological specificity matches those of kappa receptors.