Effects of antiglaucoma drugs GLC756, a novel dopamine D2 agonist and D1 antagonist, and timolol on endotoxin-induced TNF-alpha release in serum of rats.

PURPOSE: Anti-inflammatory activity of an antiglaucoma drug may be an advantage for long-term treatment of glaucoma since it may reduce the risk of treatment-related inflammatory processes in outer compartments of the eye and probably also prevent or delay progression of glaucomatous retinal neurodegeneration. In this study, the effect of GLC756, a novel mixed dopamine D 2 receptor agonist and dopamine D 1 receptor antagonist, and timolol on endo-toxin-induced cytokine tumor necrosis factor-alpha (TNF-alpha) release in serum was examined. METHODS: For endotoxin-induced TNF-alpha release, 8-week-old Lewis rats were intravenously injected with 160 microg lipopolysaccharide (LPS) from Salmonella typhimurium. GLC756, timolol, or betamethasone were either systemically (1 mg/kg SC for 5 days) or topically (0.4%, 0.5%, and 0.1%, respectively, 20 microL eye drops given 16 times over 48 hours in left and right eye) administered. TNF-alpha was measured in serum 2 and 48 hours after LPS induction. RESULTS: A marked TNF-alpha increase in serum was found 2 hours after LPS induction. Administration of GLC756 and betamethasone, systemically and topically, decreased TNF-alpha release. However, due to large scattering of mean values only the effect of systemically administered GLC756 was statistically significant. In contrast, timolol increased TNF-alpha values stronger than LPS alone. CONCLUSIONS: The significant suppression of LPS-induced TNF-alpha increase by GLC756 suggests an additional anti-inflammatory potential of the dopaminergic compound in the treatment of glaucoma.

Effects of latanoprost and GLC756, a novel dopamine D2 agonist and D1 antagonist, on cultured normal human dermal fibroblasts.

PURPOSE: Proliferation of subconjunctival fibroblasts plays a critical role in scarring and failure of glaucoma filtering surgery. Long-term topical glaucoma medications appear to increase fibroblast proliferation. In this study, the effects of topical antiglaucoma drugs latanoprost and GLC756, a novel dopamine D2 agonist and D1 antagonist, on cultured normal human dermal fibroblasts (NHDF) were examined. METHODS: The NHDF cell line was incubated with latanoprost, prostaglandin F2alpha (PGF2alpha), GLC756, or 5-fluorouracil as a positive control at concentrations of 3 and 30 microM for 6, 18, and 24 hours. Fibroblast growth was measured by 5-bromodeoxyuridine (BrdU) uptake using laser scanning cytometry. RESULTS: Latanoprost and PGF2alpha had a biphasic response on the number of cultured NHDF positively stained with BrdU. A stimulating effect on proliferation occurred early, 6 hours after incubation, and an inhibitory effect 18 to 24 hours after incubation. GLC756, in contrast, revealed only inhibitory effects on BrdU uptake 18 to 24 hours after incubation. The pattern of GLC756 was similar to that of the positive control 5-fluorouracil. CONCLUSIONS: Latanoprost seemed to have a biphasic response on the proliferation of cultured NHDF. First there was a stimulating thereafter a secondary negative modulating effect. GLC756 had a fully antiproliferative effect on the NHDF, indicating an additional potential of novel dopamine compounds for topical glaucoma medication.

Effects of anti-glaucoma drugs timolol and GLC756, a novel mixed dopamine D2 receptor agonist and D1 receptor antagonist, on endotoxin-induced-uveitis and -arthritis in rats.

Anti-glaucoma drugs exhibiting anti-inflammatory properties are desirable for the long-term treatment of glaucoma since they may reduce the risk for treatment-related inflammatory processes in outer compartments of the eye. The purpose of this study was to evaluate potential anti-inflammatory effects of two topically and systemically applied anti-glaucoma drugs i.e. GLC 756, a novel mixed dopamine D2 receptor agonist and D1 receptor antagonist, and timolol a beta-adrenoceptor antagonist using endotoxin-induced uveitis (EIU) and arthritis in rats as an in vivo model. For EIU, 8-week-old Lewis rats were intravenously injected at 160 microg lipopolysaccharide (LPS) from Salmonella typhimurium. GLC756, timolol, or betamethasone, as a positive control, were either topically (0.4%, 0.5%, and 0.1%, respectively, 16-times 20 microL eye drops during 48 h) or systemically (1mg/kg subcutaneous for 5 days) administered. Cell infiltration in tissue of the eye and knee joint were assessed histopathologically and in special compartments of the eye by confocal microscopy 48 h after LPS-induction. Numerous infiltrating cells were detected in the eyes after LPS-induction and half of the animals showed arthritis. Topical and systemic pre-treatment with GLC756 and timolol resulted in reduced cell infiltration in the eye. In addition, GLC756 reduced, whereas timolol increased the incidence of arthritis. Betamethasone suppressed almost completely the cell infiltration in the eye and the incidence of arthritis. In conclusion, the observations that GLC756 reduced cell infiltration in the eye and the incidence of arthritis after LPS-induction is compatible with anti-inflammatory properties of this drug. By contrast, timolol produced no consistent anti-inflammatory effect since both inhibitory as well as stimulatory effects on inflammatory processes were seen.

Pharmacological characterisation of 5-HT receptors positively coupled to adenylyl cyclase in the rat hippocampus.

The pharmacological properties of 5-hydroxytryptamine (5-HT) receptors positively coupled to adenylyl cyclase in the rat hippocampus were investigated using selective agonists and antagonists. 5-HT (0.008-125 microM) stimulated cyclic AMP formation in homogenates of rat hippocampus in a concentration-dependent manner. The maximal increase in cyclic AMP formation occurred at 1 microM (141+/-6%) and the half-maximal effect (EC50) at 50+/-22 nM. Cyclic AMP accumulation induced by 1 microM 5-HT was partly inhibited by the selective 5-HT1A receptor antagonist WAY 100,635 (1 microM), the selective 5-HT4 receptor antagonist SB 203,186 (1 microM), and the 5-HT2A/c/ 5-HT7 receptor antagonist mesulergine (25 microM). WAY 100,635, SB 203,186 and mesulergine inhibited the effect of 5-HT (1 microM) by 47%, 33% and 49%, respectively. The combination of WAY 100,635 (1 microM) with SB 203,186 (1 microM) or mesulergine (25 microM) resulted in stronger inhibition than with each antagonist alone, and the combination of all three antagonists produced almost total blockade (95%) of 5-HT-induced cyclic AMP accumulation. 5-Carboxamidotryptamine (5-CT; 0.008-125 microM), a 5-HT1/5-HT7 receptor agonist, and SDZ 216-454 (0.008-125 microM), a selective 5-HT4 receptor agonist, concentration-dependently stimulated cyclic AMP formation, but the maximal effect of each agonist was smaller than that of 5-HT alone. SDZ 216-454 (5 microM) and 5-CT (5 microM) in combination stimulated cyclic AMP formation in an additive manner. 8-OH-PIPAT and 8-OH-DPAT, two selective 5-HT1A agonists, produced a small but significant increase in cyclic AMP formation at concentrations above 0.04 microM and 10 microM, respectively. These findings suggest that at least three 5-HT receptor subtypes, i.e. 5-HT1A, 5-HT7 and 5-HT4 receptors, are involved in mediating 5-HT-induced cyclic AMP formation in rat hippocampus.

Imaging dopamine D4 receptors in the living primate brain: a positron emission tomography study using the novel D1/D4 antagonist [11C]SDZ GLC 756.

The dopamine D4 receptor has lately attracted interest since it has been hypothesized to be involved in the pathogenesis and pharmacotherapy of neuropsychiatric diseases. The present study provides first in vivo evidence of dopamine D4 receptors in primate brain using a [11C]benzo[g]quinoline, the novel radioligand [11C]SDZ GLC 756 ([11C]GLC: in vitro dissociation constants at human receptor clones [nM]: 1.10 at D1; 0.40 at D2; 25 at D3; 0.18 at D4.2; 6.03 at D5). Dynamic positron emission tomography scans were performed on healthy baboons (Papio hamadryas, n = 3). Specific receptor binding (SB) was calculated for striatum and neocortex (frontal, temporal, parietal, and occipital) based on the differences between the regional and the cerebellar concentration of [11C]. Blockade of D1 and D5 receptors by SCH23390 (1.7 pmol/kg) diminished SB in the striatum by 55 +/- 4% (mean +/- standard deviation, P < 0.05) and in the frontal cortex by 13 +/- 8% (P < 0.05) when compared to SB in the unblocked state (SB(D1-D5)). In the presence of the dopamine antagonists SCH23390 (1.7 micromol/kg) and raclopride (5.7 pmol/kg)--which mask the D1, D2, D3, and D5 subtypes--SB of [11C]GLC to D4 receptors (SB(D4)) was demonstrated in the striatum and all cortical regions of interest. In the striatum, the ratio of SB(D4)/SB(D1-D5) was 0.13 +/- 0.07. In the neocortex, SB(D4)/SB(D1-D5) was notably higher (0.77 +/- 0.29; mean of all cortical regions of interest). The widespread distribution of dopamine D4 receptors suggests a basic functional role of this receptor subtype in the modulation of cortical and subcortical neuronal activity.

Dopamine D2-like sites in schizophrenia, but not in Alzheimer's, Huntington's, or control brains, for [3H]benzquinoline.

Although the basis of schizophrenia is not known, evidence indicates a possible overactivity of dopamine pathways. In order to detect any new dopamine receptor-like sites which may be altered in schizophrenia, the present study used a new radioligand, a [3H]benzo[g]quinoline. The receptors were labelled by this ligand in the presence of other drugs to block the known dopamine D1, D2, D3, or D5 receptors (no D4-selective ligands are available to block D4). Using this method, we found that schizophrenia brain striata had elevated levels of a D2-like site not detected in control human postmortem brains or in Alzheimer's, Huntington's, or Parkinson's disease brains. The ligand acted as an agonist at this D2-like site, because binding was abolished by guanine nucleotide. The binding of the ligand to the D4 receptor, however, was not sensitive to guanine nucleotide. The site differed from D2 itself, because S- and R-sulpiride were equally potent at the D2-like site. The D2-like sites were present in rat and mouse brain but were absent in brain slices from transgenic mice where D2 had been knocked out. The abundance of the receptor was not related to premortem use of antipsychotic drugs. Future research should examine the biochemical differences between the D2 dopamine receptor and these D2-like sites in schizophrenia.

Effects of dopamine D-1 and D-2 receptors on intraocular pressure in conscious rabbits.

This investigation was designed as a randomized, placebo-controlled, double-masked, crossover study in NZW rabbits with normal intraocular pressure (IOP) to investigate dopaminergic effects on IOP. SKF 38393, a selective D1-receptor agonist, increased, and SDZ PSD-958, a selective D1-receptor antagonist, decreased IOP, respectively. The selective D2-receptor agonist quinpirole decreased IOP, whereas the selective D2 receptor antagonist metoclopramide had no significant effect. Combinations of quinpirole with SDZ PSD-958 decreased IOP in an additive manner. SDZ GLC-756, a mixed D1-receptor antagonist/D2-receptor agonist, decreased IOP in a dose-dependent manner with a maximum effect greater than the maximum effects produced either by the D1-receptor antagonist SDZ PSD-958 and the D2-receptor agonist quinpirole. The effect of SDZ GLC-756 could only be partially blocked by the selective D2-receptor antagonist metoclopramide suggesting that both D1-receptor blockade and D2-receptor stimulation participate in its IOP-lowering effect. Tonography suggests that SDZ GLC-756 has no significant effect on outflow facility. Furthermore, the results suggest that both D1 and D2 receptors each play an independent role in the regulation of IOP in rabbits. Thus, simultaneous blockade of D1 receptors and stimulation of D2 receptors may provide a new pharmacological approach for the treatment of ocular hypertension frequently associated with glaucoma.

SDZ PSD 958, a novel D1 receptor antagonist with potential limbic selectivity.

SDZ PSD 958, a novel benzo[g]quinoxaline derivative exhibits the properties of a potent orally active selective D1 receptor antagonist. It has high affinity for D1-like receptors (D1, D5; pKi = 9.7-9.8) labelled by [3H]SCH23390 and is at least 400 fold less active at D2-like receptors (i.e. D2, D4) labelled by [3H]spiperone. Effects in functional tests are consistent with D1 receptor antagonist properties. SDZ PSD 958 inhibited apomorphine-induced rearing in mice and prevented prolongation of novelty-induced locomotion in rats elicited by the selective D1 receptor agonist CY 208-243. By contrast, SDZ PSD 958 did not induce catalepsy and only weakly inhibited apomorphine-induced stereotyped gnawing in rats. This suggests that SDZ PSD 958 preferentially inhibits responses mediated by dopamine systems innervating the limbic system.

Topical SDZ GLC-756, a novel dopamine D-1 antagonist and D-2 agonist, lowers intraocular pressure in conscious rabbits.

This investigation was carried out to evaluate the effect of SDZ GLC-756, a novel dopamine D-1 antagonist and D-2 agonist, on intraocular pressure (IOP) in rabbits. A randomized, placebo-controlled, double-masked, crossover study with topical application of SDZ GLC-756 eyedrops [0.015% (n = 10), 0.03% (n = 10), 0.0625% (n = 10), 0.125% (n = 9), 0.25% (n = 10), 0.5% (n = 14)] and vehicle alone (placebo-control) to the right eye was performed in New Zealand White rabbits. The contralateral eye received no treatment. IOP was measured using a pneumatonometer. Topical SDZ GLC-756 significantly lowered IOP in a dose-dependent manner (maximal IOP-lowering effect 1 approximately 2 hours after administration) in the treated eye and, to a lesser extent, in the contralateral eye. The duration of action was approximately 4 hours. The simultaneous D-1 antagonistic and D-2 agonistic properties of SDZ GLC-756 may provide a new pharmacological approach to the treatment of glaucoma, which deserves further investigation.

SDZ GLC 756, a novel octahydrobenzo[g]quinoline derivative exerts opposing effects on dopamine D1 and D2 receptors.

SDZ GLC-756, a novel octahydrobenzo[g]quinoline derivative, is equipotent in displacing [3H]SCH23390 from dopamine D1 receptors and [3H]205-501 from dopamine D2 receptor binding sites. It blocks dopamine sensitive adenylate cyclase with the same potency as SCH23390, indicating antagonist properties at dopamine D1 receptors. On the other hand, SDZ GLC 756 inhibits electrically evoked acetylcholine release from rat striatal slices with the same potency as the selective dopamine D2 receptor agonist bromocriptine. This effect is blocked by spiperone suggesting that it is mediated by dopamine D2 receptor activation. The opposing action of SDZ GLC 756 on dopamine D1 and D2 receptors is also evident in vivo. SDZ GLC 756, like SCH23390, blocks apomorphine-induced rearing in mice. On the other hand, it inhibits prolactin secretion and produces circling in unilateral 6-OHDA-lesioned rats, which is compatible with stimulant properties at dopamine D2 receptors. This drug might be a new tool to study linkage between dopamine D1 and D2 receptors.

New insights into the biology of schizophrenia through the mechanism of action of clozapine.

Many studies have detected in the brain of schizophrenic patients various morphological and structural abnormalities in various regions and in particular in the cortical and limbic areas. These abnormalities might in part result from neurodevelopmental disturbances suggesting that schizophrenia might have organic causes. These abnormalities may be the primary event in schizophrenia and be responsible for altered dopaminergic, but not only dopaminergic, neurotransmission in these regions. If schizophrenia is in some way strictly related to brain morphological abnormalities it becomes hard to believe that a curative treatment will ever be possible. Considering this scenario, treatment of schizophrenia will be restricted to symptomatic and preventive therapy and therefore, more effective and better tolerated antipsychotics are necessary. The widely used classical antipsychotic drugs present some disadvantages. They do not improve all symptoms of schizophrenia, are not effective in all patients, produce a number of unpleasant and serious, and partly irreversible, motor side effects. The atypical antipsychotic clozapine constitutes a major advance in particular for patients not responding to conventional neuroleptics. To explain the unique therapeutic effect of clozapine many hypothesis have been proposed. Most of the explanations given so far assume that the D2 blockade is the basis for the antipsychotic activity of clozapine and that the difference in respect to other antipsychotics is due to the contribution of other receptor interactions. Considering the dopaminergic receptor, in particular the recently discovered D4 receptor subtype, it has been observed that even if several classical neuroleptics exhibit high affinity to the D4 receptor, clozapine is more selective for this subtype compared to D2 receptors. Moreover clozapine, differently from all other conventional neuroleptics, is a mixed but weak D1/D2 antagonist. This observation has prompted speculation that the synergism between D1 and D2 receptors might allow antipsychotic effects to be achieved below the threshold for unwanted motor side effects. Probably the D1 antagonistic activity exerted by clozapine at low doses enhances preferentially the extracellular concentration of dopamine in specific areas of the brain, such as the prefrontal cortex, where a dopaminergic hypoactivity has been suggested to be in part responsible for negative symptoms of schizophrenia. The clozapine enhancement of dopaminergic activity in this brain area might explain its efficacy against schizophrenia negative symptoms. However, it cannot be excluded that the affinities displayed by clozapine for other nondopaminergic receptors also contribute to its unique therapeutic profile. The various hypotheses mentioned in this review need to be further validated or disproved. The only way to do that is developing new drugs where the postulated mechanistic profile is specifically realized and to clinically test these compounds.

Effect of adding the D-1 agonist CY 208-243 to chronic bromocriptine treatment of MPTP-monkeys: regional changes of brain dopamine receptors.

1. Eleven monkeys were administered N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): eight were treated with bromocriptine for one week and then CY 208-243 (four monkeys) or saline (four monkeys) was added to the bromocriptine treatment. 2. Addition of CY 208-243 increased the therapeutic response observed with the ergot alone without inducing dyskinesia. 3. Following MPTP, [3H]-SCH 23390 specific binding to D-1 receptors as well as [3H]-spiperone and [3H]-N-n-propylnorapomorphine specific binding to D-2 receptors increased in posterior striatum compared to control animals, whereas [3H]-SKF 38393 binding to D-1 receptors tended to decrease. 4. Dopamine receptor density was unchanged in anterior striatum of untreated MPTP-monkeys. 5. In the posterior striatum, both dopaminergic treatments decreased towards control values [3H]-SCH 23390, [3H]-spiperone and [3H]-N-n-propylnorapomorphine binding whereas they did not significantly change [3H]-SKF 38393 specific binding. [3H]-SKF 38393 specific binding increased in anterior striatum of bromocriptine-treated MPTP-monkeys, compared to untreated MPTP-animals, and this increase was abolished in animals treated with bromocriptine+CY 208-243. 6. The present study shows that in MPTP-monkeys, treated or not with DA agonists, the D1 and D2 receptor changes are concentrated in the posterior striatum and that denervation appears to cause a shift from the high to the low affinity agonist state of D1 receptors but not for the D2 subtype.

Quantification of optic nerve blood flow changes using magnetic resonance imaging.

PURPOSE: To evaluate the possibilities of magnetic resonance imaging (MRI) for quantification of pharmacologically induced changes in optic nerve microcirculation. METHOD: T2-weighted MRI sequences were used to image the eye, optic nerve, and frontal cortex in rats. Two sets of control images before and one set during Gd (DTPA) infusion were recorded. Blood flow values for two regions of the optic nerve (an anterior part, including the optic nerve head, and a more posterior part) and the frontal cortex were calculated by image analysis from the change in signal intensity, as already reported for cerebral blood flow. For each rat, a control experiment before drug administration and a second experiment 30 minutes after subcutaneous injection of either placebo (n = 7), timolol (n = 7), or SDZ GLC-756, a dopamine D-1 antagonist and D-2 agonist (n = 7), were carried out in a double-blind fashion. RESULTS: Mean basal blood flow values were found between 29.4 and 45.6 ml/100 g per minute in the anterior part of the optic nerve, 38.3 and 42.9 ml/100 g per minute in the posterior part of the optic nerve, and 68.0 and 75.0 ml/100 g per minute in the frontal cortex. Placebo and timolol did not cause significant changes. SDZ GLC-756 significantly increased blood flow by 238% +/- 65% in the anterior part and by 87% +/- 40% in the posterior part of the optic nerve. CONCLUSIONS: These results suggest that MRI provides quantification of optic nerve blood flow and that dopaminergic substances increase optic nerve blood flow.

Effect of adding the D1 agonist CY 208-243 to chronic bromocriptine treatment. I: Evaluation of motor parameters in relation to striatal catecholamine content and dopamine receptors.

A group of four cynomolgus monkeys previously rendered parkinsonian by the toxin 1-methyl-4-phenyl,1,2,3,6-tetrahydropyridine (MPTP) were observed in locomotion cages equipped with photocells during four periods of 7 days during which they received saline or two doses of the D1 agonist CY 208-243. The larger dose of 0.5 mg/kg produced a significant increase in locomotion in three of four animals. A second group of eight monkeys also previously rendered parkinsonian by MPTP and having received no other treatment were given a daily treatment of bromocriptine 1.66 mg/kg orally daily during 4 weeks. In four of the animals, after a week on bromocriptine alone, the D1 agonist CY 208-243 was added in increasing doses of 0.05, 0.1, and 0.5 mg/kg. The motor response as measured by locomotion, hand dexterity, and a disability score improved progressively at least in some of the animals on bromocriptine alone. The addition of CY 208-243 produced a more striking improvement of all three parameters, which appeared to be dose dependent. Biochemical analysis of the brain of these animals plus one control and one MPTP untreated monkey showed a > 90% loss of dopamine in the striatum in six of the eight treated monkeys. Both D2 and D1 dopamine receptors were increased in density by denervation, but both treatments abolished this increase for the D2 receptors while increasing the affinity of the D1 receptors.

Structure-activity relationships in the trans-hexahydroindolo[4,3-ab]phenanthridine ("benzergoline") series. 2. Resolution, absolute configuration, and dopaminergic activity of the selective D1 agonist CY 208-243 and its implication for an "extended rotamer-based dopamine receptor model".

4,6,6a,7,8,12b-Hexahydroindolo[4,3-ab]phenanthridines ("benzergolines") was the first structural class of potent and selective dopamine D1 agonists lacking a catechol group. In order to determine the enantioselectivity of the 7-methyl derivative in the adenylate cyclase assay, its 5,5a-dihydro precursor was resolved and both enantiomers oxidized to the final products. The biological activity was found to reside entirely in the (-)-enantiomer, (-)-1 (CY 208-243). An X-ray study of its (-)-mandelic acid salt revealed a 6aR,12bR absolute configuration, which, in confirmation of the structure hypothesis, corresponds to that of the ergolines. Unexpectedly, an axial conformation of the N-methyl group was observed in the crystal structure. In contrast, subsequently analyzed crystals of the free base of (-)-1 revealed an equatorial conformation of the N-methyl group, which, we assume, represents the bioactive conformation. Based on the determined absolute configuration, (-)-1 could be oriented in a previously described "rotamer-based dopamine receptor model", which allowed the localization of a "subtype selectivity-inducing site" (aryl binding site at the D1 receptor, steric barrier at the D2 receptor), marked by the conformationally fixed "additional" phenyl group of the benzergoline molecule.

Somatostatin inhibits the activity of adenylate cyclase in cultured human meningioma cells and stimulates their growth.

It has been reported previously that most human meningiomas have receptors for somatostatin. Here we report the results of investigations of the effect of somatostatin and the somatostatin analog octreotide on the growth in vitro of human meningioma cells. Neither somatostatin nor its analog showed a direct growth inhibitory action on cultured human meningioma cells. Rather, there was a slight but significant stimulation of growth in the presence of somatostatin. The somatostatin receptors in meningioma tissue were shown to be functional since somatostatin inhibited forskolin-stimulated formation of cAMP by meningioma membranes. In addition, cAMP inhibited the growth of cultured meningioma cells. We conclude that the stimulation by somatostatin of the growth of human meningioma cells in vitro is caused by its inhibitory effect on cAMP formation. These results suggest that therapeutic trials of patients with (recurrent) inoperable meningiomas with somatostatin analogs have to be carried out with great caution.

Dopamine agonists potentiate antiakinetic effects of competitive NMDA-antagonists in monoamine-depleted mice.

The competitive NMDA-antagonists SDZ EAA-494 and CGP 37849 and the mixed D-1/D-2 dopamine agonists CI 201-678 and SDZ 205-152 reverse akinesia in monoamine-depleted mice in a dose dependent manner. Combination of threshold doses of NMDA-antagonists with dopamine agonists markedly enhances anti-akinetic effects. CI 201-678 which in addition to D-1 and D-2 receptors stimulates alpha-2 receptors produces a stronger effect than SDZ 205-152 which is devoid of alpha-2 agonist activity. The results indicate that concomitant blockade of NMDA-receptors and activation of dopamine receptors results in synergistic or at least additive motor stimulatory effects.

trans-hexahydroindolo[4,3-ab]phenanthridines ("benzergolines"), the first structural class of potent and selective dopamine D1 receptor agonists lacking a catechol group.

In contrast to the many selective dopamine (DA) D2 receptor agonists known, only two prototypes of selective D1 receptor agonists have been described; both show preference for the periphery due to their catechol partial structures. Our search for non-catechol, selective D1 agonists was based on the hypothesis that D1 selectivity could be conferred upon ergolines by annulation with a phenyl ring. The target molecules, trans-4,6,6a,7,8,12b-hexahydroindolo-[4,3-ab]phenanthridi nes ("benzergolines"), were efficiently synthesized by using the Ninomiya enamide photocyclization reaction. These compounds were found to be as active as the most potent D1 agonists in the adenylate cyclase D1 receptor model, but showed no activity in the ACh release D2 receptor assay. The acquired subtype selectivity of the novel structures was accompanied by an enhanced potency and efficacy as compared to the corresponding ergolines. This points to a D1 affinity enhancing, D2 receptor discriminating role for the additional phenyl group and provides further support for the existence of a D1 receptor specific accessory aryl binding site. Thus the benzergolines represent the first structural class of potent and selective D1 agonists lacking a catechol group which should allow an efficient central nervous system penetration. On the basis of these results, the D1 agonist pharmacophore has to be revised in the sense that potent activity requires neither a catechol function nor an orthogonal conformation of the aromatic rings.

Differential effects of somatostatin on adenylate cyclase as functional correlate for different brain somatostatin receptor subpopulations.

In homogenates of rat hippocampus and striatum, but not substantia nigra, somatostatin (SRIF) inhibits forskolin-activated adenylate cyclase in nanomolar concentrations. However, SRIF can also stimulate adenylate cyclase in micromolar concentrations in homogenates of rat hippocampus and substantia nigra. The SRIF octapeptide SMS 201-995 solely inhibits the forskolin-activated adenylate cyclase in the 3 preparations. These results suggest that the SRIF-specific stimulation of adenylate cyclase may be a functional correlate for the brain-specific SRIF receptor subpopulation, whereas the SRIF and SMS 201-995 inhibition of stimulated adenylate cyclase correlate with the SRIF receptor subpopulation present in brain and non-neuronal tissues.