Melatonin reduces the need for sedation in ICU patients: a randomized controlled trial.

BACKGROUND: Critically ill patients suffer from physiological sleep deprivation and have reduced blood melatonin levels. This study was designed to determine whether nocturnal melatonin supplementation would reduce the need for sedation in patients with critical illness. METHODS: A single-center, double-blind randomized placebo-controlled trial was carried out from July 2007 to December 2009, in a mixed medical-surgical Intensive Care Unit of a University hospital, without any form of external funding. Of 1158 patients admitted to ICU and treated with conscious enteral sedation, 82 critically-ill with mechanical ventilation >48 hours and Simplified Acute Physiology Score II>32 points were randomized 1:1 to receive, at eight p.m. and midnight, melatonin (3+3mg) or placebo, from the third ICU day until ICU discharge. Primary outcome was total amount of enteral hydroxyzine administered. RESULTS: Melatonin treated patients received lower amount of enteral hydroxyzine. Other neurological indicators (amount of some neuroactive drugs, pain, agitation, anxiety, sleep observed by nurses, need for restraints, need for extra sedation, nurse evaluation of sedation adequacy) seemed improved, with reduced cost for neuroactive drugs. Post-traumatic stress disorder prevalence did not differ between groups, nor did ICU or hospital mortality. Study limitations include the differences between groups before intervention, the small sample size, and the single-center observation. CONCLUSION: Long-term enteral melatonin supplementation may result in a decreased need for sedation, with improved neurological indicators and cost reduction. Further multicenter evaluations are required to confirm these results with different sedation protocols.

Treatment of symptomatic lumbar spinal degenerative pathologies by means of combined conservative biochemical treatments.

Research in spine surgery has proposed new soft and less invasive techniques. These are the results of our experience with oxygen-ozone therapy, which we could experiment within the Italian National Health System over 3 years. A total of 1,920 patients were admitted on the basis of unselected enrolment because of lumbosciatic pain. Patients were divided into three groups: (A) Patients with degenerative disc disease and arthropathy: 509 (26.5%), (B) Patients with failed back surgery syndrome (FBSS): 1,027 (53.489%), and (C) Patients with pure herniated lumbar disc: 384 (20%). The rationale of the treatment for all these different pathologies we have taken into consideration is the biochemical mechanism by which they can engender pain and dysfunction. Treatment for group A: paravertebral injection and phleboclysis (two cycles of 6 sessions, one each 3 days) +endoscopic neurolysis. Treatment for group B: paravertebral injection and phleboclysis (two cycles of 6 sessions, one each 3 days) + endoscopic neurolysis with intradiscal procedure (named percutaneous peridurodiscolysis). Treatment for group C: paravertebral injection (two cycles of 6 sessions, one each 3 days) + percutaneous discolysis.The perceived quality of result for this minimally invasive procedure makes oxygen-ozone therapy an interesting weapon in the hands of doctors. Furthermore, if the technique loses its clinical effectiveness, it can be repeated without harm for the patient, and costs for the health organization are notably very low, above all if compared to surgical procedures.We underline the need that this treatment should be performed in protected structures, in operative rooms, under anesthesiologic control, and in the hands of specialists.

Pineal and cortical melatonin receptors MT1 and MT2 are decreased in Alzheimer's disease.

The pineal hormone melatonin is involved in physiological transduction of temporal information from the light dark cycle to circadian and seasonal behavioural rhythms, as well as possessing neuroprotective properties. Melatonin and its receptors MT1 and MT2, which belong to the family of G protein-coupled receptors, are impaired in Alzheimer's disease (AD) with severe consequences to neuropathology and clinical symptoms. The present data provides the first immunohistochemical evidence for the cellular localization of the both melatonin receptors in the human pineal gland and occipital cortex, and demonstrates their alterations in AD. We localized MT1 and MT2 in the pineal gland and occipital cortex of 7 elderly controls and 11 AD patients using immunohistochemistry with peroxidase-staining. In the pineal gland both MT1 and MT2 were localized to pinealocytes, whereas in the cortex both receptors were expressed in some pyramidal and non-pyramidal cells. In patients with AD, parallel to degenerative tissue changes, there was an overall decrease in the intensity of receptors in both brain regions. In line with our previous findings, melatonin receptor expression in AD is impaired in two additional brain areas, and may contribute to disease pathology.

Penetration of amphotericin B in human lung tissue after single liposomal amphotericin B (AmBisome) infusion.

The distribution of amphotericin B in lung tissue was studied in 18 patients with primary or secondary lung cancer who underwent thoracotomy and pulmonary resection. At different times before surgery the patients were treated with liposomal amphotericin B 1.5 mg/kg by i.v. infusion over 1h. Blood and lung tissue samples were collected during surgery (one subject for each collecting time) and assayed for amphotericin B levels by HPLC. Due to surgical requirements, it was possible to obtain data from the 10th to the 25th h after the end of infusion. Plasma amphotericin B concentrations progressively decreased from 3.4 microg/ml at the 10th h to 1 microg/ml at the 25th h after the end of intravenous infusion. In lung tissue samples the lowest amphotericin B concentration (about 1 microg/g) was observed at the 10th h, then a progressive increase was observed with the highest value (2.5 microg/g) determined at the 25th h.

Aging and vestibular system: specific tests and role of melatonin in cognitive involvement.

Balance disorders are frequent with aging. They are particularly important because they decrease social autonomy of the aged subjects and they often provoke falls. The cause is always multifactorial. There is evidence that aging affects multiple sensory inputs, as well as the muscoloskeletal system and central nervous system ability to perform sensorimotor integration. For the evaluation of decreased balance skills in elderly, a specific questionnaire has been prepared, in order to identify high risk of falling called falling risk inventory (FRI) questionnaire, and a complex psycho-sensory-motor test has been studied by means of posturography, in order to detect specific vestibular impairment. Regarding ethiopathogenesis of balance disorders in aged subjects, because the decline of behavioral and cognitive performances are due also to decline of biological rhythm control, the role of melatonin (the hormone regulating circadian rhythms, being strictly connected with cerebellar function, and it is well known that cerebellum acts in elderly both at motor and cognitive regulation. The goals of the present paper are: (i) To present a self-administered FRI questionnaire aimed at identifying possible causes of falls and quantifying falling risk in aged. (ii) To validate posturography as a specific test to investigate vestibular involvement in elderly in correlation with FRI. (iii) To present a complex behavioral test (NT) aimed at evaluating both spatial orientation and spatial memory in elderly, factors involved into the genesis of complex dizziness and unsteadiness. (iv) To evaluate the role of melatonin in cognitive involvement in dizzy, old subjects due to the functional correlations between circadian rhythms, cerebellum balance disturbances and cognitive disorders. General conclusions are: FRI correlates with falling risk. Posturography identifies specific vestibular impairments correlated to balance disorders and elderly falls. Spatial orientation is altered in about 40% of dizzy patients but no significant differences are revealed in melatonin rhythm. Spatial memory is highly altered only in subjects with inversion of circadian melatonin rhythm it is possible to hypothesize that the alteration of the normal circadian melatonin rhythm plays some role in the genesis of dizziness in a subpopulation of patients.

Effect of multiple doses of clarithromycin and amoxicillin on IL-6, IFNgamma and IL-10 plasma levels in patients with community acquired pneumonia.

Inflammation is crucial for the pathogenesis of both infectious and chronic obstructive pulmonary diseases. It is therefore important to modulate pulmonary inflammation in patients with these lung disorders. Macrolide antibiotics modulate inflammation in vitro and in in vivo by inhibiting the production of proinflammatory cytokines and prostaglandin E2, neutrophil chemotactic activity and elastase activity. This study evaluates the effect of clarithromycin (500 mg b.i.d. x 7 days) in comparison to amoxicillin (1 g t.i.d. x 7 days) in patients with community acquired pneumonia by testing plasma levels of IL-6, IFNgamma and IL-10 before starting therapy and at the 3rd and 7th days of therapy. Clarithromycin significantly decreased plasma levels of IL-6 and significantly increased those of IFNgamma and IL-10 at the 3rd and 7th day in comparison to basal levels. In patients treated with amoxicillin a significant decrease in IL-6 plasma levels was observed at the 7th day of therapy, probably in relation to the resolution of inflammatory symptoms. In the same patients IFNgamma plasma levels decreased during treatment while IL-10 plasma levels were unaffected.

Nocturnal anomalous movement reduction and sleep microstructure analysis in parkinsonian patients during 1-night transdermal apomorphine treatment.

This study analyzed the macrostructure and microstructure of sleep in 12 parkinsonian patients under basal conditions (T0) and during 1-night treatment (T1) with a new formulation of apomorphine. This new formulation consisted in a microemulsion of apomorphine administered by the transdermal route, able to provide a constant release of the drug over several hours (APO-TD). Sleep analysis at T1 compared with T0 revealed a 16% increment of total sleep time, a 12% increment of sleep efficiency, a 16% increment of stage 3 and 4 non-REM sleep, a 15% reduction of periodic limb movements index, a 22% reduction of arousal index, and a 23% reduction of cycling alternating patterns/non-REM. We conclude that APO-TD may be able to reduce nocturnal anomalous movements, akinesia, and rigidity in Parkinson's disease, and may reduce the disturbed sleep typical of Parkinson's disease.

Redox balance in patients with Down's syndrome before and after dietary supplementation with alpha-lipoic acid and L-cysteine.

The aim of the present study was to investigate the possible normalizing effect of antioxidants on certain parameters indicative of oxidative stress in Down's syndrome (DS). The study was performed in pediatric patients with DS with proven redox imbalance, who were advised to take a dietary supplementation composed of alpha-lipoic acid and L-cysteine for several treatment cycles (one treatment cycle = 30 days dietary supplementation plus 30 days wash-out). Serum thiol groups, serum total and septic reactive oxygen species (ROS) and total antioxidant status of serum were determined before and after dietary supplementation, using commercially available kits. In all the evaluable patients (n = 20), after 3.8 +/- 1.1 treatment cycles, thiol group serum concentrations and total antioxidant status of serum significantly increased (p < 0.0001 for both parameters) in comparison with basal values, while serum total and septic ROS significantly decreased (p < 0.0001 for both parameters). On the basis of these results it is impossible to demonstrate the clinical effects of the biochemical normalization obtained in patients with DS after supplying alpha-lipoic acid and L-cysteine. These data suggest that delaying the clinical expression of redox imbalance in patients with DS might be feasible by normalizing their redox balance.

Pharmacodynamics of levofloxacin and ciprofloxacin in a murine pneumonia model: peak concentration/MIC versus area under the curve/MIC ratios.

During the last decade some studies have shown that the area under the curve (AUC)/MIC ratio is the pharmacodynamic index that best predicts the efficacies of quinolones, while other studies suggest that the predictive value of the peak concentration/MIC (peak/MIC) ratio is superior to the AUC/MIC ratio in explaining clinical and microbiological outcomes. In classical fractionated dose-response studies with animals, it is difficult to differentiate between the AUC/MIC ratio and the peak/MIC ratio because of colinearity. Three different levofloxacin and ciprofloxacin dosing regimens were studied in a neutropenic mouse pneumonia model. The different regimens were used with the aim of increasing the AUC/MIC ratio without changing the peak/MIC ratio and vice versa. The first regimen (RC) consisted of daily doses of 5 up to 160 mg/kg of body weight divided into one, two, or four doses. In the second regimen (R0), mice were given 1.25 mg/kg every hour from 1 to 23 h, while the dose given at 0 h was 2.5, 5, 10, 20, 40, or 80 mg/kg. In the third regimen (R11), mice also received 1.25 mg/kg every hour from 0 to 23 h; but in addition, they also received 2.5, 5, 10, 20, 40, or 80 mg/kg at 11 h. The level of protein binding was also evaluated. The results indicate that the unbound fraction (f(u)) was concentration dependent for both levofloxacin and ciprofloxacin and ranged from approximately 0.67 to 0.88 for both drugs between concentrations of 0.5 and 80 mg/liter. The relationships between the AUC/MIC ratio and the number of CFU were slightly better than those between the peak/MIC ratio and the number of CFU. There was no clear relationship between the amount of time that the concentration remained above the MIC and effect (R(2) < 0.1). For both drugs, the peak/MIC ratio that resulted in a 50% effective concentration was lower for the R0 and R11 dosing regimens, indicating the importance of the AUC/MIC ratio. The same was true for the static doses. Survival studies showed that for mice treated with the low doses the rate of survival was comparable to that for the controls, but with the higher doses the rate of survival was better for mice receiving the R0 regimen. We conclude that for quinolones the AUC/MIC ratio best correlates with efficacy against pneumococci and that the effect of the peak/MIC ratio found in some studies could be partly explained by concentration-dependent protein binding.

Measurement of cefaclor and amoxicillin-clavulanic acid levels in middle-ear fluid in patients with acute otitis media.

Concentrations of cefaclor (CFC) or amoxicillin-clavulanic acid (AMX/CA) in middle-ear fluid collected preserving the stability and clearing the cell contents has been compared to those obtained using the traditional method. Sixty-seven children with effusive otitis media were treated orally with CFC (20 mg/kg of body weight) or AMX/CA (20 mg/kg) (4:1 ratio). The concentrations in cell-free fluid (C-) appear higher than those in the total fluid (C+) (as assayed traditionally).

Controlled-release transdermal apomorphine treatment for motor fluctuations in Parkinson's disease.

This study evaluated the efficacy in Parkinson's disease (PD) of a new pharmacologic preparation of apomorphine included in microemulsions and administered by transdermal route, which provides a constant release of the drug for several hours (Apo-TD). Twenty-one PD patients with motor fluctuations were treated with L-dopa alone, with L-dopa plus oral dopamine-agonists, or with L-dopa plus Apo-TD. Apo-TD improved UPDRS-III and tapping test scores in "off" conditions, and reduced duration of "off" periods; no improvement in "on" conditions occurred. We conclude that Apo-TD shows its efficacy particularly by reducing "off" period duration and disability rather than improving motor performances in "on" conditions and therefore it seems a promising treatment for uncontrolled "off" phases in PD patients.

An observational study on the epidemiology of respiratory tract bacterial pathogens and their susceptibility to four injectable beta-lactam antibiotics: piperacillin, piperacillin/tazobactam, ceftazidime and ceftriaxone.

Bacterial infections of the respiratory tract account for a large proportion of total medical consultations in general practice. In recent years, antibiotic resistance has increased alarmingly in a number of bacterial species that are common causes of these infections. The aim of this observational study was to determine the antibiotic resistance of microbial agents isolated from patients with acute or acutely exacerbated respiratory infections. Subjects recruited as potential sources of bacteria were either outpatients seen in a number of specialized clinics and hospital practices, or hospitalized patients. Overall, 648 consecutive patients (67% male, mean age 48.1+/-27.0 years) with infection of the upper or lower respiratory tract were observed during a 13-month period. A total of 551 pathogenic microbial strains were isolated and tested for their in vitro susceptibility to piperacillin, piperacillin/tazobactam, ceftazidime, and ceftriaxone. Among all isolates, the four most frequent pathogens were Pseudomonas aeruginosa (132 isolates, 24%), Streptococcus pyogenes (99 isolates, 18%), Staphylococcus aureus (93 isolates, 17%), and Klebsiella pneumoniae (46 isolates, 8%). The susceptibility of gram-positive isolates ranged from 97.5% to 95.1%, and no remarkable difference was found in the antibacterial activity of tested b-lactam antibiotics. The susceptibility of gram-negative isolates to piperacillin and piperacillin/tazobactam was also similar: 96.5% and 97.1%, respectively. In contrast, differences were found between piperacillin (or piperacillin/tazobactam) and either ceftazidime (p=0.003) or ceftriaxone (p<0.0003) in gram-negative isolates. We conclude that, despite the extensive use of beta-lactam antibiotics (piperacillin, ceftazidime, and ceftriaxone) in medical practice during the past three decades, the susceptibility of the most common pathogens involved in the etiology of upper and lower respiratory tract infections to these antibiotics is still high. In particular, bacterial resistance developed by gram-positive organisms against piperacillin is negligible and not alarming.

2-N-acylaminoalkylindoles: design and quantitative structure-activity relationship studies leading to MT2-selective melatonin antagonists.

Several indole analogues of melatonin (MLT) were obtained by moving the MLT side chain from C(3) to C(2) of the indole ring. Binding and in vitro functional assays were performed on cloned human MT1 and MT2 receptors, stably transfected in NIH3T3 cells. Quantitative structure-activity relationship studies showed that 4-methoxy-2-(N-acylaminomethyl)indoles, with a benzyl group in position 1, were selective MT2 antagonists and, in particular, N-[(1-p-chlorobenzyl-4-methoxy-1H-indol-2-yl)methyl]propanamide (12) behaved as a pure antagonist at MT1 and MT2 receptors, with a 148-fold selectivity for MT2. We present a topographical model that suggests a lipophilic group, located out of the plane of the indole ring of MLT, as the key feature of the MT2 selective antagonists.

Synthesis, pharmacological characterization and QSAR studies on 2-substituted indole melatonin receptor ligands.

A number of 6-methoxy-1-(2-propionylaminoethyl)indoles, carrying properly selected substituents at the C-2 indole position, were prepared and tested as melatonin receptor ligands. Affinities and intrinsic activities for the human cloned mt1 and MT2 receptors were examined and compared with those of some 2-substituted melatonin derivatives recently described by us. A quantitative structure activity relationship (QSAR) study of the sixteen 2-substituted indole compounds, 5a-k, 1, 8-11, using partial least squares (PLS) and multiple regression analysis (MRA) revealed the existence of an optimal range of lipophilicity for the C2 indole substituent. There are also indications that planar, electron-withdrawing substituents contribute to the affinity by establishing additional interactions with the binding pocket. No mt1/MT2 subtype selectivity was observed, with the relevant exception of the 2-phenethyl derivative 5e, which exhibited the highest selectivity for the h-MT2 receptor among all the compounds tested (MT2/mt1 ratio of ca. 50). Conformational analysis and superposition of 5e to other reported selective MT2 ligands revealed structural and conformational similarities that might account for the MT2/mt1 selectivity of 5e.

A new melatonin receptor ligand with mt1-agonist and MT2-antagonist properties.

It has been difficult, so far, to obtain melatonin analogs possessing high selectivity for the respective melatonin receptors, mt1 and MT2. In the present work, we report the synthesis and pharmacological characterization of a new compound N-¿2-[5-(2-hydroxyethoxy)-1H-indol-3-yl)] ethyl¿ acetamide or 5-hydroxyethoxy-N-acetyltryptamine (5-HEAT). To assess the activity of the compound, the following tests were performed: affinity determination for the high- and low-affinity receptor states (2-[125I]iodomelatonin binding), potency and intrinsic activity in inducing G protein activation ([35S]GTPgammaS binding assay). 5-HEAT showed little selectivity for the mt1 receptor, with pKi values of 7.77 for mt1 and 7.12 for the MT2 receptors, respectively. 5-HEAT was able to differentiate between the high- and the low-affinity receptor states in the mt1 but not in the MT2 receptor. 5-HEAT induced a high level of G protein activation when acting through the mt1 receptor, with a relative intrinsic activity of 0.92. On the contrary, it elicited only minimal MT2 receptor-mediated G protein activation, with a relative intrinsic activity of 0.16, and was also able to inhibit the melatonin-induced MT2 receptor-mediated G protein activation, with a pKB value of 7.4. In conclusion, it appears that 5-HEAT possesses very different efficacies at the two melatonin receptors, behaving as a full melatonin receptor agonist at the mt1 and as an antagonist/weak partial agonist at the MT2 receptor. Therefore, it is a promising ligand for use in functional studies aimed at distinguishing between the effects mediated by the different melatonin receptors in the human.

Production and characterization of antibodies directed against the human melatonin receptors Mel-1a (mt1) and Mel-1b (MT2).

We report the production of polyclonal antibodies directed against the human melatonin receptors Mel-1a (mt1) and Mel-1b (MT2) by means of antigenic synthetic peptides with sequences unique to these proteins. Immunostaining on NIH3T3 cells stably transfected with Mel-1a and Mel-1b cDNA gave intense reactions. Neither the preimmune serum nor cross-tested antisera showed any reactivity. These polyclonal antibodies will be essential immunocytochemical tools to study the human melatonin receptors distribution at subcellular level.

In vitro comparative dynamics of modified-release clarithromycin and of azithromycin.

Antibacterial kinetics of modified-release clarithromycin (CLA) and azithromycin (AZI) against respiratory tract pathogens were compared in relation to their pharmacokinetic profile. The study was carried out in three strains of Streptococcus pneumoniae, group A beta-hemolytic Streptococcus pyogenes, Moraxella catarrhalis and Haemophilus influenzae, respectively, exposed to concentration gradients of CLA and AZI simulating human serum pharmacokinetics after administration of 500 mg p.o. in a single dose. Bactericidal kinetics were assessed by counting the number of survivors before each change in concentration over a period of 36 h. The minimal inhibitory concentrations (MICs) of CLA and AZI were evaluated at time 0 and after 36 h of exposure to antibiotics in the surviving organisms. The results showed that CLA and AZI, in the experimental conditions adopted, had different antibacterial kinetics. Moreover, the addition of the 14-OH metabolite of CLA at the same concentrations reached in human serum exerted a bactericidal effect against two strains of H. influenzae resistant to CLA and AZI. An increase in MICs was observed against S. pyogenes and H. influenzae, with higher values for AZI.

Synthesis and in vitro anti-mycobacterium activity of N-alkyl-1, 2-dihydro-2-thioxo-3-pyridinecarbothioamides. Preliminary toxicity and pharmacokinetic evaluation.

Disseminated infections with Mycobacterium tuberculosis (MT) and Mycobacterium avium complex (MAC) are increasingly opportunistic diseases in patients with advanced acquired human immunodeficiency syndrome (AIDS). A series of N-alkyl-1, 2-dihydro-2-thioxo-3-pyridinecarbothioamides has been synthesized, and MICs for MT and MAC strains, either standard or isolated from infected patients, have been determined. Preliminary tests show a good activity and a very low toxicity for some derivatives. Pharmacokinetic studies in the rat show a very rapid elimination from the body after intravenous administration and a poor absorption after oral administration.

In vitro antibacterial activity of men 10700, a new penem antibiotic.

We report here the antibacterial activity of the new penem antibiotic Men 10700 against a total of 740 gram-positive and gram-negative clinical isolates, in comparison to imipenem, meropenem, cefotaxime, ceftriaxone, ciprofloxacin and gentamicin. Men 10700 has shown a wide spectrum of antibacterial activity, with a potent activity both against gram-positive species (with the exception of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis) as indicated by minimal inhibitory concentration (MIC(90)) values < or =0.5 mg/l, and gram-negative species, with MIC(90) values generally < or =2 mg/l. Men 10700 was the most potent antibiotic against methicillin-susceptible S. aureus and S. epidermidis, while the overall spectrum of activity resembled that of imipenem; meropenem was more active against most gram-negative species. In comparison with third-generation cephalosporins, Men 10700 demonstrated superior activity against methicillin-susceptible S. aureus and S. epidermidis and some gram-negative species such as Morganella morganii, Serratia spp. and Enterobacter cloacae; moreover, in contrast to third-generation cephalosporins, Men 10700 showed moderate activity against Enterococcus spp. The activity of Men 10700 against penicillin-resistant Streptococcus pneumoniae (10 strains) and some gram-negative strains selected for their resistance to cefotaxime (20 strains) was particularly interesting.

Ligand efficacy and potency at recombinant human MT2 melatonin receptors: evidence for agonist activity of some mt1-antagonists.

NIH3T3 fibroblast cells transfected with the full-length coding region of the MT2 human melatonin receptor stably expressed the receptor that is coupled to a pertussis toxin-sensitive G protein and exhibits high affinity for melatonin (K(I) = 261 pM). The order of apparent affinity for selected compounds was: 4-phenyl-2-propionamidotetralin (4P-PDOT) > 2-phenylmelatonin > 2-iodomelatonin > 2-bromomelatonin > 6-chloromelatonin > or = melatonin > luzindole > N-acetyl-tryptamine > or = N-[(2-phenyl-1H-indol-3-yl)ethyl]cyclobutanecarboxamide (compound 6) > N-acetylserotonin. 4P-PDOT exhibited a very high selectivity (approximately 22,000 times) for the MT2 receptor with respect to the mt1 receptor subtype, as tested in comparative experiments with membrane preparations from NIH3T3 cells stably transfected with the human mt1 receptor. MT2 melatonin receptors mediated incorporation of [35S]-GTPgammaS into isolated membranes via receptor catalyzed exchange of [35S]-GTPgammaS for GDP. The relative intrinsic activity and potency of the compounds were subsequently studied by using [35S]-GTPgammaS incorporation. The order of potency was equal to the order of apparent affinity. Melatonin and full agonists increased [35S]-GTPgammaS binding by 250% over basal (taken as 100%). Luzindole did not increase basal [35S]-GTPgammaS binding but competitively inhibited melatonin-stimulated [35S]-GTPgammaS binding, thus exhibiting antagonist action. The other two mt1 antagonists used here, 4P-PDOT and N-[(2-phenyl-1H-indol-3-yl)ethyl]cyclobutanecarboxamide, behaved as partial agonists at the MT2 subtype, with relative intrinsic activities of 0.37 and 0.39, respectively. These findings show, for the first time, important differences in the intrinsic activity of analogues between the human mt1 and MT2 melatonin receptor subtypes.