Characterization of brain mGluR5 binding in a pilot study of late-life major depressive disorder using positron emission tomography and [¹¹C]ABP688

The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in the pathophysiology of mood and anxiety disorders and is a potential treatment target in major depressive disorder (MDD). This study compared brain mGluR5 binding in elderly patients suffering from MDD with that in elderly healthy volunteers using positron emission tomography (PET) and [(11)C]ABP688. Twenty elderly (mean age: 63.0 ± 6.3) subjects with MDD and twenty-two healthy volunteers in the same age range (mean age: 66.4 ± 7.3) were examined with PET after a single bolus injection of [(11)C]ABP688, with many receiving arterial sampling. PET images were analyzed on a region of interest and a voxel level to compare mGluR5 binding in the brain between the two groups. Differences in [(11)C]ABP688 binding between patients with early- and late-onset depression were also assessed. In contrast to a previously published report in a younger cohort, no significant difference in [(11)C]ABP688 binding was observed between elderly subjects with MDD and healthy volunteers. [(11)C]ABP688 binding was also similar between subgroups with early- or late-onset depression. We believe this is the first study to examine mGluR5 expression in depression in the elderly. Although future work is required, results suggest potential differences in the pathophysiology of elderly depression versus depression earlier in life.

Plasma Aβ and PET PiB binding are inversely related in mild cognitive impairment

OBJECTIVE

To evaluate the relations between PET Pittsburgh compound B (PiB-PET) binding (amyloid imaging) and plasma Aβ in patients with mild cognitive impairment (MCI) and similarly aged controls.

METHODS

In 20 patients with MCI and 19 cognitively intact controls (case-control study), PiB binding potential (BP(nd)) was assessed in 4 regions, and total brain excluding cerebellum, referenced to cerebellar binding. The mean of plasma Aβ levels measured in duplicate was analyzed.

RESULTS

Plasma Aβ42/Aβ40 ratio was decreased in MCI compared to controls (mean 0.15 SD 0.04 vs mean 0.19 SD 0.07, p = 0.03) but Aβ40 (p = 0.3) and Aβ42 (p = 0.06) levels did not differ between the 2 groups. PiB BP(nd) was increased in MCI compared to controls in the cingulate (p = 0.02), parietal (p = 0.02), and total brain (p = 0.03), but not in prefrontal cortex (p = 0.08) or parahippocampal gyrus (p = 0.07). Linear regression analyses adjusting for age, sex, and cognitive test scores showed that low Aβ42/Aβ40 ratio was associated with high cingulate, parietal, and total brain PiB binding (0.01< p ≤ 0.05). These associations between PiB binding and the Aβ42/Aβ40 ratio were strongest in PiB-positive subjects and within the MCI group.

CONCLUSIONS

Though cross-sectional, the findings support the "sink" hypothesis that increased brain Aβ is accompanied by lower peripheral levels of Aβ, particularly the Aβ42/Aβ40 ratio in patients with MCI. The association between PiB binding and the plasma Aβ42/Aβ40 ratio suggests possible use of plasma Aβ combined with PiB binding as a risk biomarker with potential clinical application.

Hippocampal and entorhinal atrophy in mild cognitive impairment: prediction of Alzheimer disease

OBJECTIVE

To evaluate the utility of MRI hippocampal and entorhinal cortex atrophy in predicting conversion from mild cognitive impairment (MCI) to Alzheimer disease (AD).

METHODS

Baseline brain MRI was performed in 139 patients with MCI, broadly defined, and 63 healthy controls followed for an average of 5 years (range 1 to 9 years).

RESULTS

Hippocampal and entorhinal cortex volumes were each largest in controls, intermediate in MCI nonconverters, and smallest in MCI converters to AD (37 of 139 patients converted to AD). In separate Cox proportional hazards models, covarying for intracranial volume, smaller hippocampal volume (risk ratio [RR] 3.62, 95% CI 1.93 to 6.80, p < 0.0001), and entorhinal cortex volume (RR 2.43, 95% CI 1.56 to 3.79, p < 0.0001) each predicted time to conversion to AD. Similar results were obtained for hippocampal and entorhinal cortex volume in patients with MCI with Mini-Mental State Examination (MMSE) scores > or = 27 out of 30 (21% converted to AD) and in the subset of patients with amnestic MCI (35% converted to AD). In the total patient sample, when both hippocampal and entorhinal volume were entered into an age-stratified Cox model with sex, MMSE, education, and intracranial volume, smaller hippocampal volume (RR 2.21, 95% CI 1.14 to 4.29, p < 0.02) and entorhinal cortex volume (RR 2.48, 95% CI 1.54 to 3.97, p < 0.0002) predicted time to conversion to AD. Similar results were obtained in a Cox model that also included Selective Reminding Test (SRT) delayed recall and Wechsler Adult Intelligence Scale-Revised (WAIS-R) Digit Symbol as predictors. Based on logistic regression models in the 3-year follow-up sample, for a fixed specificity of 80%, the sensitivities for MCI conversion to AD were as follows: age 43.3%, MMSE 43.3%, age + MMSE 63.7%, age + MMSE + SRT delayed recall + WAIS-R Digit Symbol 80.6% (79.6% correctly classified), hippocampus + entorhinal cortex 66.7%, age + MMSE + hippocampus + entorhinal cortex 76.7% (85% correctly classified), age + MMSE + SRT delayed recall + WAIS-R Digit Symbol + hippocampus + entorhinal cortex 83.3% (86.8% correctly classified).

CONCLUSIONS

Smaller hippocampal and entorhinal cortex volumes each contribute to the prediction of conversion to Alzheimer disease. Age and cognitive variables also contribute to prediction, and the added value of hippocampal and entorhinal cortex volumes is small. Nonetheless, combining these MRI volumes with age and cognitive measures leads to high levels of predictive accuracy that may have potential clinical application.

Olfactory deficits in patients with mild cognitive impairment predict Alzheimer's disease at follow-up

OBJECTIVE

This study evaluated the predictive utility of olfactory identification deficits in patients with mild cognitive impairment for follow-up diagnosis of probable Alzheimer's disease.

METHOD

Ninety outpatients with mild cognitive impairment were examined at 6-month intervals. Matched healthy comparison subjects (N=45) were examined annually. The University of Pennsylvania Smell Identification Test was given at baseline.

RESULTS

Olfaction scores were lower in patients with mild cognitive impairment than in healthy comparison subjects. Seventy-seven patients were followed up; 19 were diagnosed with Alzheimer's disease by 2 years. Patients with low olfaction scores (< or =34 of 40), and patients with low olfaction scores who reported no subjective problems smelling, were more likely to develop Alzheimer's disease than other patients. In a Cox proportional hazards model adjusted for age, sex, modified Mini-Mental State score, and education, low olfaction scores did not predict time until development of Alzheimer's disease, but low olfaction scores accompanied by lack of awareness of olfactory deficits predicted time to development of Alzheimer's disease. This effect remained when attention or memory measures replaced modified Mini-Mental State score in the model. In patients with high Mini-Mental State scores (> or =27 of 30), low olfaction with lack of awareness remained a significant predictor of Alzheimer's disease. Olfaction scores of 30-35 showed moderate to strong sensitivity and specificity for diagnosis of Alzheimer's disease at follow-up.

CONCLUSIONS

In patients with mild cognitive impairment, olfactory identification deficits, particularly with lack of awareness of olfactory deficits, may have clinical utility as an early diagnostic marker for Alzheimer's disease.

A double-blind, placebo-controlled study of risperidone addition in serotonin reuptake inhibitor-refractory obsessive-compulsive disorder

BACKGROUND

To date, only 1 controlled study has found a drug (haloperidol) to be efficacious in augmenting response in patients with obsessive-compulsive disorder (OCD) refractory to serotonin reuptake inhibitor (SRI) monotherapy; patients with comorbid chronic tic disorders showed a preferential response. This report describes the first controlled study of risperidone addition in patients with OCD refractory to treatment with SRI alone.

METHODS

Seventy adult patients with a primary DSM-IV diagnosis of OCD received 12 weeks of treatment with an SRI. Thirty-six patients were refractory to the SRI and were randomized in a double-blind manner to 6 weeks of risperidone (n = 20) or placebo (n = 16) addition. Behavioral ratings, including the Yale-Brown Obsessive Compulsive Scale, were obtained at baseline and throughout the trial. Placebo-treated patients subsequently received an identical open-label trial of risperidone addition.

RESULTS

For study completers, 9 (50%) of 18 risperidone-treated patients were responders (mean daily dose, 2.2 +/-0.7 mg/d) compared with 0 of 15 in the placebo addition group (P<. 005). Seven (50%) of 14 patients who received open-label risperidone addition responded. Risperidone addition was superior to placebo in reducing OCD (P<.001), depressive (P<.001), and anxiety (P =.003) symptoms. There was no difference in response between OCD patients with and without comorbid diagnoses of chronic tic disorder or schizotypal personalty disorder. Other than mild, transient sedation, risperidone was well tolerated.

CONCLUSION

These results suggest that OCD patients with and without comorbid chronic tic disorders or schizotypal personality disorder may respond to the addition of low-dose risperidone to ongoing SRI therapy.

Cerebral blood flow and metabolism in late-life depression and dementia

Late-life depression (LLD) is characterized by abnormalities in cerebral blood flow (CBF) and cerebral metabolic rate (CMR) for glucose. Unlike younger adults with major depression, global cortical CBF and CMR reductions have been reported in LLD. Patients with LLD are also characterized by topographic abnormalities, most commonly involving selective prefrontal, superior temporal, and anterior parietal cortex. The fate of these abnormalities with response to antidepressant treatment is highly uncertain, and heterogeneous findings have been reported in younger samples with major depression. The limited data in LLD suggest that response to electroconvulsive therapy or antidepressant medications does not involve reversal of baseline abnormalities but rather accentuation of prefrontal deficits. At minimum, these paradoxical findings suggest that abnormalities in CBF and CMR may be persistent in LLD and a trait characteristic. Characteristic profiles of CBF and CMR abnormalities have also been demonstrated in samples with Alzheimer's disease (AD) and other types of dementia. Functional imaging has shown sensitivity to disease severity and progression. Nonetheless, there is limited information regarding the sensitivity and specificity of the functional imaging modalities in the differential diagnosis of dementias. At present, the evidence does not support the use of functional imaging in isolation as a diagnostic tool. Rather, these imaging modalities may be considered as an adjunct to careful clinical assessment, either to improve diagnosis in early cases or to assist in subtyping difficult cases.

Limited efficacy of ketoconazole in treatment-refractory major depression

The authors examined the efficacy of ketoconazole in 16 adults with treatment-refractory major depressive disorder. Subjects participated in a 6-week, double-blind, placebo-controlled trial. Assessments of mood were made using the Hamilton Rating Scale for Depression (HAM-D), the Beck Depression Inventory (BDI), and the Clinical Global Impression Scale (CGI). Results showed that none of eight patients randomly assigned to receive placebo and two of eight patients randomly assigned to receive ketoconazole met criteria for response. As a group, patients assigned to receive ketoconazole showed no significant reductions in HAM-D, BDI, or CGI scores during the 6-week trial compared with those receiving placebo. These findings suggest a limited efficacy for ketoconazole in patients with treatment-refractory major depression.

Reduced brain serotonin transporter availability in major depression as measured by [123I]-2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane and single photon emission computed tomography

BACKGROUND

Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem [123I] beta-CIT SPECT and platelet [3H]paroxetine binding.

METHODS

Drug-free depressed and healthy subjects were injected with 211 +/- 22 MBq [123I] beta-CIT and imaged 24 +/- 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V3" = (brainstem-occipital)/occipital), a measure proportional to the binding potential (Bmax/Kd), was used for all comparisons.

RESULTS

Results showed a statistically significant reduction in brainstem V3" values in depressed as compared to healthy subjects (3.1 +/- .9 vs. 3.8 +/- .8, p = .02). Platelet [3H]paroxetine binding was not altered (Bmax = 2389 +/- 484 vs. 2415 +/- 538 fmol/mg protein, p = .91) and was not significantly correlated with brainstem [123I] beta-CIT binding (r = -0.14, p = .48).

CONCLUSIONS

These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression.

A randomized, placebo-controlled dose-comparison trial of haloperidol for psychosis and disruptive behaviors in Alzheimer's disease

OBJECTIVE

The goal of this study was to compare the efficacy and side effects of two doses of haloperidol and placebo in the treatment of psychosis and disruptive behaviors in patients with Alzheimer's disease.

METHOD

In a 6-week random-assignment, double-blind, placebo-controlled trial (phase A), haloperidol, 2-3 mg/day (standard dose), and haloperidol, 0.50-0.75 mg/day (low dose), were compared in 71 outpatients with Alzheimer's disease. For the subsequent 6-week double-blind crossover phase (phase B), patients taking standard- or low-dose haloperidol were switched to placebo, and patients taking placebo were randomly assigned to standard- or low-dose haloperidol.

RESULTS

For the 60 patients who completed phase A, standard-dose haloperidol was efficacious and superior to both low-dose haloperidol and placebo for scores on the Brief Psychiatric Rating Scale psychosis factor and on psychomotor agitation. Response rates according to three sets of criteria were greater with the standard dose (55%-60%) than the low dose (25%-35%) and placebo (25%-30%). The advantage of standard dose over low dose was replicated in phase B. In phase A, extrapyramidal signs tended to be greater with the standard dose than in the other two conditions, primarily because of a subgroup (20%) who developed moderate to severe signs. Low-dose haloperidol did not differ from placebo on any measure of efficacy or side effects.

CONCLUSIONS

The results indicated a favorable therapeutic profile for haloperidol in doses of 2-3 mg/day, although a subgroup developed moderate to severe extrapyramidal signs. A starting dose of 1 mg/day with gradual, upward dose titration is recommended. The narrow therapeutic window observed with haloperidol may also apply to other neuroleptics used in Alzheimer's disease patients with psychosis and disruptive behaviors.

Tryptophan depletion during continuous CSF sampling in healthy human subjects

The tryptophan (TRP) depletion paradigm has been employed to investigate mood and behavioral effects of acutely lowering plasma TRP, and presumably brain serotonin (5-hydroxytryptamine [5-HT]) levels through administration of a special diet and/or amino acid drink. Our goal was to test the assumption that a corresponding fall in central levels of TRP and 5-HT (measured by its major metabolite, 5-hydroxyindoleacetic acid [5-HIAA]) occurs during the standard execution of this method in healthy adult subjects. Three males and two females completed the protocol, which included a one-day low-TRP diet and a TRP-free amino acid drink. Lumbar puncture was performed, with placement of an indwelling catheter connected to a peristaltic pump and fraction collector. Cerebrospinal fluid (CSF) was sampled continuously for a 13.5-hour period (before, during, and after the drink), with fractions removed every 15 minutes. Plasma samples were simultaneously obtained. CSF TRP levels and plasma TRP levels were highly correlated, falling a mean of 92% and 85% from baseline, respectively. CSF nadirs were reached several hours after plasma nadirs. CSF 5-HIAA decreased modestly (24% to 40%, mean 31% change from baseline), with lowest concentrations observed 8-12 hours after the amino acid drink. These data suggest that TRP depletion results in substantial declines in central 5-HT turnover.

A double-blind, placebo-controlled study of risperidone in adults with autistic disorder and other pervasive developmental disorders

BACKGROUND

Neurobiological research has implicated the dopamine and serotonin systems in the pathogenesis of autism. Open-label reports suggest that the serotonin2A-dopamine D2 antagonist risperidone may be safe and effective in reducing the interfering symptoms of patients with autism.

METHODS

Thirty-one adults (age [mean+/-SD], 28.1+/-7.3 years) with autistic disorder (n=17) or pervasive developmental disorder not otherwise specified (n=14) participated in a 12-week double-blind, placebo-controlled trial of risperidone. Patients treated with placebo subsequently received a 12-week open-label trial of risperidone.

RESULTS

For persons completing the study, 8 (57%) of 14 patients treated with risperidone were categorized as responders (daily dose [mean+/-SD], 2.9+/-1.4 mg) compared with none of 16 in the placebo group (P<.002). Risperidone was superior to placebo in reducing repetitive behavior (P<.001), aggression (P<.001), anxiety or nervousness (P<.02), depression (P<.03), irritability (P<.01), and the overall behavioral symptoms of autism (P<.02). Objective, measurable change in social behavior and language did not occur. Nine (60%) of 15 patients who received treatment with open-label risperidone following the double-blind placebo phase responded. Other than mild, transient sedation, risperidone was well tolerated, with no evidence of extrapyramidal effects, cardiac events, or seizures.

CONCLUSION

Risperidone is more effective than placebo in the short-term treatment of symptoms of autism in adults.

The neurobiology of tryptophan depletion in depression: effects of intravenous tryptophan infusion

BACKGROUND

Previous work has suggested that acute depletion of the serotonin (5-HT) precursor tryptophan (TRP) causes transient compensatory changes in the 5-HT system that might be exploited for their antidepressant effects. In this study, neuroendocrine and mood responses to intravenous (i.v.) infusion of TRP were examined in order to evaluate central 5-HT function in depressed patients undergoing acute TRP depletion.

METHODS

Thirty-eight drug-free patients with DSM-III-R major depression participated. Each patient underwent two randomized, double-blind TRP depletion tests, one sham and one active. At the estimated time of maximum TRP depletion, each patient received an i.v. infusion of TRP 100 mg/kg. Blood was obtained for serum cortisol, prolactin, and growth hormone. Mood was assessed using standardized rating scales.

RESULTS

The cortisol response to i.v. TRP was significantly greater during TRP depletion than during sham depletion. Depressive symptoms showed a tendency to decrease after i.v. TRP following active, but not sham, TRP depletion.

CONCLUSIONS

These findings are consistent with the present hypothesis and previous evidence that acute TRP depletion in drug-free depressed patients induces compensatory upregulation of postsynaptic 5-HT receptors. These changes are insufficient to serve as a means of effecting clinical improvement, but suggest that the antidepressant properties of rapid, marked manipulations of 5-HT function warrant further study.

Repeated stress, like vasopressin, sensitizes the excitatory effects of corticotropin releasing factor on the acoustic startle reflex

In the rat, evidence now suggests a neurotransmitter function for the neuropeptides arginine vasopressin (AVP) and corticotropin releasing factor (CRF), implicating them in various autonomic, behavioral, and neuroendocrine responses to stress. Repeated AVP/CRF release in the pituitary portal circulation, due to stress, sensitizes and potentiates the release of ACTH from the anterior pituitary. Using a neuroanatomically well-defined behavior, the acoustic startle reflex in the rat, we sought to determine whether an interaction between AVP, CRF and stress might also occur centrally as measured by increased behavioral sensitivity to AVP or CRF given directly into the brain. The first experiment tested whether repeated intraventricular (i.c.v.) infusion of AVP would lead to an increase in the excitatory effect of a subthreshold dose of AVP on the acoustic startle reflex when infused 48 h later. Different groups of rats were infused with various doses of AVP (0.3, 3, or 30 ng) or vehicle on Day 1 and tested for startle over the next 60 min. On Day 2, 48 h later, all animals were infused with a single dose of AVP (300 pg) and tested for startle. Infusion of AVP on Day 1 did not increase startle consistently at any dose, but did lead to a sensitized excitatory effect of AVP on startle on Day 2 which was non-monotonically related to the dose of AVP given on Day 1. Experiment 2 tested whether AVP on Day 1 would sensitize the excitatory effects on startle of CRF given i.c.v. on Day 2. Different groups of rats were infused i.c.v. with various doses of AVP (10, 30, 100, 300 pg) or vehicle on Day 1. On Day 2, 48 h later, all rats were infused with a subthreshold dose of CRF (0.25 microg). Infusion of AVP on Day 1 led to a sensitized excitatory effect of CRF on startle on Day 2 which was non-monotonically related to the dose of AVP given on Day 1. In experiment 3, we tested whether footshocks given on Day 1 would sensitize the excitatory effect of CRF on startle tested 48 h later. Different groups were given footshocks (0.2, 0.4, 0.8, 1.6 mA) on Day 1. On Day 2, 48 h later, all rats were infused with a subthreshold dose of CRF (0.25 microg). Footshocks given on Day 1 led to a sensitized excitatory effect of CRF on startle on Day 2 which was non-monotonically related to the intensity of footshock on Day 1. Taken together, these results suggest that an interaction between AVP, CRF and stress may occur centrally, consistent with other studies showing similar interactions peripherally. This may provide a model system for analyzing how prior stress leads to enhanced behavioral reactions to subsequent stressors and a mechanism to explain dysregulation of the stress response.

Effects of antiglucocorticoid treatment on 5-HT1A function in depressed patients and healthy subjects

Clinical studies suggest that 5-HT1A receptor function may be blunted in depression, while 5-HT1A agonists may possess antidepressant activity. Preclinical findings implicate changes in 5-HT1A receptor sensitivity in the mechanism of antidepressant action. The hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis in depression could be related to those observations, since 5-HT1A receptors are inhibited by glucocorticoids. To evaluate the interaction of the HPA and 5-HT1A systems, we pretreated 15 unipolar depressed patients and 12 healthy control subjects with the antiglucocorticoid ketoconazole (KTCZ) prior to administration of a test dose of the 5-HT1A agonist ipsapirone (IPS). Neuroendocrine (ACTH, cortisol, growth hormone), physiological (hypothermia), and behavioral responses to IPS were assessed. As expected, KTCZ inhibited cortisol biosynthesis, but non-HPA responses to IPS were not enhanced. This study failed to show that glucocorticoid modulation of 5-HT1A receptor function is altered in depression.

Antiglucocorticoids as Treatments for Depression : Rationale for Use and Therapeutic Potential

There is considerable interest in the possible antidepressant properties of antiglucocorticoids. Studies of the hypothalamic-pituitary-adrenal (HPA) axis in depression, coupled with increasing recognition of the importance of glucocorticoids in brain function, strongly support such interest.Psychiatric symptomatology in Cushing's syndrome (a disorder involving hypersecretion of cortisol), the adverse cognitive effects of glucocorticoids, and the suppressive effects of conventional antidepressants on HPA function all suggest that HPA abnormalities could cause or contribute to depression. However, the psychiatrie effects of glucocortieoids and glucocorticoid withdrawal suggest that HPA hyperactivity compensates for some other defect. While preliminary clinical studies suggest that both glucocorticoids and antiglucocorticoids may have efficacy in depression, the toxicity and loss of efficacy of available drugs during long term administration will probably necessitate the development of new agents to advance this field.

Lack of efficacy of clozapine monotherapy in refractory obsessive-compulsive disorder

OBJECTIVE

The authors assessed the efficacy of clozapine monotherapy for adults with treatment-resistant obsessive-compulsive disorder.

METHOD

Twelve adults with refractory obsessive-compulsive disorder participated in a 10-week, open-label, systematic trial of clozapine. They were assessed with the Yale-Brown Obsessive Compulsive Scale, the Hamilton Depression Rating Scale, and the global improvement item of the Clinical Global Impression (CGI) scale.

RESULTS

None of the 10 patients who completed the trial was a responder. No significant change was observed in obsessive-compulsive or depressive symptoms or in scores on the CGI global improvement item.

CONCLUSIONS

These findings suggest that clozapine monotherapy is not effective for most adult patients with treatment-resistant obsessive-compulsive disorder.

Novel linear antagonists of the antidiuretic (V2) and vasopressor (V1) responses to vasopressin

We report the solid phase synthesis of a series of 16 linear analogues of the cyclic antagonist of the antidiuretic (V2) and the vasopressor (V1) responses to arginine vasopressin (AVP), d(CH2)5[D-Tyr(Et)2, Val4]AVP(A). Peptide 1, the linear precursor of (A), (CH2)5(SH)-CH2-CO-D-Tyr(Et)-Phe-Val-Asn-Cys-Pro-Arg-Gly-NH2 was modified at position six with alpha-L-aminobutyric acid (Abu) to give peptide 2. Further modifications of the Abu6 analogue (No. 2) at position one by substituting cyclohexylacetic acid (Caa), cyclohexylpropionic acid (Cpa), 1-adamantaneacetic acid (Aaa), phenylacetic acid (Phaa), tert.-butylacetic acid (t-Baa), isovaleric acid (Iva), propionic acid (Pa), L-penicillamine (P), tert.-butoxycarbonyl (Boc) or omitting any substituent at this position, and/or in combination with Arg-NH2(9), Ala-NH2(9), D-Arg8-Arg-NH2(9), and desGly9 modifications yielded the remaining 14 peptides. All 16 peptides were examined for agonistic and antagonistic potencies in AVP V2 and V1 assays in rats. Apart from the Cpa analogue and the analogue lacking any substituent in the 1-position, all exhibit substantial V2 and V1 antagonism. A number are as potent as (A) as V2 antagonists. With an anti-V2 pA2 = 8.11 +/- 0.07, Aaa-D-Tyr(Et)-Phe-Val-Asn-Abu-Pro-Arg-Arg-NH2 (No. 6) is as potent as any cyclic AVP V2 antagonist reported to date. The PaI analogue of No. 6 exhibits promising anti-V2/anti-V1 selectivity. These findings prove conclusively that a ring structure is not a requirement for recognition of or for binding to AVP V2 or V1 receptors. This discovery thus offers a promising new approach to the design of peptide and non-peptide antagonists of AVP and perhaps also to other cyclic peptides such as somatostatin, atrial-natriuretic factor, insulin, and the recently discovered endothelin. Some of these linear antagonists may be of value as pharmacological tools and as therapeutic agents.

No requirements of cyclic conformation of antagonists in binding to vasopressin receptors

Early reports that acyclic analogues of oxytocin and vasopressin (AVP) have drastically reduced agonistic activities established as dogma that an intact hexapeptide ring structure is essential for the pharmacological activities of analogues of neurohypophysial hormones. Thus, virtually all the many hundreds of agonistic and antagonistic analogues of the neurohypophysial peptides that have been reported contain an intact ring. Here we report that an intact ring is not essential for binding of antagonistic AVP analogues to vasopressor (V1) or antidiuretic (V2) AVP receptors. In fact, one acyclic AVP analogue seems to be about as potent as any previously reported cyclic V2 antagonist. This finding suggests new possibilities for the design of AVP analogues as pharmacological probes and for therapeutic use. Similar modifications might be useful in the design of analogues of other cyclic peptides, such as calcitonin, somatostatin and the atrial natriuretic factors.

Arterial blood gases before, during, and after nitrous oxide:oxygen administration

The use of nitrous oxide as an anesthetic or analgesic agent frequently raises concerns about the possibility of post-inhalational diffusion hypoxemia. We undertook a study in 20 healthy volunteers to determine whether hypoxemia occurs after the self-administration by face mask of a 50:50 mixture of nitrous oxide and oxygen for 15 minutes, followed by breathing room air. Blood gases were measured through an in-dwelling arterial cannula before, during, and after inhalation of the mixture, at time O, five, ten, and 15 minutes, and then 30 seconds, 45 seconds, 2 1/2 minutes, five, and ten minutes following room air breathing. Ten of the 20 subjects breathed a control gas, a mixture of 50% nitrogen: 50% oxygen. No subject demonstrated arterial hypoxemia at any time before, during, or after self-administration of the gas mixture. In the ten subjects who self-administered the control gas there were no significant differences in the PaO2 values while they breathed either gas at any corresponding sampling time. We conclude that diffusion hypoxia is not seen in normal subjects following self-administration of a mixture of 50:50 nitrous oxide and oxygen.

Triage success in disasters: dynamic victim-tracking cards

A dynamic victim-tracking card developed for use in community or hospital disaster exercises was tested during two hospital and two airport disaster drills. Use of the card in 375 "patients" allowed testing of the ability to evaluate the decisions of triage, the early medical intervention for "victims," and the ongoing treatment of patients with a changing medical status. The card was successful in simulating realistic changes that may occur in critically ill and injured patients. Of the 126 "patients" evaluated in an actual exercise, 55 (43.6%) were placed in the proper triage category. Four patients "died" as a result of poor initial evaluation and treatment. Medical decisions during hospital and community disaster exercises can be more realistically tested and more accurately documented with the use of the dynamic victim-tracking card.

Effect of varied training techniques on field endotracheal intubation success rates

A pool of 146 mobile intensive care unit paramedics was divided into four equal groups and trained in the technique of direct laryngoscopic endotracheal intubation of cardiac arrest or deeply comatose patients. Group 1 was selected from supervisors and crew chiefs and trained as preceptors. The remaining paramedics were assigned to three other study groups. Groups 1 and 2 were trained with a didactic presentation followed by manikin practice, an animal laboratory exercise, and operating room experience. Group 3 had no OR experience; Group 4 had only didactic/manikin training. Intubations were observed by preceptors on scene. During the study period of 27 months, 689 of 763 patients (90.3%) were successfully intubated by 122 paramedics. While results suggest variation in skill levels according to training group (Group 1, 92.4%; Group 2, 87.6%, Group 3, 83.3%; Group 4, 76.9%), statistical analysis allowing for the variables of seniority and number of intubations performed by personnel failed to reveal differences in groups attributable to training programs. Complication rates were relatively low for all groups, the most common being prolonged intubation attempts. A significant improvement in the skill was seen as the study progressed when groups are pooled and compared. The findings suggest that endotracheal intubation of deeply comatose or cardiac arrest patients is a field procedure that can be performed safely and skillfully by well-monitored paramedical personnel. Operating room or animal laboratory experience may increase initial success levels, but these factors do not appear to greatly influence eventual performance or incidence of complications of the procedure.

Field endotracheal intubation by paramedical personnel. Success rates and complications

One-hundred thirty mobile intensive care unit paramedics were trained in the technique of direct laryngoscopic endotracheal intubation of cardiac arrest or deeply comatose patients. Three attempts at intubation were permitted. Of the 779 patients studied, 701 (90.0 percent) were successfully intubated: 57.9 percent on the first attempt, 26.1 percent and 5.5 percent on the second and third respectively. Reported and observed complications of the procedure numbered 74 (9.5 percent) of the 779 patients included in the study. There were three unrecognized esophageal intubations. The success rate rose to more than 94 percent toward the end of the study. It is concluded that endotracheal intubation of deeply comatose patients is a field procedure safely and skillfully performed by well-trained and monitored paramedical personnel, with success and complication rates at least comparable to other invasive airway techniques.