The existence of a relationship between increased serum alanine aminotransferase levels detected in premarketing clinical trials and postmarketing published hepatotoxicity case reports

BACKGROUND

Drug-induced liver injury (DILI) profile in most drugs' available information is based on both the incidence of alanine aminotansferase (ALT) elevations in clinical trials and published case reports.

AIM

To assess the relationship between ALT elevations in clinical trials and the number of published case reports in the postmarketing setting.

METHODS

Hepatotoxic drugs were identified from product labelling and classified in high-medium risk (Black Box Warning or Precautions section) or low risk (a statement in the Adverse Reactions section). Incidence of ALT elevations (> or = 3 x ULN) for drug (I(D)) and placebo (I(C)) treated patients in premarketing clinical trials and DILI published case reports were retrieved from product labelling and MEDLINE.

RESULTS

The median I(C) was 10/1000. The high-medium-risk drugs' median I(D) was significantly higher compared with low-risk drugs (17/1000 vs. 10/1000; P = 0.046). Chi-squared test, absolute difference and odds ratio comparing I(D) and I(C) identified 35%, 51% and 77% of high-medium-risk drugs respectively. Less number of case reports were associated with low- than high-medium-risk drugs (1 vs. 7; P = 0.001). A high odds ratio in clinical trials (I(D) vs. I(C)) was the strongest predictor of published DILI case reports.

CONCLUSION

A relationship between increased ALT incidence in premarketing clinical trials and postmarketing published case reports exists.

The diagnosis of drug-induced liver disease

The diagnosis of drug-induced liver injury is often one of exclusion with initial suspicion based on circumstantial evidence. The natural history, characteristics and limitations of this exclusion process are revised. Also, the numerous published attribution algorithms for evaluation of drug-related liver abnormalities are described and their characteristics and differences are illustrated with true patients from our clinical experience. Situations that complicate the diagnosis such as age, sex, concomitant use of other drugs, genetic polymorphism in metabolic pathways involved in activation or disposition of therapeutic drugs and drug-drug interactions are described. Finally, developing approach to diagnosis of drug-induced liver injury, different of attribution algorithms, are evaluated and explained using a new method based in a Bayesian approach developed and published by the authors. The authors' vision of all these potential advances and their clinical utility is provided.

Efficacy and tolerance of metamizole versus morphine for acute pancreatitis pain

BACKGROUND/AIMS

Morphine has been contraindicated for pain treatment in acute pancreatitis because of its presumed opioid-induced sphincter of Oddi dysfunction. However, scientific evidence supporting a deleterious influence on the clinical course is absent. This pilot study was undertaken to evaluate the efficacy and adverse events of metamizole versus morphine in acute pancreatitis.

METHODS

16 patients with acute pancreatitis were randomized to receive 10 mg/4 h s.c. (n = 8) morphine or 2 g/8 h i.v. (n = 8) metamizole. Pain scores were recorded every 4 h during 48 h after admission by a Visual Analogue Scale. Pethidine was additionally administered as a rescue therapy.

RESULTS

75% of patients achieved pain relief in the metamizole group versus 37.5% in the morphine group within 24 h of hospitalization (6/8 vs. 3/8; p: n.s.). The mean time to achieve pain relief was shorter in the metamizole group (10 +/- 6.6 vs. 17 +/- 18.3 h; p: n.s.). At the end of the study, 75% of patients achieved pain relief in the metamizole group versus 50% in the morphine group. Three patients in each group needed pethidine: 2 out of 3 achieved pain control in the metamizole group vs. 0 out of 3 in the morphine group.

CONCLUSIONS

Intravenous metamizole shows a non-significant association with a quicker pain relief than morphine s.c. in acute pancreatitis. A larger randomized controlled trial should be desirable to confirm this result. and IAP.

Functional status of beta-2-adrenoceptor in isolated membranes of mature erythrocytes from patients with cirrhosis and oesophageal varices

Propranolol is a widely used drug for prophylaxis of variceal bleeding in patients with cirrhosis, but not all patients show an adequate clinical response. This variability may be in relation to beta adrenoceptor activity, but no information is available in this setting. Thirty-nine patients with advanced cirrhosis and presence of oesophageal varices were sequentially included. We studied the function of beta-2-adrenoceptor in isolated membranes of mature erythrocytes obtained from patients by measuring cyclic AMP (cAMP) production before and after isoproterenol. Blood samples obtained from 11 healthy volunteers were used as control. Patients showed a six-fold increase in the mean basal cAMP production as compared to healthy volunteers. Isoproterenol produced a small, non-significantly and highly variable increase in the AC activity in patients compared with controls. cAMP values remain stable after three months of continuous treatment with oral beta-blockers in both groups. Patients without antecedent of variceal bleeding or with an active alcohol intake showed a significantly higher isoproterenol effect. In conclusion, beta-receptor function in human erythrocytes membranes is altered in patients with cirrhosis and oesophageal varices.

Morphine-3-glucuronide prevents tolerance to morphine-6-glucuronide in mice

Daily subcutaneous (s.c.) pretreatment with morphine-3-glucuronide (6 mg/kg) was found to reduce morphine-6-glucuronide (4 mg/kg s.c.)-induced antinociception, with no decrease in the effect over 5 days. Morphine-6-glucuronide administration (4 mg/kg s.c.) on Day 6, without morphine-3-glucorinide pretreatment, results in a significant increase in antinociception (from 24% on Day 5 to 70%; p< or =0.05). Morphine-3-glucuronide may prevent tolerance to morphine-6-glucuronide by reducing morphine-6-glucuronide-induced antinociception.

Pharmacokinetic variations of acetaminophen according to liver dysfunction and portal hypertension status

AIM

To study the pharmacokinetic and metabolism profiles of a single dose of acetaminophen in patients with cirrhosis.

METHODS

Oral acetaminophen (1000 mg) was administered to seven healthy subjects and 14 patients with cirrhosis (nine Child-Pugh A or B and five Child-Pugh C grade), being five without and nine with oesophageal varices. Plasma levels of acetaminophen and its metabolites were determined by HPLC.

RESULTS

Patients showed a higher mean area under the curve concentration-time (67.4 +/- 22.4 mg h/L vs. 38.8 +/- 4.3 mg h/L; P = 0.01), a lower clearance (166.7 +/- 85.0 mL/min vs. 367.8 +/- 62.5 mL/min; P = 0.01) and higher elimination half-life (3.8 +/- 1.1 h vs. 2.0 +/- 0.4 h; P = 0.01) of acetaminophen than healthy volunteers. The appearance in blood and the urinary excretion of metabolites in patients did not differ from healthy subjects. Absorption profile was faster in patients. Patients with lower mean and systolic arterial pressure had lower AUC of acetaminophen, independently of liver dysfunction stage.

CONCLUSIONS

Patients with cirrhosis had a higher AUC and lower clearance of acetaminophen. Acetaminophen attained earlier therapeutic concentrations in patients with oesophageal varices. Mean and systolic arterial pressures were significantly associated with AUC suggesting the importance of the haemodynamic function on the pharmacokinetics of acetaminophen in patients with cirrhosis.

Risk of drug-induced agranulocytosis: the case of calcium dobesilate

BACKGROUND

In the last 20 years, some cases of agranulocytosis associated with calcium dobesilate consumption in Spain have been reported. A high risk of dobesilate-associated agranulocytosis (121 cases per million per year) calculated using both a case-control and a case-population strategy has been published. However few spontaneous reports have been noted in the same period of time. No explanation exists for this disagreement.

METHODS

Estimated incidence rates of agranulocytosis in the IAAAS study and the calculated risk of dobesilate-associated agranulocytosis were used as background risks in a Poisson-based methodology, to calculate the number of coincidental reports of agranulocytosis among patients treated with dobesilate. The influence of treatment duration, notification rate and population characteristics were calculated.

RESULTS

During the period 1978-2000, a total of 23 cases would have taken place if the background risk of agranulocytosis were 4.7 per million per year (IAAAS's risk); however, only 9 spontaneous cases of agranulocytosis associated to dobesilate were noted. A simulation showed that with notification rates equal to or higher than 17%, it was not possible to exclude that the 9 cases were false-positives. With notification rates equal or inferior to 16%, it would be unlikely that cases of agranulocytosis were noted in this population with a risk of 4.7 per million per year; therefore, it is necessary to assume a higher agranulocytosis risk. More than 1 case per year could be a false-positive if the background risk of agranulocytosis is 9.5 per million per year, this being the appropriate risk for a population of patients older than 60 years. The duration of treatment beyond 30 days increases the probability of a random coincidence of the intake of drug and an agranulocytosis event.

CONCLUSIONS

The disagreement between calculated dobesilate-associated agranulocytosis risk and the number of noted spontaneous reports may be explained by at least three different factors: under-reporting, duration of treatment and age of patients. It is possible, with the methodology presented, to estimate the influence of these factors to avoid confusion with possible false-positive cases and then to design the correct prospective trial that can provide the true agranulocytosis risk.

A new Poisson and Bayesian-based method to assign risk and causality in patients with suspected hepatic adverse drug reactions: a report of two new cases of ticlopidine-induced hepatotoxicity

OBJECTIVE

The diagnosis of drug-induced hepatotoxicity is based on circumstantial evidence and is often inaccurate. We have designed a method based on published data to assign causality to suspected cases of drug-induced hepatotoxicity.

DESIGN

Forty-seven published cases of ticlopidine-induced hepatotoxicity were identified by a Medline-based literature search. Data regarding abnormal liver function in patients receiving ticlopidine were obtained from the only published placebo-ticlopidine clinical trial (the Canadian American Ticlopidine Study; CATS). Thus, we calculated the maximum number of expected hepatotoxicity cases in patients exposed to ticlopidine and those not exposed to the drug by means of the Poisson distribution. The calculated odds ratio was used as a prior odd for subsequent quantification, using a Bayesian-based approach, of individual ticlopidine-induced hepatotoxicity likelihood. Concretely, the prior odd is modified by several separate likelihood ratios: age; sex; AST level; ALT level; alkaline phosphatase level; total bilirubin level; latent period of adverse reaction appearance; and period of remission of adverse reaction. This methodology was applied to two new cases of suspected ticlopidine-induced hepatotoxicity.

RESULTS

The prior probability of ticlopidine-induced hepatotoxicity derived from CATS data is 61.29%. This is in contrast with the 28.83% incidence rate of drug-induced liver alterations in the general population. Alkaline phosphatase levels and total bilirubin levels were six times the normal values among individuals with ticlopidine-induced hepatotoxicity than in the general population. They were the most relevant likelihood ratios of the Bayesian model to establish a high level of causality relationship between a hepatotoxicity event and ticlopidine use.

CONCLUSIONS

The proposed method, which links information from clinical trials with the profile of clinical hepatotoxicity of a drug defined from published cases reported after a drug is marketed, can be a useful tool for drug postmarketing surveillance research.

A prospective study of the clarithromycin-digoxin interaction in elderly patients

The study was a prospective observational trial carried out to assess the clarithromycin-digoxin interaction in elderly patients chronically taking digoxin. Digoxin concentrations were determined before and after concomitant treatment with clarithromycin. A Bayesian approach was used to calculate digoxin pharmacokinetics. In the seven patients who were studied there was a significant increase in digoxin concentration after 4-7 days of clarithromycin treatment; digoxin clearance and elimination rate constant were 56-60% lower and elimination half-life was 82% longer. The pharmacokinetic clarithromycin-digoxin interaction in the elderly may be much more frequent than has been assumed up to now.

[Toxic hepatitis associated with tamoxifen use. A case report and literature review]

Tamoxifen is an antiestrogenic drug that acts by binding to the estrogen receptor. The drug is used as a co-adjuvant treatment in advanced breast cancer expressing the oestrogen-receptor protein. Clinical trials of tamoxifen have shown its efficacy in reducing mortality and recurrence rates over a five-year treatment. Cases of tamoxifen-associated hepatotoxicity have been described, including cholestasis with or without cytolysis and steatohepatitis. We report the case of a female patient who developed hepatic alterations while undergoing continuous tamoxifen treatment. We also present an overview of similar cases published to date and comment on the advisability of continuing or suppressing this treatment in patients with hepatotoxicity or after a five-year treatment period.

Genetic variability in morphine sensitivity and tolerance between different strains of rats

The development of tolerance, the sensitivity to morphine and the effective morphine plasma concentrations have been studied in Sprague-Dawley (SD-U) and Wistar (W) rats. Daily administration of morphine (10 mg/kg/12 h for 9 days) in W rats produced a reduction in morphine antinociception from day 1 (12+/-0 s) to day 9 (6.7+/-1. 9 s). Morphine antinociception in the SD-U rats did not change over the period of treatment. Naloxone abolished the antinociception of morphine in both opiate naive and chronically treated SD-U rats. The pharmacokinetic parameters of morphine and morphine-3-glucuronide did not differ significantly between strains. Both naive and chronically treated SD-U rats required smaller doses of morphine than W rats to obtain a maximum antinociceptive effect. Plasma concentrations following administration of the same dose of morphine, did not differ between strains or days of treatment. The range of morphine concentrations required to obtain a maximum effect were lower in SD-U rats, both on day 1 and day 8 when compared to W rats. These results show differences between the two strains with regard to both morphine sensitivity and development of tolerance, whilst also suggesting that the differences do not have a kinetic basis.

A beta-2-adrenergic receptor activates adenylate cyclase in human erythrocyte membranes at physiological calcium plasma concentrations

More information is needed about the subtype of the beta-adrenergic receptor coupled to the G-protein-adenylate cyclase (AC) system in human erythrocytes and about the optimal experimental conditions to study this system. In this study we describe the characteristics of spontaneous and beta-agonist-activated AC in human erythrocytes. Human erythrocyte membranes were isolated and AC activity was utilized to assess the quantity of cAMP. Our data show that the subtype beta-2 is the functional beta-adrenergic receptor involved in such activation; this modifies the beta-adrenergic-stimulated activity of AC in human erythrocytes. Isoproterenol in a medium with calcium (1-10 mM, range that includes physiological plasma concentrations) enhances the activation of AC; this effect was blocked by propranolol, but not by atenolol. We conclude that in human erythrocytes subtype beta-2 is the functional beta-adrenergic receptor and that such a response depends to a large extent on Ca(2+) concentrations.

[Bio-equivalence and generic drugs. Studies of bio-equivalence. II. Special situations. Reflections on problems which may arise with drugs habitually used in neurology]

OBJECTIVE

To discuss some controversial aspects and special situations which should be considered when assessing the use of generic drugs, especially those frequently used in neurology.

DEVELOPMENT

We discuss the difference between the concept of average bio-equivalence and individual bio-equivalence, and the implications the selection of one or other criterion may have in the treatment of individual patients with carbamazepine. We also discuss the peculiarities and problems concerning bio-equivalence in the case of drugs with non-linear pharmacokinetics, controlled-release formulations, racemic drugs with two or more stereo-isomers and when there are differences in the excipients of different formulations of the same drug.

CONCLUSIONS

There are drugs in which it may be very difficult to show the bio-equivalence of a generic formulation because of its pharmacokinetic characteristics as occurs in the case of controlled-release drugs, the presence of active metabolites or differences in their enantiomers or even due to problems with the excipients used, although if the therapeutic range is wide and these variables are controlled in the studies done, the conclusions regarding bio-equivalence may be valid.

[Bioequivalence and generic drugs. I. Studies of bioequivalence, considering the theoretical basis, design and use]

OBJECTIVES

To describe the studies done before a generic drug is marketed.

DEVELOPMENT

We reflect on the concept of bioequivalence and its limitations, then describe the parameters on which a study of bioequivalence is based and explain the statistical hypothesis of bioequivalence. Finally, we explain the process of a clinical trial of bioequivalence and how the results are analyzed, using a clinical trial as an example. We show how 'carry-over', formulation and period effects are analyzed; and also how bioequivalence may be evaluated by using different approximations: construction of the confidence interval, confidence hypothesis and nonparametric approximations. Finally, we mention the methods used to estimate the size of the sample required in a study of this kind.

CONCLUSIONS

Studies of bioequivalence, even the simplest, have peculiarities of design and statistical basis which are markedly different from other clinical trials. When generic drugs are marketed it is important to know about the peculiarities and characteristics of the studies on which affirmation of the bioequivalence of these products is based.

Anticonvulsant effects of nimodipine and two novel dihydropyridines (PCA 50922 and PCA 50941) against seizures elicited by pentylenetetrazole and electroconvulsive shock in mice

In animal models of epilepsy, calcium entry blockers have shown anticonvulsant properties. We studied the antiepileptic effects of nimodipine and two novel dihydropyridines, a calcium antagonist (PCA 50922) and a calcium agonist (PCA 50941), on pentylenetetrazole seizure and maximal electroshock seizure (MES) in mice. Anticonvulsant profile of nimodipine and PCA 50922 was similar to that of clonazepam, but markedly different from that of phenytoin. None of the doses of the PCA 50941 showed anticonvulsant effect.

Neuroprotection by the novel calcium antagonist PCA50938, nimodipine and flunarizine, in gerbil global brain ischemia

Calcium is involved in the physiopathology of cerebral ischemia. Calcium antagonists might prevent the calcium overload and death of cells from ischemically compromised tissue. We compare the neuroprotective effect of various doses (0.2, 0.5 and 1 mg/kg) of two dihydropyridines, nimodipine and the novel 1,4-dihydropyridine derivative PCA50938, and flunarizine in the gerbil model of global ischemia. Improvements in morbidity were observed 2 h after the end of carotid occlusion (McGraw's scale) with 0.5 mg/kg of flunarizine, all doses of PCA50938 and 0.2 mg/kg nimodipine. Neuronal loss in the CA1 sector of the hippocampus was examined. The animals treated with 0.5 mg/kg flunarizine and those treated with 1 mg/kg PCA50938 showed a significant reduction in the percentage of damaged neurons in the hippocampal CA1 area, 72 h after transient ischemia. None of the animals treated with 0.5 mg/kg flunarizine had more than 80% of the evaluated neurons altered. We conclude that PCA50938 and flunarizine may act as neuroprotective drugs with different patterns of dose-response and neuroprotective-morbidity-mortality relationships, in the model of global cerebral ischemia in the gerbil. Flunarizine has a narrow therapeutic range.

Morphine and morphine-6-glucuronide plasma concentrations and effect in cancer pain

The relationships between plasma morphine and metabolite (M3G and M6G) concentrations and analgesic efficacy were investigated in an open study of 39 cancer pain patients receiving chronic oral morphine therapy with either morphine sulfate solution or controlled-release morphine tablets. There were no differences in morphine, metabolite kinetics, or analgesic efficacy between equivalent doses of conventional or controlled-release formulations. The increase in morphine plasma concentration after a dose (1 hr for normal release, 2 hr for controlled release) was correlated significantly with the dose of morphine (r = 0.914, P < 0.001). There was a significant reduction in pain intensity (P < 0.05) and increase in pain relief (P < 0.001) after the dose of morphine administration, when compared with the predose score. One-half of the patients had mild and tolerable adverse effects. Patients were classified by mean pain relief between doses as having optimal, moderate, or poor pain control. No simple relationship was found between morphine plasma concentration and pain control. Morphine plus M6G concentrations in the "optimal control" group (751.2 +/- 194 nmol/L), however, were more than twice those found in the "moderate control" group (276.9 +/- 41.9 nmol/L) (P < 0.05), and no patient in the moderate control group had a morphine plus M6G concentration greater than 405 nmol/L. These results support the importance of M6G in morphine analgesia. For these hospitalized patients, there appeared to be a therapeutic range of morphine plus M6G plasma concentrations for optimal pain control with a lower limit of 400 nmol/L predose.

[Drug-induced extrapyramidal disorders]

We analyze 402 drug-adverse events consisting of movement disorders or aggravation of parkinsonisms, submitted to Sistema Español de Farmacovigilancia until 1994. Our aim is to know patient characteristics and the drugs related with these submissions. Most of them (64) belong to calcium-entry blocker group (31%) and benzamides (27%). Case age intervals more frequent were 11-30 and 60-80 years-old and the events affect predominantly females. The percentage of serious adverse events were near 80%. We think that drug-related parkinsonisms have high prevalence rate and that the role of calcium-entry blockers in these events should be considered at the moment to prescribe groups.

Monitoring serum levels of gentamicin to develop a new regimen for gentamicin dosage in newborns

The newborns studied had gestational ages ranging between 23-44 weeks, weights ranging between 725-4510 g, and were treated with standard doses of gentamicin (5.2 +/- 1.0 mg/kg/day). The gentamicin serum peak and trough levels were unrelated to administered doses, and a large proportion of patients had low (peak less than 4 micrograms/ml in 12%) or potentially toxic concentrations (trough greater than 2 micrograms/ml in 55%). The pharmacokinetic parameters (t1/2e, 8.2 +/- 4.8 h and Vd, 0.64 +/- 0.22 L/kg) varied markedly between patients. The newborn's weight, age, gestational age, and serum creatinine were factors of importance for the variability of gentamicin serum levels. The newborns were divided into four groups: gestational period less or more than 37 weeks and age below or above 7 days. These groups had different gentamicin serum levels and pharmacokinetic parameters. The results suggest that a gentamicin dosage regimen based on the division of newborn patients into subgroups or calculated from individual pharmacokinetic characteristics would decrease the risk of obtaining potentially toxic or subtherapeutic gentamicin concentrations after the use of standard doses.

Changes in gentamicin serum levels and pharmacokinetic parameters in the newborn in the course of treatment with aminoglycoside

Gentamicin serum levels were determined in an unselected group of newborns treated with standard doses of the drug to study the changes in pharmacokinetic parameters (trough and peak serum levels/dose ratio, serum level increases/dose ratio, elimination half-life, and distribution volume) 48, 96, and 144 h after commencing treatment. However, no significant changes in the pharmacokinetic parameters were found in different groups of neonates, classified according to gestational age and days of life during the study period. It appears that the dose of gentamicin once it has been individually established does not have to be changed, at least during the first week of treatment.

Potentiation of K+-evoked catecholamine release in the cat adrenal gland treated with ouabain

1 A vigorous catecholamine secretory response was evoked by small increments (2-10 mM) of the extracellular concentration of K+ ([K+])o) in cat adrenal glands treated with ouabain (10(-4) M), and perfused with Krebs-bicarbonate solution at room temperature. 2 The secretory response depends on [K+]o; increments of [K+]o as small as 2 mM for 2 min evoked a clear secretory response; at 10-17.7 mM K+, the maximal secretory response was observed. In normal glands, not treated with ouabain, no increase of the rate of catecholamine output was observed by raising [K+]o up to 17.7 mM for 2 min. 3 The K+ secretory response was time-dependent, requiring at least 1 min to be initiated; on continued exposure to 10 mM [K+]o, the enhanced response remained for at least 1 h. 4 In low [Na+]o, the K+-secretory response was unchanged. However, in 0-Ca2+, high-Mg2+ solutions, or in the presence of D600, an organic Ca2+ antagonist, it was abolished. 5 The K+-induced secretory response was not altered in the presence of tetrodoxin or tetraethylammonium. 6 It is concluded that ouabain potentiated the catecholamine secretory response to raised [K+]o by increasing the amount of Ca2+ available to the secretory machinery through (a) mobilization of an enhanced pool of membrane-bound Ca2+, (b) activation of membrane Ca2+ inward current; or (c) decrease of intracellular Ca2+ buffering systems. The activation by ouabain of a membrane Na+-Ca2+ exchange system is not involved in this K+-secretory response. It is suggested that the plasma membrane ATPase enzyme system, by changing the affinity of its Ca2+ binding sites, might control the availability of this cation to the secretory machinery and, therefore, modulate catecholamine secretion in the adrenal gland.

Origin of guinea-pig plasma dopamine beta-hydroxylase

1 Exposure of guinea-pigs to a CO2-enriched atmosphere (20% CO2, 25% O2, 55% N2) for 1 to 5 h caused a marked, progressive increase of plasma dopamine beta-hydroxylase (DBH) activity which reached its peak after 2 h of CO2 exposure and then gradually decreased. The increase was abolished by mecamylamine administration before exposure in CO2. Plasma levels of noradrenaline (NA) also increased after CO2 exposure. 2 Guanethidine administration, before exposure to CO2, abolished the increase of plasma NA but potentiated the increase of circulating DBH. Phenoxybenzamine injection, before exposure to CO2, also potentiated the increase of plasma enzyme activity. In both cases, DBH activity was increased to almost 10 times the basal circulating enzyme levels. 3 Injection of 6-hydroxydopamine (6-OHDA) caused a pronounced decrease of DBH activity in the right atrium, thoracic aorta and spleen; the adrenal enzyme activity was unchanged. Exposure to CO2 of 6-OHDA-treated animals still evoked a dramatic increase of plasma DBH activity comparable to that found in control animals. 4 The increase of plasma DBH activity evoked by exposure to CO2 of adrenalectomized animals was considerably diminished. 5 These data suggest that in the guinea-pig, the adrenal is the main source of the increase of circulating DBH activity evoked by exposure of the animals to a CO2-enriched gas mixture.

On the release of catecholamines and dopamine-beta-hydroxylase evoked by ouabain in the perfused cat adrenal gland

1 Secretion of catecholamines (CA) and dopamine-beta-hydroxylase (DBH) activity from the retrogradely perfused cat adrenal gland was studied following ouabain infusion. Perfusion with ouabain (10(-4) M) for 10 min caused a gradual release of CA in the effluent which reached its peak 30 min after the ouabain pulse, and was maintained constant for at least 1 h. The effect of ouabain seemed to be irreversible. 2 Mecamylamine, while blocking the CA secretory effects of acetylcholine (ACh) perfusion, did not affect the secretion of CA evoked by ouabain. In denervated adrenal glands, ouabain-induced CA secretion was similar to that in the contralateral, innervated gland. However, physostigmine perfusion potentiated the CA secretory effects of ouabain. 3 The release of CA evoked by ouabain was accompanied by a proportional release of DBH activity. The time course of appearance of DBH activity followed the pattern of CA release. 4 The CA and DBH outputs in response to a pulse of ouabain were suppressed in the absence of calcium. Calcium reintroduction to a calcium-free perfused, ouabain-treated gland not only restored but greatly potentiated the release of CA and DBH. The amplitude of the secretory response to calcium reintroduction in ouabain-treated glands was proportional to the extracellular calcium concentration, and was antagonized by an external sodium-deficient medium. 5 These data demonstrate that ouabain releases CA from the perfused cat adrenal gland by a calcium-dependent exocytotic mechanism. The secretory effect of ouabain is not secondary to the release of ACh from cholinergic nerve terminals present in the adrenal gland, but due to a direct action on the chromaffin cell itself. In addition, the results suggest that this action is exerted through redistribution of monovalent cations secondary to the inhibition by the glycoside of the sodium pump. Such monovalent cation redistribution may cause a rise of intracellular ionized calcium levels through the activation of an internal sodium-dependent calcium influx system probably located in the chromaffin cell membrane.

Tissue and plasma catecholamines and dopamine beta-hydroxylase activity of various animal species after neurogenic sympathetic stimulation

1. The effects of reserpine and exposure to a stressing atmosphere containing 20% CO2 for 5 hr on catecholamine (CA) levels and dopamine beta-hydroxylase (DBH) activity of adrenal, spleen and plasma of cat, rabbit, rat and guinea-pig were studied. 2. Twenty-four hr after an I.P. injection of reserpine, the CA contents of the adrenals and spleens were markedly reduced in all the four species studied. Adrenal and splenic DBH activity was unchanged in reserpine treated cats and rats. The enzyme activity decreased by 28 and 36% in adrenals of rabbits and guinea-pigs, and a 33% diminution was observed in the spleens of both species. 3. A marked rise in guinea-pig plasma DBH activity was obtained 24 hr after reserpine, while plasma DBH activity was unchanged in the rat. 4. Exposure of rats to a stressing atmosphere containing 20% CO2 for 5 hr increased the circulating noradrenaline (NA) levels by 600%, but plasma DBH activity remained unchanged. CO2 exposure caused both, an increase in plasm NA levels and DBH activity in the guinea-pig (950% and 100%, respectively). 5. The combined treatment with reserpine plus immediate exposure to CO2 produced a 230% rise in rat plasma NA with no concomitant change in DBH activity. A similar treatment caused a 75% fall of NA levels and an increase in DBH activity of 600% in the guinea-pig. 6. The ratios of total DBH activity to CA in the spleen and adrenal were much higher in the guinea-pig than in the rat. The fraction of the total DBH activity that can be solubilized by osmotic shock of purified adrenomedullary chromaffin granules was 28% in the rat and 71% in the guinea-pig. If one makes the assumption that 'soluble' and 'releasable' DBH may be equated, the amount of 'releasable' DBH into the circulation is much greater in the guinea-pig than in the rat. 7. The results suggest that the guinea-pig is a better model than the rat to study circulating DBH activity as an index of exocytotic CA release from adrenergic neurones and adrenal medulla, and therefore of sympathetic activity. The results also indicate that previous data trying to correlate sympathetic activity with circulating DBH activity carried out in the rat have to be reconsidered in the light of data obtained in the guinea-pig.

Release of noradrenaline by the ionophore X537A from normal and reserpinized guinea-pig atrium

The effects of ionophore X537A on the release of 3H-noradrenaline and its metabolites from the superfused guinea-pig left atrium were investigated. Concentrations of ionophore of 10 and 30 mocrometer greatly increased the release of tritium. Of the total increase in radioactivity elicited by X537A 44% was accounted for as noradrenaline and 50% was due to deaminated metabolites. The ionophore-evoked release of tritium was independent of the extracellular calcium ions and was not affected by agents which modify calcium movements such as verapamil, ryanodine, ruthenium red and tetracaine. X537A released 3H-noradrenaline from extragranular sites in MAO-inhibited atria from reserpine-treated animals and this release was also calcium independent. It is concluded that the ability of X537A to release noradrenaline from vesicular or cytoplasmic sites is not related to its ability to couple with and transport calcium ions through membranes. The ionophore might modify the ionic distribution outside and inside the neuronal membrane which would lead to leakage of the transmitter.