Effects of ischemia and reperfusion on cardiac tolerance to oxidative stress

Oxidative stress may affect cardiac function and metabolism. Oxidants are normally inactivated by reacting with reduced glutathione (GSH), with resulting formation and release of oxidized glutathione (GSSG). However, ischemia might affect glutathione metabolism. This might render ischemic hearts less resistant against subsequent oxidant injury during reperfusion, and it might also affect the reliability of GSSG measurements as a means to investigate oxidative stress in reperfused hearts. We compared the metabolic and functional consequences of an oxidant load in control rabbit hearts and in hearts reperfused after 30 min of normothermic total ischemia. In controls, H2O2 infusion (H2O2; 5-30 microM) induced a dose-dependent stimulation of GSSG release and a progressive impairment of cardiac function. At these doses, H2O2 challenge of postischemic hearts resulted in biochemical and functional changes identical to those observed in controls. Release of lactate dehydrogenase (LDH) and of GSH was negligible, similar in both groups. In additional experiments, infusion of H2O2 at a much higher dose (200 microM) elicited a further increase in GSSG release from both groups, although GSSG concentrations were lower in postischemic hearts. The functional effects of the 200 microM H2O2 infusion were similar in both groups, all hearts showing rapid and irreversible deterioration of function. Occurrence of irreversible cell injury was also manifested by a large release of LDH and GSH to a similar extent in both groups. These data demonstrate that cardiac tolerance toward oxidants is largely unaffected by a relatively brief episode of severe ischemia and indicate that GSSG release can be reliably used to investigate oxidative stress in reperfused hearts.

Blood-brain barrier dysfunctions following systemic injection of kainic acid in the rat

Changes in blood-brain barrier (BBB) permeability and cerebral metabolic activity following intravenous injection of kainic acid (KA; 6, 12 mg/Kg) in rats were assessed by calculating respectively a blood-to-brain transfer constant (Ki) for [14C]alpha-aminoisobutyric acid and local cerebral glucose utilization (LCGU) values, at different times (1 h, or acute seizures phase, and 48 h, or chronic pathology phase) after the induction of seizures. A significant increase in the local permeability of the BBB was observed 1 h after the injection of KA 6 mg/Kg (eliciting no significant changes in cerebral metabolic activity, except within the frontal cortex and the hippocampus) and 12 mg/Kg (which induced a marked and widespread enhancement of LCGU). On the contrary, during the pathology phase, persistent regional increases in Ki values were evidenced in rats treated with the lowest dose of the convulsant, but not in rats injected with KA 12 mg/Kg (a dose able to cause extensive neuronal damage). Thus one can speculate that: 1) KA-induced regional changes in the permeability of the BBB are not correlated with changes in neuronal activity; 2) opening of the BBB is not reliably associated with neuronal injury.

Biochemical and electrophysiologic evidence that propofol enhances GABAergic transmission in the rat brain

The influence of propofol, a new intravenous anesthetic agent, on brain gamma-aminobutyric acid (GABA)-ergic transmission has been investigated both in vitro and in vivo. In vitro, propofol, like benzodiazepines, 1) markedly enhanced 3H-GABA binding in cortical membrane preparations; 2) potentiated muscimol-induced stimulation of 36Cl- uptake in membrane vesicle preparations (the propofol potentiating effect was antagonized by bicuculline); and 3) inhibited 35S-TBPS binding to unwashed membrane preparations from rat cerebral cortex. Finally, propofol failed to displace 3H-flunitrazepam from its binding site, indicating that its site of action in brain is different from that of benzodiazepines. In vivo, the effect of propofol was studied using single-unit recording of the electrical activity of both nondopaminergic neurons in the pars reticulata of the substantia nigra (PR neurons) and of dopaminergic neurons in the pars compacta of the substantia nigra (DA neurons). PR neurons are known to be inhibited by GABA-mimetic drugs and benzodiazepines, whereas DA neurons are tonically inhibited by PR neurons. The intravenous administration of propofol, in a fat emulsion formulation, produced a brief dose-dependent inhibition of the firing rate of PR neurons. The dose producing 50% inhibition of the firing rate was calculated to be 1.2 +/- 0.1 mg/kg. The inhibitory effect lasted less than 5 min. Repeated injections of propofol reproduced the same inhibitory response, whereas continuous infusion (0.5 mg.kg-1.min-1) produced a persistent inhibition of neuronal firing. The inhibitory effect of propofol on PR neurons was potentiated by diazepam and reversed by picrotoxin and bicuculline but was not influenced by the benzodiazepine antagonist Ro 15-1788. These findings suggest that propofol exerts a GABA-mimetic action on PR neurons by acting on a site distinct from the benzodiazepine recognition site. Unlike benzodiazepines, propofol inhibited the firing rate of DA neurons with a potency proportional to its inhibitory effect on PR neurons. The inhibition of DA neurons was reversed by bicuculline and picrotoxin. The results suggest that propofol enhances the inhibitory control over DA neurons by strionigral GABAergic neurons.

Comparing core needle to surgical biopsies in breast cancer for cell kinetic and ploidy studies

The evaluability and reliability of proliferative activity (expressed as 3H-thymidine labeling index, 3H-TdR LI) and ploidy determinations on core needle biopsies were compared with those obtained on surgical material from the same breast cancers. The evaluability of 3H-TdR LI on core needle biopsies was markedly lower than that on surgical material (53% vs 100%), and the association between 3H-TdR LI values in the 16 cases with both evaluable determinations was poor (rs = 0.45). Conversely, determinations of ploidy on core needle biopsy and surgical material provided superimposable results, in terms of evaluability (91% vs 100%) and reliability (rs = 0.99). Further efforts are needed to improve sampling procedures for a reliable assessment of biological markers.

Twenty-four-hour activity of felodipine extended release in chronic stable angina pectoris

To investigate the antiischemic efficacy and duration of action of the dihydropyridine calcium antagonist felodipine, 15 patients with stable exertional angina were enrolled in a double-blind, crossover study comparing 2 doses (5 and 10 mg) of felodipine extended release (ER) and placebo given once daily for 1 week. Bicycle exercise tests were repeated at the end of each treatment period 4 and 24 hours after dosing. Four hours after dosing with both felodipine doses, only 5 patients discontinued the exercise test because of greater than 2 mm of ST-segment depression, whereas 10 continued until exhaustion (p less than 0.01 vs placebo). Compared with placebo, total exercise time was increased by 19% (p less than 0.001), with no difference between doses. After 24 hours, exercise duration was prolonged up to physical exhaustion in 6 patients taking felodipine 10 mg (p less than 0.05 vs both placebo and felodipine 5 mg); moreover, 11 patients taking 10 mg and 5 taking 5 mg increased time to 1 mm of ST depression greater than or equal to 15% compared with exercise time during the placebo test. Mean time to 1 mm of ST depression at 24 hours was increased by 8% with 5 mg and by 18% with 10 mg (p less than 0.001 vs placebo; p less than 0.01 between doses). Total exercise time at 24 hours was increased with both doses (p less than 0.001), with greater efficacy with the 10-mg dose (p less than 0.05 vs 5 mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen radicals generated at reflow induce peroxidation of membrane lipids in reperfused hearts

To test whether generation of oxygen radicals during postischemic reperfusion might promote peroxidation of cardiac membrane lipids, four groups of Langendorff-perfused rabbit hearts were processed at the end of (a) control perfusion, (b) 30 min of total global ischemia at 37 degrees C without reperfusion, (c) 30 min of ischemia followed by reperfusion with standard perfusate, (d) 30 min of ischemia followed by reperfusion with the oxygen radical scavenger human recombinant superoxide dismutase (h-SOD). The left ventricle was homogenized and tissue content of malonyldialdehyde (MDA), an end product of lipid peroxidation, was measured on the whole homogenate as well as on various subcellular fractions. Reperfusion was accompanied by a significant increase in MDA content of the whole homogenate and of the fraction enriched in mitochondria and lysosomes. This phenomenon was not observed in hearts subjected to ischemia but not reperfused, and was similarly absent in those hearts which received h-SOD at reflow. Reperfused hearts also had significantly greater levels of conjugated dienes (another marker of lipid peroxidation) in the mitochondrial-lysosomal fraction. Again, this phenomenon did not occur in ischemic hearts or in reperfused hearts treated with h-SOD. Unlike the effect on tissue MDA and conjugated dienes, reperfusion did not significantly stimulate release of MDA in the cardiac effluent. Treatment with h-SOD was also associated with significant improvement in the recovery of cardiac function. In conclusion, these data directly demonstrate that postischemic reperfusion results in enhanced lipid peroxidation of cardiac membranes, which can be blocked by h-SOD, and therefore is most likely secondary to oxygen radical generation at reflow.

Ex vivo binding of t-[35S )butylbicyclophosphorothionate: a biochemical tool to study the pharmacology of ethanol at the gamma-aminobutyric acid-coupled chloride channel

The effects of acute administration of ethanol on t-[35S]Butylbiclophosphorothionate (35S-TBPS) binding measured ex vivo in unwashed membrane preparations of rat cerebral cortex were investigated. Ethanol, given i.g., decreased in a dose-related (0.5-4 g/kg) and time-dependent manner the binding of 35S-TBPS. This effect was similar to that induced by the administration of diazepam (0.5-4 mg/kg i.p.). Scatchard plot analysis of this radioligand binding revealed that ethanol, differently from diazepam, decreased the apparent affinity of 35S-TBPS recognition sites whereas it failed to change the density of these binding sites. The effect of ethanol on 35S-TBPS binding could not be reversed by the previous administration to rats of the benzodiazepine receptor antagonist, Ro 15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H- imidazo[1,5a][1,4]benzodiazepine-3-carboxylate). Vice versa, the benzodiazepine receptor partial inverse agonist, Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H- imidazo[1,5a][4,4]benzodiazepine-3-carboxylate) (8 mg/kg i.p.), prevented completely ethanol-induced decrease of 35S-TBPS binding. The ability of Ro 15-4513 to prevent the action of ethanol was shared by the anxiogenic and proconvulsant beta-carboline derivatives, FG 7142 (N-methyl-beta-carboline-3-carboxamide) (12.5 mg/kg i.p.) and ethyl-beta-carboline-3-carboxylate (0.6 mg/kg i.v.), which, per se, enhanced this parameter. Moreover, ethanol (0.5-4 g/kg) was able to reverse the increase of 35S-TBPS binding elicited by the s.c. injection of isoniazid (350 mg/kg) and to clearly attenuate the severity of tonic-clonic seizures produced by this inhibitor of the GABAergic transmission.(ABSTRACT TRUNCATED AT 250 WORDS)

"In vivo" administration of valproate decreases t-[35S]butylbicyclophosphorothionate binding in the rat brain

The effect of the "in vivo" administration of sodium valproate on t-[35S]butylbicyclophosphorothionate (35S-TBPS) binding measured "ex vivo" in the rat cerebral cortex was investigated. Sodium valproate produced a decrease of 35S-TBPS binding. The maximal effect (-32%) was reached with the dose of 400 mg/kg i.p., 60 min after the administration of the drug. Saturation experiments revealed that the effect of sodium valproate was due to a decrease in the total number of binding sites with no changes in the affinity constant. A small dose of diazepam (0.5 mg/kg, i.p.), which per se does not modify 35S-TBPS binding, markedly potentiated the inhibitory effect of sodium valproate on 35S-TBPS binding. Moreover, the "in vitro" addition of sodium valproate to cortical membranes failed to modify 35S-TBPS binding, indicating that the effect of the "in vivo" administration of this drug is not due to its direct interaction with the chloride associated binding sites. These results strongly suggest that this drug enhances the function of GABAergic synapses at the level of the GABA-coupled chloride channel. This conclusion supports the hypothesis that an enhancement of GABAergic transmission plays a role in the molecular mechanism involved in the antiepileptic action of sodium valproate.

Neurochemical action of the general anaesthetic propofol on the chloride ion channel coupled with GABAA receptors

The effect of propofol, a novel short acting anaesthetic, on the function of the GABAA/ionophore receptor complex was studied in vitro in cortical membrane preparations from rat cerebral cortex and was compared with the action of pentobarbital and alphaxalone, two general anaesthetics known to enhance GABAergic transmission. Propofol, mimicking the action of pentobarbital and alphaxalone, increased [3H]GABA binding, reduced [35S]TBPS binding and enhanced muscimol-stimulated 36Cl- uptake in a concentration-dependent manner. While the efficacy of the drugs in affecting these biochemical parameters was similar, they differed markedly in potency being alphaxalone greater than propofol greater than pentobarbital. However, separate sites of action or different mechanisms for these drugs can be suggested by the result that the concomitant addition of propofol either with alphaxalone or pentobarbital or diazepam produced a simple additive inhibition of [35S]TBPS binding as well as an additive enhancement of [3H]GABA binding and muscimol-stimulated 36Cl- uptake. The effect of propofol at the level of the GABA/ionophore receptor complex seems to be strictly dependent on the interaction of GABA with its recognition site. In fact, the specific GABAA receptor antagonist bicuculline antagonized the decrease of [35S]TBPS binding as well as the enhancement of [3H]GABA binding and muscimol-stimulated 36Cl- uptake induced by propofol. On the other hand, propofol was able to enhance [3H]GABA binding in membranes previously incubated with the specific chloride channel blocker picrotoxin. Finally, the finding that propofol fails to affect [3H]flunitrazepam binding together with the failure of Ro 15-1788 and PK 11195 to antagonize its effect on [35S]TBPS binding excludes a direct interaction at the level of benzodiazepine recognition sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet activating factor involvement in splanchnic artery occlusion shock in rats

Splanchnic artery occlusion shock was induced in anesthetized rats by clamping the splanchnic arteries for 45 min. The survival rate, plasma levels of thromboxane B2 (TxB2) and 6-keto-PGF1 alpha, serum and peritoneal levels of macrophage tumor necrosis factor (TNF alpha), the phagocytotic and killing activity of peritoneal macrophages and white blood cells count were evaluated. Shocked rats died within 2 h, while all sham-shocked rats survived more than 6 h. Plasma TxB2 and 6-keto-PGF1 alpha levels were increased in rats subjected to splanchnic artery occlusion shock compared to the levels in sham-shocked animals. Serum and peritoneal macrophage TNF alpha levels were undetectable in sham-shocked rats, whereas shocked rats exhibited increased levels of TNF alpha. Moreover, splanchnic artery occlusion shock reduced peritoneal macrophage phagocytotic and killing activity, and also produced severe leukopenia. A specific receptor antagonist of platelet activating factor (PAF), L-652, 731 (an i.v. bolus of 3.2 mg/kg 2 min after removal of the clamps followed, 5 min thereafter, by a continuous infusion of 0.16 mg/kg per min for 30 min) significantly increased the survival rate, lowered plasma TxB2 levels and reduced both serum and macrophage TNF alpha levels in shocked rats. In addition, L-652,731 completely restored macrophage phagocytosis, partially improved macrophage killing and significantly inhibited leukopenia. Finally, the administration of L-652,731 had beneficial effects on the cardiovascular changes induced by splanchnic artery occlusion shock. These findings are consistent with the involvement of PAF in splanchnic artery occlusion shock and indicate that PAF produces shock through direct and indirect (TxB2-mediated and TNF alpha-mediated) actions.

[The synaptic ribbons in the retina of the turtle (Pseudemys scripta elegans): ultrastructural and chronobiological study]

The Authors investigate the morphology and the behaviour of the synaptic ribbons (NS) in the outer plexiform layer of the retina of the turtle Pseudemys scripta elegans during the 24 hrs cycle; the animals were subjected to a light-dark cycle = 12:12 hours. New ultrastructural features are demonstrated in the rod arciform density and in the fibers connecting the central axis of the ribbon with the presynaptic membrane (Figs. 1 A-B). As to chronobiological data, the existence of different kinds of ribbons, each typical of a single period of the 24 hrs cycle is excluded: identical NS can likewise be observed at different hours of the day and under various environmental light stimulations (Figs. 2-3-4). Furthermore, it is also demonstrated that during the light period, every rod synapse in the outer plexiform layer has a typical ultrastructural topography of its own (Figs. 5 A-B-C). During the dark period, the ribbon with its neighbouring vesicles moves towards the nucleus, thus leaving the synaptic region (Figs. 6 A-B-C). From the analysis of our results, we are of the opinion that all previously demonstrated changes in number are only in part dependent on cyclic disruption and reconstruction. On the contrary, they can be the result of a different topographical arrangement of the organelles. When NS modify their relationship with the presynaptic membrane of the rods, they may behave as switch on the nervous circuits of the retina and play a facilitatory or inhibitory role on the discharge of synaptic vesicles during the different periods of the 24 hrs cycle.

The general anesthetic propofol enhances the function of gamma-aminobutyric acid-coupled chloride channel in the rat cerebral cortex

The effect of the general anesthetic propofol on t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to unwashed membrane preparations from rat cerebral cortex was studied and compared to that of other general anesthetics (pentobarbital, alphaxalone) which are known to enhance GABAergic transmission. Propofol produced a concentration-dependent complete inhibition of [35S]TBPS binding, an effect similar to that induced by pentobarbital and alphaxalone, although these agents differ markedly in potency (alphaxalone greater than propofol greater than pentobarbital). The concomitant addition of propofol either with alphaxalone or pentobarbital produced an additive inhibition of [35S]TBPS binding, suggesting separate sites of action or different mechanisms of these drugs. Moreover, although bicuculline (0.1 microM) completely antagonized the propofol-induced inhibition of [35S]TBPS binding, the effect of this anesthetic was not due to a direct interaction with the gamma-aminobutyric acidA (GABAA) recognition site. In fact, propofol, like alphaxalone and pentobarbital, markedly enhanced [3H]GABA binding in the rat cerebral cortex. Finally, propofol was able to enhance [3H]GABA binding in membranes previously incubated with the specific chloride channel blocker picrotoxin. Taken together these data strongly suggest that propofol, like other anesthetics and positive modulators of GABAergic transmission, might exert its pharmacological effects by enhancing the function of the GABA-activated chloride channel.

Premonitory symptoms in migraine without aura: a clinical investigation

Thirty-three out of 100 patients affected by migraine without aura, reported premonitory symptoms in at least 50% of attacks and were considered to be affected by complete or premonitory common migraine. This group had a greater positive familiarity for migraine, a lower mean age of onset, and a higher average number of trigger factors compared with other patients. These three differences were statistically significant; hence we hypothesized that patients with migraine attacks generally preceded by premonitory symptoms have a stronger constitutional migraine trait with a premature weakening of their antinociceptive adaptation systems to the environment and to stressful events.

[Clinico-diagnostic and therapeutic considerations on retroperitoneal liposarcoma]

Two patients with retroperitoneal liposarcoma are presented to determine the accuracy of diagnostic methods and the role of surgical treatment. In both the patients the large retroperitoneal liposarcoma recurred locally after surgery. Histological features, clinical presentation, diagnostic procedures, extent of surgical resection and adjuvant treatment are reviewed. These data suggest that an aggressive surgical approach followed by adjuvant postoperative irradiation is the treatment of choice in primary and recurrent neoplasms.

[Enamel mineralization in rats subjected to an excess fluoride diet: SEM study]

Aim of our present work is to investigate with the SEM the process of enamel mineralization in the lower incisors of albino rats submitted for 21 days (a single amelogenetic cycle) to an hyperfluoric diet (five folds more than the normal). Our observations were performed on specimens fractured 8, 12 and 16 mm from the cervical loop transversally along the major axis of the incisor. It was demonstrated that the three different phases of enamel maturation were slower, so that, when the incisor erupted, mineralization was not completed and localized areas of demineralization were present. The authors are of the opinion that all morphological changes are dependent on the effect of fluoride on ameloblasts, either during their secretory or modulatory phases. On the basis of our results attention is pointed on the possible lesions of the enamel dependent from an unwary fluoride administration, particularly when decidual teeth are still present.

[The prognostic assessment of dilated cardiomyopathy: a follow-up of 138 patients]

A total of 138 patients with idiopathic dilated cardiomyopathy were assessed and followed-up between July 1973 and October 1985 in order to evaluate prognostic risk indicators. Of these 102 were male and 36 were female with a mean age of 49.1 years. Each patient underwent physical examination, electrocardiography, echocardiography, cardiac catheterization and coronary angiography. The mortality rate was low for the first 3 years (respectively 8, 12.5 and 20%) while it was 57.5 at the end of the 5-year follow-up period. Univariate analysis at the time of the diagnosis revealed that five factors were predictive of the clinical course at the end of the fifth year: the NYHA functional class IV (p less than 0.0001); LV ejection fraction less than 0.30 (p less than 0.01); left ventricular failure, bi-ventricular failure and left ventricular end-diastolic pressure greater than 20 mmHg (p less than 0.05). Multivariate analysis was used to determine which combination of factors could most accurately predict survival. The most important prognostic factor was again the IV NYHA functional class (p less than 0.01) and, to a lesser degree, left ventricular end-diastolic pressure (p less than 0.05). The present study underlines that the survival rate of patients with dilated cardiomyopathy depends upon the selection of patients. This can explain the low 3-year mortality found in our patients. The NYHA functional class may be a useful practical guide for cardiac transplantation.

[Use of synthetic resin cases for the scanning electron microscopic study of the kidney tubule system]

Aim of our present work was to investigate a new method to study the three-dimensional arrangement, the length and the diameter of the different parts of the renal tubules. The ureter was cannulated after blocking the urinary flow with a binding of the ureter itself at its intermediate third, and injected in it against flow a synthetic resin (Mercox) normally used for vascular corrosion casts. It was demonstrated that the binding maintained only for 24 hours is adequate for morphological studies of the urinary tracts from papillar ducts until the Henle's loop. On the contrary the binding maintained for 7 days induced marked changes in the tubular architecture similar to the first anatomo-pathological changes of the nephrosclerosis following a chronic obstructive nephropathy.

Fractional shortening/end-systolic stress correlation in the evaluation of left ventricular contractility in patients treated by acetate dialysis and lactate haemofiltration

Fractional shortening/end-systolic stress (FS/ESS) correlation by echocardiography is a reliable index of left ventricular function. Acetate infusion or preload reduction due to water compartment re-equilibrium may induce ventricular derangements during dialytic treatment. In 13 patients on lactate haemofiltration (LHF) (mean age 56.8 +/- 11.9 years on regular dialytic treatment (RDT) for 75.3 +/- 56.5 months) and in seven patients on acetate haemodialysis (AHD) (mean age 48 +/- 10.7 years; on RDT for 43.9 +/- 49.2 months) fractional shortening/end-systolic stress was evaluated before and after single dialytic session. The following biochemical parameters were also studied: haematocrit (Htc), plasmatic osmolarity, ionised Ca, Na, K, and blood gases. In both groups the mean fractional shortening/end-systolic stress correlation maintained the same correlation coefficient before and after treatment (r = -0.68, P less than 0.001). Lactate haemofiltration and acetate haemodialysis by reducing the volume expansion and preload (mean interdialytic body-weight increase 2.5 +/- 0.8 kg in our patients), may decrease left ventricular contractility (Starling's law). Furthermore, acetate was postulated as a myocardial depressant. Dialysis-induced myocardial contractility variations plotted against fractional shortening/end-systolic stress correlation allowed the division of our patients into four different groups: (1) patients with increased fractional shortening and reduced end-systolic stress; (2) patients with unchanged fractional shortening and reduced end-systolic stress; (3) patients with reduced fractional shortening and increased end-systolic stress; and (4) patients with reduced fractional shortening and unchanged or reduced end-systolic stress. These groups include patients treated with either lactate haemofiltration or acetate haemodialysis. Our data cannot confirm the postulated acetate myocardial depressant activity.(ABSTRACT TRUNCATED AT 250 WORDS)

[J-reservoir in the treatment of ulcero-hemorrhagic rectocolitis]

The Authors report their experience on ileal-anal anastomosis with a J-pouch. A videotape illustrates the surgical technique. At last functional results are shown.

Abdominal migraine in adults. Case reports

The association between headache and gastrointestinal symptoms is typical of migraine and useful for diagnosis. Diagnosis is difficult when migraine consists only of gastrointestinal symptoms without headache. In such a situation differential diagnosis is very widespread, sometimes implying diagnostic and therapeutic delays with unpleasant consequences for the patient and embarrassment for the physician. We report on the troubled clinical history of three adults with abdominal equivalents.

Cancer chemoprevention. A review of ongoing clinical studies

The mass of experimental data on various possibilities of inhibiting the carcinogenic process is growing rapidly. However, the biological complexity of carcinogenesis and the intrinsic limitations of the animal models make it often very difficult to identify the real potentially effective agents among the hundreds currently being proposed. In fact, more than 600 potentially chemopreventive agents have been identified and approximately 30 of them are presently being tested in humans. The great heterogeneity of these compounds (they belong to over 20 different classes of chemicals) might be a positive feature as it indicates that a variety of approaches is possible and that the options for selecting effective compounds will be numerous. In recent years, what could be called 'clinical chemoprevention' (that is controlled studies to evaluate in human subjects the efficacy of potentially chemopreventive agents) has developed considerably: according to American estimates 4 chemopreventive agents were tested clinically in 1981, 10 in 1985 and 18 in 1988. The number of reported preclinical investigations was 10 in 1985 and 75 in 1988. This rapid expansion has obviously led to some confusion in terminology and in the evaluation of primary results; at present there is still a need for further investigations to better define clinical chemoprevention and to differentiate it from chemotherapy.