Disproportionately elevated proinsulin levels in type 2 diabetic patients treated with sulfonylurea.

OBJECTIVE: Hyperproinsulinemia in type 2 diabetic subjects has recently been accepted as an independent cardiovascular risk factor. Moreover, it has been confirmed that high proinsulin concentrations stimulate amylin secretion by pancreatic beta-cells and amyloid accumulation within pancreatic islets leading to impairment of pancreatic islets secretory function. The association between sulfonylureas administration and secretory function of pancreatic beta-cells, especially concerning insulin precursor peptides, is not sufficiently elucidated. Preliminary studies by our research group revealed that the fasting proinsulin serum concentration is significantly higher in type 2 diabetic patients treated with sulfonylureas than in a well-matched group treated with insulin only. METHODS: A total of 101 subjects with type 2 diabetes were treated either with sulfonylureas (n = 32), with insulin (n = 40), with sulfonylureas + insulin (n = 17) or with diet alone (n = 12). RESULTS: The basal secretory function in the four groups were comparable (C-peptide fasting serum level > 0.5 ng/l). An effect of fasting glycemia, long-term metabolic control (HbA1c), postprandial hyperglycemia (1,5-anhydro-D-glucitol), insulin resistance (HOMA(IR)score) and diabetes duration on the fasting proinsulin serum level in the subjects treated could be excluded. CONCLUSION: The disproportionately high proinsulin levels are due to sulfonylureas therapy. The effect is independent of fasting glycemia, long-term metabolic control, postprandial hyperglycemia, diabetes duration and peripheral insulin resistance.

Blockade of the polyamine site of NMDA receptors produces antinociception and enhances the effect of morphine, in mice.

The possible effect of ifenprodil--a potent antagonist at the polyamine site of the NMDA receptor complex--on nociceptive threshold and morphine analgesia was investigated in mice. In the hot plate test, the intraperitoneal (i.p.) injection of ifenprodil significantly prolonged the reaction time of mice at the dose of 30 mg/kg, and increased the analgesic effect of morphine. In the phenylquinone writhing test, ifenprodil reduced the number of abdominal constrictions of mice starting from the dose of 2.5 mg/kg i.p., and increased the effect of morphine. The effect of ifenprodil on pain threshold was prevented by naloxone. Moreover, ifenprodil antagonized the pain threshold-reducing effect of alpha-melanocyte-stimulating hormone (0.05 microgram/mouse, intracerebroventricularly). These data show that blockade of the polyamine site of the NMDA receptor complex produces analgesia and increases the analgesic effect of morphine.

Decrease in [3H]flunitrazepam receptor binding in rats tolerant to the effects of nitrazepam.

Studies were performed to evaluate the binding of [3H]flunitrazepam to cell membranes from the brain cortex of rats that were made tolerant, by the i.p. administration of nitrazepam once daily, to the anxiolytic and sedative effects (after 14 days) and the anticonvulsant action (electroshock, after 28 days) of nitrazepam. A significant decrease in the number of specific [3H]flunitrazepam binding sites was found only in the group that was tolerant to the anticonvulsant effect. The same experiments were also carried out with oxazepam. Since there were no signs of tolerance, the administration of the drug, 10 mg/kg once daily i.p., was continued for 6 weeks. No tolerance occurred and there were no changes in [3H]flunitrazepam binding site density. We conclude that tolerance to the anticonvulsant effect of nitrazepam could be related to the down-regulation of the benzodiazepine receptors.

Influence of cystamine on pharmacokinetics and pharmacodynamics of nitrazepam.

The influence of cystamine on pharmacokinetics of nitrazepam was studied. Experiments were performed on the third day after the administration of cystamine, since the author's previous investigations showed that the protective action of cystamine in radiation sickness was strongest at this time. CA premedication resulted in more rapid resorption, lower level of nitrazepam in blood, and more rapid elimination of the drug.

Influence of the vaccine Polyvaccinum mite on the nasal mucosa.

The necessity of prolonged administration of the vaccine Polyvaccinum prompted this study on the effect of the preserving agent on the nasal mucosa. Buffered physiologic saline solution containing 0.1--0.4% phenol, and the vaccine containing 0.1--0.4% phenol or 0.01% merthiolate were applied for 12 weeks on the nasal mucosa of rabbits. The nasal mucosa, parenchymal organs and adrenals were studied macroscopically and histologically, and immunologic studies were made. On the basis of the results, preservation of Polyvaccinum mite with 0.4% phenol is suggested.

Caffeine does not bind covalently to liver microsomes from different animal species and to proteins and DNA from perfused rat liver.

Caffeine was found not to bind covalently to liver microsomal proteins from mice, rats and rabbits. Microsomes metabolized caffeine only to a limited extent, the highest rate (about 2% of the substrate concentration) being obtained with rabbit microsomal preparations. The rat liver perfusion technique represents a good model for in vitro caffeine biotransformation studies and therefore for covalent binding experiments. After 2 h perfusion caffeine was extensively metabolized mainly to dimethyl and monomethyl xanthines, a minor pathway to 1,3,7-trimethyluric acid was also seen. However, covalent binding studies using the liver perfusion technique did not reveal any appreciable amount of caffeine metabolites irreversibly bound to either microsomal and total proteins and to DNA.

Metabolism of caffeine to 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil in the isolated, perfused liver from control or phenobarbital-, beta-naphthoflavone- and 3-methylcholanthrene-pretreated rats.

Caffeine metabolism to 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil was studied in the isolated, perfused rat liver. The [2-14C]-labelled drug and metabolites were separated by thin-layer chromatography or high-pressure liquid chromatography. The chemical structure of 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil was confirmed by mass spectrometry and it was quantitatively determined by liquid scintillation counting. 6-Amino-5-[N-methylformylamino]-1,3-dimethyluracil is one of the major metabolites of caffeine found in the perfusion medium. The kinetics of caffeine elimination and of the uracil metabolite formation were studied up to 2 h perfusion time using livers from control rats and rats pretreated with phenobarbital, beta-naphthoflavone or 3-methylcholanthrene. Phenobarbital pretreatment did not modify the rate of caffeine elimination or the extent of 6-amino-5-[N-methylformylamino]-1,3-dimethyluracil formation. In contrast, there was a highly significant inducing effect on both drug elimination and formation of the uracil metabolite in perfusions of livers from beta-naphthoflavone- and 3-methylcholanthrene-pretreated animals.

GLC-mass fragmentographic determination of saccharin in biological fluids.

A specific and sensitive method is described for the determination of saccharin in biological fluids. The compound is extracted as its methyl derivative following a salt-solvent pair procedure and assayed by GLC with either flame-ionization or mass fragmentographic detection using ethylated or trideuteromethylated saccharin, respectively, as the internal standard for quantitation. Detector response was linear over concentrations of 50 mg/ml--10 micrograms/ml with multiple-ion detection mass fragmentography and from 2 micrograms/ml up to milligram levels with flame-ionization detection. Interference from endogenous substrates was never observed. Plasma kinetics and urinary elimination of saccharin in healthy human volunteers given the sweetener orally, acutely (50 mg/60 kg of body weight) or for 5 days (130 mg/60 kg of body weight/day divided over the three main meals), also are reported.

Arene oxides in styrene metabolism, a new perspective in styrene toxicity?

The metabolism of styrene was studied in the rat after intraperitoneal administration of the cold and the 14C-labeled compound. In addition to phenylethylene glycol, mandelic acid, benzoic acid and hippuric acid, phenolic metabolites, namely, 4-vinylphenol, p-hydroxymandelic acid, p-hydroxybenzoic acid, and p-hydroxyhippuric acid, were identified in the urine of the treated animals. These biotransformation products were characterized by mass spectrometry and by comparative thin layer chromatography with standard compounds. Results of covalent binding studies of 14C-phenylethylene glycol to rat liver microsomal proteins suggest that these phenolic compounds may be formed as a result of chemical rearrangements of unstable arene oxides, reactive intermediates possibly implicated in styrene toxicity.

Effects of acamprosate and scopolamine on the working memory of rats in a three-panel runway task.

The aim of this study was to evaluate the effect of treatment with single (1x) and multiple (10x) doses of the anti-craving compound acamprosate (AC, calcium acetyl homotaurinate) on working memory in rats, using in a three-panel runway test. We measured tasks after the animals were treated with AC (500 mg/kg/d, i.p.); scopolamine (SC, 0.5 mg/kg/d, i.p.), a cholinergic muscarinic receptor antagonist; or both drugs concomitantly (ACSC), either for 1 day (1x) or daily for 10 consecutive days (10x). Neither 1x not 10x AC alone had a significant effect on working memory task performance, whereas treatment with SC alone had a significantly negative effect on the ability of the rats to complete the tasks. Rats receiving ACSC performed better than those receiving SC alone, making fewer errors and displaying shorter latency, similar to the performance of the control group. These observations support the hypothesis of an indirect involvement of AC in the cholinergic system.

The effects of midazolam and morphine on analgesic and sedative activity of ketamine in rats.

The aim of this study was to investigate possible interactions between the analgesic activity of ketamine (an N-methyl-D-aspartate antagonist), midazolam (a benzodiazepine derivative) and morphine using the tail-flick test in rats. Animals were treated s.c. with ketamine (1.0-10.0 mg/kg), midazolam (0.3 mg/kg), or morphine (0.6 mg/kg) alone. or in combination The strongest analgesic effect of ketamine was observed after 3.0 mg/kg. In higher doses no enhancement of ketamine activity were found. After morphine and ketamine (3.0 mg/kg) or morphine, midazolam and ketamine co-administration. higher antinociceptive effects compared to ketamine activity were found. Rats administered midazolam and ketamine (3.0 mg/kg) showed a decrease of the effect of ketamine analgesia, and the antinociceptive effect of the three-component mixture was lower than after co-injection of morphine and ketamine. The interaction of these two compounds with ketamine (5.0 mg/kg) occurred in a different manner, because midazolam led to a strong enhancement of ketamine analgesia. After morphine and ketamine (5.0 mg/kg) administration, very weak increase of ketamine analgesia was observed. The results of this study allow better understanding of the alteration of the analgesic effects of low doses of ketamine under the influence of morphine and midazolam.

Plasma anhydro-D-glucitol (1,5-AG) as an indicator of hyperglycaemic excursions in pregnant women with diabetes.

AIMS: To evaluate the use of the plasma 1,5-anhydro-d-glucitol (1,5-AG) level as a possible marker for glucose excursions in pregnant women with diabetes. METHODS: The study group consisted of 55 pregnant women with diabetes (gestational diabetes mellitus-GDM, n = 28 or pre-gestational diabetes mellitus -PGDM, n = 27), without hepatic or renal insufficiency, gestational age range 5-38 weeks. In each patient, 24-h glucose profile, glycated haemoglobin and 1,5-AG plasma levels were measured. Mean blood glucose (MBG) and M-value (by Schlichtkrull) were calculated. MBG, M-value and maximal daily glycaemia (MxG) were used as indexes of daily glycaemic excursions. RESULTS: A significant correlation was found between the 1,5-AG plasma level and MxG [r = (-0.3)] and between the 1,5-AG level and M-value [r = (-0.36)]. There was no association between the 1,5-AG level and gestational age. Multivariate regression analysis, with 24-h glucose profile, gestational age and MxG as independent variables, showed that MxG was the main parameter determining the 1,5-AG plasma level [beta = (-0.68)]. The M-value, the coefficient of glucose fluctuations, also determined the 1,5-AG level but with lower statistical power [beta = (0.41)]. No statistical differences were found in the group with HbA(1c) < 6% or > 6% for 1,5-AG and M-value, while MBG was higher in poorly controlled patients (HbA(1c) > 6%). CONCLUSIONS: The plasma 1,5-AG level may be a useful marker of daily glucose excursion in pregnant women with diabetes, as an adjunct to HbA(1c) monitoring.

Effect of multiple doses of clonazepam on the nitroreductase activity in hepatic microsomal preparation from rat.

The hepatic microsomal nitroreductase activity and urinary excretion of the sum of the main metabolites of clonazepam (CNZ) were investigated in rats that had received 7 daily injections of 2 mg/kg of the compound. Despite the significant decrease in CNZ nitroreductase activity, there was only poor correlation between the enzyme activity and excretion of the assayed metabolites.

Pharmacokinetic disposition of pethidine under tolerance.

Under tolerance, evoked by multiple doses of pethidine (PD), the serum and brain tissue content of PD was related to diminished analgesic activity. Even though in tolerant rats no enhancement of PD biotransformation in the liver could be recognized (as followed by the measurement of hepatic esterase and N-demethylase activity), the amounts of both PD and nor-PD excreted in urine were increased under tolerance. The authors conclude that the faster disposition of PD may contribute to the development of tolerance.

Development of tolerance to pethidine in rats, pretreated or not, with beta-naphtoflavone or SKF 525 A.

Tolerance to the analgesic effect of pethidine (PD) in rats, treated with a dose of 15 mg/kg of the compound twice daily at 12 h intervals for 1-3 weeks, was assessed using both, heat and current irritating stimuli. Tolerance could be detected earlier by the current irritating method, than by the hot plate technique. Pretreatment with beta-naphtoflavone did only slightly affect the development of tolerance to the antinociceptive effect of PD. In contrast after one week of treatment with SKF 525 A PD retained its analgesic effect. The prolonged pretreatment with SKF 525 A did not prevent the development of tolerance to the analgesic effect of PD.

Pharmacodynamics and pharmacokinetics of psycholeptic drugs in the course of radiation disease. The effect of premedication with cystamine on pharmacodynamics and Pharmacokinetics of nitrazepam.

Pharmacodynamics and pharmacokinetics of psycholeptic drugs in the course of radiation disease (I). Effect of premedication with cystamine on pharmacodynamics and pharmacokinetics of nitrazepam. Acta Physiol. Pol. 1977, 28 (2): 161--168. In the experiments carried out on rats the radiation disease was evoked by exposure to 600 R. The strongest radioprotective action of cystamine was found on the 3-rd day of radiation disease. The tendency to normalization of both the pharmacodynamics (exploring mobility and anticonvulsant action) and pharmacokinetics of nitrazepam in the animals premedicated with cystamine was described.

Development of tolerance to benzodiazepines. I. Changes in the systems of central nervous system neurotransmitters during long-term administration of nitrazepam.

A purpose of the study was determination of the relationships between the brain levels of neuro-mediators: noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) and the development of tolerance to the sedative and anticonvulsive action of Nitrazepam. It was found that during tolerance development the GABA level increased in the cerebral tissue and changes appeared in the activity state of the serotoninergic system.

Differences in the development of tolerance to various benzodiazepines.

Anticonvulsant, sedative and anxiolytic effects of the following benzodiazepines, administered chronically by the intraperitoneal route, were assessed: nitrazepam (NTZ), diazepam (DZ), oxazepam (OXZ), chlordiazepoxide (CDX) and temazepam (TMZ). The action of NTZ in tests for sedative, anticonvulsant and anxiolytic effects rapidly changed upon a repeated daily treatment, which suggests development of tolerance, while no tolerance developed to such effects of OXZ. The stimulating effect of DZ was found not earlier than after 5 weeks of chronic treatment, but no tolerance to the anxiolytic action was observed, and the anticonvulsant action was even potentiated. The stimulating action and tolerance to the anxiolytic effects of CDX and TMZ developed rapidly, but was accompanied with an only slight decrease in the anticonvulsant effect.

Pharmacokinetic aspects of habituation to benzodiazepines.

In state of tolerance to the sedative effect of nitrazepam (NTZ) its pharmacokinetic properties are changed: the absorption is slowed down, the elimination, in contrast, is accelerated due to the rapid biotransformation. The NTZ content in brain tissue is increased significantly with respect to the brain levels of animals treated with a single dose of NTZ. In animals of only moderate intensity of tolerance produced by oxazepam (OX) the brain concentrations of OX are correlated with the developed tolerance.