Hepatic glucose-6-phosphatase activity in non-insulin dependent diabetics. Effect of enzyme-inducing drugs

The role of glucose-6-phosphatase (G6Pase) in postreceptional glucose handling in non-insulin dependent diabetics ( NIDDs ) was in investigated by comparing the enzyme values in diagnostic liver biopsy samples with fasting blood glucose (BG), immunoreactive insulin (IRI) and plasma antipyrine half-life (T/2). The NIDDs , treated with sulphonylureas, had elevated serum aminotransferase and alkaline phosphatase values associated with fatty liver with or without fibrosis. G6Pase activity was reduced in the NIDDs compared with subjects who had undergone gallstone surgery (p less than 0.001), insulin dependent diabetics (p less than 0.001), and age- and sex-matched non-diabetics (p less than 0.001). G6Pase was inversely related to BG and antipyrine T/2, but not to IRI or conventional liver function tests. Therapy with phenobarbital and medroxyprogesterone acetate, known inducers, increased G6Pase activity, shortened antipyrine T/2, reduced BG and did not alter IRI, in four NIDDs . Low liver G6Pase activity in NIDDs may hence be one factor underlying the impaired glycemic control.

Variation in 5' promoter region of the APOE gene contributes to predicting ischemic heart disease (IHD) in the population at large: the Copenhagen City Heart Study

The objective of this study was to evaluate whether an increased hazard of developing ischemic heart disease (IHD) is associated with any of the three genotypes A560T832/A560T832, A560T832/A560G832 and A560T832/T560T832, defined by variations in two non-coding SNPs in the 5' promoter region of the apolipoprotein E (APOE) gene. These genotypes were selected because they distinguished between high and low levels of HDL-C, TG and/or T-C in our earlier study of multiple samples defined by gender and population. We found a significant increase (p<0.05) in the hazard of IHD in females with the A560T832/T560T832 genotype that remained significant after fitting the effects of dyslipidemia, other established risk factors, and the structural isoform variations of the ApoE molecule. We discuss why this statistically significant genetic predictor may not be an appropriate screening test for IHD in the Danish population at large.

Utility of the Arg/Gln polymorphism of the factor VII (FVII) gene, serum lipid levels and body mass index in the prediction of the FVII:C and FVII:Ag in North Karelia; a cross-sectional and prospective study

The arginine/glutamine (Arg/Gln) polymorphism of the factor VII (FVII) gene is associated with variation in coagulation activity (FVII:C) and antigen concentration (FVII:Ag) of the FVII protein. We estimated frequency distributions of the Arg and Gln alleles and respective genotypes in North Karelia, and evaluated the utility of this polymorphism, serum lipids, and body mass index (BMI) in the prediction of the distributions of FVII:C and FVII:Ag in a cross-sectional study and in a prospective cohort study. The sample comprised 203 males and 262 females (aged 45-64 years) who were seen twice, in 1992 and 1995. The Arg/Arg genotype and the Arg allele frequencies were among the highest reported so far (86 and 93% respectively, in men; and 89 and 94% respectively, in women). Intragenotypic means of both FVII:C and FVII:Ag were significantly higher in the Arg/Arg genotype than in the Arg/Gln genotype in both genders. Also, intragenotypic variances were different in different genotypes in females. Regression relationships between the FVII:C and FVII:Ag and serum triglyceride, and total cholesterol levels and BMI were positive in both genotypes in both genders, which has not been found in other populations. In prospective analyses, average changes in the FVII:C and FVII:Ag were genotype specific in both genders, as were also regression relationships between these changes and changes in triglyceride level in females (P = 0.065 for FVII:C and P = 0.061 for FVII:Ag). A consequence of these complex genetic architectures is that predictive utility of the Arg/Gln genotypes depends on population, gender, serum lipid levels, and BMI, and changes in these factors over time.

Sequence diversity and large-scale typing of SNPs in the human apolipoprotein E gene

A common strategy for genotyping large samples begins with the characterization of human single nucleotide polymorphisms (SNPs) by sequencing candidate regions in a small sample for SNP discovery. This is usually followed by typing in a large sample those sites observed to vary in a smaller sample. We present results from a systematic investigation of variation at the human apolipoprotein E locus (APOE), as well as the evaluation of the two-tiered sampling strategy based on these data. We sequenced 5.5 kb spanning the entire APOE genomic region in a core sample of 72 individuals, including 24 each of African-Americans from Jackson, Mississippi; European-Americans from Rochester, Minnesota; and Europeans from North Karelia, Finland. This sequence survey detected 21 SNPs and 1 multiallelic indel, 14 of which had not been previously reported. Alleles varied in relative frequency among the populations, and 10 sites were polymorphic in only a single population sample. Oligonucleotide ligation assays (OLA) were developed for 20 of these sites (omitting the indel and a closely-linked SNP). These were then scored in 2179 individuals sampled from the same three populations (n = 843, 884, and 452, respectively). Relative allele frequencies were generally consistent with estimates from the core sample, although variation was found in some populations in the larger sample at SNPs that were monomorphic in the corresponding smaller core sample. Site variation in the larger samples showed no systematic deviation from Hardy-Weinberg expectation. The large OLA sample clearly showed that variation in many, but not all, of OLA-typed SNPs is significantly correlated with the classical protein-coding variants, implying that there may be important substructure within the classical epsilon 2, epsilon 3, and epsilon 4 alleles. Comparison of the levels and patterns of polymorphism in the core samples with those estimated for the OLA-typed samples shows how nucleotide diversity is underestimated when only a subset of sites are typed and underscores the importance of adequate population sampling at the polymorphism discovery stage. [The sequence data described in this paper have been submitted to the GenBank data library under accession no. AF261279.]

Utility of the predictors of coronary heart disease mortality in a longitudinal study of elderly Finnish men aged 65 to 84 years is dependent on context defined by Apo E genotype and area of residence

A common assumption underlying most genetic studies is that individuals with different genotypes respond similarly to exposure to internal (epigenetic and background genotype effects) and external (ecological) environments. Here we evaluate whether this assumption is true in individuals with different genotypes of the gene coding for the apolipoprotein E (Apo E) molecule, an important determinant of the metabolic fate of plasma lipids and lipoproteins. We addressed whether the utility of known risk factors of coronary heart disease (CHD) in the prediction of CHD death in a 5-year follow-up is the same for the two most common Apo E genotypes, epsilon3/3 and epsilon4/3, in two cohorts of elderly Finnish men (age at baseline: 65-84 years), one in Eastern and the other in Southwestern Finland. The CHD mortality rate was higher in the epsilon4/3 than in the epsilon3/3 genotype in both cohorts (11.1 versus 7.8%, Pr = 0.281 in the Eastern cohort and 19.6 versus 8.2%, Pr = 0.002 in the Southwestern cohort). In the Eastern cohort, serum high density lipoprotein (HDL) cholesterol level was identified as a strong predictor of CHD death in the epsilon3/3 genotype (beta = -2.155, Pr = 0.019). In the Southwestern cohort, age (beta = 0.139, Pr = 0.006), body mass index (BMI) (beta = 0.149, Pr = 0.016), and serum total cholesterol level (beta = 0.453, Pr = 0.051) were identified as strong predictors in the epsilon3/3 genotype, as were smoking (beta = 0.236, Pr = 0.008) and BMI (beta = -0.124, Pr = 0.057) in the epsilon4/3 genotype. The latter observation indicates that in Southwestern Finland the probability of CHD death decreases with increasing BMI in elderly men with the epsilon4/3 genotype, while in their counterparts with the epsilon3/3 genotype the risk increases with increasing BMI. This difference was statistically significant (Pr = 0.002). These observations clearly argue against the assumption that individuals with different genotypes respond similarly to exposures to internal and/or external environments. These observations are consistent with a complex pathobiology of CHD involving biochemical and physiological agents that are under the influence of interactions between genetic and environmental factors. Information about these interactions is necessary for developing a more precise risk assessment and ultimately to improve public health and clinical strategies to prevent this devastating disease both at the individual and population levels.

Genotyping of human cytochrome P450 2A6 (CYP2A6), a nicotine C-oxidase

Cytochrome P450 2A6 (CYP2A6) is a polymorphic enzyme responsible for the oxidation of certain precarcinogens and drugs and is the major nicotine C-oxidase. The role of CYP2A6 for nicotine elimination was emphasised recently by the finding that smokers carrying defective CYP2A6 alleles consumed fewer cigarettes [Pianezza et al. (1998) Nature 393, 750]. The method used for CYP2A6 genotyping has, however, been found to give erroneous results with respect to the coumarin hydroxylase phenotype, a probe reaction for the CYP2A6 enzyme. The present study describes an allele-specific PCR genotyping method that identifies the major defective CYP2A6 allele and accurately predicts the phenotype. An allele frequency of 1-3% was observed in Finnish, Spanish, and Swedish populations, much lower than described previously.

An ecological study of association between coronary heart disease mortality rates in men and the relative frequencies of common allelic variations in the gene coding for apolipoprotein E

Three common alleles, epsilon2, epsilon3, and epsilon4, of the gene coding for apolipoprotein E (apoE) have been identified as predictors of interindividual variation in measures of lipid and lipoprotein metabolism, and ultimately risk of coronary heart disease (CHD), within many populations. Here we evaluated the utility of the geographic distribution of these alleles for prediction of interpopulation variation in average level of serum total cholesterol and other traditional risk factors, and CHD mortality rate. We employed published estimates of the relative frequencies of the three common apoE alleles, average levels of risk factors such as serum total cholesterol, systolic and diastolic blood pressure, body mass index, smoking prevalence and CHD mortality rate for nine population-based samples of middle-aged males studied by the international WHO MONICA Project. There was approximately a 10-fold difference between the highest and lowest CHD mortality rate. Of the traditional risk factors, variation in the average level of serum total cholesterol was the best predictor (approximately 33%) of the observed interpopulation variation in estimates of CHD mortality rate (Pr=0.10). Variation in the relative frequency of the epsilon4 allele predicted approximately 50% of interpopulation variation in average serum total cholesterol level (Pr=0.02) and 75% of the variation in CHD mortality rate (Pr=0.002) when information about variation in the other risk factors and the epsilon2 and epsilon3 alleles is ignored. Furthermore, variation in the relative frequency of the epsilon4 allele predicted approximately 40% of the variation in CHD mortality rate (Pr=0.02) after considering the contribution of variation in average serum total cholesterol level. Average serum total cholesterol level was estimated to increase by 0.114 mmol/l (4.405 mg/dl), and CHD mortality rate by 24.5/100000, for an increase of 0.01 in the relative frequency of the epsilon4 allele. The predictive utility of the epsilon2 and epsilon3 alleles was considerably less than that of the epsilon4 allele. For the sample of populations considered, the geographic distribution of the apoE alleles can be a statistically significant predictor of interpopulation variation in both the average serum total cholesterol level and CHD mortality rate. In particular, the epsilon4 allele may confer valuable ecological risk information.

A biometrical study of the relationship between sodium-lithium countertransport and triglycerides

We addressed the question: Is there evidence that allelic variation in a single unmeasured gene that has a large effect on maximal activity of erythrocyte sodium-lithium countertransport (Na-Li CNT) also has pleiotropic effects on variation in plasma triglyceride levels? Complex segregation analysis models that included plasma triglyceride levels as a covariate were considered as explanations for interindividual variation in Na-Li CNT. A sample of 711 healthy adults from 254 pedigrees enrolled in the Rochester Family Heart Study was selected for this study. The majority of the pedigrees supported the hypothesis that variations in a single unmeasured non-transmitted environmental factor have large effects on the Na-Li CNT distribution. Only gender-specific first-order covariate parameters were necessary in the complex segregation models suggesting that the form of the relationship between Na-Li CNT and plasma triglyceride level was not influenced by variation in the inferred environmental factor with large effects. Stratification of the sample by this inferred environmental factor resulted in three classes of individuals with significant differences in the distributions of coronary heart disease risk factor traits, as well as interindividual variation in both Na-Li CNT and plasma triglyceride levels. These results, along with other observations from the Rochester Family Heart Study sample, emphasize the complex and multifactorial nature of the causes of interindividual variation in Na-Li CNT. Our study further suggests that new research strategies are needed for studying the relationships between genetic and environmental variation and variation in quantitative traits such as Na-Li CNT that have been identified as risk factors for hypertension.

Genotypes with the apolipoprotein epsilon4 allele are predictors of coronary heart disease mortality in a longitudinal study of elderly Finnish men

Earlier we reported that allelic variation in the gene coding for apolipoprotein (apoE is a significant predictor of variation in the risk of coronary heart disease (CHD) death in a longitudinal study of elderly Finnish men. Here we address the question: which of the apoE genotypes confers the risk information in these men, and whether such information persists after other CHD risk factors are considered? We followed two cohorts of elderly Finnish men aged 65 to 84 years, one in Eastern (n = 281) and the other in the Southwestern (n = 344) Finland for 5 years during which 26 (9.3%) of the men from the Eastern cohort and 40 (11.6%) of the men in the Southwestern cohort died from CHD. Baseline high density lipoprotein (HDL) cholesterol and (HDL cholesterol)2 in the Eastern cohort and age, and total and HDL cholesterol and smoking status in the Southwestern cohort were significant predictors of CHD death (P < 0.05). The apoE genotypes were significant predictors in the Southwestern cohort at P = 0.02 and in the Eastern cohort at P = 0.18. In multivariable models, information about apoE genotypes improved the prediction at P = 0.1O level of statistical significance in both cohorts. When genotypes were considered separately, the episilon2/4 combined with the epsilon4/4 in the Eastern cohort (odds ratio = 7.69, 95% CI = 1.67-35.52) and the epsilon 3/4 in the Southwestern cohort (odds ratio = 2.44, 95% CI = 1.165.10) had sigificantly greater odds of CHD death compared to the common F3/3 genotype. We conclude that apoE genotypes confer risk information about CHD death in two cohorts of elderly Finnish men in a longitudinal study, and this information persists after adjustment for other CHD risk factors. Because different genotypes were predictors in these two cohorts, we further conclude that the utility of a particular genotype as a predictor of CHD death in other populations may depend on the distribution of risk factor profiles at baseline, geographically defined environmental exposures, the CHD mortality history, and the evolutionary history of background genotypes in the population considered.

Apolipoprotein E polymorphism, Alzheimer's disease and vascular dementia among elderly Finnish men

An association between late-onset Alzheimer's disease, vascular dementia and the common polymorphic alleles of the gene coding for apolipoprotein E, epsilon 2, epsilon 3, and epsilon 4, was assessed in a population sample of 393 elderly Finnish men aged 70 to 89 years. Of them, 7% suffered Alzheimer's disease and 3% had vascular dementia. Among those who suffered Alzheimer's disease, there was a statistically significant excess of the epsilon 4 allele. No such an association was observed between the apolipoprotein E alleles and vascular dementia. We conclude that the apolipoprotein E polymorphism confers information about a risk of Alzheimer's disease in this population sample of elderly Finnish men.

Hypertension and overweight associated with hyperinsulinaemia and glucose tolerance: a longitudinal study of the Finnish and Dutch cohorts of the Seven Countries Study

To elucidate the role of hypertension as part of the insulin resistance syndrome, the longitudinal relationships of hypertension and overweight with hyperinsulinaemia and glucose tolerance were examined in the Dutch and Finnish cohorts of the Seven Countries Study (Zutphen, and east and west Finland). Three cohorts of men, born between 1900 and 1919, were first examined in 1959/1960. At the 30-year follow-up survey a 2-h glucose tolerance test was carried out on 619 of the surviving men, and fasting insulin was also measured. Blood pressure and body mass index (BMI) were measured several times during the entire 30-year follow-up period. In cross-sectional analyses, men with diabetes and impaired glucose tolerance at the 30-year follow-up examination had a significantly higher systolic blood pressure and a higher prevalence of hypertension than men with normal glucose tolerance, independent of age, cohort and BMI (p < 0.01). These differences had already been seen 5, 20 and 30 years earlier. Subjects with hyperinsulinaemia (fasting insulin > or = 9.2 mU/l) had a higher BMI and a higher prevalence of hypertension. This cross-sectional association with hypertension was independent of age, cohort and BMI. BMI levels of men with hyperinsulinaemia had been shown to be higher 5, 20 and 30 years earlier, but blood pressure levels had not. These results indicate that hypertension is independently associated with glucose tolerance and insulin resistance in three Caucasian cohorts. Changes in blood pressure precede abnormal glucose tolerance but not hyperinsulinaemia; therefore, glucose tolerance appears to be a stronger correlate of hypertension than hyperinsulinaemia.

Apolipoprotein E polymorphism predicts death from coronary heart disease in a longitudinal study of elderly Finnish men

BACKGROUND

There is ample evidence from cross-sectional studies of an association between allelic variation of the gene coding for apolipoprotein E (apoE) and interindividual variation in plasma lipids, and the presence of coronary heart disease (CHD). There have been no prospective studies, however, to evaluate the usefulness of allelic variation of the apoE gene for predicting CHD.

METHODS AND RESULTS

Two samples of elderly Finnish men were followed for 5 years, one in the east (n = 297) and the other in the southwest of Finland (n = 369). At baseline, when the apoE genotypes were assessed, the men were 65 to 84 years old. At the end of the follow-up, the vital status of each man was determined, and cause of death was coded. At baseline, relative frequencies of the three alleles-epsilon 2, epsilon 3, and epsilon 4--were 0.037, 0.827, and 0.136 in the eastern and 0.062, 0.763, and 0.175 in the southwestern samples, respectively (chi 2 = 8.89, df = 2, P < .012 for difference between the samples). During the 5-year follow-up, a total of 28 deaths from CHD were recorded in the eastern and 42 in the southwestern sample. Relative CHD mortality was not heterogeneous between the samples. Among those who died from CHD, there was a doubling of the relative epsilon 4 allele frequency in both samples (chi 2 = 4.70, df = 1, P < .03 for the eastern sample; chi 2 = 7.11, df = 1, P < .01 for the southwestern sample).

CONCLUSIONS

Allelic variation in the apoE gene is a statistically significant predictor of CHD death in these samples of elderly Finnish men.

Diabetes mellitus, impaired glucose tolerance and mortality among elderly men: the Finnish cohorts of the Seven Countries Study

We studied the association of glucose intolerance with total and cause-specific mortality during a 5-year follow-up of 637 elderly Finnish men aged 65 to 84 years. Total mortality was 276 per 1000 for men aged 65 to 74 years and 537 per 1000 for men aged 75 to 84 years. Five-year total mortality adjusted for age was 364 per 1000 in diabetic men, 234 per 1000 in men with impaired glucose tolerance and 209 per 1000 in men with normal glucose tolerance. The relative risk of death among diabetic men was 2.10 (95% confidence interval 1.26 to 3.49) and among men with impaired glucose tolerance 1.17 (95% confidence interval 0.71 to 1.94) times higher compared with men with normal glucose tolerance. Cardiovascular disease was the most common cause of death in every glucose tolerance group. The multivariate adjusted relative risk of cardiovascular death was increased (1.55) in diabetic patients, albeit non-significantly (95% confidence interval 0.84 to 2.85). Diabetes resulted in an increased risk of cardiovascular mortality among men aged 65-74 years but not among the 75- 84-year-old men. Relative risk of death from non-cardiovascular causes was slightly increased among diabetic subjects. In conclusion, diabetes mellitus is a significant determinant of mortality among elderly Finnish men.

Prevalence of diabetes mellitus and impaired glucose tolerance in the middle-aged population of three areas in Finland

The prevalence of diabetes mellitus and impaired glucose tolerance (IGT) was determined in a random sample of the population aged 45-64 years in three areas of Finland. The two-hour oral glucose tolerance test was repeated in subjects whose first test suggested abnormal glucose tolerance. In the final classification, based on the results of the two tests, the age-standardized prevalence of diabetes, according to the WHO criteria was 5.7% (95% confidence interval (CI): 4.3-7.1) in men and 4.6% (95% CI: 3.6-5.0) in women. The prevalence of IGT was 3.1% (95% CI: 2.1-4.1) in men and 5.1% (95% CI: 3.9-6.3) in women. Among those aged 55-64 years the prevalence was 6.9% in men and 7.5% in women. The prevalence of diabetes and IGT were not different between the three areas. The age-specific mean values of fasting and two-hour blood concentrations and the 90th percentiles of the blood glucose distributions were also not different between the areas. The prevalence of IGT and diabetes increased with age more steeply among women than men. The median of fasting blood glucose did not change, but the 90th percentile increased with increasing age. The entire distribution of two-hour blood glucose shifted towards higher values with ageing, but the major increase was seen for the 95th percentile. The majority of the diabetic subjects were aware of their condition. The awareness was better among men than women.

Time dependent effects of medroxyprogesterone acetate on hepatic ultrastructure in rats

The present study demonstrates that MPA treatment may alter liver ultrastructure in rats. This was seen as a slight cytoplasmic vacuolization in light microscopy. In electron microscopy the most striking findings were the increase in the size of hepatocytes, the volume of smooth endoplasmic reticulum (SER) and the number of mitochondria. Minor changes in mitochondrial size and structure, and SER outline were also obtained. The amount of rough endoplasmic reticulum was decreased and bleb formation was common. The effect of MPA on liver ultrastructure was time-dependent. The main changes were found in rats receiving MPA daily for seven days. Most of the observed changes disappeared within 17 days after the cessation of the regimen. MPA induced alterations in liver morphology may partly be due to induction phenomenon although the hormonal property of MPA also may play some etiological role.

Effects of enzyme induction therapy on glucose and drug metabolism in obese mice model of non-insulin dependent diabetes mellitus

We evaluated the effects of phenobarbital, an inducer, on plasma glucose and serum immunoreactive insulin levels and on hepatic glucose and drug metabolism using an animal model of non-insulin dependent diabetes mellitus. Genetically obese (ob/ob) mice, characterized by hyperglycaemia, hyperinsulinaemia, fatty liver and obesity were selected. The impairment of diabetic state with age was associated with increased activities of NADPH producing enzymes, whereas mixed function oxidase system remained unaltered. Phenobarbital reduced serum immunoreactive insulin and plasma glucose levels and decreased gluconeogenesis. Hepatic glucose phosphorylating enzyme activity increased and glucose releasing enzyme activity decreased. The demand for NADPH in drug oxidation reactions, caused by the induction phenomenon, was reflected in the elevated activities of the NADPH producing enzymes in pentose phosphate pathway and in the activities of isocitrate dehydrogenase and malic enzyme from mitochondrial oxidation reactions. Glucose metabolism of lean littermates indicated that phenobarbital induction normalizes impaired intracellular glucose handling but leaves normal glucose metabolism unaltered. Hepatic glucose production rate was related to plasma glucose, NADPH producing enzyme activities and cytochrome P450 content in the obese and lean mice.

Medroxyprogesterone acetate (MPA) enhances liver NADPH-generating enzyme activities in normal rats

The aim of the present study was to evaluate the effects of medroxyprogesterone acetate (MPA), an inducer of liver drug metabolism, on the ability of liver to generate NADPH, a reducing cofactor for drug oxidation reactions in normal rats and to compare these results with those obtained in rats receiving phenobarbital (PB), a well known inducer of liver drug metabolism. The results showed that: 1. Administration of MPA (100 mg/kg body wt) for a week increased liver wt and NADPH cytochrome P-450 reductase activity, suggesting that the compound induced liver drug metabolism. 2. The regimen also increased the activities of two NADPH generating enzymes, isocitrate dehydrogenase and malic enzyme, suggesting that MPA enhanced the capacity of normal liver tissue to produce NADPH. 3. Phenobarbital treatment increased the activities of three NADPH generating enzymes, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and malic enzyme, suggesting that MPA and PB differ in their effects on the liver NADPH-producing system.

Hepatic mixed function oxidase system and enzymatic glucose metabolism in rats

Therapy with enzyme inducing drugs may improve glycemic control in patients with non-insulin-dependent diabetes mellitus. We evaluated the role of a mixed function oxidase system on glucose metabolism with an animal model. Rats were treated with an inducer (phenobarbital), an inhibitor (cimetidine) and a hepatotoxin (carbon tetrachloride) for a week to cause alterations in the liver. The mixed function oxidase system was assayed by determination of the cytochrome P-450 content and NADPH cytochrome c reductase in liver. Carbohydrate metabolism was evaluated by determining blood glucose, enzymes associated with glucose phosphorylation in the liver (glucokinase, hexokinase), glucose storage as glycogen and enzymatic delivery, glucose-6-phosphatase, and peripheral tissue by determining phosphorylating enzyme (hexokinase) and a key glycolytic enzyme (pyruvate kinase) and glycogen content in muscles. The therapy with the inducer enhanced glucose utilization in liver and storage in muscles. The inhibitor decreased the mixed function oxidase system, reduced glucose phosphorylating, but not gluconeogenetic enzymes, in the liver and increased glycolysis in muscles. Carbon tetrachloride, a hepatotoxin, impaired mixed function oxidase, glucose phosphorylating and delivering enzyme activity in liver, reduced blood glucose and caused glycogen accumulation in muscles. The function of liver microsomal enzyme system seems to be closely related to enzymatic glucose metabolism in the liver and muscles.

Sulphonylureas and glucose metabolism in phenobarbital induced rats

The addition of phenobarbital (PB) to a sulphonylurea (SU) regimen may improve glycemic control in patients with non- insulin dependent diabetes mellitus (NIDDM, type II). Since SU reactions may be modified, we investigated glucose metabolism in rats with combined PB and SU treatment. Chlorpropamide (CHL) and glibenclamide (GB) were selected as SU drugs. The combination of PB to the CHL or GB regimens induced the drug metabolism enzymes excluding aminopyrine N-demethylase activity, which was enhanced by GB but not CHL. The CHL and GB treatments lowered blood glucose (BG) concentration and decreased hepatic glucose-6-phosphate phosphohydrolase (G6P hydrolase) activity and glycogen reserves in the rats. The concomitant administration of PB and the SUs decreased hepatic G6P hydrolase activity and glycogen content in the animals, whereas the BG level remained unaltered. The hepatic glycogen content was decreased more markedly in the CHL plus PB than in the CHL alone treated animals. The findings suggests that enzyme inducers modify the action of SU in rats. Hepatic drug and glucose metabolizing enzymes seems also to respond to distinct PB plus SU combinations in different ways.

Medroxyprogesterone acetate and phenobarbital induce NADPH producing enzyme activities in rats with a chemical liver injury

The administration of medroxyprogesterone acetate (MPA) and phenobarbital (PB) improves liver function in rats with liver damage. This was seen here as increased aryl hydrocarbon hydroxylase (AHH) activity after therapy with MPA or PB in rats with a chemical liver injury, produced by dimethylnitrosamine (DMN). Hepatic glucose-6-phosphatase (G6Pase) activity, an index of glucose metabolism was also normalized in the MPA treated rats. The present study further shows that MPA induced hepatic malic enzyme (ME) and isocitrate dehydrogenase (ICDH) activities and PB enhanced glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH) and ME activities in the DMN pretreated rats. This suggests that MPA and PB enhanced the capacity of altered liver tissue to generate NADPH, a cofactor in the monooxygenase system, which may, in part, enhance the restoration of drug hydroxylation in the rats. Since G6PDH, 6PGDH and ME participate in glucose metabolism, the finding that the compounds influenced these enzymes in distinct ways, may explain the different effects of MPA and PB on the restoration of glucose metabolism.

Metabolism of medroxyprogesterone acetate and hepatic drug metabolism activity

The effect of microsomal enzyme activity on the hepatic metabolism of medroxyprogesterone acetate (MPA), measured in vitro, and the MPA concentrations in liver and plasma were investigated in rats with intact and injured livers before and after MPA therapy. The amount of total MPA metabolites and the activity of drug-metabolizing enzyme system changed in a parallel manner in the livers. The ratio of liver/plasma concentration of MPA was decreased in the liver injury. The hepatic metabolism of MPA is accelerated during MPA treatment in rat.

A comparison of the effects of phenobarbital and medroxyprogesterone acetate on drug and glucose metabolism in rats with chemical liver injury

The effects of medroxyprogesterone acetate (MPA) and phenobarbital (PB) on hepatic glucose and drug metabolism were investigated in male rats after liver injury, induced with dimethylnitrosamine (DMN). MPA normalized fasting blood glucose (BG) and serum immunoreactive insulin (IRI) levels and enhanced hepatic glucose-6-phosphatase (G6Pase) and NADPH cytochrome P450 reductase activities and glycogen and cytochrome P450 (cytP450) contents after liver injury. PB improved hepatic glycogen and cytP450 contents and NADPH cytP450 reductase activity in DMN pretreated rats. The increase in drug metabolism was more pronounced after PB than MPA therapy whereas MPA had more effect on glucose metabolism than had PB. This suggests that the inducing properties of these compounds diverge from each other.

Effects of medroxyprogesterone acetate on hepatic glucose metabolism and microsomal enzyme activity in rats with normal and altered liver

Effects of medroxyprogesterone acetate (MPA) on hepatic glucose handling and drug metabolism were investigated in female rats with intact and damaged liver. Hepatic glucose-6-phosphatase activity, glycogen content and fasting blood glucose were assessed as indices of glucose metabolism. Cytochrome P-450 content and NADPH-cytochrome P-450 reductase activity were assayed to reflect liver drug metabolism. Liver injury was induced by dimethylnitrosamine and carbon tetrachloride. The results demonstrate that hepatic glucose handling and drug metabolism were changed in a parallel fashion in intact, damaged and induced liver. The MPA-induced changes in glucose metabolism were slight in intact animals, whereas the compound has an increasing effect on glucose and drug metabolism in rats with damaged liver. The findings demonstrate the MPA enhances the normallization of hepatic glucose and drug metabolism in damaged liver.

Treatment of noninsulin-dependent diabetes mellitus with enzyme inducers

Although treated adequately with antidiabetic drugs, diet, exercise, and education, patients with noninsulin-dependent diabetes mellitus (NIDDM) may develop resistance to treatment. In NIDDM hepatic microsomal enzyme activity is reduced and since postreceptional glucose metabolism is influenced by these enzymes, we treated the subjects with enzyme-inducing drugs. These inducers (phenobarbital and medroxyprogesterone acetate) when added as adjuvant therapy to sulfonyl urea regimen, reduced blood glucose and plasma insulin, and increased microsomal enzyme activity (as indicated by increased antipyrine metabolism). A trial with placebo did not alter serum glucose levels. Body weight fell and serum aminotransferase levels were normalized. These changes were reflected by reduction of liver fat content (determined by light microscopy), by increased surface density of smooth endoplasmic reticulum, and by repairation of the plasma cell membrane of hepatocytes, as seen in electron micrographs. Activation of postreceptional events in hepatocytes may thus be a new approach in the treatment of therapy-resistant type II diabetes.