Immunohistochemical localization of betacellulin, a new member of the EGF family, in normal human pancreas and islet tumor cells

Betacellulin (BTC) purified from mouse beta cell tumor (betaTC-3) is a new member of the epidermal growth factor (EGF) family which can bind receptor tyrosine kinase, EGF receptor (erbB1) and erbB4. It has been demonstrated that proBTC mRNA was abundantly expressed in human pancreas tissue, and that BTC converted amylase-secreting rat acinar cell line (AR42J) into insulin-secreting cells, suggesting that BTC might be important for the growth and/or differentiation of islet cells. However, the cell type producing BTC in the pancreas has not been clarified. In this study, we examined the localization of BTC in human pancreas and islet cell tumors. Immunohistochemistry using specific antibodies to human BTC revealed that this protein was produced in alpha cells and duct cells, and probably in beta cells in normal adult pancreas. Furthermore, strong immunoreactivity to BTC was detected in primitive duct cells of the fetal pancreas, and both insulinoma and glucagonoma cells also showed positive immunoreactivity to BTC. EGF receptor (erbB1) and erbB4 were expressed mainly in islet and duct cells, and duct cells, respectively. These results demonstrate the localization of BTC and its receptors, and suggest that BTC may be one of the factors that have physiologically important roles such as growth and differentiation of islet cells in the human pancreas.

Behavior-related changes in the activity of substantia nigra pars reticulata neurons in freely moving rats

As one of the primary targets of the striatum, the substantia nigra pars reticulata (SNr) has been hypothesized to play a role in normal motor behavior. Specifically, inhibition of usually high, tonic SNr output is predicted to correlate with motor activation. While support for this has come primarily from electrophysiological studies in primates performing goal-directed movements, we tested this hypothesis in rats behaving in an open-field arena. SNr single-unit activity was recorded during spontaneous bouts of open-field behavior (e.g., head and body movements, locomotion) and after rats were given D-amphetamine (1.0 mg/kg, s.c.), which reliably increases motor activity and elevates the firing of motor-related striatal neurons. Prior to drug administration, SNr neurons had either regular, slightly irregular or irregular firing patterns when animals rested quietly. During movement, some inhibitions were observed, but the majority ( approximately 79%) of analyzed units increased firing by as much as 38%. Regardless of the predrug behavioral response of the cell, amphetamine strongly inhibited firing rate ( approximately 90% below nonmovement baseline) and changed firing pattern such that all cells fired irregularly. Subsequent injection with the dopamine antagonist haloperidol (1.0 mg/kg, s.c.) reversed amphetamine-induced inhibitions in all tested cells, which supports a role for dopamine in this effect. These results suggest that the pattern of striatal activity established by amphetamine, which may be critical for determining the drug-induced behavioral pattern, is represented in the SNr regardless of the predrug behavioral response of the cell.

[Introduction and some problems of the rapid time series laboratory reporting system]

We introduced an on-line system of biochemical, hematological, serological, urinary, bacteriological, and emergency examinations and associated office work using a client server system NEC PC-LACS based on a system consisting of concentration of outpatient blood collection, concentration of outpatient reception, and outpatient examination by reservation. Using this on-line system, results of 71 items in chemical serological, hematological, and urinary examinations are rapidly reported within 1 hour. Since the ordering system at our hospital has not been completed yet, we constructed a rapid time series reporting system in which time series data obtained on 5 serial occasions are printed on 2 sheets of A4 paper at the time of the final report. In each consultation room of the medical outpatient clinic, at the neuromedical outpatient clinic, and at the kidney center where examinations are frequently performed, terminal equipment and a printer for inquiry were established for real-time output of time series reports. Results are reported by FAX to the other outpatient clinics and wards, and subsequently, time series reports are output at the clinical laboratory department. This system allowed rapid examination, especially preconsultation examination. This system was also useful for reducing office work and effectively utilize examination data.

Immunological abnormalities in islets at diagnosis paralleled further deterioration of glycaemic control in patients with recent-onset Type I (insulin-dependent) diabetes mellitus

AIMS/HYPOTHESIS

To determine whether the clinical heterogeneity observed in the development of Type I (insulin-dependent) diabetes mellitus correlates with immunohistochemical differences observed at diagnosis.

METHODS

Patients (n = 17) with recent-onset diabetes clinically considered to be insulin dependent (Type I), underwent pancreatic biopsy for immunohistological analysis. These patients were divided into two groups based on the presence or absence of islet immunological abnormalities (insulitis or hyperexpression of MHC class I antigens or both). The patients were also HLA typed and tested for islet cell antibodies and antibodies to glutamic acid decarboxylase (GAD-Ab). All patients were followed monthly for 2 years and their fasting plasma glucose, haemoglobin A1c and daily insulin doses were recorded. The clinical course of patients with islet immunological abnormalities was compared with that of patients without those abnormalities.

RESULTS

Patients with and without islet immunological abnormalities did not differ with regard to HLA type or islet cell antibodies. Antibodies to glutamic acid decarboxylase correlated with the presence of insulitis and MHC class I hyperexpression. These local immunological abnormalities were also associated with higher haemoglobin A1c values (p < 0.05) and a trend towards greater insulin requirements. Further, patients with the islet abnormalities had higher fasting plasma glucose concentrations 2 years after the biopsy than at the time of the biopsy (p < 0.05).

CONCLUSION/INTERPRETATION

The heterogeneous clinical course observed following diagnosis in patients with Type I diabetes correlates with islet immunological abnormalities. Insulitis and hyperexpression of MHC class I correlate with deteriorating glycaemic control.

Changes in islet capillary angioarchitecture coincide with impaired B-cell function but not with insulin resistance in male Otsuka-Long-Evans-Tokushima fatty rats: dimorphism of the diabetic phenotype at an advanced age

The Otsuka-Long-Evans-Tokushima fatty (OLETF) rat is a genetic model of spontaneous development of non-insulin-dependent diabetes mellitus (NIDDM) established as an inbred strain after 20 generations of selective breeding. Although they are thought to be genetically homogeneous, they show a dimorphism regarding the diabetic phenotype at an advanced age, with one remaining obese and modestly diabetic while the other becomes lean and overtly diabetic. To clarify the causes for this divergence, we examined the physical, biochemical, and histopathological features in rats at 50 weeks of age, including an analysis of islet angioarchitecture. Sixty-one of 85 male OLETF rats lost weight, while the remainder remained obese. Mean nonfasting plasma glucose in the lean group was 21.8+/-4.6 mmol/L, significantly higher versus the obese group (10.5+/-1.4 mmol/L) and the age-matched control Long-Evans-Tokushima-Otsuka (LETO) group (7.1+/-0.6 mmol/L). Morphological studies of the pancreas from the lean group showed enlarged multilobulated fibrotic islets with a paucity of B cells, whereas islets from the obese group appeared slightly enlarged and showed a relative abundance of B cells. The fine capillaries that form a network in the islets were extremely sparse in the lean group, resulting in a defective glomerular-like configuration, whereas those from the obese group were dense, forming a nearly typical glomerular-like configuration. Increased plasma insulin responses to oral and intravenous (i.v.) glucose and i.v. glucagon loads were nearly absent in the lean group, while they were evident in the obese group, although to a lesser extent compared with the LETO group. Mean insulin secretory output from the perfused pancreas in response to 11.1 mmol/L glucose in the lean group (3.5+/-2.2 pmol/20 min) was significantly lower versus the obese group (8.8+/-6.5 pmol/20 min) and LETO group (22.0+/-10.8 pmol/20 min). Similarly, pancreatic insulin content was significantly lower in the lean group (9.3+/-6.1 microg) versus the others (26.1+/-17.3 microg for obese and 41.1+/-24.8 microg for LETO). In vivo insulin-stimulated glucose uptake measured by a euglycemic clamp technique was significantly higher in the lean group compared with the obese group. These results demonstrate that the dimorphism regarding the diabetic phenotype in male OLETF rats at 50 weeks of age was due to differences in the number of islet B cells, which could be the result of a variation in the capacity for B-cell proliferation among male OLETF rats.

Pharmacokinetic analysis of the cardioprotective effect of 3-(2,2, 2-trimethylhydrazinium) propionate in mice: inhibition of carnitine transport in kidney

The site of action of 3-(2,2,2-trimethylhydrazinium) propionate (THP), a new cardioprotective agent, was investigated in mice and rats. I.p. administration of THP decreased the concentrations of free carnitine and long-chain acylcarnitine in heart tissue. In isolated myocytes, THP inhibited free carnitine transport with a Ki of 1340 microM, which is considerably higher than the observed serum concentration of THP. The major cause of the decreased free carnitine concentration in heart was found to be the decreased serum concentration of free carnitine that resulted from the increased renal clearance of carnitine by THP. The estimated Ki of THP for inhibiting the reabsorption of free carnitine in kidneys was 52.2 microM, which is consistent with the serum THP concentration range. No inhibition of THP on the carnitine palmitoyltransferase activity in isolated mitochondrial fractions was observed. These results indicate that the principal site of action of THP as a cardioprotective agent is the carnitine transport carrier in the kidney, but not the carrier in the heart.

Dysfunctions of the epididymis as a result of primary carnitine deficiency in juvenile visceral steatosis mice

The juvenile visceral steatosis mutant mice serve as an animal model of primary carnitine deficiency, classified as the sudden infant death syndrome. The defect in carnitine uptake was recently found to be due to a defect in the carnitine transporter gene. We herein report, for the first time, the characteristics of epididymal dysfunction in juvenile visceral steatosis mice. At 8-9 weeks of age, the epididymis was deformed and weight was significantly increased. Histologically, the duct of the proximal epididymis was dilated due to the accumulation of an unusually high level of spermatozoa. Spermatozoa were extravasated from the epididymal duct into the stroma. In contrast, the duct of the distal epididymis was constricted and contained no spermatozoa. Thus, the epididymal disorder causes obstructive azoospermia, leading to infertility.

Aromatase inhibition reduces dendritic growth in a sexually dimorphic rat spinal nucleus

The rat lumbar spinal cord contains the steroid-sensitive spinal nucleus of the bulbocavernosus (SNB), whose motoneurons innervate perineal muscles involved in copulatory reflexes. In normal males, SNB motoneuron dendrites grow exuberantly through postnatal (P) day 28. This growth is steroid dependent: Dendrites fail to grow in males castrated at P7, but grow normally in castrates treated with testosterone or its metabolites, dihydrotestosterone combined with estrogen. Treatment with either metabolite alone supports dendritic growth, but not to the level of testosterone-treated or intact males. In this study, we tested the hypothesis that aromatization of androgens to estrogens was involved in the masculine development of SNB dendrites. Motoneuron morphology was assessed in normal males and males treated daily (P7-28) with fadrozole, a potent aromatase inhibitor (0.25 mg/kg, subcutaneously) or saline vehicle (n = 4-6/group). SNB motoneurons were retrogradely labeled with cholera toxin-horseradish peroxidase at P28 (when dendritic length is normally maximal) and reconstructed in three dimensions. Comparable labeling was seen across groups; it was equivalent in both the rostrocaudal and radial extents. However, dendritic lengths in fadrozole-treated males were significantly below those of intact or saline-treated males. Neither SNB somata size nor target muscle weight differed across groups. These results suggest that aromatization of androgens to estrogens is necessary for development of masculine SNB dendritic morphology.

Cardiomegaly in the juvenile visceral steatosis (JVS) mouse is reduced with acute elevation of heart short-chain acyl-carnitine level after L-carnitine injection

The long-term administration of L-carnitine was very effective in preventing cardiomegaly in juvenile visceral steatosis (JVS) mice, which was confirmed by heart weight as well as the lipid contents in heart tissue. After i.p. injection of L-carnitine, the concentration of free carnitine in heart remained constant, although serum free carnitine level increased up to 80-fold. On the other hand, a significant increase in short-chain acyl-carnitine level in heart was observed. These results suggest that increased levels of short-chain acyl-carnitine, not free carnitine, might be a key compound in the protective effect of L-carnitine administration in JVS mice.

A missense mutation of mouse OCTN2, a sodium-dependent carnitine cotransporter, in the juvenile visceral steatosis mouse

Carnitine is an essential cofactor for the mitochondrial beta-oxidation of long-chain fatty acids. The juvenile visceral steatosis (JVS) mouse, an animal model of systemic carnitine deficiency, is inherited in an autosomal recessive manner. Recently, a human OCTN2 gene encoding a sodium-dependent carnitine cotransporter was isolated and mapped to human chromosome 5q31. Since the mouse jvs locus was assigned to the region of chromosome 11 where it is syntenic to human chromosome 5q31, we isolated the mouse octn2 gene and screened for its mutation in the jvs mouse. DNA sequencing analysis disclosed a missense mutation from CTG (Leu) to CGG (Arg) at codon 352 located within the sixth transmembrane domain of octn2. This amino acid replacement possibly causes the conformational change of the protein that leads to dysfunction of the gene product. Hence, we conclude that octn2 is a candidate gene responsible for the JVS mouse.

Three novel integrin beta3 subunit missense mutations (H280P, C560F, and G579S) in thrombasthenia, including one (H280P) prevalent in Japanese patients

We analyzed three unrelated Japanese patients with type II Glanzmann thrombasthenia (GT) for associated mutations. Polymerase chain reaction and subsequent direct sequencing of platelet RNA and genomic DNA revealed three single nucleotide substitutions of the integrin beta3 subunit gene (His (CAT)-280 to Pro (CCT), Cys (TGT)-560 to Phe (TTT), and Gly(GGC)-579 to Ser(AGC)). Interestingly, the three unrelated patients all had the H280P mutation; one was homozygous and the other two heterozygous for this mutation. Ectopic expression of wild type and mutant complexes in Chinese hamster ovary cells revealed decreased surface expression of the mutated alphaIIbbeta3 complexes, thus demonstrating that these mutations may result in the mild GT phenotypes. The identification of three unrelated patients having the same mutation (H280P) suggests that this mutation might be prevalent in the Japanese thrombasthenic population.

Circulating leptin did not associate with the development of the hyperglycemia accompanied by insulin insensitivity in spontaneous noninsulin dependent diabetes mellitus model Otsuka-Long-Evans-Tokushima-Fatty rats

Leptin, the product of the ob gene, has been reported to regulate feeding behavior and energy metabolism. Plasma leptin concentration was strongly correlated with body fat content in humans. It is well known that increased body fat content is accompanied by insulin insensitivity. In order to study the relationship between serum leptin level and metabolic variables, we performed caloric restriction on Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats, a model of noninsulin dependent diabetes mellitus. The male OLETF rats were allocated at random to three groups: 100% group, and 85% and 70% groups (which consumed 85% and 70% of the amount of food consumed by the 100% group, respectively). A significant correlation between serum leptin level and the body fat content, body weight, triglyceride, and fasting plasma glucose was observed. Using a partial correlation analysis to control for body fat content, however, the correlation between serum leptin and these variables disappeared. No significant changes in serum leptin levels were observed before and after a 1 h hyperinsulinemic euglycemic clamp test. In conclusion, serum leptin was significantly correlated with body fat content rather than fasting plasma glucose, serum insulin and insulin sensitivity. This suggests that circulating leptin per se may not result in hyperinsulinemia and insulin insensitivity in the OLETF rat.

[Active laboratory consultation for the clinical supporting system in the general hospital]

As an active laboratory-initiated consultation, we describe the patient-oriented laboratory comment, a kind of interpretative report, on selected abnormal test results. Appropriate laboratory data check and clinical finding checks are necessary as a precondition for effectively reporting laboratory comments. Over the past five years, we reported 303 laboratory comments on hematologic and chemical test results. Clinical finding checks were performed on only 0.05% of the total number of these tests, but the frequency of reported laboratory comments after clinical finding checks were 6.3% in chemical test results and 47.1% in hematologic test results. As in our previous report, 33% of laboratory comments had an effect on diagnosis and treatment. For effective laboratory-initiated consultation, we must establish standard methods for laboratory data check and for selection of clinical finding checks. In addition, not only consultation but liaison service is needed for the clinical laboratory.

Leptin affects pancreatic endocrine functions through the sympathetic nervous system

The effects of leptin on the secretion of insulin and glucagon were examined. In an experiment involving insulin response to an i.v. glucose load in vagotomized rats, the plasma concentrations of insulin were significantly lower in the leptin (20 nmol/kg BW)-treated group than in a control group. However, in intact rats and rats that had undergone both vagotomy and chemical sympathectomy, this suppressive effect of leptin on insulin secretion was not detected. In an experiment involving a hypoglycemia-induced glucagon secretion test in intact rats, an i.v. injection of leptin (20 nmol/kg BW) augmented the plasma glucagon response to hypoglycemia. In the case of sympathectomized rats, however, this stimulative effect of leptin on glucagon secretion was not detected. In an experiment with perfused rat pancreas, the addition of leptin (20 nM) to the perfusate slightly suppressed insulin secretion, but had no effect on basal or glucopenia-induced glucagon secretion. In intact rats infused with leptin (0.31 micromol/day), the expression of uncoupling protein-1 messenger RNA in interscapular brown adipose tissue was increased, whereas no such effect of leptin on the uncoupling protein-1 messenger RNA expression was observed in brown adipose tissue in chemically sympathectomized rats. These findings suggest that leptin might indirectly affect pancreatic endocrine functions, probably through its stimulative effects on the sympathetic nervous system.

Effect of partial pancreatectomy on beta-cell mass in the remnant pancreas of Wistar fatty rats

Wistar fatty rat, which has been established by transferring the fa gene of Zucker fatty rat to the Wistar Kyoto rat, has many features in common with human NIDDM. It exhibits hyperglycemic obesity with hyperinsulinemia and insulin resistance. It is unclear, however, whether a defect in the beta-cell proliferation is related to the onset of diabetes mellitus together with insulin resistance in this model rat. To determine this, we compared non-fasting plasma glucose levels, insulin content and beta-cell mass in the remnant pancreas of Wistar fatty rats with those in their diabetic-resistant lean counterparts after a 70% partial pancreatectomy. We also examined whether such a defect, if present, could be improved by either phlorizin or nicotinamide. We further investigated if there were any differences in these parameters between the phenotypically identical but genotypically different Wistar lean rats with a gene type of homogeneous Fa/Fa and that of heterogeneous Fa/fa. Male rats, 6 weeks of age, were allocated at random into two groups: 70% pancreatectomy (Px) and sham-pancreatectomy (sham). A sustained hyperglycemia was evident in the Px Wistar fatty rats after surgery, which was accompanied by a reduction of insulin content and beta-cell mass in the remnant pancreas. The changes in insulin content and beta-cell mass were unaffected by restoration of normoglycemia, induced by phlorizin injection. The administration of nicotinamide partially ameliorated the sustained hyperglycemia by a slight but not significant increase in beta-cell mass. No discernible difference in the above parameters was observed between the Wistar lean rats with Fa/Fa and those with Fa/fa. These findings suggest that Wistar fatty rats have a poor capacity for proliferation of pancreatic beta-cells, which causes the onset of overt diabetes along with insulin resistance due to extreme obesity.

A role of nicotinamide-induced increase in pancreatic beta-cell mass on blood glucose control after discontinuation of the treatment in partially pancreatectomized OLETF rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of NIDDM, is normoglycemic at a young age. However, they become hyperglycemic, even at a young age as a result of a 70% pancreatectomy, which is associated with insufficient proliferation of beta-cells. Administration of nicotinamide ameliorates the sustained hyperglycemia by increasing beta-cell proliferation. In order to further understand its mode of action, we studied how long nicotinamide is effective, in terms of ameliorating hyperglycemia, as evidenced by an increase in beta-cell mass, after its administration, in partially pancreatectomized OLETF rats. Male rats, 6 weeks of age, were allocated at random to two groups, 70% pancreatectomy (Px) and sham-pancreatectomy (sham). The Px group was divided into three subgroups, based on treatment with either nicotinamide (350 mg/kg), phlorizin (400 mg/kg) or saline, which continued until 4 weeks after surgery, and were sacrificed at 4, 6, or 8 weeks after surgery. A 70% Px resulted in sustained hyperglycemia in the saline-treated Px rats, which was ameliorated by administration of either phlorizin or nicotinamide, showing the non-fasting blood glucose levels reached to or near the levels found in the sham rats. After cessation of phlorizin injection, non-fasting blood glucose level increased rapidly, reaching the level of the saline-treated Px rats at the end of the experiment, whereas after cessation of nicotinamide injection, non-fasting blood glucose increased gradually to a level which was significantly lower than that observed in the saline-treated Px rats. An increased beta-cell mass, 62.7 +/- 7.8% of total beta-cell mass induced by nicotinamide at 4 weeks, decreased gradually, reaching the level of pretreatment, 30.3 +/- 4.0% 4 weeks after cessation of the treatment. The findings in this study suggest that ameliorated hyperglycemia as a result of proliferated beta-cells during the administration of nicotinamide may results in showing beta-cell exhaustion (a majority of beta-cell degranulation) once stopping injection, as compared with phlorizin treated group in this model rat.

Ovarian hormone-induced beta-cell hypertrophy contributes to the homeostatic control of beta-cell mass in OLETF female rat, a model of Type II diabetes

A sexual dimorphism regarding the incidence of diabetes mellitus in OLETF rat, a model of Type II diabetes, has been reported. As a result, the effects of ovarian hormones on beta cells per se was examined by comparing the capacity of beta-cell proliferation and changes in blood glucose and plasma insulin concentrations after a 70% pancreatectomy. All female animals were randomly assigned to two protocols. The rats involved in protocol I received either a 70% pancreatectomy (Px) or a sham pancreatectomy (sham) at 6 weeks of age, along with their diabetes-resistant counterparts, female LETO rats, which served as normal controls. The rats belonging to protocol II were given an ovariectomy (Ox) at 5 weeks of age, and one week later, they were subjected to either Px or the sham operation, with/without hormone (estradiol, 50 microg/kg; testosterone, 1 mg/kg) replacement. The findings indicate that the capacity for compensatory growth of beta cells after Px was affected by both sex hormonal and genetic components, since a 70% Px resulted in sustained hyperglycaemia within the first week after surgery, but was ameliorated by an increase in beta-cell mass thereafter in the non-Ox Px OLETF rats. The Ox also caused a decline in beta-cell mass which could be improved by replacement with ovarian hormones. Not only endogenous but also replacement ovarian hormones, led to a beneficial effect on beta cells per se in OLETF female rats. This was reflected by an increased beta-cell mass accompanied by a parallel increase in plasma immunoreactive insulin concentration. The effects of ovarian hormones, however, contributed to the beta-cell hypertrophy rather than expansion of the beta-cell population to achieve glucose homeostasis, as evidenced by an increased area of individual beta-cell after Px rather than an increased BrdU-labelling index for the beta cells. The present study suggests that ovarian hormone-induced beta-cell hypertrophy may typically occur, to compensate for changes in functional demand as the results of a 70% Px in female OLETF rats.

Leptin receptor signal transduction: OBRa and OBRb of fa type

We report herein the characterization of activities of signal transduction for three types of leptin receptors (OBRs) from rats, the OBRa, OBRb, and OBRb with fa mutation (OBRb-fa), by measurement of the levels of tyrosine phosphorylation of STAT3 (signal transducers and activators of transcription 3) and MAPK (mitogen-activated protein kinase), which are induced by leptin stimulation of CHO cells stably expressing the OBR (CHO-OBRb, CHO-OBRa, or CHO-OBRb-fa cells). As the result of leptin stimulation, enhanced levels of tyrosine phosphorylation of STAT3 and MAPK were detected in CHO-OBRb cells. In CHO-OBRb-fa cells, enhancement levels for both were lower than those in CHO-OBRb cells. In CHO-OBRa cells, only the phosphorylation of MAPK was detected. These data suggest that these reduced signaling activities cause obesity in fa/fa rats and that OBRa, which has been generally thought to be inactive at signaling, actually transmits signals through the MAPK pathway.

Gene-dose effect on carnitine transport activity in embryonic fibroblasts of JVS mice as a model of human carnitine transporter deficiency

Recently, the marked decline in renal carnitine reabsorption has been thought to account fotr the systemic carnitine deficiency in juvenile visceral steatosis (JVS) mice. We have conducted a kinetic analysis using embryonic fibroblasts derived from normal, heterozygous, and homozygous jvs mice and found that the high-affinity carnitine transporter (Km = 5.5 microM), which shows Na+ and temperature dependency and stereospecificity, is defective in homozygous jvs mice. Moreover, a gene dose-dependent decrease of carnitine transport activity, which was due to a decrease in the number of the transporter molecules, was found in heterozygous jvs mice. Similar phenomena have been observed in human primary carnitine deficiency. Therefore, JVS mice may be useful for understanding this extremely rare human hereditary disorder.

Characteristics of cardiac hypertrophy in the juvenile visceral steatosis mouse with systemic carnitine deficiency

The juvenile visceral steatosis (JVS) mouse exhibits hereditary systemic carnitine deficiency and develops cardiac hypertrophy. The aim of this study was to clarify the characteristics of cardiac hypertrophy in the JVS mouse. Total carnitine content in IVS mouse heart was about 10% of that of control mouse heart at 4 and 8 weeks of age. The heart weight/body weight ratio was bigger in JVS mice than that in control mice at 2 weeks of age, and this difference in ratio increased with age. The wall areas of both ventricles and septum in JVS mice were larger than those of the control mice at 2 and 8 weeks. The myocyte diameter in both ventricular walls and septum in JVS mice was longer than that of the control mice. On electron microscopy, the percent of mitochondria in the myocyte was 66% in JVS mice, and 37% in control mice. The percent of lipid fraction in JVS mice was six-fold higher than that in control mice. Total content of adenine nucleotides in JVS mouse heart was about 60% of that in control mouse heart. Adenylate energy charge in JVS mouse heart was 63 and 45% of that in the control mouse heart at 4 and 8 weeks, respectively. Overall, the cardiac enlargement observed in this animal model could be accounted for by a proportional increase in the myocyte diameter in the ventricles and septum, accompanied by an increase in mitochondria. Furthermore, this cellular growth is associated with decreases in the levels of ATP and ADP, and adenylate energy charge.

Mitochondrial abnormalities in a murine model of primary carnitine deficiency. Systemic pathology and trial of replacement therapy

Mitochondrial abnormalities and effectiveness of replacement therapy were examined in a murine model of systemic carnitine deficiency, namely the juvenile visceral steatosis (JVS) mouse. Homozygous JVS mice revealed severe lipid deposition and abnormal mitochondria in liver, heart, skeletal muscle, and kidney, but there was no pathological change in the nervous system, though they showed cerebral signs. There were numerous ragged-red fibers in muscles, but enzyme activities of the respiratory chain were intact. Histograms of oxidative and nonoxidative muscle fibers showed an increase in small and oxidative muscle fibers in 4-week-old JVS mice, but this difference no longer existed in 8-week- or 1-year-old JVS mice. On the contrary, Mn-superoxide dismutase immunostaining of muscle showed a focal increase in every age of JVS mice. With L-carnitine treatment, JVS mice could survive for a year, but to some extent, there were the same pathological changes as those seen in untreated mice.

Effect of exercise training and food restriction on endothelium-dependent relaxation in the Otsuka Long-Evans Tokushima Fatty rat, a model of spontaneous NIDDM

We investigated whether endothelial function may be impaired in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, a model of spontaneous NIDDM. The effect of exercise training and food restriction on endothelial function was also studied. OLETF rats were divided into three groups at age 16 weeks: sedentary, exercise trained, and food restricted (70% of the food intake of sedentary rats). Otsuka Long-Evans Tokushima rats were used as the age-matched nondiabetic controls. Endothelium-dependent relaxation of the thoracic aorta induced by histamine was significantly attenuated in the sedentary or food-restricted rats, and exercise training improved endothelial function. Relaxation induced by sodium nitroprusside, a donor of nitric oxide, did not differ significantly among groups. Both exercise training and food restriction significantly suppressed plasma levels of glucose and insulin and serum levels of triacylglycerol and cholesterol and reduced the accumulation of abdominal fat. Insulin sensitivity, as measured by the hyperinsulinemic-euglycemic clamp technique, was significantly decreased in sedentary rats but was enhanced in exercise-trained and food-restricted rats. The urinary excretion of nitrite was significantly decreased in sedentary and food-restricted rats compared with nondiabetic rats and was significantly increased in exercise-trained rats. These results indicate that exercise training, but not food restriction, prevents endothelial dysfunction in NIDDM rats, presumably due to the exercise-induced increase in the production of nitric oxide.