Effects of metal ions on the utilization of glucose and on the influence of insulin on it by the isolated rat diaphragm

A fermentation product of Cordyceps sinensis increases whole-body insulin sensitivity in rats

OBJECTIVE

CordyMax trade mark Cs-4 (Cs-4) is a standardized mycelial fermentation product of Cordyceps sinensis, a fungus that has been used for various pharmacologic, metabolic, and ergogenic purposes. The goal of this investigation was to determine the effects of oral Cs-4 administration on whole-body insulin sensitivity, skeletal muscle glucose transport, and endurance performance.

DESIGN

We studied different indices of carbohydrate metabolism in rats that received Cs-4 orally at a dose of 2 g/kg of body weight daily for 30 days.

RESULTS

C-peptide response observed during the oral glucose tolerance test (OGTT) after 10 days of treatment was significantly decreased in the Cs-4-treated group (Cs-4, 52,802 +/- 4,124 vs. control, 70,696 +/- 6309 pM x 120 min; p < 0.05). The integrated insulin area under the curve (53.3 +/- 4.9 ng/mL x 120 minutes) and the glucose-insulin index (6.6 +/- 0.6 units) obtained from the OGTT were significantly decreased (p < 0.01) in the Cs-4-treated group compared to their vehicle-treated counterparts (82.1 +/- 8.1 ng/mL x 120 minutes; 9.9 +/- 0.7 units) after 20 days of treatment. Neither integrated glucose area under the curve observed during either OGTT, basal- or insulin-stimulated 2-deoxyglucose transport nor skeletal muscle GLUT-4 concentrations were affected by Cs-4 treatment. In addition, swim time to exhaustion did not differ between groups in this animal model.

CONCLUSION

We conclude that CordyMax Cs-4 may have potential beneficial effects by maintaining whole-body glucose disposal with a less pronounced increase in insulin secretion after a carbohydrate challenge, however, its effects on endurance performance remain questionable.

Nutritional factors adversely influencing the glucose/insulin system

For the majority of people, particularly if they do not smoke, the food they eat is the largest controllable factor determining their long-term health. The disproportionate consumption of foods high in fat, especially high in saturated fat, and high in simple sugars at the expense of foods high in complex carbohydrate and unsaturated fat has the potential of inducing abnormal metabolic processes in a normal healthy individual and to promote chronic degenerative diseases. Some of the effects of individual macronutrients such as fat, refined sugars and alcohol in promoting abnormalities in glucose/insulin system are presented. These nutrients were chosen because they also have the ability to alter oxidative state of the individual, which in turn could affect the glucose/insulin system. This review focuses on the role of dietary nutrient interactions in influencing the glucose/insulin system through the generation of reactive oxygen species. The importance of dietary macronutrient interaction with micronutrients such as copper and iron and the potential it has in affecting the glucose/insulin system is addressed.

Effect of lithium on plasma glucose, insulin and glucagon in normal and streptozotocin-diabetic rats: role of glucagon in the hyperglycaemic response

1. Lithium salts, used in the treatment of affective disorders, may have adverse effects on glucose tolerance in man, and suppress glucose-stimulated insulin secretion in rats. 2. To study the interaction of these effects with pre-existing diabetes mellitus, plasma glucose and insulin responses to lithium chloride were measured in male Wistar rats made diabetic with intraperitoneal streptozotocin, and in normal controls. 3. In both normal and diabetic anaesthetized rats, intravenous lithium (4 mEq kg-1) caused a rise in plasma glucose. In absolute terms, the rise was greater in diabetic (5.2 mmol l-1) than in normal rats (2.3 mmol l-1). 4. Plasma insulin concentrations were reduced by lithium in normal rats, but the low insulin concentrations measured in the diabetic rats were not significantly changed. 5. After intravenous glucose (0.5 g kg-1), lithium-treated diabetic rats showed a second rise in plasma glucose at 60-90 min without any insulin response, while normal rats showed typically reduced insulin responses and initial glucose disappearance rates. 6. Intravenous glucose reduced plasma glucagon concentrations to a greater extent in normal than in diabetic rats, but lithium induced an equal rise in plasma glucagon in both groups, with a time-course similar to that of the hyperglycaemic effect. 7. The hyperglycaemic action of lithium is greater in the hypoinsulinaemic diabetic rats and appears to involve a stimulation of glucagon secretion in both normal and diabetic animals.

Glucose homeostasis in magnesium-deficient rats

Glucose homeostasis was studied in rats fed diets containing 750,200, or 100 mg/kg Mg for 6 to 8 weeks, from the age of 4 weeks. Weight gain of the rats receiving 200 and 100 mg/kg diets was decreased. This resulted from both a lower food intake and reduced effectiveness of the ingested food. Fed or fasting plasma glucose levels were similar in the three groups. During an intravenous glucose tolerance test, the rate of glucose disappearance was higher in Mg 100 rats than in controls. By contrast, during an oral glucose tolerance test, the rise in plasma glucose was greater and more sustained in Mg 100 rats. During both tests, the insulin response was markedly lower in Mg-deficient rats than in controls. This could be partially due to the reduced insulin content of the pancreas of these animals. The impairment of tolerance to oral glucose was corrected by 5 weeks on a high-Mg diet. After intravenous injection of insulin, the fall in plasma glucose levels was also slightly more pronounced in Mg 100 rats. During no test did we observe a significant difference between glucose or insulin responses in Mg 200 or Mg 750 rats. These results, thus, show that chronic Mg deficiency alters several parameters of glucose homeostasis in the rat.

The role of calcium in stimulation of sugar transport in muscle by lithium

We have investigated the relation between the stimulation of sugar transport by Li+ and Li+-induced changes in cellular Ca2+ distribution. The fluxes of 3-O-[14C]methyl-D-glucose and 45Ca were measured in hemidiaphragm, soleus, and cardiac muscles of the rat, and cellular levels of Ca2+, Na+ and K+ were determined. Li+ increased in parallel the fluxes of 3-O-[14C]methyl-D-glucose and 45Ca in rat hemidiaphragm and soleus muscles. Sugar transport and Ca2+ efflux were also stimulated by Li+ in Ca2+-free medium, suggesting that in addition to increasing sarcolemmal Ca2+ influx, Li+ may also cause the release of Ca2+ from intracellular storage sites, presumably the mitochondria. Mitochondria were isolated from preparations of rat ventricular muscle exposed to Li+, and their Ca2+ content was determined. In rat cardiac muscle, Li+ stimulation of sugar transport was associated with decreased mitochondrial Ca2+ levels (indicating mitochondrial Ca2+ release) only under conditions of deteriorating mitochondrial function. Thus, Li+-induced changes in cellular Ca2+ distribution, which would increase cytosolic Ca2+ levels, were associated with stimulation of sugar transport. These observations support the hypothesis that the increased availability of cytosolic Ca2+ regulates the activity of the sugar transport system in muscle.

Affective disorders, diabetes mellitus and lithium

There appears to be an association between affective disorders and diabetes mellitus independent of the use of lithium in treatment. Prior studies have suggested that lithium treatment may impair glucose tolerance or produce frank diabetes in certain patients. Metabolic complications of the diabetic state, such as hyperosmolality and salt depletion increase lithium absorption and the risk of toxicity even at generally acceptable serum levels. The management of patients with diabetes and affective disorders on prophylactic lithium is discussed.

The distribution of a glucose load in lithium treated rats

The distribution of an intravenous glucose load was investigated in rats without and with previous lithium administration. Lithium caused an increased rate of glycogen formation in muscle tissue but not in liver tissue. Uptake of a 14C-labelled glucose load in skin, liver, muscle, fat and brain was measured. Lithium increased the uptake of labelled glucose in skin and muscle with a concomitant decrease of the amount in blood. The findings are in agreement with an increased glucose tolerance after lithium administration as the uptake was increased in the tissues of quantitative importance for the disposal of a glucose load.

Intravenous glucose tolerance in lithium treated rats

A method for performing intravenous glucose tolerance tests in anaesthetized rats was developed, and factors influencing basal glucose tolerance was investigated. Glucose tolerance increased with increasing weight and body temperature, but decreased with fasting. Lithium administration increased glucose tolerance. The increase varied with the dose and the time interval between administration and glucose tolerance test. There was an immediate increase in glucose tolerance after lithium administration, which lasted under special conditions up to 24 hours. The duration was depending on the dose given and the fasting state of the animal.

Insulin action in isolated fat cells. I. Effects of divalent cations on the stimulation by insulin of glucose uptake

The effects of divalent cations, in particular Ca2+ and Mg2+, on glucose uptake by rat isolated fat cells in the presence and absence of insulin have been studied. EDTA (disodium salt) was used to deplete the bovine serum albumin present in the incubation medium of endogenous divalent cations prior to incubation with the cells, but was not present in the incubation medium during the incubation of the cells. The removal of Ca2+ and Mg2+ from the incubation medium did not affect the basal glucose uptake, but abolished the ability of insulin to stimulate glucose uptake by the cells. Addition of 25 microM MgCl2 or CaCl2 to the incubation medium restored a significant insulin stimulation, and this stimulation was maximal when 0.1 mM MgCl2 or CaCl2 had been added. SrCl2 and BaCl2 were also effective in restoring the insulin stimulation, but did not substitute fully for Ca2+ and Mg2+ in the incubation medium. Possible explanation for these observations are discussed.

Lithium treatment and glucose tolerance in manic-melancholic patients

Intravenous glucose tolerance was measured in manic-melancholic patients given one daily lithium-dose for relapse prevention. It was found that glucose tolerance was increased for some hours after each lithium administration. In the first week of treatment glucose disposal rate was increased up to 12 h after lithium ingestion. In long-term treated patients glucose tolerance was increased 2 h after administration but not 12 h after. Fasting glucose was increased 2 h after lithium administration in long-term treated patients. Concomitant changes in lactate triglycerides, free-glycerol and electrolytes were measured in serum.

The relationship between the transport of glucose and cations across cell membranes in isolated tissues. IX. The role of cellular calcium in the activation of the glucose transport system in rat soleus muscle

1. The role of cellular Ca2+ in the transport of glucose has been investigated by determining the time-course of tension development and the release of 45Ca and 3-0-[14C]methylglucose from preloaded rat soleus muscles. 2. Electrical stimulation, 2,4-dinitrophenol (0.05 mM) and hyperosmolarity (200 mM mannitol) were all found to induce a rapid rise in tension and the rate coefficient of 45Ca release, which coincided with an acceleration of 3-0-[14C]methylglucose efflux. 3. Caffeine (10 mM) or exposure to K+ -substituted buffer induced a rapid increase in tension and the release of 45Ca, but a much later stimulation of 3-0-methylglucose efflux. This delayed response may be related to the fact that both factors induce a pronounced suppression of the effect of various agents known to stimulate sugar transport.4. Following a washout period of 120 min at 0 degreesC, the return to 30 degrees C elicited a prompt transient rise in the rate coefficient for the release of 45Ca and 3-0-[14C]meth ylglucose to levels, respectively, 2.8 and 14.6 times the control levels measured at 30 degrees C. The magnitude of these peaks appeared to be a function of the duration of the exposure to 0 degrees C. Cooling also led to a stimulation of the uptake of 3-0-[14C]methylglucose, and phlorizin suppressed the rise. 5. It was not possible to detect any significant effect of insulin on basal tension or on the influx or efflux of 45Ca. However, in a hyperosmolar environment, insulin (10-100 munits/ml) induced a marked further rise in tension, indicating that the hormone can elicit a redistribution of cellular Ca2+. 6. It is concluded that a rise in the cytoplasmic concentration of free Ca2+ constitutes a part of the mechanism by which the glucose transport system is activated by a variety of stimuli, perhaps also insulin.

Some factors affecting the response of muscle to insulin

1. The effect of various changes in the composition of the supporting medium on the capacity of isolated rat diaphragm to incorporate amino acids into its protein has been studied. 2. Replacement of most of the normal ionic constituents by sucrose is inhibitory towards protein synthesis, as is also substitution of choline or K(+) for Na(+). 3. The capacity of the tissue to respond to a stimulatory effect of insulin is impaired in the sucrose media and under certain conditions in the absence of Na(+), particularly when Na(+) is replaced by K(+) and the (14)C-labelled amino acid is presented at a relatively high concentration. 4. Cutting of the tissue before incubation also decreases incorporating capacity and markedly decreases responsiveness to insulin. 5. In abnormal media the cellular content of ATP falls sharply. 6. The ATP content of the tissue also declines in the presence of 2-deoxyglucose. This change is prevented by the addition of glucose but not of pyruvate and succinate. 7. Although affecting the rate of amino acid incorporation the ATP content is not thought generally to limit sensitivity to insulin.