Prostaglandylinositol cyclic phosphate synthase activity in the liver of insulin-resistant rhesus monkeys before and after a euglycemic hyperinsulinemic clamp.

Prostaglandylinositol cyclic phosphate (cPIP), functionally a cAMP antagonist, is a novel, low-molecular weight mediator of insulin action. Both essential hypertension and type 2 diabetes may be associated with a reduction of cPIP synthesis. In intact cells and in plasma membranes, cPIP synthesis is stimulated by insulin, which activates cPIP synthase by tyrosine phosphorylation. We measured the activities of cPIP synthase in the homogenates of freeze-clamped and then lyophilized liver samples from five insulin-resistant, adult rhesus monkeys, obtained under basal fasting conditions and again under maximal insulin stimulation during a euglycemic hyperinsulinemic clamp. The mean cPIP synthase activity in basal samples (0.33 +/- 0.09 pmol/min/mg protein) was not significantly different at the end of the clamp (0.24 +/- 0.11 pmol/min/mg protein). Basal cPIP synthase activityVoL 12, No. 1, 2001 was directly related to both basal cAMP content and basal fractional activity of cAMP-dependent protein kinase (PKA): r=0.85, p<0.05 and r=0.86, p<0.05, respectively. In turn, insulin-stimulated cPIP synthase activity was inversely related to both the insulin-stimulated fractional activity of PKA (r=0.89, p<0.02) and the insulin-stimulated total PKA activity: r=0.94, p<0.005. The findings suggest that in the liver of insulin-resistant rhesus monkeys, cPIP synthase activity, which leads to the synthesis of the low-molecular weight mediator cPIP, may oppose cAMP synthesis and PKA activity.

[Bioavailability of carotenoids]. / Biodostupnost' karotinoidov.

The review analysis of the gradual process of the assimilation of carotenoids in the living organism depending upon various factors of both external and internal environment is given. Elucidation of in time mechanisms of uptake of carotenoids can be of both theoretical and practical significance. It will allow to modify the composition of carotenoids-based drugs, dietary additives and balanced diets, to work out the recommendations on its dosage regimen for different groups of people.

[Arachidonic acid metabolism in the neutrophilic granulocytes in lymphogranulomatosis]. / Obmen arakhidonovoi kisloty v neitrofil'nykh granulotsitakh pri limfogranulematoze.

Metabolism of arachidonic acid in neutrophils was studied in vitro in blood samples obtained from 36 patients with Hodgkin's disease of various stage and histology and 32 healthy donors. The basic metabolites were: leucotriene B4, such products of its omega-oxidation as 20-hydroxy-leucotriene B4 (20-OH-LTB4) and 20-carboxy-leucotriene B4 (20-COOH-LTB4), and 5-hydroxyeicosatetraenic acid. Their profile proved identical in patients with Hodgkin's disease and healthy donors. Most patients with Hodgkin's disease showed a decrease in leucotriene B4 and 5-hydroxyeicosatetraenic acid and an increase in the level of omega oxidation of leucotriene B4 as assessed by omega catabolite/leucotriene B4 ratio. The levels of 5-hydroxyeicosatetraenic acid and leucotriene B4 omega-oxidation were found to depend upon histology and stage of Hodgkin's disease. They were nearly normal in patients with stage III, mixed cellular disease, B-symptoms and signs of biologic activity of tumor. A direct correlation was established between the level of leucotriene B4 omega oxidation in neutrophils and that of ceruloplasmin in blood serum of patients with various stages of Hodgkin's disease.

C-peptide does not alter carbohydrate metabolism in isolated mouse muscle.

The effects of C-peptide on carbohydrate metabolism in isolated mouse soleus muscle were studied. C-peptide, at concentrations up to 1,000 nM, had no effect on [14C]glucose incorporation into glycogen, glycogen synthase activity, or 2-deoxyglucose uptake. These data demonstrate that C-peptide has no direct effect on the measured parameters of carbohydrate metabolism in isolated mouse muscle.

Prostaglandylinositol cyclic phosphate (cPIP): a novel second messenger of insulin action. Comparative analysis of two kinds of "insulin mediators".

Insulin induces a broad spectrum of effects over a wide time interval. It also stimulates the phosphorylation of some cellular proteins, while decreasing the state of phosphorylation of others. These observations indicate the presence of different, but not necessarily mutually exclusive, pathways of insulin action. One well-known pathway represents a phosphorylation cascade initiated by the tyrosine kinase activity of the insulin receptor followed by involvement of different MAP-kinases. Another pathway suggests the existence of low molecular weight insulin mediators whose synthesis and/or release is initiated by insulin. Comparable analysis of two kinds of insulin mediators, namely inositolphosphoglycans and prostaglandylinositol cyclic phosphate (cPIP), has been carried out. It has been shown that the expression of a number of enzymes, such as phospholipase A(2), phospholipase C, cyclo-oxygenase and IRS-1-like enzyme, could regulate the biosynthesis of cPIP in both normal and diabetes-related conditions. Data on the activity of a key enzyme of cPIP biosynthesis termed cPIP synthase (IRS-1-like enzyme) in various monkey tissues before and twice during an euglycemic hyperinsulinemic clamp have been presented. It has been concluded that in vivo insulin increases cPIP synthase activity in both liver and subcutaneous adipose tissue of lean normal monkeys. It has been also suggested that abnormal production of cPIP could be related to several pathologies including glucocorticoid-induced insulin resistance and diabetic embryopathy. Further studies on cPIP and other types of insulin mediators are necessary to aid our understanding of insulin action.

Insulin mediators in man: effects of glucose ingestion and insulin resistance.

Insulin mediators (inositol phosphoglycans) have been shown to mimic insulin action in vitro and in intact mammals, but it is not known which mediator is involved in insulin action under physiological conditions, nor is it known whether insulin resistance alters the mediator profile under such conditions. We therefore investigated the effects of glucose ingestion on changes in the bioactivity of serum inositol phosphoglycan-like substances (IPG) in healthy men and insulin resistant (obese, non-insulin-dependent diabetic) men. Two classes of mediators were partially purified from serum before and after glucose ingestion. The first was eluted from an anion exchange resin with HCl pH 2.0, and bioactivity was determined by activation of pyruvate dehydrogenase in vitro. The second was eluted with HCl pH 1.3, and bioactivity was determined by inhibition of cyclic AMP-dependent protein kinase. In healthy men, the bioactivity of the pH 1.3 IPG was not altered by glucose ingestion, whereas bioactivity of the pH 2.0 IPG increased to approximately 120% of the pre-glucose ingestion value at 60-240 min post-glucose ingestion (p < 0.05 vs pre-glucose). There was no change in either IPG after glucose ingestion in the insulin-resistant group. These data suggest that the pH 2.0 IPG plays an important role in mediating insulin's effect on peripheral glucose utilization in man under physiological conditions. The data further show, for the first time, a defective change in the bioactivity of an insulin mediator isolated from insulin-resistant humans after hyperinsulinaemia, suggesting that inadequate generation/release of IPGs is associated with insulin resistance.