In vitro influence of sublethal hypoxia on differentiation of the 3T3-L1 preadipose cell line and its physiological implications.

Exposure of cultures of 3T3-L1 preadipose cells to nitrogen for 16 hours kills almost all of the cells, but after exposure to 5% oxygen for 16 hours most of the cells survive, and recover when culture is continued in 20% oxygen. The extent of recovery depends on the insulin concentration of the medium. Isotope incorporation and flow cytometry experiments show that exposure to 5% oxygen for 16 hours growth arrests the cells and leads to an elongation of the G1-phase of the cell cycle. When 3T3-L1 cells are growth arrested in the presence of 5% oxygen and allowed to recover in the presence of 5 microg/ml insulin under 20% oxygen, they can be induced to differentiate by treatment with carbacyclin during the period of growth arrest. Activity of the marker enzyme glycerol-3-phosphate dehydrogenase increases from 46.5+/-17 mU/mg protein to 1506+/-271 mU/mg protein. The extent of differentiation is exponentially related to the concentration of carbacyclin in the medium.

In vitro influence of oxygenation on lipogenesis of rat adipose tissue.

Pre-incubation of rat adipose tissue from ad lib fed rats in gas mixtures containing a range of oxygen concentrations from 0% oxygen to 20% oxygen showed that incorporation of isotopes of glucose into carbon dioxide and tissue were increased after pre-incubation for a period of 14-16 hours in a gas atmosphere containing 5% oxygen. This increase required the presence of 1.2 U/ml insulin in the pre-incubation medium and it was augmented by the presence of 2.8 x 10(-7) M prostaglandin F2 alpha. Incorporation into tissue was shown to be mainly into glyceride-glycerol. Similar results were obtained with isolated fat cells.

In vitro influence of oxygenation on enzymes of rat adipose tissue.

Pre-incubation of rat adipose tissue from ad lib fed rats in the presence of 1.2 U/ml insulin and 2.8 x 10(-7) M prostaglandin F2 alpha for 16 hours in a gas atmosphere of 5% O2 led to an increase in glucose-6-phosphate dehydrogenase activity. No increase in glycerol-3-phosphate dehydrogenase or hexokinase activities were noted. Actinomycin D (50 micrograms/ml) and dehydroepiandrosterone (120 micrograms/ml) attenuated this increase and the increase in incorporation of [1-14C] glucose into carbon dioxide and tissue seen under these conditions. No increase in glucose-6-phosphate dehydrogenase was seen when pre-incubation was made in a gas atmosphere containing 20% O2. Although dehydroepiandrosterone inhibited both enzyme activity and isotope incorporation in a 20% O2 gas atmosphere, actinomycin D was without effect.

The extended Pedersen hypothesis.

The Pedersen hypothesis of fetal macrosomia in neonates born to diabetic mothers has been extended. In neonates born to gestational diabetic mothers, it is suggested that an intrinsic fetal pancreatic beta-cell hyperplasia 'pulls' glucose across the placenta, i.e. assists in glycemic control of the mother. The initial increase in fetal size due to fetal hyperinsulinism gives rise to developing hypoxemia, and the limitation in fetal oxygen availability alters differential tissue utilization of glucose, increases alpha-glycerophosphate synthesis in fetal adipocytes, and gives rise to a further increase in fetal adiposity.

Value of acetylated haemoglobin assay in fetal assessment.

Acetylation of fetal haemoglobin, probably a post-translational, intracellular, enzyme-mediated reaction, depends upon an adequate supply of glucose and oxygen to the fetus and the nature of the diabetes (if present) in the mother. These complicating factors limit the general usefulness of acetylated fetal haemoglobin assay in fetal assessment.

Aetiology of pulmonary dysfunction in total hip replacement operations. The influence of nifedipine on the factors involved.

Patients undergoing total hip replacement surgery who developed pulmonary dysfunction (PD) demonstrated evidence of complement activation and increased thromboxane A2 (TXA2) synthesis. In a double-blind study nifedipine (Adalat; Bayer-Miles) was shown to inhibit complement activation and TXA2 synthesis and thus appears to offer protection against PD.

The role of oxygen deficiency and cytosolic reactions in cell growth.

It has been suggested that a decrease in the availability of oxygen to certain tissues may lead to increased metabolism of glucose through the hexose monophosphate shunt pathway and to increased synthesis of polyols, in particular myoinositol. It is further suggested that these "cytosolic reactions" result in stimulation of the phosphatidylinositol cycle by increasing substrate availability (i.e. phosphatidate, diglyceride and inositol). A relative decrease in local oxygen availability may therefore play a role in cell proliferation and differentiation and in the etiology of cancer, diabetic sequelae and obesity.

Obesity in perspective.

Attitudes to obesity are changing. It is currently regarded as a common, multifactorial disorder with serious medical and psychological consequences. It is also resistant to treatment. Recent research with experimental animals has given new insights into the molecular pathology of this condition and gives some hope of novel therapeutic intervention.

Acetylated fetal haemoglobin in neonates born to mothers with established and gestational diabetes.

Birth weight ratios (BWRs) and cord blood C-peptide values were significantly higher in neonates born to mothers with well-controlled gestational diabetes (GD) than in those born to mothers with well-controlled established diabetes (ED) or mothers with normal results on glucose tolerance testing. The neonates born to the ED mothers had the highest cord blood acetylated fetal haemoglobin (Hb F1) values, and these values correlated with cord C-peptide values. The cord C-peptide values in the GD group correlated with BWRs, but not with Hb F1 values. These results suggest differential tissue utilization of glucose in neonates born to mothers with different types of diabetes.

Value of glycosylated haemoglobin determination in diabetic pregnancy.

A single measurement of total maternal glycosylated haemoglobin (Hb A1) in the late third trimester of a diabetic pregnancy is of limited value in assessing diabetic control. There was no significant correlation between maternal Hb A1 values and neonatal C-peptide values or birth-weight ratios. An isolated Hb A1 measurement is not sufficiently sensitive to monitor the control of diabetes during pregnancy nor is it useful in predicting perinatal outcome.

Secondary changes in diabetes mellitus with particular reference to retinopathy and neuropathy.

It has previously been suggested (1) that respiratory modulation of the action of insulin on glucose metabolism may contribute to macrosomia in neonates from diabetic mothers. It was proposed that this was due to a relative hypoxaemia which resulted in an increase in glucose metabolised through the hexose monophosphate shunt pathway in fetal adipocytes. This could be understood on the basis of the Crabtree-Pasteur Effects. It is now suggested that a similar mechanism may lead, in certain tissues, to an increase in the metabolism of glucose through polyol pathways and that this may play a role in the development of diabetic sequelae.

C-reactive protein. Properties and biological action with particular reference to systemic lupus erythematosus.

A dramatic increase in serum C-reactive protein levels occurs in response to specific bacterial infection or tissue damage. This protein forms part of the acute-phase response, and it appears to function as an independent but relatively nonspecific part of the immune response. It has many properties in common with specific IgG. Absence of an adequate C-reactive protein response may play a role in the pathogenesis of systemic lupus erythematosus.

Lung function and plasma levels of thromboxane B2, 6-ketoprostaglandin F1 alpha and beta-thromboglobulin in antigen-induced asthma before and after indomethacin pretreatment.

The effect of specific antigen challenge on the lung function of eight allergic asthmatic patients after placebo and indomethacin pretreatment has been investigated. Plasma levels of thromboxane B2(TxB2), metabolite of thromboxane A2, 6-keto-PGF1 alpha, metabolite of epoprostenol, (prostacyclin, PGI2) and beta-thromboglobulin (beta TBG) following antigen challenge in these eight patients have also been measured after placebo and indomethacin pretreatment. Each patient underwent two antigen inhalations 1 week apart. One challenge took place after 4 days pretreatment with indomethacin capsules 25 mg four times daily, and the other took place following 4 days placebo pretreatment, one matched capsule four times daily. The order of administration was random but balanced and blind with respect to the patient. Following placebo pretreatment two patients presented with an early antigen response only, four presented with a biphasic antigen response and two presented with a delayed antigen response only. The asthmatic response for each patient was consistent on re-exposure. Indomethacin pretreatment suppressed the delayed antigen induced asthmatic response. This suppression was reproducible. There was a rise in plasma TxB2 levels on antigen challenge following placebo pretreatment but not following indomethacin pretreatment, whereas there was a rise in 6-keto-PGF1 alpha after antigen challenge following indomethacin but not placebo pretreatment. No significant change in plasma beta TBG or platelet counts from control values was observed following antigen challenge with either placebo or indomethacin pretreatment. It is suggested that the production of PGI2 and suppression of TxA2 by indomethacin pretreatment contribute to the suppression of the delayed antigen induced asthmatic response and that platelets play a minimal role in this process.

Evidence of hypoxaemia and distribution of minor haemoglobin components in the cord blood of neonates born to diabetic mothers.

The oxygenation status of normal and diabetic (White's classification A and B) mothers and their neonates was investigated. The diabetic patients had significantly increased maternal total haemoglobin and P50 values and the percentage of fetal haemoglobin was increased in cord blood taken at delivery in this group. There was a significant positive correlation between maternal P50 values and the percentage of fetal haemoglobin in cord blood. The cord blood 2,3-diphosphoglycerate, inorganic phosphate and P50 values were also increased in neonates born to diabetic mothers and these infants had a significantly increased birth weight ratio. The results are consistent with the presence of fetal hypoxaemia in the late third trimester of diabetic pregnancy in which obvious maternal vascular disease has been excluded.

Prostaglandin effects in the neuroendocrine mammalian brain.

Various prostaglandins (PGs) have been found in several areas of the brain. PGs of the E series have been found in the pituitary and pineal glands and the median eminence, and they have been shown to influence hypothalamic endocrine-release characteristics and release of melatonin from the pineal gland. It has been suggested that they may act, along with membrane phospholipids, as a link between neuronal depolarization, calcium uptake and neurotransmitter release. They may also influence postsynaptic effects of neurotransmitters. These latter effects may be due to interaction with membrane phospholipid- and cyclic nucleotide-induced changes of specific protein kinases. The PGs may act as intracellular mediators of neuro-endocrine control.

Evidence of hyperinsulinaemia and hypoxaemia in the cord blood of neonates born to mothers with gestational diabetes.

Increased cord blood C-peptide levels in neonates born to mothers with gestational diabetes (GD) were directly correlated with the increased relative birth weight ratio (BWR) of these neonates. In addition, the percentage oxygen saturation of the cord blood was inversely correlated with cord blood C-peptide levels and with the relative BWR. These correlations were absent in neonates delivered to normal mothers. The results indicate the presence of both hyperinsulinaemia and mild hypoxaemia in neonates of mothers with GD. In poorly controlled diabetic pregnancy this hypoxaemia may constitute an important fetal risk factor.

Neonatal pancreatic function in infants born to mothers with gestational and overt diabetes.

Neonatal pancreatic function was assessed in infants born to non-diabetic mothers and to mothers with well-controlled gestational diabetes (GD) and overt diabetes (OD) using cord blood C-peptide estimations and the calculation of cord C-peptide/glucose ratios. Exaggerated pancreatic function was present in infants born to mothers with GD. In these infants the increased cord C-peptide values and cord C-peptide/glucose ratios correlated with their increased birth weight ratios. These results could not be explained on the basis of maternal hyperglycaemia and a possible intrinsic difference in pancreatic response between infants born to mothers with GD and those born to mothers with OD is suggested.

Methylprednisolone and the adult respiratory distress syndrome.

Total hip replacement was carried out on 22 patients under general anaesthesia. Of these, 10 were pretreated with methylprednisolone (30 mg/kg); 1 of these developed the adult respiratory distress syndrome (ARDS) and had high levels of thromboxane B2 (TXB2) 5 minutes after fixation of the femoral prosthesis and at the end of the operation. The other 12 patients served as controls; 5 of them developed ARDS and had statistically significant higher TXB2 levels than the other 7 control patients who remained well. All patients who did not develop ARDS had low TXB2 levels. TXB2 and beta-thromboglobulin levels followed the same trend and there was good correlation (r=0,6806; P less than 0,01) at the end of the operation in the control group patients who developed ARDS. There was no statistical difference in 6-keto-PGF1 alpha levels between the patients who developed ARDS and those in the control group who remained well. Steroids reduce arachidonic acid metabolism by inhibiting the release of substrate for cyclo-oxygenase and lipoxygenase activity. Patients prone to ARDS thus benefit from methylprednisolone administration.