Adrenergic inhibition of insulin secretion involves pertussis toxin-sensitive and -insensitive mechanisms

We studied the involvement of Bordetella pertussis toxin (PTX)-sensitive G proteins in the inhibition by adrenaline of insulin secretion from the isolated rat pancreas. The -90% inhibition induced by adrenaline (0.05 microM) was partially abolished after in vivo PTX pretreatment. The residual inhibitory effect of adrenaline in PTX-pretreated rats was suppressed by the alpha 2-adrenoceptor antagonist, yohimbine, but was not modified by the alpha 1-adrenoceptor antagonist, prazosin. Thus, the alpha 2-inhibitory effect of adrenaline on B-cells is mediated by both PTX-sensitive and PTX-insensitive mechanisms.

Binding characteristics of the new thromboxane A2/prostaglandin H2 receptor antagonist [3H]BAY U 3405 to washed human platelets and platelet membranes

The new thromboxane A2 antagonist [3H]BAY U 3405 was characterized for its binding to washed human platelets and platelet membranes. In washed platelets the specific binding was reversible, selective and stereospecific, but not saturable. The dissociation constant (Kd) was 6 +/- 2.5 nM, the number of specific binding sites 1177 +/- 306 per platelet. Three structurally different thromboxane A2 (TXA2)/prostaglandin H2 (prostaglandin endoperoxide) (PGH2) receptor ligands completely inhibited the specific binding of [3H]BAY U 3405 in a concentration-dependent manner, indicating that the observed high affinity binding site is the TXA2/PGH2 receptor. In platelet membranes, however, specific [3H]BAY U 3405 binding showed saturability in addition to reversibility, selectivity, and stereospecifity. The Kd of the binding was 9.6 +/- 2.3 nM in kinetic studies and 8.7 +/- 3.7 nM in saturation studies, the inhibition constant (Ki) was 10 +/- 1.1 nM in displacement studies. The TXA2/PGH2 receptor agonists U 46619 and CTA2, and the antagonists Daltroban (BM 13505), I-PTA-OH and SQ 29548 all completely inhibited the specific binding of [3H]BAY U 3405 thus defining the observed binding site as the TXA2/PGH2 receptor. In conclusion, the data suggest that the previously reported TXA2 antagonism of BAY U 3405 is mediated by binding to a specific high affinity binding site of human platelets and platelet membranes that represents the TXA2/PGH2 receptor.

P2y purinoceptor responses of beta cells and vascular bed are preserved in diabetic rat pancreas

1. To investigate the effect of experimental diabetes on the P2y purinoceptor responses of pancreatic beta-cells and vascular bed, we used adenosine-5'-O-(2-thiodiphosphate) (ADP beta S), a potent and stable P2y agonist. This work was performed in the isolated perfused pancreas of the rat. 2. Diabetes was induced by streptozotocin (66 mg kg-1, i.p.). Five weeks after the induction of diabetes, on the day of pancreas isolation, the animals displayed marked hyperglycaemia (37.6 +/- 2.7 mM). Age-matched rats were used as controls. 3. Insulin response to a glucose stimulation from 5 to 10 mM was completely lost and stimulation of insulin release by the sulphonylurea, tolbutamide (185 microM), was drastically impaired in the diabetic pancreas (maximum responses were 1.5 +/- 0.4 and 7.0 +/- 1.4 ng min-1 for diabetic and age-matched rats respectively). 4. In contrast, in the diabetic pancreas ADP beta S (15 microM), infused in the presence of glucose 5 mM, elicited an immediate and significant insulin release similar to that observed in the age-matched pancreas (maximum responses were 7.6 +/- 1.5 and 6.7 +/- 1.3 ng min-1 respectively). This ADP beta S stimulating effect occurred independently of the glucose concentration (5, 8.3 and 28 mM) in the diabetic pancreas. On pancreatic vascular resistance, ADP beta S induced a similar vasodilatation in diabetic and age-matched rats. 5. In conclusion, ADP beta S retains its insulin stimulatory and vasodilator effects in experimental diabetes; P2y purinoceptors could therefore be considered as a new target for the development of antidiabetic drugs.

pH dependency of the binding of [3H]BAY U 3405 and various non-labelled ligands to the thromboxane A2/prostaglandin H2 receptor of human platelet membranes

[3H]BAY U 3405 was used to characterize the effect of acidic and alkaline pH values on the binding of the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor of human platelet membranes. The specific binding of [3H]BAY U 3405 largely increased upon acidification up to pH 5.8. Saturation binding studies revealed an increase in binding affinity without change in the number of binding sites. At pH 7.4 the Kd was 8.7 +/- 3.7 nM (Bmax = 6.6 +/- 0.6 pmol/mg protein) compared to 1.2 +/- 0.2 nM (Bmax = 6.1 +/- 0.6 pmol/mg protein) at pH 5.8. A more than 10-fold higher rate of association was observed at pH 5.8 compared to pH 7.4, while the rate of dissociation showed only minor changes. The kinetically derived dissociation constant was 1 nM (pH 5.8) and 9.6 nM (pH 7.4). The pH dependency of the binding of structurally different non-labelled ligands to the TXA2/PGH2 receptor was evaluated by inhibition studies at pH 5.8 and pH 7.4. BAY U 3405, daltroban, CTA2, and U 46619 showed significantly higher affinities at pH 5.8. In contrast, I-PTA-OH and GR 32191 had a higher affinity at pH 7.4. No significant difference was seen with SQ 29548 at the observed pH values. A second protonable group within the molecules I-PTA-OH, GR 32191, and SQ 29548 might be responsible for the observed differences.

The output and outcome of two types of formal health structures--health post and creche--for nutritional interventions for preschool children in two urban, low-income communities of Belo Horizonte, Brazil (1986)

In order to observe the nutritional and health status of pre-school children, the output and outcome of two formal health services -health post and creche- for this vulnerable group in two urban slum areas of Belo Horizonte, Brazil were studied in 1986. A total of 420 children were surveyed, 254 children randomly selected from the communities and 156 from three creches. Growth monitoring was not undertaken systematically, and mothers did not have growth control charts. When a child had diarrhea, mothers preferred to apply home remedies or to buy proprietary drugs rather than to consult medical personnel. 72% of mothers reported using ORT, and 11% suspending feeding completely. After three month of life, 50% of infants were receiving some breast milk. 75% of children were immunized completely. The prevalence of health and nutrition indicators such as anemia (50% vs. 30%), parasitosis (87% vs. 70%), and stunting (28% vs. 20%) was worse in the creches than in the communities.

Evidence for a glutamate receptor of the AMPA subtype which mediates insulin release from rat perfused pancreas

1. The effect of L-glutamate has been studied on insulin secretion by the isolated perfused pancreas of the rat. The glutamate receptor subtype involved has been characterized. 2. In the presence of a slightly stimulating glucose concentration (8.3 mM), L-glutamate (5 x 10(-5)-4 x 10(-3) M) induced an immediate, transient and concentration-dependent insulin response. On the other hand, in the presence of a non stimulating glucose concentration (2.8 mM), L-glutamate (10(-3) M) did not modify the basal insulin secretion. 3. The three non-NMDA receptor agonists, kainate (10(-4)-10(-3) M), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA, 5 x 10(-5)-10(-4) M) and quisqualate (5 x 10(-6)-5 x 10(-5) M) all provoked a transient and concentration-dependent insulin response from pancreas perfused with 8.3 mM glucose. Compared with glutamate, kainate exhibited a similar efficacy, whereas AMPA and quisqualate elicited only a 3 fold lower maximal insulin response. In contrast, NMDA (10(-4)-10(-3) M) was ineffective. 4. An antagonist of non-NMDA receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5 x 10(-5) M) totally prevented the stimulatory effect of L-glutamate (4 x 10(-4) M) and kainate (2 x 10(-4) M). In contrast, the NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ((+) MK801) was without effect. 5. The insulin secretory effect of glutamate (4 x 10(-4) M) was not affected by atropine (3 x 10(-7) M) or tetrodotoxin (3 x 10(-6) M). 6. Quisqualate at a high maximally effective concentration (4 x 10(-4) M) inhibited glutamate (10(-3) M) or kainate (4 x 10(-4) M)-induced insulin release. 7. This study shows that L-glutamate stimulates insulin secretion in rat pancreas, by acting on an excitatory amino acid receptor of the AMPA subtype.

Organ- and age-specific replication of polyomavirus in mice

A novel organ- and age-specific pattern of polyomavirus DNA replication in mice is described. Two broadly defined classes of response to polyomavirus infection were observed: class I organs (mammary gland, bone, and skin) responded with high levels of replication in neonate mice and moderate levels in adults; class II organs (kidney, liver, and lung) responded with high levels in neonates and very low levels in adults. Thus, aging affected replication in all organs, and organ specificity was superimposed on this age-related decrease. We argue that the organ- and age-specific pattern likely reflects in part the activities of a multiplicity of general or tissue-specific, age-dependent transcription factors, which modulate viral replication or viral transcription or both. Interestingly, the majority of tumors in mice infected as neonates or as immunoincompetent adults originate in class I organs, suggesting that the ability to replicate in adult tissues is an important factor controlling polyomavirus oncogenesis. From the analysis of the infection process in adult mammary glands, a novel mode of polyomavirus infection emerged which contrasts with that derived from observations of tissue culture systems. A nonproductive infection was seen, characterized by very low levels of live virus (in the range of 10(-4) PFU per cell) and maintenance of the viral genome in an unintegrated, moderately replicating state. Maintenance of the viral genome was accomplished without integration into host cell DNA in all three tumor-prone organs, both prior to as well as beyond oncogenesis.

Arachidonic acid induces an increase in the cytosolic calcium concentration in single pancreatic islet beta cells

The insulin secretagogue D-glucose induces both accumulation of nonesterified arachidonic acid (35 microM) in pancreatic islets and a rise in beta cell cytosolic [Ca++]i. Arachidonate amplifies both voltage-dependent Ca++ entry in secretory cells and depolarization-induced insulin secretion. Here, arachidonate induced a biphasic rise in [Ca++]i of Fura-2AM loaded beta cells which increased with arachidonate concentration (5-30 microM), was reversed upon washout, and was unaffected by the arachidonate oxygenase inhibitor BW755C. The sustained phase of the rise was abolished by removal of extracellular Ca++ and amplified by depolarization with KCl. The accumulation of nonesterified arachidonate in islets stimulated by D-glucose may therefore promote the D-glucose-induced rise in beta cell [Ca++]i.

Evidence for a direct stimulatory effect of cibenzoline on insulin secretion in rats

The effect of cibenzoline succinate, a new antiarrhythmic agent, was studied on insulin secretion in rats. Experiments were performed both in vivo and in vitro using two preparations: the isolated perfused pancreas and isolated islets. In anaesthetized rats, cibenzoline was able to increase plasma insulin levels and to reduce glycaemia. These effects were observed at 1 mg/kg i.v. in fed rats and at 3 mg/kg i.v. in fasted rats. In the isolated pancreas perfused in the presence of a slightly stimulating glucose concentration (8.3 mM), cibenzoline (2 and 6 microM) elicited a progressive and sustained insulin response in a concentration-dependent manner. In the presence of a non-stimulating glucose concentration (4.2 mM), cibenzoline was ineffective at 2 microM and slightly increased basal insulin release at 6 microM. In isolated islets incubated with 8.3 mM glucose, cibenzoline (6 and 20 microM) caused a concentration-dependent stimulation of insulin release. It is concluded that cibenzoline stimulates insulin secretion by a direct action on pancreatic B cells in rats.

pH-dependent binding of the TXA2/PGH2-receptor of human platelet membranes to various ligands

[3H]-BAY U 3405 was used to characterize the pH-dependency of the binding of various ligands to the TXA2/PGH2-receptor of human platelet membranes. Maximum binding of [3H]-BAY U 3405 is achieved at pH 5.8. In inhibition studies the ligands Daltroban, CTA2, and U 46619 also show a higher affinity at pH 5.8 compared to pH 7.4. In contrast, the ligands I-PTA-OH and GR 32191 have a higher affinity at pH 7.4. No difference is seen with SQ 29548. The ligands I-PTA-OH, GR 32191, and SQ 29548 have a second protonable group in common, which is thought to be the reason for the different pH-dependent binding.

Endogenous atrial natriuretic factor is involved in the natriuresis following sodium loading in rats with chronic heart failure

STUDY OBJECTIVE

Plasma levels of atrial natriuretic factor are increased in chronic heart failure; however, it is still controversial whether these raised levels contribute to the diuresis and natriuresis in this setting. To address this issue the potential contribution of endogenous atrial natriuretic factor in the renal excretion of a moderate oral sodium load in a rat model of chronic heart failure was studied.

DESIGN

A monoclonal antibody against atrial natriuretic factor was used for specific antagonisation of its in vivo effects. Animals were subjected to oral sodium loading (30 ml.kg-1 0.9% NaCl, 2.5% dextrose) at baseline, immediately after, and 5 d after injection of monoclonal antibody or control solvent.

EXPERIMENTAL MATERIAL

Sham operated rats and rats with chronic heart failure due to myocardial infarction (infarct size 35(SEM 4)% of left ventricle) were studied 4-5 weeks after surgery.

MEASUREMENTS AND MAIN RESULTS

The renal excretion of cyclic guanosine monophosphate (cGMP), which represents a specific marker for the activation of the atrial natriuretic factor system, was markedly increased in infarcted rats, at 17.9(SEM 3.4) vs 5.8(1.2) nmol.kg-1, p less than 0.01. Atrial natriuretic factor antibody given immediately before sodium loading reduced the natriuretic response (0-4 h period) in infarcted rats from 1270(171) to 805(76) mumol.kg-1 (p less than 0.01) but not in sham operated animals. Similarly, the excretion of cGMP was only decreased by atrial natriuretic factor antibody in infarcted rats, from 29.8(6.3) to 20.7(3.7) nmol.kg-1. The reduction in sodium and cGMP excretion in infarcted rats was confirmed with a purified antibody preparation.

CONCLUSIONS

Endogenous atrial natriuretic factor appears to be involved in the natriuresis following a moderate oral volume load in chronic heart failure. Thus the raised concentrations found in chronic heart failure may contribute to the regulation of urinary sodium excretion under these conditions despite the fact that the diuretic effects of exogenous atrial natriuretic factor are attenuated in chronic heart failure.

Measurement of regional myocardial blood flow with multiple colored microspheres

BACKGROUND

The use of radioactive microspheres (RM) for the measurement of regional myocardial blood flow (RMBF) is limited and inaccessible to many investigators due to radiation safety concerns and radioactive waste disposal problems. Therefore, a new method for the measurement of RMBF using colored microspheres (CM) was developed.

METHODS AND RESULTS

Polystyrene spheres (diameter, 15 +/- 0.1 [SD] micron; density, 1.09 g/ml) were dyed with one of five colors. With the injection of CM into the left atrium or into a coronary perfusion line, RMBF and its distribution can be determined. CM are extracted from the myocardium and blood by digestion with potassium hydroxide and subsequent microfiltration. The dyes are then recovered from the CM within a defined volume of a solvent, and their concentrations are determined by spectrophotometry. The separation of composite absorbance spectra by spectrophotometry with the CM technique was as good as the separation of energy spectra by a gamma-counter using the RM technique. Leaching of dye from the CM was less than 0.1% during a 2-month period in vitro. Significant leaching of dye from the microspheres also did not occur during 8 hours in the blood and myocardium of four anesthetized dogs in vivo. For further validation of this method, pairs of CM and RM (15.5 +/- 0.1 [SD] microns) were simultaneously injected under five different RMBF conditions (range, 0-10 ml/[min.g]) into the left anterior descending coronary artery of four anesthetized pigs, with coronary inflow as a flow reference, or into the left atrium of four anesthetized dogs using aortic blood withdrawal as a reference. The relation between RMBF determined by CM and RM was CM = 0.01 + 1.00.RM (r = 0.98, n = 1,080 data points) in the pigs, and CM = -0.19 + 0.92.RM (r = 0.97, n = 1,813 data points) in the dogs.

CONCLUSIONS

Measurement of RMBF with CM yields values very similar to those of RM. Their use is less expensive and avoids all the disadvantages related to radioactivity, thus offering an alternative method for as many as five RMBF measurements in a single experiment.

Diabetes alters the responses of glucagon secreting cells and vascular bed to isoprenaline and forskolin in vitro in rat pancreas

Diabetes is known to disturb pancreatic glucagon secreting alpha cell function and blood flow control. In a previous study we could show that streptozotocin-induced diabetes suppressed adenosine stimulating effect on glucagon secretion and reduced its vasodilatory properties; since the nucleotide exerts these effects by activation of A2 purinergic receptors known to be positively coupled to adenylate cyclase, we investigated the effect of streptozotocin diabetes on the responses of alpha cells and vascular bed to stimulation of adenylate cyclase through 2 different ways: 1) with isoprenaline by activation of beta adrenergic receptor positively coupled to the enzyme; 2) with forskolin by direct activation of the catalytic unit of adenylate cyclase. In the isolated perfused pancreas of normal rats, isoprenaline (0.01 microM) or forskolin (1 microM) induced a +200 to +300% increase of glucagon secretion and a 20 to 30% increase of pancreatic vascular flow rate. In pancreas of 5-week diabetic rats, alpha cell responses to isoprenaline and forskolin were completely suppressed and the vasodilatory effects of both drugs were significantly reduced (-35 to -50%). Long term in vivo insulin treatment with glycaemia normalization was able to correct both defects. We can conclude that streptozotocin diabetes suppresses glucagon secretion and reduces pancreatic vasodilatation not only in response to activation of receptors positively coupled to adenylate cyclase but also to a direct activation of this enzyme.

Late diagnosis of hip dislocation in infants

To determine the rate of late diagnosis of hip dislocations in infants, 26,455 newborns were examined by or under the supervision of the authors from 1976 to 1988. The incidence of examinations positive for dislocated or dislocatable hips was 3.8/1,000. The incidence of known late cases was 4/26,455 (0.2/1,000). Because follow-up of all initial examinations was not possible, this rate is probably artificially low. Hip screening programs with direct pediatric orthopaedic supervision can be successful, but late cases will still occur.

The relationships between selected anthropometric and socio-economic data in schoolchildren from different social strata in Rio de Janeiro, Brazil

The nutritional status according to anthropometric data was assessed in 756 schoolchildren from 5 low-income state schools and in one private school in the same part of Rio de Janeiro, Brazil. The prevalence of stunting and wasting (cut-off point: less than 90% ht/age and less than 80% wt/ht) ranged in the public schools from 6.2 to 15.2% and 3.3 to 24.0%, respectively, whereas the figures for the private school were 2.3 and 3.5%, respectively. Much more obesity was found in the private school (18.0%) than in the state schools (0.8-6.2%). Nutritional problems seem to develop more severely in accordance with the increasing age of the children. Therefore it appears advisable to assess schoolchildren within the context of nutritional surveillance system.