Inhibitory effects of synthetic rat C-peptide 1 on insulin secretion in the isolated perfused rat pancreas

The effects of synthetic rat C-peptide 1 on insulin secretion from the isolated perfused rat pancreas was studied. The perfusion technique was according to the procedure described by Grodsky et al (1963) with a few modifications. After about 20 min of stabilization, the pancreas was perfused for 40 min with synthetic rat C-peptide 1 (100 ng/ml), during which (at 20 min) glucose concentration was switched from 2.7 to 16.6 mM. Insulin response to glucose (16.6 mM) was significantly decreased by the addition of the rat C-peptide 1 in advance when compared with those not pretreated with the C-peptide. In other experiments, the pancreas was exposed to glucose infusion (16.6 mM) for 60 min. 20 min after the start of glucose infusion, the C-peptide (100 ng/ml) was interposed for 20 min. The insulin secretion was reduced by the addition of the C-peptide. It is postulated that the C-peptide may have a role in the regulatory mechanism of the insulin secretion.

Effect of althesin (CT-1341) on thyroid-adrenal function in man

The effects of althesin on adrenocortical and thyroid function were investigated by measuring plasma concentrations of cortisol, thyroxine (T4) and free thyroxine index (FTI) in 29 surgical patients. Althesin did not change the plasma cortisol concentrations from the preanaesthetic control value; however, the concentrations increased significantly after the start of surgery and thereafter. Althesin anaesthesia per se decreased slightly, but significantly, plasma T4 concentration, but did not influence the FTI value. The surgical operation increased the FTI value slightly but significantly. Our data would suggest that Althesin anaesthesia can be used in patients who have abnormal adrenocortical or thyroid activity.

Secretory regulation of endocrine pancreas: Cyclic AMP and glucagon secretion

Activation of adrenergic beta receptors has been found to stimulate insulin release in vitro that may be mediated through the augmentation of cyclic AMP in the beta cell. The activation of adrenergic alpha receptors in the beta cell inhibits the insulin release. The present studies have shown that isoproterenol (0.62 mug/ml) and sodium dibutyryl cyclic AMP (50 mug/ml) stimulate the insulin secretion and inhibit the glucagon secretion in the presence of 50 mg/100 ml glucose by the isolated pancreatic perfusion of the rat, while norepinephrine (0.5 mug/ml) inhibits the insulin secretion induced by 150 mg/100 ml glucose and stimulates the glucaton secretion. Theophylline (50 mug/ml) does not stimulate the insulin and the glucagon secretion. When norepinephrine is added to theophylline, the output of glucagon does not occur. From these results it can be deduced that the pancreatic alpha cell function may be inhibited by elevation of intracellular cyclic AMP, in contrast to the beta cell function which is stimulated by an increment of cyclic AMP.

Cation content and transport characteristics of the sickle-cell erythrocyte and their relationship with structural changes in the membrane

1. The intra-erythrocytic concentrations of sodium and potassium and the water content have been determined for haemoglobin (Hb) SS cells and negroid Hb AA cells.

2. The erythrocyte concentration of sodium was 40% higher and potassium 10% lower in the Hb SS than in the Hb AA cells. The cell water expressed as % weight of cell (corrected for trapped plasma) was identical for both cell types.

3. Normal Caucasian erythrocytes with Hb AA contained 40–50% less sodium but about the same potassium concentration as negroid Hb AA cells.

4. Potassium efflux into buffered iso-osmotic sucrose medium was much faster in Hb SS than in negroid Hb AA cells; ouabain-sensitive active sodium transport was twice as fast in the sickle-cell erythrocytes. Passive sodium efflux of erythrocytes suspended in a physiological medium was similarly faster in Hb SS cells.

5. Under the conditions of the experiments not less than 85% of the Hb SS erythrocytes appeared biconcave. Electron-microscopic examination of ultra-thin sections of Hb SS cells revealed marked discontinuities in the membrane. This suggests definite membrane alterations, which have probably resulted from the sickling-unsickling cycles occurring during the life-span of the cells.

6. It is suggested that the enhanced active sodium transport in the Hb SS erythrocyte is secondary to the augmented passive cation efflux, which in turn results from the leakiness of the erythrocyte membrane produced by the sickling-unsickling process.