Human C-peptide in normal and diabetic subjects

Concentrations of human C-peptide, IRI (immunoreactive insulin) and glucose were determined during oral glucose tolerance test (1.75 g glucose/kg ideal body weight) in 14 normal persons (N), 9 maturity-onset diabetics (DI) and 10 insulin-requiring diabetics (DII) never treated with insulin and in 3 formerly insulin treated diabetics. The mean fasting levels of C-peptide and IRI in the first three groups were: N: 0.37 +/- 0.02 nM and 0.048 +/- 0.009 nM, DI: 0.86 +/- 0.17 nM and 0.11 +/- 0.029 nM, DH: 0.37 +/- 0.04 nM and 0.063 +/- 0.009 nM. One hour after oral glucose ingestion, the respective values increased to: N: 2.53 +/- 0.20 nM and 0.52 +/- 0.077 nM, DI: 2.49 +/- 0.31 nM and 0.49 +/- 0.11 nM, DH: 0.49 +/- 0.05 nM and 0.11 +/- 0.014 nM. Although secreted from the pancreas in equimolar concentrations, the molar ratio of C-peptide to insulin in peripheral blood was about 7 in the fasting state, falling to about 5 in the glucose stimulated condition. Maturity-onset diabetics had higher fasting levels of C-peptide than normal subjects, in agreement with the IRI levels. Three patients previously treated with insulin and having insulin antibodies showed C-peptide responses significantly below the normal range. In one of these patients, the test was repeated 9 months later when the insulin antibodies had disappeared, and the C-peptide response observed at that time was much higher. It is suggested that insulin antibodies cause an impaired IRI - and consequently C-peptide response - by constantly removing insulin from the granules in the B-cell. In normal humans the peripheral C-peptide responses to the oral glucose load showed less relative variation than do the insulin responses. Therefore, a radioimmunoassay for C-peptide in addition to the assay for insulin will provide supplementary information on insulinsecretion.     

Human chorionic gonadotropin-like substance in plasma of normal nonpregnant subjects and women with breast cancer

To understand ectopic hormone secretion in cancer we compared the plasma concentrations of the hCG-like substance in normal nonpregnant subjects and in women with breast cancer. In 45 normal men the plasma concentrations did not vary with age (median, 5 pg/ml; range, less than 3-169) whereas in 45 normal women they increased after menopause (median, 48 pg/ml; range, less than 5 -569, n = 20, P less than 0.0001). In 56 women with breast cancer the plasma concentrations of the hCG-like substance after menopause were much higher than in normal women (median, 202 pg/ml; range, 14-1561; n = 35; P less than 0.001), with no abnormally high pituitary gonadotropin values and no relationship with the tumor burden (same median after mastectomy, 198 pg/ml; n = 21). This hCG-like substance was glycosylated and similar to standard hCG according to molecular size, ionic strength, and immunoreactivity. Our data are compatible with the following conclusions: 1) the plasma concentration of the hCG-like substance is normally very low but dependent on gonadal function in women. Its source might be the pituitary gland or peripheral tissues. 2) Its concentration is much increased in postmenopausal women with breast carcinoma. This increase is found with normal pituitary gonadotropin values and is independent of the tumor burden, suggesting it is of extrapituitary and nontumoral origin.     

The effect of dopaminergic antagonists on plasma aldosterone in normal subjects and patients with hypopituitarism

Although angiotensin II, ACTH and potassium are generally acknowledged as major factors in regulating the influences on aldosterone secretion, it has recently been reported that dopamine is a potent inhibitor of aldosterone secretion in man and animals. In the present study, we investigated the effect of two kinds of dopaminergic receptor antagonists, metoclopramide and sulpiride, on plasma aldosterone concentration (PAC) and serum prolactin (PRL) in man. Normotensive volunteers and patients with hypopituitarism were injected with metoclopramide (10 mg i.v.) or sulpiride (10 mg i.m.). In normal volunteers, metoclopramide increased both PAC and PRL levels, and showed a maximum level at 30 minutes after injection. In patients with hypopituitarism, PAC tended to increase without change of PRL, which suggested that the increase in PAC by metoclopramide might have a direct inhibitory effect on the dopaminergic receptor in the adrenal gland. Moreover another antagonist, sulpiride also increased PRL but contrary tended to decrease PAC. These results suggested that PRL responses to both inhibitors were mediated by dopaminergic antagonist activity at the level of pituitary receptors. However dopamine-induced modulation of aldosterone secretion may be different from that of PRL at dopaminergic receptors. These results suggested that modulatory inhibition of aldosterone secretion by dopamine may be affected by difference of affinity of dopamine to receptor as organ specificity, or different affinity of metoclopramide and sulpiride to adrenal dopamine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Direct measurement of plasma proinsulin in normal and diabetic subjects

Over 650 separate plasma samples from ninety-five subjects in whom oral glucose tolerance tests were performed were analyzed for glucose, total immunoreactive insulin (TIR) and immunoreactive proinsulin (IRP) content. These subjects were divided into seven groups: (1) young normal subjects (twenty to forty years old), (2) older normal subjects (forty to sixty years old), (3) young diabetic subjects (twenty to forty years old), (4) older diabetic subjects, normal weight (forty to sixty years old), (5) older diabetic subjects, obese (forty to sixty years old), (6) obese subjects (forty to sixty years old), and (7) borderline diabetic subjects. IRP levels, total IRP response and the ratio of IRP:TIR response were established for each group. Age apppeared to be a significant factor in influencing IRP levels in the normal subjects since the older subjects (group 2) had a significantly greater IRP response and IRP: TIR response than the younger subjects (group 1). Obesity and carbohydrate intolerance were each associated with slightly increased IRP levels, but the combination of obesity and carbohydrate intolerance was associated with marked increases in IRP levels and a significant increase in IRP:TIR response. The duration of diabetes may be important in the pattern of IRP release since rises in IRP levels after the oral intake of glucose occurred earlier (by thirty minutes) in both the young diabetic and borderline diabetic subjects (groups 1 and 7) than in the other groups.     

Diurnal changes in plasma lipoproteins in normal subjects and diabetics

Summary Significant diurnal variations in levels of total plasma cholesterol, HDL cholesterol and LDL cholesterol were found in the majority of 12 normals, 13 maturity onset and 14 insulin requiring diabetics. The variations in total cholesterol and its lipoprotein subfraction were more marked in diabetics. These variations were not correlated in either diabetic group with glucose control as assessed by the level of glycosylated haemoglobin. The significance of the diurnal changes in total plasma cholesterol and the lipoprotein subfractions in relation to arteriovascular disease is discussed.     

Lipoproteins and plasma cholesterol esterification in normal and diabetic subjects

Serum lipoproteins, separated by preparative ultracentrifugation and the activity of the plasma enzyme lecithin: cholesterol acyltransferase (LCAT) have been measured in insulin-dependent diabetics, non-insulin-dependent diabetics and in age-matched non-diabetic controls. In the insulin-dependent diabetics, mean total serum cholesterol and high density lipoprotein cholesterol (HDL-C) concentrations were significantly higher than in controls. Non-insulin-dependent diabetics had significantly raised total triglycerides and cholesterol, but HDL-C levels were essentially normal. The increased low density lipoprotein cholesterol (LDL-C) in both diabetic groups was statistically significant in men. A methodological study of HDL separation techniques was carried out to facilitate interpretation of these findings. Mean LCAT activity, by a method reflecting combined enzyme and substrate effects was significantly increased in these diabetic groups. The results confirm recent reports of a raised HDL-C in those insulin-dependent diabetics who are prone to coronary heart disease.     

Disappearance of bovine insulin from plasma in diabetic and normal subjects

Disappearance curves for radioiodinated and immunoreactive bovine insulins were determined and analyzed in 30 subjects (5 normal volunteers and 25 diabetic patients). Simultaneous determinations were made of blood glucose and of insulin binding by insulin antibodies. There was significant negative association between the disappearance of bovine insulin from plasma and the insulin-binding level of circulating insulin antibodies. The presence of diabetes, the clinical character of the diabetes (whether stable or unstable), and the presence of chronic diabetic complications, of themselves, had no apparent significant influence that could be separated from the effect of circulating levels of insulin-binding antibodies on the disappearance of bovine insulin from plasma.     

Aerosol therapy with Sch 1000. Short-term mucociliary clearance in normal and bronchitic subjects and toxicology in normal subjects.

The anticholinergic bronchodilator drug, Sch 1000, was administered as an aerosol by a metered-dose inhaler (200 microgram) to six normal and six bronchitic subjects. The short-term effect on mucociliary clearance was assessed and compared to a placebo (propellant and dispersal agent) in a double-blind crossover study. Mucociliary clearance in the normal group was significantly faster with administration of Sch 1000 than with placebo (P less than 0.01). There was no significant difference between the effects of administration of Sch 1000 and placebo on mucociliary clearance in the bronchitic group. Pulmonary function was significantly increased by therapy with Sch 1000 (as compared to administration of placebo) in the bronchitic group for two hours (P less than 0.05) and in the normal group for one hour (P less than 0.05). In another study, 12 normal subjects inhaled aerosols containing 40 microgram of placebo or 400 microgram of Sch 1000 from metered-dose inhalers on separate days in a randomized double-blind fashion. A significant sustained improvement in pulmonary function (P less than 0.05) and a transient fall in diastolic blood pressure were observed after administration of Sch 1000.     

beta-Endorphin stimulates plasma renin and aldosterone release in normal human subjects

To determine the effect of beta-endorphin on the renin-angiotensin-aldosterone system, human synthetic beta-endorphin (0.3, 1.0, and 3.0 micrograms/kg X min) was infused iv in normal subjects. Each dose was administered for 30 min, and a control infusion of 5% dextrose and water was given on another day. Ten subjects were studied recumbent and in balance while ingesting a 10-meq Na+ diet. Plasma renin activity (PRA), plasma aldosterone (PA), and plasma cortisol (F) were measured basally and every 30 min for 210 min. The increments in PRA and PA above basal significantly (P less than 0.05) increased (3.1 +/- 1.2 ng/ml X h and 12.2 +/- 5.3 ng/dl, respectively; P less than 0.05) at the end of the beta-endorphin infusion. beta-Endorphin also significantly (P less than 0.01) suppressed F levels. Since in the low salt study, beta-endorphin suppressed F release while stimulating renin secretion, an additional five subjects were pretreated with dexamethasone (0.5 mg every 6 h) and were studied in balance while ingesting a 200-meq Na+ diet to suppress the renin-angiotensin system. Significant (P less than 0.025) increments in PRA (2.1 +/- 0.7 ng/ml X h) and PA (4.1 +/- 1.7 ng/dl) levels above basal were again found during the sequential dose infusion of beta-endorphin (0.3, 1.0, and 3.0 micrograms/kg X min). However, PA elevations were sustained for at least 120 min after the beta-endorphin infusion was stopped despite a drop in PRA 90 min earlier. In additional studies, an attempt was made to define the minimal effective dose of beta-endorphin by 60-min infusions (0.03, 0.1, and 0.3 micrograms/kg X min) in subjects on a 200-meq Na+ diet who were dexamethasone pretreated. The PRA and PA levels rose significantly (P less than 0.05) above basal at the 0.3 micrograms/kg X min dose, but not at the 0.03 or 0.1 micrograms/kg X min dosage levels. There were no changes in blood pressure or potassium during either the 10 or 200-meq Na+ studies. Thus, beta-endorphin stimulates aldosterone release in vivo. However, the underlying mechanisms are complex, since renin levels also increased. The data suggest that the early aldosterone rise may be secondary to an increase in renin release, but renin cannot account for the sustained postinfusion elevations of aldosterone.     

A study of folic-acid-binding protein in normal subjects.

6 normal females were found to have a level of folic-acid-binding protein (FABP) in their sera (mean level 345 pg/ml). Lysates of their various leucocytes were assayed and FABP found exclusively in the polymorph fraction. The sera and lysates were fractionated by Sephadex G-200 gel column chromatography and the molecular weight of the FABP appeared to be approximately 40,000. A hitherto unreported inhibitory effect of heparin on folate binding was noticed. Studies have been performed on folic-acid-binding protein (FABP) in various pathological states, but the levels found in normal people are usually considered too low to permit investigation. In an earlier study [3], 6 normal females were found to have levels in excess of 300 pg/ml whilst the mean level of 94 controls was 76 pg/ml. Sera and leucocyte lysates from these people have been used to estimate the molecular weight of FABP in normal people.     

High-affinity folate binding in leukocyte lysate from normal subjects: effect of concentration of binding protein, temperature and pH

Folate binding in lysate prepared from leukocytes containing large amounts of the folate-binding protein was studied in equilibrium dialysis experiments (pH 7.4, 37 degrees C). Binding displayed positive cooperativity, and the binding affinity increased with decreasing concentration of binding protein (affinity constants in the range of 5 X 10(9) l/mol to 7 X 10(10) l/mol). Both phenomena could be interpreted in terms of ligand binding to a polymerizing system where the affinity of ligand for the oligomer is greater than its affinity for the polymer prevailing at high concentrations of the binding protein. Binding affinity was decreased at a low temperature (7 degrees C) and particularly at pH 5.0 where positive cooperativity also disappeared. The binder (Mr approximately 25,000-30,000) eluted in the front effluent after DEAE-Sepharose CL-6B chromatography of the lysate at pH 6.3.     

The relationship between plasma concentration and plasma disappearance rate of immunoreactive insulin in normal subjects

Summary To investigate the mechanism of insulin degradation in normal subjects, a kinetic model of insulin disappearance was constructed: insulin was assumed to be extracted from plasma by two independent processes, one saturable and one non-saturable. On the basis of these assumptions, a linear (non-proportional) relationship between steady-state plasma insulin concentration and steady-state plasma disappearance rate was predicted over the concentration range studied. Constant infusion experiments were performed on eight healthy normal subjects, normoglycaemia and fasting plasma C-peptide concentrations being maintained during the experiments. Agreement was found between the predictions of the model and the experimental results, and it is concluded that insulin degradation in normal subjects may be described in terms of two processes: one that is saturated at physiological plasma insulin concentrations and one that is apparently non-saturable over a wide concentration range.