The metabolic effects of biosynthetic human proinsulin in individuals with type I diabetes.

To assess the significance of deficiency of circulating proinsulin in patients with type I diabetes mellitus, we studied the metabolic effects of biosynthetic human proinsulin in 24 patients. After withdrawing insulin, an infusion of proinsulin to physiological plasma levels did not prevent elevations of plasma glucose or beta-hydroxybutyrate. During steady state infusions of insulin and proinsulin, 13.

Familial hyperinsulinemia due to a structurally abnormal insulin. Definition of an emerging new clinical syndrome.

We have identified a patient with mild diabetes, marked fasting hyperinsulinemia (89 to 130 microU of insulin per milliliter), and a reduced fasting C-peptide: insulin molar ratio of 1.11 to 1.50 (normal, greater than 4).

C-peptide as a measure of the secretion and hepatic extraction of insulin. Pitfalls and limitations.

The large and variable hepatic extraction of insulin is a major obstacle to our ability to quantitate insulin secretion accurately in human subjects. The evidence that C-peptide is secreted from the beta cell in equimolar concentration with insulin, but not extracted by the liver to any significant degree, has provided a firm scientific basis for the use of peripheral C-peptide concentrations as a semiquantitative marker of beta cell secretory activity in a variety of clinical situations. Thus, plasma C-peptide has proved to be extremely valuable in the study of the natural history of type 1 diabetes, to monitor insulin secretion in patients with insulin antibodies, and as an adjunct in the investigation of patients with hypoglycemic disorders.

Human insulin B24 (Phe----Ser). Secretion and metabolic clearance of the abnormal insulin in man and in a dog model.

We have already demonstrated that a hyperinsulinemic, diabetic subject secreted an abnormal insulin in which serine replaced phenylalanine B24 (Shoelson S., M. Fickova, M.

Metabolism of C-peptide in the dog. In vivo demonstration of the absence of hepatic extraction.

The in vivo hepatic metabolism of connecting peptide (C-peptide) in relation to that of insulin has not been adequately characterized. A radioimmunoassay for dog C-peptide was therefore developed and its metabolism studied in conscious mongrel dogs, with sampling catheters chronically implanted in their portal and hepatic veins and femoral artery. The hepatic extraction of endogenous C-peptide under basal conditions was negligible (4.

Predominance of renal and absence of hepatic metabolism of pancreatic polypeptide in the dog.

Pancreatic polypeptide (PP) metabolism was studied in the dog. Metabolic clearance rate (MCR) of PP was found to be 9.5 +/- 0.

Lack of glucagon response to hypoglycemia in type I diabetics after long-term optimal therapy with a continuous subcutaneous insulin infusion pump.

Counterregulatory hormonal responses were studied in six patients after 4-18 mo treatment with a continuous subcutaneous insulin infusion pump. In response to insulin-induced hypoglycemia, significant increases in epinephrine, norepinephrine, cortisol, and growth hormone were measured in all subjects, while in five of the six patients glucagon levels did not increase at all. The persistence of these abnormal glucagon responses despite long-term optimal glucose control suggests that they are not due to hyperglycemia per se, but are due rather to a specific alpha cell abnormality.

Plasma somatostatin 28 increases in response to feeding in man.

Tissue somatostatin-like immunoreactivity (SLI) consists of a number of molecular species including the cyclic tetradecapeptide or SRIF, an N-terminally extended form of SRIF termed somatostatin-28, as well as larger precursor peptides. The function and nature of circulating SLI is not well understood. In this report, we describe techniques for the definition of the components of plasma SLI in normal human plasma.

Differences in the hepatic and renal extraction of insulin and glucagon in the dog: evidence for saturability of insulin metabolism.

The metabolism of exogenously infused porcine insulin and glucagon was assessed concurrently in normal fasted dogs under anaesthesia. Hepatic and renal extraction of glucagon were 25.6 +/- 2.

Differential immunoreactivity of plasma glucagon components in man: studies with different glucagon antibodies.

To evaluate the relationship between glucagon antibody antigenic determinants and selective reactivity with plasma void volume (Vo) and lower molecular weight immunoreactive glucagon (IRG) components, we studied plasma IRG levels and molecular profiles in normal subjects and patients with disturbances in plasma glucagon levels using three glucagon antibodies, 30K and P7 raised against the whole peptide and antibody X4 raised against the C-terminal tryptic fragment of glucagon. In normal subjects and pancreatectomized patients, plasma IRG levels were 2- to 3-fold higher with the C-terminus-directed antibody X4 than with either 30K or P7, but in glucagonoma and uremic patients, this discrepancy was smaller. Gel filtration analysis revealed that these antibodies reacted identically with 3500 mol wt IRG and 9000 mol wt IRG in normal, glucagonoma, pancreatectomized, and uremic plasma.

Aldose reductase inhibition improves nerve conduction velocity in diabetic patients.

To assess the potential role of polyol-pathway activity in diabetic neuropathy, we measured the effects of sorbinil--a potent inhibitor of the key polyol-pathway enzyme aldose reductase--on nerve conduction velocity in 39 stable diabetics in a randomized, double-blind, cross-over trial. During nine weeks of treatment with sorbinil (250 mg per day), nerve conduction velocity was greater than during a nine-week placebo period for all three nerves tested: the peroneal motor nerve (mean increase [+/- S.E.

The in vivo metabolism of somatostatin 28: possible relationship between diminished metabolism and enhanced biological action.

We have compared the metabolism of infused somatostatin 14 (SS14) and somatostatin 28 (SS 28) in anesthetized dogs. After iv infusion of either peptide, plasma SS-like immunoreactivity (SLI) coeluted from Bio-Gel P10 columns with the corresponding synthetic peptide marker. The hepatic extraction, renal extraction, MCR, and plasma half-life of plasma SLI and after SS28 infusion were 11.

Relation of counterregulatory responses to hypoglycemia in type I diabetics.

We compared counterregulatory metabolic and hormonal responses in 8 normal controls with responses in 16 Type I (insulin-dependent) diabetics, 7 of whom had had repeated attacks of severe hypoglycemia, in an effort to determine whether these responses are related to the occurrence of hypoglycemia in the latter group. In response to insulin-induced hypoglycemia, peak values for glucose production (5.7 +/- 0.

Evidence for the presence of somatostatin 28 in plasma.

Somatostatin-like immunoreactivity (SLI) from dog and rat plasma eluted from Biogel P-6 columns as three distinct peaks. A large-molecular-weight peak was present in the void volume of the column, an intermediate-sized peak (SLI28) coeluted with synthetic somatostatin 28 (S-28), and a small-molecular-weight peak (SLI14) coeluted with SRIF. Material from the SLI28 peak diluted in parallel to the S-28 standard in the radioimmunoassay and behaved identically to S-28 on high pressure liquid chromatography (HPLC).

Surface receptors for pancreatic hormones in dog and rat hepatocytes: qualitative and quantitative differences in hormone-target cell interactions.

In order to evaluate potential differences in the kinetics of peptide hormone-receptor interactions in hepatocytes of different species, we developed a simple procedure for the isolation of canine hepatocytes. Cells (obtained by collagenase perfusion of an extirpated dog liver lobe) were isolated with uniform high viability and yield. In addition, isolated dog hepatocytes tolerated incubation for at least 4 hr in defined medium with only a slight decrease in viability and with no change in the kinetics of [125I]iodoinsulin or [125I]iodoglucagon binding to cell-surface receptors.

Glucose ingestion in dogs alters the hepatic extraction of insulin. In vivo evidence for a relationship between biologic action and extraction of insulin.

Oral glucose (25 g) fed to seven healthy, conscious dogs resulted in an increase in peripheral plasma glucose from 109 +/- 3 to 178 +/- 10 mg/dl. Concurrently serum insulin increased in the portal vein to levels approximately threefold greater than those in the periphery. Hepatic insulin delivery rose from 10.

Hepatic and renal metabolism of somatostatin-like immunoreactivity. Simultaneous assessment in the dog.

The hepatic and renal metabolism of somatostatin-like immunoreactivity (SLI) was assessed simultaneously in an in vivo dog model. The hepatic extraction of this peptide was 29.4 +/- 2.

Hepatic extraction of plasma immunoreactive glucagon components. Predilection for 3500-dalton glucagon metabolism by the liver.

This study examines quantitatively the extraction of plasma immunoreactive glucagon (IRG) components by the liver. It was shown that the liver has a predilection for removal of the 3500-dalton biologically active IRG component with virtually no extraction of the other IRG fractions. Hepatic extraction of whole plasma IRG was 25.

A familial glucagonoma syndrome: genetic, clinical and biochemical features.

A family with multiple endocrine neoplasia type I (MEN-I) is described in which three members had A-cell pancreatic tumors. Two of these members had classic glucagonoma syndromes. The proband, a 62 year old woman, had a high (less than or equal to 9.

Hepatic metabolism of glucagon in the dog: contribution of the liver to overall metabolic disposal of glucagon.

The hepatic extraction (HE) of glucagon (G) and insulin (I) was measured in 27 dogs, using peripheral infusion of the hormones following elimination of endogenous secretion by pancreatectomy (Px) or somatostatin (S) infusion. HE(G) was 22.5 +/- 1.

Reduction in portal vein blood flow by somatostatin.

Intravenous somatostatin boluses produced striking diminution in portal vein blood flow in dogs (maximally 40--55%). This effect was of rapid onset, without observable changes in hepatic artery flow, systemic blood pressure, pulse or central venous pressure. The duration of action was short, but could be sustained by continuous intravenous infusion.