"Big, big insulin"

Effect of streptozotocin in a case of glucagon-secreting malignant islets-cell tumor

A case of a 65-year-old woman with a pancreatic tumor secreting insulin, glucagon, and associated with high PTH levels and hypercalcemia is reported. The patient underwent two Streptozotocin (STZ) treatments (1 g iv/week for 10 weeks) after liver metastases were found. Hormonal and metabolic parameters were monitorized . Before the first STZ treatment insulin levels ranged between 78 and 132 microU/ml. After STZ administration insulin decreased and then remained lower (8-48 microU/ml) until the death of the patient. Pre-treatment glucagon levels ranged between 1.3 and 3.9 ng/ml. STZ induced a decrease of glucagon to 0.5 ng/ml. Glucagon chromatography revealed the prevalence of high molecular weight (greater than 6,000 mol wt) immunoreactive glucagon (0.9 ng/ml) drastically reduced by STZ treatment (0.15 ng/ml). Hypoaminoacidemia was observed before STZ administration, but at the end of the therapy plasma amino acid concentrations were normal. Hypercalcemia too was sensitive to STZ, but not PTH value, which remained high. The second STZ treatment performed a year later was less effective and so a chemotherapeutic protocol was started. Our findings suggest a cytolitic effect of STZ on malignant A-cell, with reduction of glucagon levels and restoration of amino acid metabolism. This effect would be useful for medical treatment of non-operable glucagon secreting tumors.

On the mechanism of the insulin-glucose interactions

Analysis of the course of D-glucose binding to insulin has shown that the mechanism of glucose-insulin interaction is a cooperative process. Binding of D-glucose molecules to insulin is facilitated by the dissociation of insulin aggregates caused by insulin-glucose interaction. Thus, insulin behaves as a system with strong positive cooperativity. The results have been treated in accordance with theories for interactions coupled to association equilibria. The data obtained support the idea that insulin monomers are the active species responsible for insulin action.

Plasma immunoreactive glucagon fractions in four cases of glucagonoma: increased "large glucagon-immunoreactivity"

Immunoreactive glucagon (IRG) fractions from plasma of 8 normal subjects and 4 patients with glucagon secreting tumors were studied by gel filtration techniques on Bio Gel P--30 and Sephadex G--50 columns. The pancreatic glucagon specific anti serum (30K) of Unger was utilized to measure IRG. Columns were calibrated with labelled albumin, proinsulin, insulin and glucagon. Four peaks were defined in normal and tumor bearing patients: peak I (greater than 20 000 mol. wt.), peak II (primarily 9000 mol. wt.), peak III pancreatic glucagon (3500 mol. wt.) and peak IV small gucagon (less than 3500 mol. wt.). Glucagonoma patients differed from our normal and reported normal subjects in that peak II contained most of the circulating IRG. The percent of IRG associated with peak II was 9.5--31.5% in normals and 39.1--61.2% in glucagonomas. Glucagon-like biological activity in an isolated hepatocyte system was demonstrated for all peaks. However, relative to immunoreactivity, peak II showed reduced activity (25--33%). Immunoassay of dilutions of all peaks revealed the probability of immuno determinants identical with procine pancreatic glucagon. The presence of heterogenous IRG peaks with biological glucagon-like activity suggest that the larger molecules may be prohormones. Further, it is possible that specific elevation of peak II may be a diagnostic feature of glucagonomas.

Neurocristopathy, neuroendocrine pathology and the APUD concept

The neurosecretory cells of the hypothalamus, and the cells of the pituitary gland and the pineal, are here grouped together as a central neuroendocrine division of the APUD series. The larger, peripheral division comprises the remainder of the original series. All the cells are proven or presumptive derivatives of neuroectoderm so that, with the present exception of the parathyroid gland and its products, peptide hormone endocrinology becomes neuroendocrinology. It follows that the pathology of the APUD cell series must be regarded as neuroendocrine and it is suggested that it can best be expressed by the term neurocristopathy (Bolande, 1974). Tumours of the series, properly neurocristomas, are preferably called apudomas because their common cytochemical (APUD) and ultrastructural characteristics provide the pathologist with a ready means of diagnosis.

Parathyroid secretion: discovery of a major calcium-dependent protein

Bovine parathyroid tissue incubated in vitro secretes a protein that is distinct from both parathyroid hormone and proparathyroid hormone and comprises about 50 percent of the total secreted protein. This protein appears to be an aggregate consisting of two or more subunits of molecular weight 70,000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Although the function of this protein is unknown, the secretion rates of both the protein and parathyroid hormone respond in parallel to changes in the concentration of calcium in the medium.

Heterogeneity of parathyroid hormone. Clinical and physiologic implications

When immunoreactive human parathyroid hormone (hPTH), extracted by three different solvents (20% acetone in 1% acetic acid, 8 M urea, or normal saline) from parathyroid glandular tissue was subjected to Sephadex G-100 gel filtration and immunoassay using two different antisera (273 and C-329), four distinct fractions were observed. The first (I), a void volume peak, was detected by both antisera with similar immunoreactivity, as was a second (II), which had the elution and sedimentation properties of highly purified bovine parathyroid hormone (bPTH); a third (III) eluted between [(125)I]growth hormone and [(125)I]insulin, sedimented with the velocity of a molecule of approximately 6,000 mol wt, and was detected primarily by antiserum 273; a final fraction (IV), detected primarily by C-329, eluted just prior to [(125)I]insulin. The elution profiles of the acetone-acetic acid and 8 M urea extracts were similar and contained fraction II as their major component. In saline extracts, however, fraction III predominated. Three fractions, having gel filtration and immunologic characteristics similar to fractions II, III, and IV, respectively, of saline glandular extracts, were detected in the plasma of patients with both primary (adenomatous or carcinomatous) and secondary hyperparathyroidism. The predominant component in every plasma was the intermediate fraction that, like III, was detected primarily by antiserum 273, while the least abundant form was consistently the final fraction, detected primarily by antiserum C-329. The first fraction, like II, was detected with about equal potency by both antisera and had an elution volume on Sephadex corresponding to that of intact bPTH. It bore a reciprocal relationship to serum calcium and disappeared from the plasma of a uremic patient during calcium infusion or following parathyroidectomy with a half-time of no more than 20 min. This component therefore probably represents biologically active hormone. The intermediate and final fractions had turnover times in the plasma of a uremic patient more than 100 times greater than the active form, remained elevated even in the presence of post-parathyroidectomy hypoparathyroidism in this patient and were presumed to be biologically inactive. The ratio of biologically inactive fragments to the active form was greater in secondary hyperparathyroidism. The evidence presented favors a glandular origin for the fragments. Comparison of hormonal assays with the two antisera reveals a striking advantage in the preoperative diagnosis of primary hyperparathyroidism with antiserum 273 that is due to the enhanced sensitivity occasioned by its detection of a biologically inactive as well as the biologically active hormonal form.