[Effect of caerulein on blood glucose, serum insulin, glucagon, prolactin and growth hormone before and after oral glucose load in healthy volunteers and diabetic patients (author's transl)]

Eleven healthy volunteers, five type I diabetics, and one type II diabetic man were examined. After an overnight fast caerulein (20 ng/kg) was injected intravenously and 60 min later an oral glucose tolerance test was performed with 100 g glucose in the normals and 25 g glucose in the diabetics. Blood pressure, pulse rate, blood glucose, serum insulin, glucagon, prolactin and growth hormone values were measured during the whole period of 240 min and compared with the same parameters in control tests in the same persons without caerulein application. None of the measured parameters were significantly influenced by caerulein. It is therefore concluded that in contrast to the stimulation of the exocrine pancreas functions of the endocrine pancreas, the pituitary gland and glucose tolerance are unchanged after caerulein.

[Disease picture and operative therapy in multiple endocrine adenomatoses (MEA sydrome)]

We have outlined the symptoms, diagnostic procedures and operative treatment of "multiple endocrine adenomatosis" (MEA I, IIa und IIb). The priority of the operative procedure whenever two or more clinical syndromes in a patient with MEA are present and the possibility of multiple tumors has to be considered carefully. When there is a tumor of an endocrine organ, it should always bethought about the MEA-syndrome. We report about 9 patients seen in our hospital.

[Exocrine pancreatic secretion, gastrin and insulin in men by intraduodenal bolus injection of calcium (author's transl)]

The possible role of calcium in human bile during the biliary stimulated exocrine pancreatic secretion was investigated in 15 healthy volunteers. Total outputs of trypsin, bicarbonate, bilirubin and volume in the duodenal juice and serum gastrin were measured during a continuous intravenous infusion of secretion (0.5 CHR U/kg/h) for 40 min. The same parameters were determined after a single intraduodenal dose of Ca++ (20 ml 13,5, 135 or 270 mval/l, n = 5 for each dose) and compared with aequivalent intraduodenal dose of Na+ and an intravenous dose of secretion/cholecystokinin (1 CHR and IDU U/kg). Low calcium (13,5 mval/l) had no effect on the output of pancreatic enzymes and bile. However the higher doses led to a significant increases of the outputs of trypsin and bilirubin, which was about 75% of the enhancement seen with secretin/cholecystokinin in the dose used. Serumgastrin secretion was significantly increased only after the higher calcium doses.--Serum insulin in peripheral venous blood venous blood was unchanged after duodenal application of 20 ml 270 mval/l calcium (n = 5). From these data one has to conclude that the Ca++-content of bile has no stimulatory effect on the exocrine pancreas and on serum gastrin and insulin.

The prostaglandins system and insulin release. Studies with the isolated perfused rat pancreas

Using the isolated perfused rat pancreas PGE2 (1 MUM and 10 muM) had no effect on basal or glucose (10 and 20 mM)-induced insulin release (IR). PGF2 alpha stimulated basal IR at 1 muM and inhibited IR at 10 muM. The glucose-induced IR was unaffected by this PG. Furosemide (5 and 10 mM) led to a monophastic IR at low glucose (glu) and to a potentiation of IR at high glu. Only high indomethacin (Indo) (50 microgram/ml) inhibited glu-induced IR. The stimulatory effect of furosemide on IR could not be inhibited by indomethacin. However mepacrine (0.1 mM) abolished the furosemide effect. Also glu-induced IR was inhibited by mepacrine. Acetylsalicylic acid (30 mg/100 ml) had no significant influence on glu-induced IR. These findings provide evidence that phospholipase activation rather than increased PG synthesis might primarily be involved in the secretory process of insulin.

Indications for a brain uptake of labelled vasopressin and ocytocin and the problem of the blood-brain barrier

Fifteen seconds after intracarotid injection of [125J]-lysine vasopressin, [3H]-ocytocin, tritiated water or [3H]-inulin, the distribution of radioactivity in 18 regions of the rat brain and in the anterior pituitary was determined. Comparing the concentration of the different tracers (in % of injected radioactivity per g brain tissue), it is assumed that a small amount of the labelled neurohormones is taken up by the brain, indicating a penetration of the blood-brain barrier and/or an accumulation within the structures of the barrier system.

Sulphydryl requirement for insulin release from the perfused pancreas. Studies with ethacrynic acid and dithiothreitol

Using the isolated, perfused rat pancreas the importance of sulphydryl groups for the secretory process of insulin was investigated. It was found that ethacrynic acid (EA, 0.075-0.6 mmol/1) caused a dose-dependent, monophasic insulin release. Addition of EA to a glucose-stimulated (20 mmol/1) pancreas led to a sudden increase in hormone release, followed by a dose-dependent inhibition of release, which was not reversible after removal of EA. The same phenomenon was seen in the presence of 20 mmol/1 leucine. Dithiothreitol (DTT, 0.1 and 1 mmol/1) had no effect on basal insulin secretion. Added to a glucose-stimulated pancreas DTT (1 mmol/1) caused a reversible inhibition of insulin release. The persistent inhibitory action of EA on glucose-induced insulin release could be reversed by simultaneous perfusion of EA and DTT. Sequential exposure of a glucose-stimulated pancreas to EA and DTT led to a rapid release of insulin, due to DTT; however, the EA-induced inhibition of insulin secretion could not be prevented. Two kinds of thiol groups in the plasma membrane and in the beta cell might be responsible for the various kinetics of insulin release induced by EA and DTT.

Regional net uptake of 14C-glucose by rat brain under the influence of corticosterone

Fifteen seconds after intracarotid injection of either 14C-glucose or tritiated water in adrenalectomized rats, the net uptake of the respective tracer by 18 brain regions and by the anterior pituitary was measured. Corticosterone added to the injection solution (1 or 100 micrograms ml-1; 0.2 ml per animal) caused a dose-dependent decrease of net uptake of 14C-glucose in twelve regions. Compared to the net uptake of tritiated water which was used as a measure of relative blood flow, it suggests that this effect, at least partially, is due to a decreased blood-brain barrier permeability to 14C-glucose. Furthermore, the regional net uptake of 14C-glucose was estimated in rats with different endogenous corticosterone levels but injected with an identical solution in each case. Statistically significant differences could be observed between adrenalectomized and restrained animals in three brain regions.

[Clinical aspects, diagnosis and treatment of organic hyperinsulinism. Experience with 46 operated patients (author's transl)]

The clinical picture of organic hyperinsulinism is presented with reference to experience in 46 operated patients. For the recognition of disease, a careful history is a decisive contribution. The hunger test showed a characteristic hypoglycemic reaction in 100%; the tolbutamide test gave a positive result in 92%. Insulinomas could be localized angiographically in 71%; in one patient this could only be done with an ERCT. The treatment of choice is operation as soon as possible. If possible, enucleation is to be given preference over pancreas resection because of the low complication rate. A search for ectopic (2%) and multiple (12%) adenomas is important. A cure was achieved in 76% of all those operated on. The hospital mortality was about 4%.

Treatment of patients with prolactinomas

Fifty-one female patients with prolactin producing tumors (PRL 1100 to 88,000 microU/ml) and 26 male patients with prolactin producing tumors (PRL 6500 to 400,000 microU/ml) were studied. Only 25% of the females had visual field defects which were present in 70% of the males. All females had amenorrhea but only 35 had galactorrhea. Hypopituitarism was rarely seen in the females but in most of the male patients. Twenty-four females and all male patients were operated (transphenoidal or transfrontal operation). PRL normalized in only eight females and in none of the males. Two patients became pregnant postoperatively, four after postoperative treatment with bromocriptine. Bromocriptine induced regular menses in 4 other patients operated by transsphenoidal route. Eight patients with microadenoma (PRL less than 4000 microU/ml) were treated with bromocriptine alone of whom two became pregnant. The males were also treated with bromocriptine leading to a significant fall of the PRL level accompanied by improvement of libido, sexual potency and headache. Two patients received radiation postoperatively, which led to a fall of PRL and improvement of visual fields. Since PRL levels remained low after withdrawal of bromocriptine for several months an antiproliferative effect of this drug is suggested. Thus differential therapy of PRL producing tumors is possible: In females selective neurosurgery can alone or combined with medical therapy normalize PRL secretion and ovarian function. In patients with microadenoma bromocriptine alone can be successful. In patients with inoperable large tumors radiation should be advocated. Additional bromocriptine therapy may be helpful to stop tumor growth and alleviate the effects of hyperprolactinemia.

[Effect of oxytocin on regional 3H-orotic acid uptake in rat brain]

The uptake of the RNA precursor [3H] orotic acid by 18 brain regions of male rats was measured after intracarotid injection and a survival time of 15 s. Ocytocin added to the injected solutions (final concentrations: 1 to 1000 mU/ml) caused a dose-dependent enhancement of tracer uptake by 11 areas. Some of these regions (e.g. hippocampus) are thought to be involved in the behavioral effects of vasopressin and other peptide hormones (Van Wimersma Greidanus et al., 1975 a). Results of experiments in which the net uptake of tritiated water was used as a measure of relative blood flow led us to the conclusion that the blood-brain barrier permeability to [3H] orotic acid rather than the cerebral blood flow is changed by ocytocin. The present results support the assumption that the enhanced precursor supply caused by ocytocin might contribute to the influence of this peptide hormone on memory consolidation.

Prolactin: a diabetogenic hormone

During an oral glucose tolerance test (OGTT) glucose and insulin levels were measured in 26 patients with prolactin-producing pituitary tumours without growth hormone excess. Basal glucose and insulin levels did not differ from the values of an age-matched control group. After glucose load the hyperprolactinaemic patients showed a decrease in glucose tolerance and a hyperinsulinaemia. Bromocriptine (CB 154), which suppressed PRL, improved glucose tolerance and decreased insulin towards normal in second OGTT. Human PRL or CB 154 had no significant influence on insulin release due to glucose in the perfused rat pancreas. These findings suggest a diabetogenic effect of PRL. CB 154 might be a useful drug in improving glucose utilization in hormone-active pituitary tumours.

[Influence of somatastatin on oral glucose tolerance in autonomous hypersecretion of growth hormone, prolactin or insulin (author's transl)]

Oral glucose tolerance tests (OGTT) were performed for two subsequent days in 4 patients with active acromegaly, 2 patients with prolactin-producing pituitary adenomas and one insulinoma patient. Thirty minutes before the second OGTT 250 mug of somatostatin were injected intravenously as a bolus followed by a somatostatin infusion (500 mug) over 21/2 hours. The OGTTs were pathologic due to the hGH- and hPRL-induced insulin antagonism; they could not be normalized or improved by somatostatin. Only the peak of the blood sugar curve was shifted from one to two and a half hours after glucose administration; insulin and hGH levels were regularly suppressed after somatostatin whereas hPRL remained unchanged in most instances. Gastrin levels increased in all patients during the OGTT, the increase was suppressed in 4 patients. These findings show that the pathologic glucose tolerance due to insulin antagonism could not be improved by somatostatin in contrast to the deteriorated glucose tolerance in insulinopenic states.

The stimulatory and inhibitory function of theophylline on amino acid-induced insulin release: studies with the perfused rat pancreas

The effects of 5 mM theophylline on L-phenylalanine, L-alanine, and L-leucine-induced insulin secretion were studied using the isolated perfused rat pancreas, varying the sequence of the stimuli. Theophylline in the absence or presence of 3 mM D-glucose caused a small amount of insulin release with a slow onset and a slight and steady increase. Theophylline had no effect on phenylalanine (5, 10, or 20 mM)-induced insulin release independent of the sequence of stimuli. Alanine (20 mM), in the absence of glucose, had no significant insulin stimulatory action. When theophylline was added during the alanine perfusion only a small insulin release, comparable to that given by theophylline alone, could be observed. However, superimposing alanine on a theophylline perfusion led to a potentiation of insulin release. The leucine-induced insulin secretion was significantly altered by the addition of theophylline. At a low concentration of leucine (5 mM) theophylline caused potentiation of leucine-induced insulin secretion. At 10 and 20 mM leucine, theophylline led to a rapid concentration-dependent inhibitory period, followed by a potentiation in the case of 10 mM leucine, and by a restoration of the secretion rate at 20 mM leucine which did not exceed the secretion rate of 20 mM leucine alone. Subsequent removal of theophylline caused a marked "off effect." When 5 or 20 mM leucine was superimposed on a theophylline perfusion, a marked dose-dependent potentiation of the biphasic leucine-induced insulin release and no inhibitory phase could be observed. From these data it must be concluded that the effect of theophylline on the insulin secretory reposure of the beta cell to theophylline and the stimulus. Possible explanations for these phenomena are discussed.

Glucoreceptor mechanisms in islets of Langerhans

A widely accepted concept has been that metabolites of glucose or factors associated with glucose metabolism, rather than glucose itself, trigger insulin release from the β cells. If this concept is correct, levels of metabolites or cofactors or of both should change within seconds of the glucose pulse. To examine the hypothesis, glucose, glucose-6-P, 6-P-gluconate, fructose-l,6-P2 plus triose-P, 3-P-glycerates plus P-enolpyruvate, ATP, ADP and P-creatine were measured in slices of individual rat islets after intravenous infusion of glucose in vivo or perfusion of the isolated pancreas with glucose in vitro. Tissue samples were obtained by quickfreezing methods as early as fifteen seconds and as late as sixty minutes following the glucose load. Insulin levels in serum and perfusate were measured concomitantly.

Insulin levels in peripheral blood rose within one minute of injection of glucose in vivo. Penetration of glucose, although very rapid, was carrier-mediated. Most of the metabolites and cofactors measured were unchanged during the first five minutes of glucose infusion. After one hour of hyperglycemia there was a marked rise in all metabolites and cofactors except ATP.

In the perfused pancreas, insulin secretion increased within 0.5 minute of the glucose stimulus and the typical biphasic response was observed. The glucose content of islets increased threefold within 0.25 minute and sixfold within 0.5 minute. The levels of all other metabolites measured were virtually unchanged during the early phase of the endocrine response, in spite of the eightfold increment in the glucose of the medium and the almost tenfold rise of insulin release.

The constancy of the islet's metabolite pattern when the islets were exposed to high glucose—particularly during the early transition phase—is remarkable, since glycolytic flux was supposedly increased severalfold.

The fact that the metabolite profile of the islets is so precisely maintained within a narrow range makes it unlikely that any of the metabolites measured might serve as triggers for insulin release. It is more likely that the glucose molecule itself exerts its releasing action by stimulating glucoreceptors located on the cell membrane.

Kinetics of insulin release from the perfused rat pancreas caused by glucose, glucosamine, and galactose

Under appropriate conditions, not only glucose but also glucosamine and galactose can serve as potent stimulants for insulin release from the isolated, perfused rat pancreas. Since galactose and, probably, glucosamine are not metabolized in the islets, and since these three compounds have in all likelihood common sites of action, it is postulated that a glucoreceptor of broad specificity is involved in the mechanism of insulin release, and that metabolism of glucose is not an essential part of the releasing action of this sugar.