Adenosine 3',5'-monophosphate in pancreatic islets: glucose-induced insulin release.

Glucose-induced release of insulin from perifused rat islets is associated with elevated islet adenosine 3',5'-monophosphate. If values for adenosine 3',5'-monophosphate are compared to insulin release during theophylline or glucose stimulation and theophylline plus glucose stimulation, it suggests a minor role for adenosine 3',5'-monophosphate in directly stimulating insulin release but a prominent role in modulating glucose-induced release of insulin.

Lack of glucagon response to hypoglycemia in diabetes: evidence for an intrinsic pancreatic alpha cell defect.

Despite excessive glucagon responses to infusion of arginine, plasma glucagon did not rise in six juvenile-type diabetics during severe insulin-induced hypoglycemia, whereas glucagon in the controls rose significantly. Thus in diabetics pancreatic alpha cells are insensitive to glucose even in the presence of large amounts of circulating insulin. An intrinsic defect common to both alpha and beta pancreatic cells-failure to recognize (or respond to) plasma glucose fluctuations-may be operative in juvenile diabetes.

Cushing's syndrome: problems in management.

CS comprises a group of disorders characterized by hypercortisolism. The variety of causes--pituitary-dependent CS (CD), adrenal tumor, and the ectopic ACTH syndrome--necessitates a variety of therapies--surgical, radiotherapeutic, and medical. Once a specific diagnosis is made, specific therapy can be instituted. Although some controversy persists regarding treatment, particularly that of CD, for most patients it is straightforward. However, in our experience with more than 60 patients, therapeutic dilemmas can arise in a number of circumstances, e.g. the patient with the radiologically normal sella or recurrent CD after adrenalectomy. In addition, the treatment of such conditions as the large ACTH-producing pituitary tumor, Nelson's syndrome, the malignant ectopic ACTH syndrome, and adrenal carcinoma is not entirely satisfactory. Our approach to these problems is illustrated by seven cases, and we emphasize that the proper management of CS requires both correct diagnosis and the logical application of all available therapies.

Adrenergic modulation of pancreatic glucagon secretion in man.

In order to characterize the influence of the adrenergic system on pancreatic glucagon secretion in man, changes in basal glucagon secretion during infusions of pure alpha and beta adrenergic agonists and their specific antagonists were studied. During infusion of isoproterenol (3 mug/min), a beta adrenergic agonist, plasma glucagon rose from a mean (+/-SE) basal level of 104+/-10 to 171+/-15 pg/ml, P < 0.0002. Concomitant infusion of propranolol (80 mug/min), a beta adrenergic antagonist, prevented the effects of isoproterenol, although propranolol itself had no effect on basal glucagon secretion. During infusion of methoxamine (0.5 mg/min), an alpha adrenergic agonist, plasma glucagon declined from a mean basal level of 122+/-15 to 75+/-17 pg/ml, P < 0.001. Infusion of phentolamine (0.5 mg/min), an alpha adrenergic antagonist, caused a rise in plasma glucagon from a mean basal level of 118+/-16 to 175+/-21 pg/ml, P < 0.0001. Concomitant infusion of methoxamine with phentolamine caused a reversal of the effects of phentolamine. The present studies thus confirm that catecholamines affect glucagon secretion in man and demonstrate that the pancreatic alpha cell possesses both alpha and beta adrenergic receptors. Beta adrenergic stimulation augments basal glucagon secretion, while alpha adrenergic stimulation diminishes basal glucagon secretion. Furthermore, since infusion of phentolamine, an alpha adrenergic antagonist, resulted in an elevation of basal plasma glucagon levels, there appears to be an inhibitory alpha adrenergic tone governing basal glucagon secretion. The above findings suggest that catecholamines may influence glucose homeostasis in man through their effects on both pancreatic alpha and beta cell function.

Increased growth hormone response to dopamine infusion in insulin-dependent diabetic subjects: indication of possible blood-brain barrier abnormality.

To test the hypothesis that cerebral capillaries, which share the embroyologic and morphologic characteristics of retinal capillaries, might have the same abnormal permeability in diabetic patients, we investigated the growth hormone response to a small amount of peripherally administered dopamine (1.5 microgram/kg.min). Consistent with the known exclusion of systemic dopamine from brain parenchyma, no rise was observed in 12 normal subjects. In 10 of 12 juvenile-onset, insulin-dependent diabetic patients, however, a substantial growth hormone rise occurred (peak value, 19.2 +/- 3.0 ng/ml [mean +/- SE]). Comparision of metabolic and cardiovascular responses to the infusion in both groups did not suggest that higher circulating levels of dopamine had been achieved in the diabetics. Other growth hormone stimuli (apomorphine in decreasing amounts, glucagon, and graded physical exercise) failed to indicate that hypothalamic hypersensitivity could account for the consistent rise. We postulate that an abnormal permeability of the blood-brain barrier in the diabetic patients permitted exposure of the hypothalamic structures regulating growth hormone secretion to a greater fraction of the infused dopamine.

Dopamine during alpha- or beta-adrenergic blockade in man. Hormonal, metabolic, and cardiovascular effects.

We studied the contribution of alpha- and beta-adrenergic receptor activation to the cardiovascular, metabolic, and hormonal effects of dopamine. At a concentration of 1.5 mug/kg.min, the infusion of dopamine in 12 normal volunteers was associated with a transient but significant rise in pulse rate, which was prevented by propranolol. Venous plasma glucose did not change throughout the experiments, and a mild increase in plasma free fatty acid levels observed during the administration of dopamine alone was antagonized by propranolol. In contrast, neither the beta-adrenergic blocker, propranolol, nor the alpha-adrenergic blocker, phentolamine, was effective in inhibiting the dopamine-induced rise in plasma glucagon (from 82+/-9 to 128+/-14 pg/ml; P < 0.005) and serum insulin (from 7.5+/-1 to 13+/-1.5 muU/ml; P < 0.005) or its suppression of plasma prolactin (from 8.5+/-1 to 5.2+/-0.8 ng/ml; P < 0.001). Although serum growth hormone levels did not change during the infusion of dopamine alone, an obvious rise occurred in three subjects during the combined infusion of propranolol and dopamine. Whereas some metabolic and cardiovascular effects of dopamine are mediated through adrenergic mechanisms, these observations indicate that this is not the case for the effects of this catecholamine on glucagon, insulin, and prolactin secretion, and thus provide further support for the theory of a specific dopaminergic sensitivity of these hormonal systems in man.

Effects of physiologic levels of glucagon and growth hormone on human carbohydrate and lipid metabolism. Studies involving administration of exogenous hormone during suppression of endogenous hormone secretion with somatostatin.

To study the individual effects of glucagon and growth hormone on human carbohydrate and lipid metabolism, endogenous secretion of both hormones was simultaneously suppressed with somatostatin and physiologic circulating levels of one or the other hormone were reproduced by exogenous infusion. The interaction of these hormones with insulin was evaluated by performing these studies in juvenile-onset, insulin-deficient diabetic subjects both during infusion of insulin and after its withdrawal. Infusion of glucagon (1 ng/kg-min) during suppression of its endogenous secretion with somatostatin produced circulating hormone levels of approximately 200 pg/ml. When glucagon was infused along with insulin, plasma glucose levels rose from 94 +/- 8 to 126 +/- 12 mg/100 ml over 1 h (P less than 0.01); growth hormone, beta-hydroxy-butyrate, alanine, FFA, and glycerol levels did not change. When insulin was withdrawn, plasma glucose, beta-hydroxybutyrate, FFA, and glycerol all rose to higher levels (P less than 0.01) than those observed under similar conditions when somatostatin alone had been infused to suppress glucagon secretion. Thus, under appropriate conditions, physiologic levels of glucagon can stimulate lipolysis and cause hyperketonemia and hyperglycemia in man; insulin antagonizes the lipolytic and ketogenic effects of glucagon more effectively than the hyperglycemic effect. Infusion of growth hormone (1 mug/kg-h) during suppression of its endogenous secretion with somastostatin produced circulating hormone levels of approximately 6 ng/ml. When growth hormone was administered along with insulin, no effects were observed. After insulin was withdrawn, plasma beta-hydroxybutyrate, glycerol, and FFA all rose to higher levels (P less than 0.01) than those observed during infusion of somatostatin alone when growth hormone secretion was suppressed; no difference in plasma glucose, alanine, and glucagon levels was evident. Thus, under appropriate conditions, physiologic levels of growth hormone can augment lipolysis and ketonemia in man, but these actions are ordinarily not apparent in the presence of physiologic levels of insulin.

Variation in thickness of the capillary basement membrane in single muscles of diabetic subjects.

Thickness of skeletal muscle's capillary basement membrane was measured in gastrocnemius and quadriceps femoris muscles of diabetic subjects. At least two different sites of each muscle studied were biopsied. Comparison of these biopsy samples revealed a marked and significant variation in thickness of the capillary basement membrane at different sites within the same muscle. In one subject so studied, this variation was found regardless of the method of fixation or the method of measurement of capillary basement membrane thickness used. Variation was present in diabetics suffering from long-term complications of the disease as well as in diabetics free of such complications. A reevaluation of the biologic significance of basement membrane thickness measurements, as presently applied, is indicated in the light of the variability of base-line values.

Reduced solubility of short-acting soluble insulins when mixed with longer-acting insulins.

Using insulins from three manufacturers, we examined the recovery by radioimmunoassay of short-acting soluble insulin when mixed with long-acting insulin as a function of the ratio of the mixture and the time of pre-mixing. In ratios of 1:2, 1:3, and 1:5 (short- to long-acting insulin), all Novo, Nordisk, and Lilly short-acting insulins tested showed a significant loss of solubility when mixed with the respective company's long-acting insulin either for less than 75 s or for 20 min before centrifugation. In ratios of 1:1, Novo's Actrapid (regular) with Monotard (lente) and Lilly's regular with lente showed no significant loss of solubility when pre-mixed for less than 75 s, and the regular insulin also showed no significant loss when pre-mixed for 20 min. However, when Lilly's regular was mixed with either NPH or ultralente in a 1:1 ratio, a significant loss of solubility of the short-acting insulin occurred regardless of time [as was also found with Nordisk's Velosulin (regular) with insulatard (NPH)]. When Lilly regular was incubated with Lilly lente in ratios of 1:3 for less than 75 s, 20 min, 4 h, and 24 h before centrifugation, there was a progressive loss of solubility. In contrast, with the same ratios and times of pre-mixing, Lilly regular when mixed with Lilly NPH showed a rapid initial loss of solubility that plateaued by 20 min before centrifugation.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma cyclic nucleotide levels in juvenile-onset diabetes.

In patients with juvenile-onset diabetes, plasma concentrations of 3',5'-adenosine cyclic monophosphate (cAMP) were significantly lower than those of norman subjects [16 +/- 4 and 24 +/- 7 pmol per milliliter (p less than 0.025), respectively] as determined in this laboratory; whereas there were essentially no differences in plasma levels of 3',5'-guanosine cyclic monophosphate (cGMP). Because cAMP inhibits cell growth and cGMP stimulates it, these findings may represent an important factor in the atherosclerotic and obliterative angiopathies of diabetic individuals. We observed that cyclic nucleotide values were the same whether or not the subjects were receiving insulin. Those given insulin plus enough glucose to maintain hyperglycemia revealed modest elevations in cyclic nucleotide levels. Thus, the ratio of cAMP to cGMP, abnormally low in juvenile-onset diabetes, is relatively independent of short-term variations in plasma levels of either glucose of insulin.

Effects of acute insulin withdrawal and administration on plasma glucagon responses to intravenous arginine in insulin-dependent diabetic subjects.

To assess further the role of insulin in the abnormal alpha-cell dysfunction found in human diabetes mellitus, the effects of acute insulin withdrawal and administration on plasma glucagon responses to intravenous arginine were studied in eight insulin-dependent diabetic subjects. Arginine infusions (30 gm. over 30 minutes) were performed during and at one and four hours after discontinuation of a 14-hour insulin infusion (1.5 U. per hour), which had rendered the subjects euglycemic, and on another occasion before and one and four hours into a five-hour infusion of insulin (1.5 U. per hour). During the last hour of the 14-hour infusion, glucagon responses to arginine (area under the curve, nanograms per milliliter per minute) were similar to those found in normal subjects (10.3 +/- 0.8 vs. 9.0 +/- 0.8, respectively). After discontinuation of the insulin infusions, glucagon responses increased progressively (p less than 0.01) to values (16.8 +/- 1.2) that exceeded those of normal subjects by four hours (p less than 0.01). These were similar to results found in the same subjects studied when their diabetes was in less than optimal control (14.9 +/- 1.3). Infusion of insulin under these conditions progressively decreased glucagon responses to arginine to values (9.6 +/- 0.8; p less than 0.01) that, at four hours, were similar to those of normal subjects and to values found at the end of the 14-hour infusion of insulin in the same diabetic individuals. These results demonstrate a rapid effect of insulin on glucagon responses to arginine and suggest that the abnormal responses seen in diabetes mellitus are the immediate result of insulin deficiency. Since abnormal glucagon responses to glucose in diabetes are not as readily corrected by insulin, the mechanisms underlying the abnormal responses to these two stimuli may differ.

Discordance of diabetic microangiopathy in identical twins.

In a pair of 19-year-old monozygotic twin girls, one developed insulin-dependent, ketosis-prone diabetes at the age of three and has required insulin for the past 16 years. Her identical twin has maintained normal oral and intravenous glucose tolerance with normal insulin release and glucagon suppression. An unequivocal hypertrophy of the muscle capillary basement membrane (1,800 +/- 148 A) was dound in the diabetic twin, while a normal thickness of 1,149 +/- 62 A was present in her nondiabetic sister. Follow-up of the present subjects and data from other discordant identical twins who have reached adulthood could determine whether muscle capillary basement membrane hypertrophy is an independent marker of genetic diabetes in adults. Discordance of diabetic microangiopathy in a pair of monozygotic twins has important implications regarding the influence of heredity and environment on diabetic microangiopathy.

The effect of chronic oral antidiabetic therapy on insulin and glucagon responses to a meal.

Nineteen maturity-onset diabetic patients receiving oral hypoglycemic therapy in a university diabetes clinic completed a study to assess the efficacy of the oral agents and to determine their effects on pancreatic islet hormone secretion. All patients were receiving sulfonylureas, and seven were also receiving phenformin. The subjects were studied as outpatients in the clinic setting on four different occasions with collections of a baseline blood sample before a standard breakfast and a second sampling two hours postprandially, twice while on their prescribed medication and twice after having been withdrawn from the medication. The values obtained during the two studies on the two studies off medications were reproducible for each subject. Analysis of the results by paired differences revealed that mean 24-hour urine glucose values deteriorated significantly (p less than 0.005) after oral antidiabetic therapy was withdrawn; similarly, mean plasma glucose values, both at baseline and two hours postprandially, rose significantly (p less than 0.001) when subjects were off medication. Baseline serum insulin values were not changed, but postprandial levels were significantly higher on oral agents (p less than 0.005). Plasma immunoreactive glucagon was significantly lower both at baseline (p less than 0.02) and postprandially (p less than 0.005) when the subjects were on their antidiabetic medications. During the trial off medication, 16 patients became symptomatic, with three of these developing symptoms severe enough to require hospitalization. It is apparent from this study that oral hypoglycemic medications can play a role in controlling symptoms in maturity-onset diabetic patients and that the beneficial effect of these agents on hyperglycemia may, in part, be explained by their stimulation of endogenous insulin secretion and partial suppression of endogenous glucagon.

Jejunoileal bypass as a treatment of morbid obesity.

Seventy-five morbidly obese patients underwent jejunoileal bypass between December 1968 and October 1975. The average weight of 45 patients who had had the bypasses for over two years stabilized at 62.4% of the maximum preoperative value. Postoperative complications included recurrent diarrhea in 11% (8/74) and serum electrolyte deficits in 64% (48/75), most of which were transient. Potassium and calcium deficiencies were usually correctable by oral supplementation, but hypomagnesemia persisted in 23% (16/71) despite supplementation. Nine percent (4/43) had biopsy-proved hepatic cirrhosis after one year. Other complications were polyarthralgia, bone demineralization, renal stones, and vasculitis. Three patients required reanastomosis to original bowel continuity; all rapidly regained weight. One died of vasculitis and hepatic failure attributable to the bypass. Jejunoileal bypass is suitable only in morbidly obese patients with particularly high motivation, whose risk factors outweigh those risks incurred through bypass.

Anovulatory effect of synthetic analogs of arginine vasotocin in the rat.

We synthesized a series of analogs of arginine vasotocin by systematically substituting each residue, and we then evaluated the anovulatory activity of these compounds in the rat, investigating the correlation between molecular structure and anovulatory, pressor, and antidiuretic activities. Substitution of the N-terminus cysteine with 3-mercaptopropanoic acid in arginine vasotocin and arginine vasopressin produced a 3- to 4-fold increase in both anovulatory and antidiuretic activity and only a 10% change in pressor activity. A similar substitution with lysine vasopressin produced no significant change in either anovulatory or antidiuretic potency; however, the pressor activity was reduced by half. Substitution of this cysteine in arginine vasotocin with 2-hydroxy-3-mercaptopropanoic acid produced an analog more potent in anovulatory activity than arginine vasotocin but less potent than [1-(3-mercaptopropanoic acid)]-arginine vasotocin. The most potent anovulatory analog synthesized was [1-(3-mercaptopropanoic acid)]-8-ornithine vasotocin, which gave a 10-fold increase in anovulatory activity, a 4-fold reduction in antidiuretic activity, and only a 10% increase in pressor potency when compared with arginine vasotocin. These data suggest that different receptors are involved in the anovulatory and antidiuretic responses, but that the anovulatory and pressor effects may be mediated through similar receptors. Further work is necessary to produce a peptide that possesses specific anovulatory activity.

Islet transplantation into rat liver: in vitro secretion of insulin from the isolated perfused liver and in vivo glucagon suppression.

Islet isografts were injected into the portal veins of rats made diabetic with streptozotocin. The isografts normalized not only plasma glucose and insulin levels but also the elevated plasma immunoreactive glucagon level. The in vitro basal insulin secretion and prompt sensitivity to glucose were shown directly by perfusing isolated livers containing transplanted islets. In vitro glucagon secretion to an arginine stimulus could not be demonstrated, although it would have been expected demonstrated, although it would have been expected in normal islets. Thus, it appears that insulin derived from transplanted islets is capable of correcting endogenous hyperglucagonemia and of ameliorating the effects of experimental diabetes while transplanted islet glucagon secretion is relatively suppressed.

Failure of somatostatin to inhibit tolbutamide-induced insulin secretion in patients with insulinomas: a possible diagnostic tool.

The effects of somatostatin on tolbutamide-stimulated insulin release were studied in 4 patients with insulin-producing tumors of the pancreas and in 6 normal subjects. In contrast to its effective inhibition of insulin release in normal subjects, somatostatin, without exception, failed to inhibit tolbutamide-induced insulin release in the patients with pancreatic beta-cell tumors. This differential effect of somatostatin may prove useful in the diagnosis of insulin-producing tumors of the pancreas.

Inhibition by somatostatin of ACTH secretion in Nelson's syndrome.

Somatostatin (GHIF), when administered as a 1-hr infusion (500 mug/hr) to 5 patients with Nelson's Syndrome;resulted in a sustained, progressive fall in plasma ACTH in each patient to 40% to 71% of basal values with a return toward initail levels after cessation of the infusion. The meanreduction in plasma ADTH was 48% (p less than 0.005). These finding suggest that GHIF receptors not fuctional or present in normal pituitary tissue are present in ACTH-producing pituitary tumors.

Growth hormone responses following double pulse oral glucose administration in various clinical states.

The 8-h double pulse oral glucose test is proposed as an alternative screening procedure for determining the adequacy of growth hormone (GH) release. The second pulse of glucose is timely in suppressing GH release and delaying it for a more predictable controlled elevation. Peak GH (mean plus or minus SD) values following the double pulse glucose test were 17 plus or minus 10.2, 16.5 plus or minus 2.2, and 1.3 plus or minus 0.5 ng/ml in normal controls, short stature patients and GH deficient patients, respectively. Peak GH values following insulin hypoglycemia were 36.9 plus or minus 13.8, 21.9 plus or minus 23.0 and 1.8 plus or minus 1.1 ng/ml in normal controls, short stature patients and GH-deficient patients. Peak GH values during a 5-h oral glucose tolerance test were 16.4 plus or minus 6.0 and 10.2 plus or minus 3.3 ng/ml in normal controls and short patients, respectively. These differences in peak GH values between the various clinical and control groups were not significantly different except for the greater GH peak values reached in short patients in the double pulse glucose test compared to the 5-h oral glucose tolerance test. The rise in GH following double pulse oral glucose is more timely predictab-e than after the 5-h oral glucose test and involves less professional time than the insulin tolerance test as it does not require close medical supervision.

Comparison of absorption of cortisone acetate and hydrocortisone hemisuccinate.

In four patients who required maintenance glucocorticoid therapy after bilateral adrenalectomy for Cushing's disease, we compared the effects of im injection and oral ingestion of cortisone acetate and hydrocortisone hemisuccinate. By the former route of administration, cortisone acetate was not effective in elevating plasma cortisol levels or in suppressing plasma adrenocorticotropin, although hydrocortisone was. When given by mouth, no significant difference was found between the two steroids. Therefore, in the treatment of acute adrenal insufficiency or in the maintenance of patients with chronic adrenal insufficiency and in their preparation for surgery or other stressful situations, we advise against im injection of cortisone acetate. Oral ingestion, however, is appropriate for maintenance.