Glucose and ATP levels in pancreatic islet tissue of normal and diabetic rats.

It has been suggested that the hyperglucagonemia observed in diabetic animals and man may be due to an impairment of glucose uptake and metabolism by the alpha-cells resulting in a decreased production of ATP. To test this hypothesis glucose, ATP, glucagon, and insulin were measured in pancreatic islets of normal and alloxan or streptozotocin diabetic rats. Two experimental approaches were used.

Hormone secretion and glucose metabolism in islets of Langerhans of the isolated perfused pancreas from normal and streptozotocin diabetic rats.

The glucose responsiveness of alpha- and beta-cells of normal as well as untreated and insulin-treated streptozotocin diabetic rats was tested in the extracorporeal perfusion system. Also assessed was the possible in vitro effect of added insulin on the glucose sensitivity of islets from untreated diabetic animals. Insulin and glucose responsiveness of the two cell types.

Approach to three-dimensional mapping of quantitative histochemical measurements applied to studies of the cochlear nucleus.

After reviewing the historical development of some procedures for localizing quantitative histochemical measurements, an approach is presented which combines some aspects of these procedures to make possible a permanent, objective record of the location of each sample. The method further allows direct comparisons to be made with drawings of other nearby sections during the process of sampling. Illustrations are given of various applications to a study of the cochlear nucleus.

Fast and slow axoplasmic flow in sciatic nerve of diabetic rats.

Accumulation of acetylcholinesterase (AChE) and choline acetylase (ChAc) activities proximal to a tie placed on the sciatic nerve was measured in control, untreated diabetic, and insulin-treated diabetic rats. In the diabetic animals AChE accumulation was reduced by about 20% and ChAc accumulation by about 40%. Insulin treatment eliminated the impairment.

Comparison of alpha- and beta-cell secretory responses in islets isolated with collagenase and in the isolated perfused pancreas of rats.

The inhibitory actions of somatostatin (100 ng./ml.) on insulin release, stimulated by high glucose (20 mM), and on glucagon release, stimulated by arginine (15 mM), were studied with two in vitro systems: the isolated perifused rat islets prepared by the collagenase procedure and the isolated perfused rat pancreas.

Adenosine triphosphate and phosphocreatine levels in cochlear structures. Use rate and effect of salicylates.

Guinea pigs were injected with various dosages of salicylate for varying time periods. The temporal bones were removed, frozen quickly, freeze-dried, and the cochlea was dissected into essential auditory component parts and subjected to microchemical analysis for phospho-creatine (P-creatine) and adenosine triphosphate (ATP) levels. It was found that high energy phosphates were not decreased by therapeutic or acutely toxic levels of salicylate.

Iodoacetate and iodoacetamide-induced alterations of pancreatic alpha- and beta-cell responses.

Iodoacetate and iodoacetamide were compared as to their capacity to block islet glycolysis and interfere with glucose inhibition of glucagon release and glucose stimulation of insulin release. Glycolysis was measured in isolated rat islet by the rate of lactate formation from 27 mM glucose. Hormone release was investigated by perfusing isolated rat pancreas with a 10 mM mixture of 19 amino acids, with and without 5 mM glucose.

Enzymes of the cholinergic system in islets of Langerhans.

Quantitative radiometric assays were employed to measure activities of choline acetyltransferase and acetylcholinesterase in freeze-dried pieces of islets of Langerhans and exocrine tissue from rat pancreas. The activities of both enzymes were about an order of magnitude higher in islets than in exocrine tissue. This difference in activity was found in rats made diabetic with streptozotocin as well as in the controls.

The role of Ca-2+ and cyclic adenosine 3':5'-monophosphate in insulin release induced in vitro by the divalent cation ionophore A23187.

Insulin release from isolated perifused pancreatic islets was stimulated by the divalent ionophore A23187 in the absence of exogenous glucose. In addition, A23187 produced a 2-fold elevation of cyclic adenosine 3':5'-monophosphate (cAMP) levels in isolated perifused islets. The elevation of cAMP levels coincided with peak insulin release.

Factors governing glucose induced elevation of cyclic 3'5' AMP levels in pancreatic islets.

Adenosine 3'5'-cyclic monophosphate (cAMP) levels of isolated perifused pancreatic islets were elevated by high levels of glucose concomitantly with initiation of enhanced insulin secretion. The rise of cAMP was biphasic and seemed to be related to the temporal biphasic kinetics of insulin release. However, the temporal profiles of cAMP level changes and of insulin release differed; the major rise of the cAMP levels was seen during the initial phase, whereas insulin secretion was more pronounced during the second phase of release.

Electrical and secretory manifestations of glucose and amino acid interactions in rat pancreatic islets.

Interactions between glucose and amino acids in rat pancreatic islets were studied by recording the intracellular membrane potential and spike discharges from the isolated perfused pancreas. It was found that L-isoleucine requires the presence of basal glucose (5 mM) in order to increase spike discharge from islet cells and depolarize the cell membrane. Similarly basal glucose is needed for insulin release by L-isoleucine.

Multiple metabolic functions of glucose in rat pancreatic islets.

Metabolic interactions between glucose and amino acids were studied with isolated rat islets using glucose utilization and lactate formation as indicators. Certain amino acids (8-10 mM) are capable of greatly stimulating lactate formation from 5mM glucose. On a molar basis L-isoleucine is the most potent stimulator in a group of twenty-six amino acids.

Differential effects of alpha- and beta-D- glucose on insulin and glucagon secretion from the isolated perfused rat pancreas.

The efficacy of alpha and beta-D-glucose in causing insulin release and suppressing glucagon release from the isolated perfused rat pancreas was tested. In order to allow simultaneous assessment of glucose effect on both alpha and beta-cells, the pancreas was continually perfused with a physiological amino acid mixture (10 mM) which provokes glucagon secretion and also stimulates the beta-cells, provided glucose is present. Under these conditions the alpha-anomer of D-glucose at 3 and 6 mM proved significantly more potent than the beta-anomer in inducing insulin release and in inhibiting glucagon secretion.

Insulin and glucose as modulators of the amino acid-induced glucagon release in the isolated pancreas of alloxan and streptozotocin diabetic rats.

The hyperglucagonemia that occurs in vivo in animals made diabetic with alloxan or streptozotocin is not suppressed by high glucose but is suppressed by exogenous insulin. These observations together with other studies suggested that insulin-dependent glucose transport and metabolism by the alpha-cells serves as the primary mechanism controlling glucagon secretion. This hypothesis was tested in the present investigation.

Glucose modulation of amino acid-induced glucagon and insulin release in the isolated perfused rat pancreas.

Interactions between glucose and arginine and a mixture of 20 amino acids found in normal rat serum were studied in the isolated perfused rat pancreas of normal rats, with release of immunoreactive glucagon and insulin as parameters. Secretion of both pancreatic hormones was low during the steady state, whether glucose (5 mM) was included in the perfusion medium or not. This glucose concentration significantly stimulated insulin release twofold and resulted in an 80% inhibition of basal glucagon release.