Transient blindness following intracranial pressure changes in a hydrocephalic child with a V-P shunt

A hydrocephalic child with a V-P shunt developed transient blindness following shunt revision. A year later, visual function deteriorated when shunt malfunction occurred. Following shunt revision, the child regained sight. The effects of intracranial hypertension and hypotension on the visual pathways are discussed.

Induction of cell surface insulin antigenicity in fibroblasts transfected with islet genomic DNA

Ltk- cells were transfected with total genomic DNA obtained from rat islets or from insulinoma cells mixed with DNA tagged with fluorescent dye. Fluorescence-activated cell sorter (FACS) was used for initial selection of successful transfectants, monitoring fluorescent DNA incorporated into the cell. For subsequent selections the cells were treated with anti-insulin antiserum labeled with fluorescent dye and selected by FACS. Beta-cell DNA, but not DNA from murine leukemic cells, induced the appearance of cell surface insulin antigenicity in fibroblasts. This phenotypic expression was transient. Together with our previous demonstration of the induction of insulin secretion in Ltk- cells [(1986) Biochem. Biophys. Res. Commun. 136, 638-644], these results indicate that beta-cell-specific characteristics can be transfected to non-endocrine cells by genomic DNA transfection.

Induction of insulin release in fibroblasts transfected with genomic rat islet DNA

L cells (tk-) were cotransfected with total genomic rat islet DNA and a plasmid containing thymidine kinase gene (ptk). Transfectants were tested for their ability to release insulin into the medium. At least 10% of the colonies contained immunoreactive insulin (IRI) during the initial two weeks. The insulin secreted competed linearly with rat insulin in RIA, the majority of the insulin antigenicity comigrating with rat insulin on G-50 Sephadex chromatography. With continuing propagation the IRI activity diminished; however 3 selected cultures demonstrated increased secretion of IRI following stimulation with glucose. These findings indicate that glucose-induced insulin secretion can be obtained in non-beta cells; however the frequency of success was below one stable transfection for every 5 X 10(8) Ltk- cells exposed to the transfection procedure.

Delayed-onset chloroquine retinopathy

Delayed-onset chloroquine retinopathy was diagnosed in a patient seven years after cessation of treatment by a total dose of 730 g of chloroquine for rheumatoid arthritis. Visual functions continued to deteriorate after the diagnosis. Periodic examinations by ophthalmoscopy and by functional tests such as EOG and visual fields should be continued in patients at risk of delayed-onset chloroquine retinopathy after discontinuance of the drug.

Pouch ileitis--recurrence of the inflammatory bowel disease in the ileal reservoir

"Pouchitis" is an inflammation of the ileal pouch that has been described as occurring after Kock's procedure--the continent ileal pouch. The case presented herein demonstrates clinical and histological features that resemble ulcerative colitis, implying that this disorder may be a recurrence of the patient's original inflammatory bowel disease and not merely a local and nonspecific process as previously suggested.

Electrophysiological correlates of visual masking

The phenomenon of paracontrast documented by means of psychophysical techniques has not been readily demonstrable using electrophysiological responses as an index of masking. We have analyzed averaged cortical potentials during presentation of visual stimuli that produce psychophysical masking. Differences in the masking profiles obtained from the two experimental conditions are apparent. However, both electrophysiological and psychophysical data do indicate an interaction between responses to an annulus and a disc which varies with the time interval between the stimuli. Both sets of data also reflect differences in masking between right and left eyes. We conclude that the cortical potentials evoked by temporally disparate stimuli do interact, but that the masking profile is not identical to the profile obtained by psychophysical methods.

Relative potencies of human and pork insulin during i.v. and oral glucose tolerance test in lean and obese persons

The biological efficacy of biosynthetic human insulin (BHI) of recombinant DNA origin was compared with that of highly purified pork insulin in subjects with normal (lean persons) and decreased (obese persons) sensitivity to insulin. Sequential i.v. administration of glucose with increasing insulin doses under somatostatin coverage was used to establish the dose-response characteristics of insulin-induced glucose clearance [insulin vs. Kg (glucose disappearance rate, %/min). Insulin was also given s.c. prior to an oral glucose tolerance test (OGTT) performed under somatostatin blockade; the appearance of insulin in serum and the modification of glucose levels were followed. The insulin vs. Kg dose-response curve was flatter and shifted to the right in obese persons compared with lean persons, demonstrating insulin resistance. In both lean and obese subjects, BHI and pork insulin had comparable effects on glucose clearance. Similarly, the effect of s.c. insulin on the serum glucose values during OGTT was the same when BHI or pork insulin were used. The absorption characteristics from the injection site were similar for both insulins. Thus, in man, human and pork insulin have similar pharmacokinetic and biological characteristics.

Dissociation of effects of insulin and contraction on glucose transport in rat epitrochlearis muscle

The effects of insulin and contraction on glucose transport and metabolism were investigated in rat epitrochlearis muscles in vitro. Insulin dose-response curves showed a threshold (approximately 50 microunits/ml) and saturation-type (approximately 1 mU/ml) kinetics, whereas isometric contraction activated glucose transport and metabolism in a linear fashion with no evidence of a threshold. Insulin and contraction increased the apparent maximal rate of uptake of the hexose transport system with minimal effect on its apparent Km. The stimulatory effects of insulin and contraction were additive; similar results were obtained with 2-deoxy-D-glucose. Contraction stimulated glucose transport in three different preparations of muscles depleted of insulin: 1) exhaustively washed for 2 h, 2) rats infused with anti-insulin serum, and 3) chronically (streptozotocin-induced) diabetic rats. Prostaglandin E2 augmented the effect of a submaximal concentration of insulin on glucose transport without exerting any effect by itself but had no effect on contraction-augmented glucose transport. It is concluded that insulin and contraction activate glucose transport and metabolism via independent mechanisms.

Correction of diabetic pattern of insulin release from islets of the spiny mouse (Acomys cahirinus) by glucose priming in vitro

Insulin release kinetics were studied in perifused islets of Langerhans, isolated from mildly hyperglycaemic and from normoglycaemic spiny mice (Acomys cahirinus), a rodent predisposed to develop spontaneously non-ketotic diabetes. In both groups, insulin response to glucose (16.7 mmol/l) was delayed in comparison with that of rat islets, the release kinetics being analogous to that of human Type 2 (non-insulin-dependent) diabetes. Thirty min priming of the isolated Acomys islets with glucose (16.7 mmol/l) resulted in potentiation of the insulin release to a second stimulation. The degree of potentiation decreased exponentially with the time interval between stimulations, showing a t1/2 of 18 min. Induction of potentiation by glucose was time-dependent, giving a maximal effect after 20 min of priming. In addition to overall amplification of the insulin response, priming with glucose accelerated markedly the initial release rates, correcting the dynamics of the response. We conclude that: (1) decreased and delayed insulin secretion is found in Acomys cahirinus before the development of hyperglycaemia; (2) induction of time-dependent potentiation in the islet by priming with glucose corrects the diabetic-type dynamics of insulin release; (3) therefore the deficient insulin release of Acomys is of a functional nature, the mechanism of potentiation bypassing the defect; (4) since insulin release in Acomys resembles that in prediabetic and diabetic man, similar conclusions might apply to the islet dysfunction in Type 2 diabetes.

Time-dependent inhibition of insulin release: suppression of the arginine effect by hyperglycaemia

Brief stimulation of the pancreas with arginine causes a refractory state which reduces the insulin response to subsequent stimulations (time-dependent inhibition). In control subjects, a pair of arginine injections (75 mg/kg) at a 30-min interval resulted in 20% reduction of peak and integrated insulin responses to the second injection. In Type 2 (non-insulin-dependent) diabetic patients and in obese subjects, the inhibitory effect of repeated arginine stimuli was abolished. Healthy subjects were made acutely hyperglycaemic (9.3 +/- 0.3 mmol/l) by the glucose clamp technique. This induced a three- to fivefold greater insulin response to arginine. Compared to the response of diabetic subjects with similar hyperglycaemia, the control subjects secreted four to nine times more insulin. When the arginine stimulation was repeated 30 min later, no inhibition was observed, the second insulin response being instead augmented 1.5- to 1.8-fold. We conclude that (1) the insulin response to arginine is markedly reduced in Type 2 diabetes; (2) arginine-induced time-dependent inhibition of insulin release is abolished in patients with minimal to moderate hyperglycaemia; (3) this is probably due to the acute synergistic action of glucose and arginine on the B cell; (4) time-dependent inhibition of insulin release may be a protective mechanism against insulin oversecretion following repetitive stimulation of the pancreas; its abolition in hyperglycaemic states may be a compensatory mechanism, allowing substantial increases in insulin output.

Time-dependent inhibition of insulin release: glucose-arginine interactions in the perfused rat pancreas

The isolated perfused rat pancreas was stimulated sequentially with arginine or glucose to analyze the time-dependent modulation of insulin release. A 10-min perfusion with arginine (5.0 mmol/l) induced 75% inhibition of the insulin response to repeated arginine stimulation 10 min later. When glucose (8.3 mmol/l) was given as two pulses, inhibition of the second insulin response was less pronounced. The inhibitory effect generated by arginine also suppressed the insulin response to glucose (27.7 mmol/l), and this inhibitory effect persisted for over 80 min. Stimulation for 30 min with glucose (27.7 mmol/l) strongly potentiated the insulin responses to a pair of arginine stimuli given 20 min later. However, despite augmented secretion rates, the insulin response to the second arginine pulse was still inhibited by 75%. When insulin secretion was strongly amplified by two 10 min pulses of the synergistic mixture of arginine (5.0 mmol/l) and glucose (8.3 mmol/l), there was no inhibition of the second insulin response. If glucose (8.3 mmol/l) was present during the first arginine stimulation only, the response to the second arginine pulse was inhibited as in control experiments. However, when glucose was added to the second arginine pulse only, the inhibition generated by the first arginine pulse did not express itself, insulin release remaining similar to control.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential control of insulin secretion and somatostatin-receptor recruitment in isolated pancreatic islets

Somatostatin receptors appear to be localized to secretory granules in pancreatic islet homogenates. Recruitment of these receptors to the islet-cell surfaces may mark the contact event between secretory granules and plasma membranes before release of insulin by fission. Isethionate, an impermeant anionic replacement for chloride, blocks the release step but does not affect receptor recruitment. By contrast, low concentrations of phenothiazine drugs, such as trifluoperazine and promethazine, inhibit both receptor recruitment and secretion. Scatchard analysis of phenothiazine effects on somatostatin receptors reveals that these drugs reduce the number of receptors but do not affect the affinity of the receptor for somatostatin. These data indicate that membrane contact and fission steps during exocytosis can be biochemically separated.

Epitrochlearis muscle. I. Mechanical performance, energetics, and fiber composition

An in vitro rat muscle preparation is described that can contract at rates of 12-240 twitches/min. Maximum dF/dt paralleled maximum twitch tension, their ratio being constant at approximately 8 ms for contraction rates of 12-120 twitches/min. Time to peak tension was 8-13 ms, time to peak dF/dt 5-8 ms, and half-relaxation time 4 ms. These parameters were unaffected by rate of contraction or duration of isometric work. Differential ATPase staining demonstrated that 60-65% of the fibers were fast-twitch white, 20% fast-twitch red, and 15% slow-twitch red. The preponderance of fast-twitch fibers correlated with the observed mechanical performance of the muscle. Muscles contracting for 60 min at rates up to 48 twitches/min maintained total adenine nucleotide content (ATP, ADP, AMP) at near resting levels. At higher twitch rates (72-240 twitches/min), total adenine nucleotide content decreased 40%, reflecting exclusively a fall in ATP in the presence of adequate phosphocreatine stores. Adequate oxygenation was reflected by lactate-to-pyruvate ratios in the range of 11-15 at all rates of contraction.

Epitrochlearis muscle. II. Metabolic effects of contraction and catecholamines

Effects of isometric contraction and catecholamines on glucose and glycogen metabolism in skeletal muscle were investigated with the in vitro rat epitrochlearis preparation. Mechanical performance and glycogenolysis exhibited two phases. During the initial 30 min, muscle work was 30% greater and glycogenolysis 8- to 10-fold faster than the steady-state values in the subsequent 3-4 h of contraction. Glucose uptake was increased by contraction and remained relatively constant during stimulation. Epinephrine (10(-9) to 10(-6) M) and norepinephrine (10(-7) to 10(-5) M) produced inotropic and glycogenolytic effects blocked by propranolol but not phentolamine. Chemical sympathectomy and propranolol blocked the initial glycogenolytic and inotropic effects produced by isometric contraction, suggesting that they were caused by the release of endogenous catecholamines. Net lactate production in resting muscles accounted for > 50% of total glucosyl units utilized. During contraction net lactate production accounted < 10-15% of total glycosyl flux indicating that rat fast-twitch pale muscle is capable of significant rates of aerobic glucose oxidation. Oleate and caprylate did not affect mechanical performance, glycogen, or glucose metabolism in resting or contracting muscles.

Cyclic nucleotide levels in the perfused rat heart subjected to hypoxia

Isolated rat hearts were subjected to hypoxic perfusion on a recirculating Langendorff apparatus. Following a 30-min-period of aerobic stabilization the hearts were perfused for 30 min with media equilibrated with 84% N2, 12%O2 and 4% CO2. At the end of the hypoxic period myocardial concentrations of cyclic AMP and cyclic GMP were determined by radioimmunoassay. Exposure to hypoxia resulted in a significant increase in cyclic AMP (p less than 0.01) and a decrease in cyclic GMP (p less than 0.05) as compared to hearts perfused for 60 min with media gassed with 96% O2. 4% CO2.