Biohybrid artificial pancreas: long-term implantation studies in diabetic, pancreatectomized dogs.

Diabetic complications such as neuropathy, retinopathy, and renal and cardiovascular disease continue to pose major health risks for diabetic patients. Consequently, much effort has focused on approaches that could replace conventional insulin therapy and provide more precise regulation of blood glucose levels. The biohybrid perfused artificial pancreas was designed to incorporate islet tissue and a selectively permeable membrane that isolates this tissue from the immune system of the recipient. Biohybrid pancreas devices containing canine islet allografts were implanted in ten pancreatectomized dogs requiring 18 to 32 units of injected insulin daily. These implants resulted in good control of fasting glucose levels in six of these animals without further exogenous insulin for periods of up to 5 months.

Influences of sinusoidal electric fields on excitability in the rat hippocampal slice.

The influence of extracellular sinusoidal electric fields on the amplitude of population spikes evoked by single test pulses in excitatory pathways to CA1 pyramidal neurons was studied in rat hippocampal slices. The fields in the tissue were of the order of EEG gradients. Stimulation at 5 Hz, a frequency representative of hippocampal theta activity, was compared with 60 Hz, which is often used in kindling procedures. Brief stimulation (5-30 s) with both 5 and 60 Hz fields (20-70 mV/cmp-p in the perfusing solution) often produced a long-term increase (longer than 10 min) of the population spike. Fields at 60 Hz, but not at 5 Hz, also induced short-term depression (1-6 min) or transient post-field excitation (15-30 s). Prolonged stimulation (3 min) emphasized this frequency dependent response: fields at 5 Hz induced long-lasting potentiation while fields at 60 Hz always resulted in progressive depression persisting for a few minutes after the end of stimulation. These effects appeared as a global response of CA1 neurons. Antidromic responses studied during blockade of synaptic transmission (0.2 mM Ca2+, 4 mM Mg2+) were depressed during and following 3 min field stimulation at either frequency, which could reflect failing calcium mechanisms in the tissue. The field influence on the potential evoked by synaptic or antidromic stimulation was independent of the phase of the sine wave at which the test pulse was delivered, arguing against a direct polarization of the cell membrane by the fields. The experimental evidence suggests a functional role for EEG-like fields in hippocampal excitability.

Long-term effects of sinusoidal extracellular electric fields in penicillin-treated rat hippocampal slices.

Rat hippocampal slices in 0, 0.25, 1.5 or 3 mM penicillin were exposed briefly to extracellular sinusoidal electric fields (20 s, 5 and 60 Hz, 20-40 mV/cm in tissue). Fields induced long-term (min) changes in population spike amplitudes in the CA1 cell layer. Post-field effects included both depression of strongly epileptiform responses and potentiation of weakly epileptiform and normal responses. Endogenous extracellular fields may participate in the dynamic regulation of the course of seizures.

Comparison between the effects of extracellular direct and sinusoidal currents on excitability in hippocampal slices.

The amplitude of population spikes in the CA1 cell layer of rat hippocampal slices was transiently altered during stimulation of the tissue with DC and sinusoidal extracellular electric fields parallel to the dendrosomatic axis of the CA1 pyramidal neurons. Field threshold was about 50 mV/cm in the tissue. Independently, long-lasting (min) increases in population spike amplitude followed sinusoidal fields as low as 7 mV/cm parallel or perpendicular to the cell axis.

Induction of delayed synchronized bursts in hippocampal slices by weak sine-wave stimulation; role of the NMDA receptor.

Weak (20-50 microA) sine-wave stimulation at 60 Hz (SWS) of either the mossy fibers or the Schaffer collaterals promoted epileptiform synchronized bursts in the CA2/3 area of rat hippocampal slices in the absence of epileptogenic agents. Following brief SWSs (2-10 sec every 5 min), delayed synchronized bursts (DSBs) were triggered by weak test pulses in either pathway and transmitted to CA1. The long (2-10 sec) refractory periods which followed synchronized bursts in CA2/3 limited their rate of occurrence. Furthermore, SWS decreased the activity for several minutes in slices that exhibited frequent bursts. DSBs were reversibly blocked by perfusion with the N-methyl-D-aspartate (NMDA) specific antagonist DL-2-amino-5-phosphono-valeric acid (APV). The involvement of NMDA receptors was further suggested by the facilitation of CA2/3 synchronized bursts in medium with NMDA (5 microM) or lacking magnesium, and by iontophoresis of NMDA in the CA2/3 stratum radiatum. The findings that SWS-induced DSBs persisted for hours in undisturbed slices, and that bursts abolished by APV reappeared during washout in control solution, suggest long-term changes in the CA2/3 synaptic region.

Transition from normal to epileptiform activity in kindled rat hippocampal slices.

We previously demonstrated kindling of synchronized bursts (ISs) by repeated sine-wave stimulation (SW: 2-5 sec, 60 Hz, 20-50 microA, every 5 min) in the CA2/3 area of rat hippocampal slices. Here we report the behavior of individual CA2/3 neurons during the kindling procedure. Intra- and extracellular recordings were obtained concurrently before, during and following SW. Test pulses and SWs were applied in CA2/3 or CA1 stratum radiatum. Neuronal response to to intracellular stimulation was tested by 100 msec depolarizing dc pulses or by 2-20 sec sinusoidal currents. The role of the N-methyl-D-aspartate (NMDA) receptor in the transition from normal responses to ISs was assessed by perfusing the slices with a specific antogonist (DL-2-amino-5-phosphono-valeric acid, APV, 50-200 microM). Our results show that kindling of ISs occurred in two steps: (1) via NMDA-dependent depolarizations during SW, or during SW-induced afterdischarges, and (2) through the recruitment of secondary, late EPSPs (1EPSPs), between consecutive SWs. ISs developed from the 1EPSPs, while the early responses (action potentials, EPSPs, and population spikes) remained unchanged. Kindling of ISs occurred with no changes in resting membrane potential, membrane resistance, or threshold of action potentials. APV did not block kindled ISs, but considerably reduced their amplitude and duration, and increased their frequency. These latter findings suggest that APV-insensitive mechanisms, activated through NMDA-dependent processes, were responsible for the triggering of ISs, and that NMDA receptor systems participated in the control of their rate of occurrence.

Evaluation of the hybrid artificial pancreas in diabetic dogs.

Immunoisolation of nonsyngeneic tissue using a selectively permeable membrane is designed to facilitate transplantation without the use of immunosuppression. The authors' studies have evaluated a hybrid artificial pancreas device that is implanted as an arteriovenous vascular shunt. Devices containing allogeneic or xenogeneic islets were implanted in diabetic dogs who had undergone pancreatectomies, and the devices eliminated the requirement for exogenous insulin for control of fasting glycemia in 11 animals for periods ranging from 1 to 8 months. Furthermore, unseeded devices in normal dogs have been shown to remain patent for over 2 years with low doses of aspirin as the only anticoagulant. These results indicate that this approach has potential as a therapy for diabetes.

Tumoral calcinosis. Case report with treatment failure.

Periarticular calcifications are the hallmark of a rare entity: tumoral calcinosis. We have followed for 90 months a nine-year-old black girl with involvement of both shoulders. Seven initial local excisions of the mass on the right shoulder were attempted without complete removal and prompt recurrence after each attempt. The entire lesion on the right side, including a cutaneous ulceration, was managed by en masse surgical excision. Preoperative inpatient medical management in the form of low calcium and low phosphorus diet was unsuccessful. Postoperatively, she has remained free of ulceration; however, after two and a half years, the right mass has again increased in size with compression of the brachial plexus. This recurrence occurred despite strict dietary control starting immediately postoperatively. Although there are many advocates of surgical excision of these lesions and, more recently, several cases reported of successful medical management, we find that often a combination approach is necessary to effectively treat tumoral calcinosis and reduce the rate of recurrence.

Diabinese-Dialume: a potential catastrophe.

An oral hypoglycemic drug (Diabinese-chlorpropamide) was given inadvertently to a nondiabetic with renal insufficiency instead of the prescribed phosphate binder (Dialume-aluminum hydroxide). It was determined from this situation that hemodialysis is of no benefit in removing the drug from serum; the hypoglycemic effect of chlorpropamide is profound in nondiabetics, and the duration of therapy with dextrose infusions can be quite prolonged. We provide recommendations regarding therapy, bedside glucose monitoring, and prevention.

Treatment of idiopathic renal magnesium wasting with amiloride.

We report a case of an 18-year-old female who presented with severe hypomagnesmia due to idiopathic renal magnesium wasting. Only a partial response was noted with magnesium oxide replacement. Treatment with the potassium-sparing diuretic amiloride led to a further rise in the serum magnesium level, a decrease in the fractional excretion of magnesium and improvement in her symptoms. This case demonstrates an effective treatment for idiopathic renal magnesium wasting.

Training for rural general practice.

OBJECTIVE: To identify requirements for vocational training and continuing education programs in rural general practice. DESIGN: A questionnaire was sent to all 487 rural doctors and 140 metropolitan and 140 provincial city general practitioners (GPs) in Queensland. A sample of medical educators, health professional and consumer representatives and rural doctors was also interviewed. Responses were compared by geographical area, practice characteristics and level of postgraduate training. RESULTS: There are significant differences between rural and urban practice profiles. Rural doctors have to practise a range of clinical skills in an environment with restricted access to health professional support, although the need for advanced training in procedural or other skills depends on the type of rural practice. Rural and urban doctors want more influence in determining continuing medical education (CME) programs. Interactive learning methods were rated as the most effective education methods by both rural and urban GPs. Rural doctors were less likely to consider that they spent enough time on CME. CONCLUSION: Vocational training programs should accommodate various rural career objectives, including those requiring advanced levels of procedural work. There is a significant unmet demand for CME tailored to the needs of individual doctors, both rural and urban, but distance and isolation may make this more critical in rural practice. These issues need to be addressed as training opportunities can contribute to improved retention of the rural medical workforce.

A sampling framework for rural and remote doctors.

A pilot survey by telephone interview, followed by a questionnaire of all rural doctors identified in Queensland, was used develop both a definition of rural practice that distinguishes it from urban general practice and a classification of rural and remote practice which assists in sampling of rural doctors. Questionnaire responses in specific geographic areas were compared using chi-square and Mantel-Haenszel chi-square tests. Several factors were found to differentiate rural from urban general practice consistently, thereby enabling a functional definition of rural practice to be developed. Within the broad group of rural doctors, gradients in practice characteristics were found to differentiate doctors in larger rural centres from those in smaller, more remote communities. These gradients were related to the distance and time of travel from support services. They formed the basis of a complex classification of rural and remote general practice. This functional definition of rural and remote medical practice should be considered by researchers of rural medicine issues when sampling rural and remote doctors. The strategies used in this study could be adapted for use in considering practice characteristics of other rural health professions.

Transplantation of islet allografts and xenografts in totally pancreatectomized diabetic dogs using the hybrid artificial pancreas.

Previously the authors reported on a Hybrid Artificial Pancreas device that maintained patent vascular anastomoses in normal dogs and, when seeded with allogeneic canine islets, maintained normal fasting blood sugars (FBS) in diabetic pancreatectomized dogs. Eventual failure of these devices was believed to be related to loss of islet viability and/or insufficient islet mass. The current study evaluates the effect of increased islet mass produced by implantation of two islet-seeded devices in pancreatectomized dogs and compares the results with those from dogs that received a single device. Twelve of fifteen dogs receiving single devices showed initial function as determined by elimination or reduction of exogenous insulin requirement; four showed initial function and seven showed extended function (100 to 284 days). Excessive weight loss (more than 20%), despite normal FBS and insulin dependence, required that four animals in this latter group be killed. Devices seeded with xenogeneic islets have met with limited success. One dog that received two bovine islet-seeded devices achieved function for more than 100 days; the remaining bovine-seeded devices (n = 8) functioned for only 3 to 16 days. Porcine islet-seeded devices were assessed by intravenous glucose tolerance tests (IVGTT). Recipients of two devices seeded with allogeneic islets demonstrated improved IVGTT results when compared to those from pancreatectomized dogs and recipients of single devices but were abnormal when compared to intact animals. Histologic examination of device and autopsy material from all failed experiments was performed and showed no mononuclear cell infiltration of the islet chamber or vascular graft material, only a few incidence of device thrombosis, and varying degrees of islet viability as judged by morphologic and immunohistochemical evaluation. The authors believe they have demonstrated progress toward the development and clinical applicability of the Hybrid Artificial Pancreas.