Biomedical subjects
Publications and source records attributed to M J Field.
Otitis media is one of the most worldwide prevalent diseases that affects children. The socioeconomic costs may exceed 3.5 billion dollars a year in the United States alone in direct and indirect costs. If a vaccine can be developed that will decrease 1% of the illness this would be significant in this country and probably even more valuable in less developed countries.
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The effects on pancreatic islet allograft survival of donor-specific blood transfusions (DST) in combination with pre- and posttransplant immunosuppression were studied. A total of 12 groups of rats (n = 105) with chemically induced diabetes underwent islet allotransplantation. Multiple DST or third-party blood transfusions (TPT) were given prior to transplantation. Pretransplant immunosuppression consisted of azathioprine and prednisolone, and low-dose cyclosporin A was used for posttransplant immunosuppression. TPT, as well as separate or combined pre- and posttransplant immunosuppression without blood transfusions, did not prolong islet allograft survival. DST resulted in either primary nonfunction of the islet allografts or a markedly decreased islet allograft survival. These findings contrast with the beneficial effect of DST on whole-organ allograft survival in rats previously described by others.
The role of cytotoxic T lymphocytes in the rejection of pancreatic islet allografts remains poorly defined. The present study was designed to assess the ability of in vitro generated cytolytic T lymphocytes to produce allospecific functional and structural damage of mouse pancreatic islets. A mixed lymphocyte-islet coculture model (MLIC) has been developed, in which islets from DBA/2J mice (H-2d) stimulate the generation of allospecific cytolytic T lymphocytes (C57B1/6, H-2b), as measured by lysis of allospecific chromium-labeled tumor targets. Responder C57B1/6 splenocytes sensitized to DBA/2J islets were harvested from the MLIC on Day 5 and cocultured with either freshly isolated DBA/2J or B10.BR (H-2K) islets. Islet injury was determined by assessment of beta cell function after 8 hr (as measured by insulin release in response to a glucose challenge) and islet destruction after 24 hr of coculture with the sensitized splenocytes. Whereas coculture of third party B10.BR islets with MLIC-sensitized C57B1/6 anti-DBA splenocytes had no effect on insulin release or structure, incubation of allospecific DBA/2J islets with these splenocytes resulted in inhibition of insulin release after 8 hr and disintegration of the islets by 24 hr. The depletion of MLIC-sensitized C57B1/6 anti-DBA splenocytes with anti-Lyt2 monoclonal antibody, but not anti-L3T4 monoclonal antibody, prevented the allospecific destruction of fresh islets by the splenocytes in culture. This study suggests that allospecific, cytotoxic T lymphocytes may play an important role in the effector mechanism of pancreatic islet allograft destruction.
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A combination of high-concentration collagenase digestion and density-gradient purification of canine pancreatic tissue made it possible to obtain relatively pure islets which could be quantified and the outcome of intrahepatic autotransplantation correlated with weight-corrected islet counts in the transplanted tissue. Of eleven dogs, seven achieved durable euglycaemia within 24 hours. All of these animals received islet doses of greater than 4,380 per kilogram of body weight. The remaining four animals became progressively hyperglycaemic necessitating sacrifice within one week; they all received islet doses of less than 4,380 per kilogram (p = 0.042). This model is therefore satisfactory for the investigation of preservation injury to islets and of allotransplantation because it identifies prospectively the transplants which ought to succeed, giving evidence for or against additional immune or ischaemic resistance to graft function.
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Ring annelation of the [(aminomethyl)aryloxy]acetic acids produced a series of substituted 6,7-dichloro-2,3-dihydrobenzofuran-2-carboxylic acids. Pharmacologic evaluation of these compounds in rats and dogs indicated that several congeners are extremely potent salidiuretics. Clearance and micropuncture experiments in rats for compound 5a confirmed the high-ceiling diuretic profile and demonstrated that 5a has a site of action at the thick ascending limb of Henle's loop.
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Duct-ligated segmental pancreas transplants with systemic venous drainage were compared to intrahepatic islet grafts for beta-cell mass (proportional to tissue insulin content) and function in diabetic Lewis rats. Rats were serially killed to measure insulin in the segmental pancreas grafts and in the liver of the islet recipients. Segmental pancreas weight was maximum and insulin concentration and content lowest (P less than 0.05) on Day 3 when acute inflammation was present. At 21 days, there was no inflammation, and graft weight had decreased, but not to Day 0 level because of normal growth; insulin concentration was similar on Days 21 and 0. At 3 months, moderate fibrosis of the graft was present, but both total insulin and insulin concentration had increased (P less than 0.05). In the recipients of islet grafts, total insulin in the liver on Day 1 was only 43% of that contained in the original islet preparation, but by 3 months the insulin content in the liver had increased to that transplanted. IVGTT K values were similar in normal rats (-3.5 +/- 0.7%) and in recipients of segmental pancreas (-4.5 +/- 1.6%) and islet (-4.0 +/- 1.5%) grafts at 3 months post transplant. Acute segmental graft pancreatitis resolved, followed by an increase in beta-cell mass. Islet cell damage during transplantation is either reversible or residual viable islets proliferate, and provide metabolic control equivalent to segmental pancreas transplants, even though the final beta-cell mass is less.
To study the effects of ADH on the transport of potassium by the distal tubule and collecting duct system, we performed simultaneous clearance and micropuncture experiments in homozygous Brattleboro rats (with hereditary hypothalamic diabetes insipidus), before and after intravenous infusion of the hormone. Final urinary flow rate was reduced by a factor of 7 after ADH, but fractional potassium excretion increased by 77% for the group as a whole. During free-flow micropuncture, there was no significant difference in fractional delivery of potassium up to the late distal tubule between control (water diuresis) and ADH conditions; thus, the increase in final urinary potassium excretion was mediated beyond this tubular site. However, flow rate of tubular fluid was decreased significantly after ADH in late distal tubular segments, where potassium secretion is a flow-dependent process. To evaluate the possibility of a direct effect of ADH on distal tubular potassium secretion, independent of changes in flow rate, we studied another group of animals by continuous microperfusion, in vivo, of single distal tubules, using an isotonic perfusion fluid so that water reabsorption would be minimal after as well as before the addition of ADH. Under these conditions, a significant stimulation of distal tubular potassium secretion by ADH could be demonstrated. We suggest that this property of ADH may serve to prevent potassium retention during periods of antidiuresis.
To determine the specific effects on renal potassium transport of acute elevations in plasma aldosterone, dexamethasone, and potassium concentrations, we studied adrenalectomized rats prepared such that each factor could be varied independently. Clearance data alone could not be used to deduce the underlying tubular transport effects, however, since infusion of each of these agents was associated with a marked change in urinary flow rate, which may itself have influenced potassium excretion. We therefore used a technique of continuous microperfusion, in vivo, of single superficial distal tubules to evaluate potassium secretion at constant luminal flow rate during each experimental maneuver. Acute aldosterone infusion was associated with a 90% stimulation of potassium secretion by microperfused tubules. However, total kidney sodium excretion and urinary flow rate were markedly reduced, and these factors opposed the direct tubular action of aldosterone, resulting in no net change in the amount of potassium excreted into the final urine. Conversely, dexamethasone had no direct effect on potassium secretion by single microperfused tubules, but it caused a sharp increase in urinary flow and sodium excretion, and secondarily enhanced urinary potassium excretion by 50%. Hyperkalemia per se stimulated renal potassium excretion both via a direct tubular effect and by increasing urinary flow rate. We conclude that urinary potassium excretion after infusion of each of these agents represents the net result of direct tubular effects and secondary flow-mediated changes.
We have studied the effects of the two enantiomeric forms of the diuretic agent, indacrinone (MK-196), upon transport of sodium and potassium by the loop of Henle and distal tubule, using the technique of continuous microperfusion, in vivo, of individual tubular segments in the rat kidney. In the loop of Henle, both the (+)-and (-)-enantiomers, when included in the tubular perfusion fluid at a concentration of 5 X 10(-4) M, inhibited the reabsorption of sodium and potassium, but the (-)-enantiomer was significantly more effective in this regard than the (+)-enantiomer. Although loop sodium reabsorption was incompletely blocked by either form of the drug, potassium reabsorption by the loop was on average abolished by (-)-MK-196 and was actually converted in some experiments to an appreciable net secretory flux. In the distal tubule, both enantiomers inhibited net sodium reabsorption, but neither affected the control level of potassium secretion. These experiments provide direct evidence that the natriuretic effect of this agent is due to actions on sodium transporting sites in the loop of Henle and distal tubule. Furthermore, because potassium transport was affected only in the loop, they suggest that the nature of the cellular cation transport mechanism influenced by the drug may be different at the two nephron sites studied.