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Biomedical subjects

A R Miller

Publications and source records attributed to A R Miller.

At least 73 records · Page 4Linked to original sources
PubMed1989

Sequential histopathologic changes in pancreaticoduodenal allograft rejection in dogs.

To determine the nature and sequence of the histologic changes in the early rejection of pancreaticoduodenal allografts and to assess the correlation between pancreaticoduodenal biopsy findings and the pathologic changes in the graft, we performed serial cystoscopically directed needle biopsies of pancreaticoduodenal allografts in 18 dogs and compared the findings with the histologic changes in 16 autografts as controls. Tissue adequate for evaluation was obtained by the biopsy technique in 70% of instances. The earliest and most characteristic manifestation of rejection was diffuse mixed inflammatory infiltrates involving the pancreatic acinar tissue and duodenum. The biopsy findings correlated well with the changes in the resected pancreatic specimens. Cellular rejection in the duodenum correlated with rejection in the pancreatic graft. There were no changes in the autografts that resembled cellular rejection. We conclude that, in the canine model, cystoscopically directed needle biopsy of pancreaticoduodenal allografts consistently provides adequate tissue for the diagnosis of rejection; the status of the graft can be monitored by serial biopsies of pancreatic acinar tissue and, possibly, by serial biopsies of the duodenal wall alone.

Animals↗
PubMed1989

Jejunal enteropathy associated with human immunodeficiency virus infection: quantitative histology.

Jejunal biopsy specimens from 20 human immunodeficiency virus (HIV) positive male homosexual patients were analysed and compared with those of a control group to determine whether the abnormalities were caused by the virus or by opportunistic infection. The degree of villous atrophy was estimated with a Weibel eyepiece graticule, and this correlated strongly with the degree of crypt hyperplasia, which was assessed by deriving the mean number of enterocytes in the crypts. The density of villous intraepithelial lymphocytes fell largely within the normal range, either when expressed in relation to the number of villous enterocytes or in relation to the length of muscularis mucosae. Villous enterocytes showed mild non-specific abnormalities. Pathogens were sought in biopsy sections and in faeces. Crypt hyperplastic villous atrophy occurred at all clinical stages of HIV disease and in the absence of detectable enteropathogens. An analogy was drawn between HIV enteropathy and the small bowel changes seen in experimental graft-versus-host disease. It is suggested that the pathogenesis of villous atrophy is similar in the two states, the damage to the jejunal mucosa in HIV enteropathy being inflicted by an immune reaction mounted in the lamina propria against cells infected with HIV.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Canine pancreaticoduodenal allotransplantation with cystoduodenostomy: an animal model with clinical application.

Most techniques described in animal models of pancreatic transplantation use either segmental or autotransplants. We employ a technique of pancreaticoduodenal allotransplantation in the dog that closely resembles the operation used in humans. The arterial supply of the entire pancreatic graft is preserved by procuring a Carrel patch of aorta encompassing the origin of the celiac and the superior mesenteric arteries. Splenic, inferior pancreaticoduodenal, and superior pancreaticoduodenal arteries remain intact with the graft. Venous drainage is through a short segment of portal vein. A 6-cm cuff of duodenum is taken with the head of the pancreas. Engraftment proceeds by placing the allograft within the peritoneal cavity of the recipient. End-to-side vascular anastomoses are constructed to distal aorta and inferior vena cava. The duodenal cuff is anastomosed to the dome of the bladder for drainage and analysis of exocrine secretions and to provide a port of entry for cystoscopically directed needle biopsy. A total pancreatectomy is performed to induce a state of diabetes. The average operating time is 5 h. Twenty-two dogs have undergone allotransplantation using this technique. Six dogs had no complications and were sacrificed after meeting criteria of their study protocol. There were three technical failures, two arterial thromboses and one exsanguination, yielding an 86% rate of successful engraftment. Three other dogs died of intussusception and three dogs died of sepsis, one secondary to wound dehiscence and one due to inadvertent common bile duct ligation during pancreatectomy. Wound problems, four dehiscences and two superficial infections, occurred only in immunosuppressed dogs.

Animals↗
PubMed1989

Strategic planning for nursing homes: a market opportunity analysis perspective.

Market opportunity analysis is a framework for systematic strategic planning involving the analysis of demand, market segments, competition, industry, and channels of referrals. This approach enables nursing homes to select target markets and to design marketing programs to attract those target markets.

Costs and Cost Analysis↗
PubMed1988

A set of test life tables for theoretical gerontology.

Prediction of life tables, which provide the most empirical information available about the statistical properties of aging, provides a rigorous test for any theory of aging as manifested at the organismic level of biological organization. For this purpose, a set of test tables for the wild boar (Sus scrofa), domestic sheep (Ovis aries), Dall sheep (Ovis dalli dalli), African buffalo (Syncerus cafer), and hippopotamus (Hippopotamus amphibius) is reconstructed from primary data taken from the literature. The tables, which exhibit a broad range of survival characteristics, satisfy the criteria that (1) the data are statistically sound, (2) their survival functions are concave, except for the limiting case of the convex wild boar function, and (3) the species are natural populations (i.e., are in the same environment in which they evolved). Each test table is reported numerically and as a least-squares regression formula for the age-specific mortality rate over a given range of age.

Actuarial Analysis↗
PubMed1988

Canine pancreaticoduodenal autotransplantation: a preparation for human pancreatic transplantation.

This canine pancreaticodunodenal autotransplantation model includes virtually the entire pancreas attached to a duodenal cuff (second portion). The blood supply is based on the superior pancreaticoduodenal artery and the venous outflow on the gastroduodenal vein. The vascular anastomoses are end-to-side to the external iliac artery and vein. Exocrine drainage is channeled through the bladder from the transplanted duodenum. This technique closely resembles whole-organ pancreas transplant in humans with a cystoduodenostomy. The bowel reconstruction consists of a Billroth I gastroduodenostomy and a cholecystoduodenostomy. The entire procedure is relatively free of major complications and may be performed in less than 4 hours.

Animals↗
PubMed1988

Jejunal mucosal architecture and fat absorption in male homosexuals infected with human immunodeficiency virus.

Diarrhoea and weight loss are common features of human immunodeficiency virus (HIV) disease. The mechanism of diarrhoea occurring in the absence of known enteropathogens is currently unknown. We have measured fat absorption, using the 14C triolein breath test, and quantitatively assessed jejunal villous architecture in 20 male homosexuals at various clinical stages of HIV disease. Enteropathogens were not detected in any subject at the time of jejunal biopsy in stool or jejunal mucosa. Partial villous atrophy was the sole histological abnormality and was detected at any clinical stage of HIV disease. The 14C triolein breath test quantitatively correlated with the degree of jejunal villous atrophy. In addition subjective presence of diarrhoea was related to the detection of fat malabsorption. Thus diarrhoeal disease in HIV infected patients in the absence of enteropathogens may be due to jejunal enteropathy and may be present at early clinical stages of HIV disease.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Gibberellin-mediated synergism of xylogenesis in lettuce pith cultures.

Major gibberellins (GAs) in lettuce (Lactuca sativa L. cv Romaine) pith explants have been identified by gas chromatography-mass spectrometry (GC-MS) or GC-selected ion monitoring (GC-SIM) as GA(1), 3-epi-GA(1), GA(8), GA(19), and GA(20). Treatment of pith explants with indole-3-acetic acid (IAA) (57 micromolar) plus kinetic (0.5 micromolar) induced xylogenesis. In this xylogenic treatment, the concentration of a biologically active, polar GA-like substance(s) increased during the first 2 days of culture, although all of the above GAs decreased (as measured by GC-SIM). In non-xylogenic treatments, where explants were cultured without exogenous hormones, or with IAA or kinetin alone, the concentration of the biologically active, polar GA-like substance(s) decreased during the first two days of culture, as did all of the above GAs (as measured by GC-SIM). Treatment of pith explants with exogenous GA(1) alone did not induce xylogenesis, but GA(1) at very low concentrations (0.0014 and 0.003 micromolar) synergized xylogenesis in the IAA plus kinetin-treated cultures. These results suggest that changes in the concentration of certain endogenous GAs may be involved in xylogenesis mediated by IAA plus kinetin in lettuce pith cultures.

Journal Article↗
PubMed1986

Oxidation of cell wall polysaccharides by hydrogen peroxide: a potential mechanism for cell wall breakdown in plants.

Incubation of cellulose, sodium carboxylcellulose, pectin, polygalacturonic acid, xylan and arabinogalactan with hydrogen peroxide (0.1-10 mM) resulted in rapid breakdown of the polysaccharides when measured by a reduction of solution viscosity or an increase in reducing groups. When the reaction mixtures were precipitated with ethanol or fractionated on G-25-300 Sephadex, low molecular weight reducing groups increased with incubation time indicating that polymer cleavage was occurring and not simply polymer modification. Oxidation was most rapid at pH 6.5 or 7.5, although secondary optima between pH 3.5 and 5.5 were also observed, depending on the polysaccharide. Purified cell walls isolated from various organs of tomato, cucumber and soybean were similarly degraded and the ethanol-soluble reaction products were partially characterized. The data support the hypothesis that hydrogen peroxide generated by peroxidase from NADH may play a role during cell wall breakdown in plants.

Catalysis↗
PubMed1985

Down regulation of the muscarinic cholinergic receptor of the rat prostate following castration.

Prostatic secretion is dependent upon the integrity of the endocrine and autonomic nervous systems and is dramatically influenced by muscarinic cholinergic analogs. In this study, we have used radioligand receptor binding methods on whole tissue homogenates and slide mounted tissue sections of rat prostate to determine whether androgens regulate the density of muscarinic cholinergic receptors in the prostate. The muscarinic cholinergic receptor binding affinities (Kd) of [3H] N-methylscopolamine in prostatic homogenates obtained from intact, castrate, and castrate rats receiving testosterone replacement (castrate + T) were similar (0.07 to 0.10 nM). The muscarinic cholinergic receptor binding capacity decreased 73 per cent following castration. Testosterone administration restored the density of muscarinic cholinergic receptors in castrate rats to intact levels. In order to ensure that the loss of receptor density was not due to a decrease in the epithelial: stromal cell ratio, the number of muscarinic cholinergic receptors per unit area of epithelium was determined in the 3 treatment groups using autoradiography on slide mounted tissue sections. The density of muscarinic cholinergic receptors in a unit area of epithelium was decreased 91 per cent following castration. Testosterone administration restored the density of muscarinic cholinergic receptors in the castrate rats to intact levels. The modulation of neurotransmitter receptors by steroid hormones may be a mechanism by which sex steroids regulate biological responsiveness of target tissues.

Androgens↗
PubMed1984

Introduction of xylem differentiation in lactuca by ethylene.

Evidence was obtained to support the hypothesis that ethylene is involved in xylem differentiation in primary pith explants of Lactuca sativa L. cv Romaine cultured in vitro. Xylem elements differentiated when explants were supplied indole-3-acetic acid (IAA) in combination with either the ethylene biosynthetic precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the ethylene-releasing agent 2-chloroethylphosphonic acid (CEPA), or kinetin. In contrast, no xylem elements differentiated in the presence of IAA, kinetin, ACC, or CEPA alone, or when kinetin was supplied together with ACC or CEPA. These results show that ethylene will substitute qualitatively for cytokinin during auxin-induced xylogenesis, and suggest that both ethylene and auxin are required for xylem differentiation in Lactuca.

Journal Article↗
PubMed1981

A computer model of the evolution of specific maximum lifespan.

To answer the question of why organisms have evolved finite and specific maximum lifespans, I have built and experimentally studied a discrete-event simulation model of the evolution of lifespan. Through natural selection, the model evolves an apparent plateau in maximum lifespan, the height of which is a decreasing function of both the intensity of niche fluctuations and specific fecundity. Evolved lifespan is therefore finite (small and essentially constant over accessible time intervals) and specific. Experiments demonstrate that the plateau is not due to group selection. Instead, it occurs because the rate of increase of maximum lifespan by natural selection - in an environment presenting a finite probability that death will occur prior to reaching the genetically specified maximum - is a decreasing function of maximum lifespan itself and asymptotically approaches zero. This supports in part a class of existing hypotheses that finite lifespan is due to an equilibrium between weak selection, as in the model, and various lifespan-decreasing processes, which however were not simulated in the present experiments. Although the model shows that such counter processes are not strictly necessary for the evolution of finite and specific maximum lifespan, my interpretation of the model's correspondence to organic evolution does imply a counter process, a bias in random genetic drift toward shorter lifespan, that is more general than those previously hypothesized.

Biological Evolution↗