Search PubMed⌕ Search

Biomedical subjects

D J Marsh

Publications and source records attributed to D J Marsh.

At least 91 records · Page 5Linked to original sources
PubMed1996

The identification of false positive responses to the pentagastrin stimulation test in RET mutation negative members of MEN 2A families.

OBJECTIVE: The pentagastrin stimulation test is the traditional test used for the identification of asymptomatic individuals in multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC). The identification of mutations in the RET proto-oncogene segregating with the disease phenotype in MEN 2A and FMTC families has made it possible to re-examine the validity of using this test for the identification of affected family members. DESIGN: Sequential and single pentagastrin stimulation test data were collected following the identification of RET mutation positive and RET mutation negative members of families with MEN 2A or FMTC. PATIENTS: RET mutations were identified in 16 Australian and New Zealand MEN 2A or FMTC families. An analysis of 39 individuals from these families was included in this study. Thirty-two individuals (14 males, 18 females) had previously been determined as RET mutation negative. Seven individuals (6 males, 1 female) had previously been determined as RET mutation positive. Two RET mutation negative males had thyroidectomy based on prior pentagastrin test results. MEASUREMENTS: Serum calcitonin levels in response to stimulation with pentagastrin were measured at 0, 1, 2, 5 and 10 minutes post injection. Mutation analysis of the RET proto-oncogene was performed in all individuals. In two RET mutation negative individuals from two MEN 2A families, thyroidectomy was performed and C-cells were quantitated in order to determine the diagnosis of C-cell hyperplasia. RESULTS: There was a statistically significant difference (P < 0.013) between RET mutation negative male and female mean peak calcitonin responses of 282 +/- 236 and 96 +/- 62 (mean +/- SD) ng/l respectively. False positive responses to pentagastrin stimulation were identified in seven individuals who were RET mutation negative in two of the 16 families. Histologic examination of the thyroid glands in the two RET mutation negative individuals who had thyroidectomy demonstrated C-cell hyperplasia in one but not in the other. CONCLUSIONS: There is considerable overlap between pentagastrin test results in individuals who are RET mutation positive and those who are RET mutation negative. These results indicate a need for routine performance of RET proto-oncogene analysis on all individuals at risk of developing MEN 2A or FMTC and a coupling of pentagastrin test results and RET proto-oncogene analysis in the decision to proceed with thyroidectomy.

Adolescent↗
PubMed1996

Somatic mutations in the RET proto-oncogene in sporadic medullary thyroid carcinoma.

OBJECTIVE: We have determined the frequency of specific mutations in the RET proto-oncogene in sporadic medullary thyroid carcinomas (MTCs) and correlated the presence or absence of a codon 918 mutation with the clinical characteristics of these tumours. DESIGN: Thirty paraffin-embedded sporadic MTCs and two frozen MTCs were collected for analysis of specific mutations in the RET proto-oncogene in codons 609, 611, 618 and 620 (exon 10); 630 and 634 (exon 11); 768 (exon 13); 883 (exon 15) and 918 (exon 16). A novel primer was designed which introduced a restriction site for Rsal in the presence of the specific codon 918 mutation (ATG-->ACG) in these tumour samples. A 'clinical-genetic' correlation was performed comparing the presence of absence of the codon 918 mutation with the following clinical characteristics: age at diagnosis, tumour size, presence or absence of metastases, MTC related morbidity, and base line calcitonin levels at diagnosis or most recent follow-up. PATIENTS: Patients were classified as having sporadic MTC if there was no family history of C-cell hyperplasia, MTC, phaeochromocytoma or parathyroid disease. Retrospective review of patient records enabled complete clinical data to be obtained in 28 of 32 patients. MEASUREMENTS: Base line calcitonin levels were measured by radioimmunoassay or calcitonin enzyme linked immunoassay. Cysteine codons in exons 10 and 11, specifically codons 609, 611, 618, 620, 630 and 634, were screened for the presence of mutations by sequence analysis. Specific mutations occurring at codons 768, 883 and 918 were screened for by restriction endonuclease digestion of PCR products. RESULTS: The mutation at codon 918ATG-->ACG was found in 21 of 32 (66%) MTCs and the mutation at codon 883GCT-->TTT was found in one of 32 MTCs. Where possible, the presence of 'germline-type' mutations in codons 609, 611, 618, 620, 630 and 634 were excluded. Ten MTCs did not have a mutation in codons 768, 883 or 918 of the RET proto-oncogene. The presence or absence of the somatic mutation at codon 918 did not correlate with any of the above clinical characteristics. CONCLUSION: Somatic mutations in the RET protooncogene occur frequently in sporadic MTCs.

Adult↗
PubMed1996

Endothelial Ca2+ in afferent arterioles during myogenic activity.

We measured endothelial Ca2+ concentration ([Ca2+]) in juxtamedullary afferent arterioles in response to step changes in perfusion pressure. Measurements were made with fura 2 using a fluorescence-imaging system designed to measure Ca2+ in whole tissues and minimize potentially harmful effects of ultraviolet illumination. The system yielded the typical sigmoidal relationship between fluorescence-emission ratio and [Ca2+] in vitro and was sensitive to endothelial Ca2+ transients elicited by bradykinin. Our goal was to determine whether changes in endothelial Ca2+ trigger events that cause myogenic vasoconstriction. Bradykinin, acting via endothelial cells, and sodium nitroprusside (SNP), acting independently, triggered vasodilation; bradykinin but not SNP increased endothelial Ca2+. Increased perfusion pressure caused vasoconstriction and a modest rise in endothelial Ca2+. Because the rise in Ca2+ with bradykinin initiates the vasodilation, the small rise in Ca2+ with pressure cannot cause vasoconstriction. Our results suggest that myogenic constriction is triggered from within vascular smooth muscle cells and that some other phenomenon, most likely increased shear stress, increases endothelial Ca2+ and modulates the myogenic reaction.

Animals↗
PubMed1996

Rapid redistribution and inhibition of renal sodium transporters during acute pressure natriuresis.

Acute arterial hypertension provokes a rapid decrease in proximal tubule (PT) Na+ reabsorption, increasing flow to the macula densa, the signal for tubuloglomerular feedback. We tested the hypothesis, in rats, that Na+ transport is decreased due to rapid redistribution of apical Na+/H+ exchangers and basolateral Na+ pumps to internal membranes. Arterial pressure was increased 50 mmHg by constricting various arteries. We also tested whether transporter internalization occurred when PT Na+ reabsorption was inhibited with the carbonic anhydrase inhibitor benzolamide. Five minutes after initiating either natriuretic stimuli, cortex was removed, and membranes were fractionated by density gradient centrifugation. Urine output and endogenous lithium clearance increased threefold in response to either stimuli. Acute hypertension provoked a redistribution of apical Na+/H+ exchanger NHE3, alkaline phosphatase, and dipeptidyl peptidase IV to higher density membranes enriched in the intracellular membrane markers. Basolateral membrane Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) activity decreased 50%, 25-30% of the alpha 1-and beta 1-subunits redistributed to higher density membranes, and the remainder is attributed to decreased activity of the transporters. Benzolamide did not alter Na+ transporter activity or distribution, implying that decreasing apical Na+ uptake does not initiate redistribution or inhibition of basolateral Na(+)-K(+)-ATPase. We conclude that PT natriuresis provoked by acute arterial pressure is mediated by both endocytic removal of apical Na+/H+ exchangers and basolateral Na+ pumps as well as decreased total Na+ pump activity.

Acute Disease↗
PubMed1996

[Ca2+]i in rat afferent arteriole during constriction measured with confocal fluorescence microscopy.

Using confocal fluorescence microscopy, we followed the time course of intracellular calcium concentration ([Ca2+]i) in vascular smooth muscle cells (VSMC) and endothelial cells (EC) of microperfused afferent arterioles isolated from rat juxtamedullary nephrons. Measurements were made while arterioles were exposed to pharmacological agonists or myogenic stimulation. Luminal addition of acetylcholine triggered an immediate increase of [Ca2+]i in EC and vasodilation. Addition of norepinephrine to the bath solution constricted the vessel and initiated periodic oscillations of [Ca2+]i in VSMC and synchronized vasomotion. Increase of perfusion pressure from 80 to 120 mmHg induced an immediate 9.6 +/- 2.9% (P < 0.05, n = 9) increase of [Ca2+]i in VSMC that was sustained. The arteriole dilated transiently when the perfusion pressure was increased, and persistent vasoconstriction to reduced diameter was observed after 35 s. When nitric oxide (NO) production in the perfused vessel was blocked with nitro-L-arginine methyl ester prior to the pressure step, similar profiles of change in VMSC [Ca2+]i were observed and persistent vasoconstriction began after 28 s. The same pressure step triggered an increase of [Ca2+]i in EC by 11.3 +/- 1.1% (P < 0.05, n = 5). These observations suggest that myogenic constriction of afferent arterioles was associated with an increase of [Ca2+]i in VSMC, and the constriction was delayed by endogenous NO production.

Animals↗
PubMed1995

Quantitation of APC mRNA in human tissues.

The aim of this study was to develop a method for quantitation of APC mRNA and to measure APC mRNA levels in human tissues. This was done using a competitive reverse transcription PCR with a synthetic RNA control. APC mRNA (pg/microgram total RNA) was quantitated in the following tissues: normal colon 133.6 +/- 69.0; normal duodenum 16.6 +/- 15.7; normal thyroid 30.4 +/- 20.3; normal esophagus 65.2 +/- 58.8; colonic carcinoma 66.5 +/- 30.3; esophageal carcinoma 54.7 +/- 26.5; papillary thyroid carcinoma 55.8 +/- 32.9 and colonic adenomas from patients with familial adenomatous polyposis 46 +/- 15. APC mRNA levels were significantly lower in the duodenum and thyroid than in the colon and esophagus. The quantity of APC mRNA was lower in colonic adenomas from FAP patients than in normal colonic mucosa (p < 0.05).

Base Sequence↗
PubMed1995

Medullary thyroid carcinoma: recent advances and management update.

Medullary thyroid carcinoma (MTC) is a malignancy of the thyroid C-cells that comprises 5-10% of all thyroid cancers. MTC occurs in both sporadic and familial forms, the latter making up 25% of all MTCs and being comprised of three distinct syndromes--multiple endocrine neoplasia type 2A (MEN 2A), multiple endocrine neoplasia type 2B (MEN 2B), and familial medullary thyroid carcinoma (FMTC). To date, screening for MTC has been performed using the pentagastrin stimulation test, which is a provocative test for calcitonin release. Germline mutations in the RET protooncogene have been identified in families manifesting these syndromes and genetic screening of individuals at risk of one of these syndromes has become integral to their clinical management. The majority of the mutations associated with MEN 2A and FMTC are tightly clustered in a cysteine-rich region of the RET receptor. A single mutation associated with MEN 2B is in the the tyrosine kinase domain of the RET receptor. Somatic mutations have been identified in the tumor tissue of individuals with sporadic MTC and may prove to be helpful markers in discerning the hereditary or sporadic nature of the MTC. There is general agreement that the primary operation for MTC should include total thyroidectomy and central neck lymph node clearance. The role of microdissection for recurrent disease awaits longitudinal evaluation. External radiotherapy, radionuclide therapy, and chemotherapy may have a role in palliation, but have not been proven to have a curative value. Prognostic factors are discussed.

Animals↗
PubMed1995

Genotype-phenotype correlation in multiple endocrine neoplasia type 2: report of the International RET Mutation Consortium.

The International RET Mutation Consortium was first convened as part of the Fifth International Workshop on Multiple Endocrine Neoplasia, Stockholm, Sweden, in an attempt to analyse the relationship of RET mutation and disease phenotype in the autosomal dominantly inherited multiple endocrine neoplasia type 2 (MEN 2) syndromes. Out of 361 families studied, 41% had MEN 2A, 17.7% MEN 2B, 6.4% FMTC and the remaining subjects were unclassified. RET mutations were detected in 87.3% of families overall. Over 93% of MEN 2B families had the RET 918 ATG-->ACG mutation, while the most frequent mutation detected in MEN 2A families was cysteine codon 634 (87% of all mutations).

Carcinoma, Medullary↗
PubMed1995

Patterns of blood pressure variability in normotensive and hypertensive rats.

We sought patterns in mean arterial pressure of normotensive rats and alterations in chronic hypertension. Pressure was recorded for 4-6 days by telemetry from conscious, unrestrained rats and sampled digitally at 3 Hz, using normotensive Sprague-Dawley rats, spontaneously hypertensive rats (SHR), and Sprague-Dawley rats with two-kidney, one-clip renovascular hypertension (2K,1C). Time series analysis was by fast Fourier transform. Power spectra were divided into ultradian (frequencies > 1/day), circadian (frequency = 1/day), and infradian (frequencies < 1/day) domains. In the ultradian band from approximately 0.1 to 10 mHz the spectra were 1/f and without distinct peaks. The slopes were not significantly different among the groups and ranged from -1.03 to -1.61. At frequencies > 10 mHz, power continued to decrease but with a lower slope. A peak centered at approximately 100 mHz was present in both normotensive and 2K,1C rats but not in SHR. SHR had significantly more ultradian power than the others. The circadian rhythm modulated power in the ultradian band. Modulation was most prominent in normotensives, in which the ultradian activity was highest during the night when rats are active and lowest during the day; less pronounced in 2K,1C; and not detectable in SHR. There are regular patterns of blood pressure fluctuations and specific modifications to the patterns by different forms of hypertension.

Activity Cycles↗
PubMed1995

Magnitude of TGF-initiated nephron-nephron interactions is increased in SHR.

We compared the tubuloglomerular feedback (TGF)-initiated nephron-nephron interaction in spontaneously hypertensive rats (SHR) and normotensive Sprague-Dawley (SD) rats. Interaction strength was assessed by measuring stop-flow pressure (delta SFP) responses in pairs of nephrons, where only one nephron of the pair was microperfused. The vascular connection was determined from casts of the nephrons and vessels; length of arteriolar separation between the two glomeruli was measured on the casts. When microperfusion rate was increased from 5 to 50 nl/min, delta SFP in perfused nephrons was 10.6 +/- 0.6 and 10.2 +/- 0.7 mmHg [not significant (NS)] in SD and SHR, respectively. In the matched unperfused nephrons from the same cortical radial artery, delta SFP was 1.3 +/- 0.2 and 2.9 +/- 0.7 mmHg (P < 0.05) in SD and SHR. When the perfused and unperfused nephron originated from different cortical radial arteries, delta SFP in the unperfused nephrons was -0.1 +/- 0.2 and 0.0 +/- 0.3 mmHg (NS) in SD and SHR, respectively. In both strains, interaction strength varied inversely with glomerular separation. When the dependence on distance was taken into account, interaction strength was about threefold greater in SHR than in SD. We conclude that the nephron-nephron interaction is significantly greater in SHR. The dependence of interaction strength on distance separating the glomeruli suggests that the interaction is propagated along the preglomerular vasculature.

Animals↗
PubMed1994

A rapid screening method for the detection of mutations in the RET proto-oncogene in multiple endocrine neoplasia type 2A and familial medullary thyroid carcinoma families.

Multiple endocrine neoplasia type 2A (MEN2A) and familial medullary thyroid carcinoma (FMTC) are autosomal dominant inherited cancer syndromes with incomplete penetrance. Following the identification of mutations in the RET proto-oncogene that segregate with the disease phenotype in MEN2A, MEN2B, and FMTC, genetic screening of individuals with mutations in RET may be performed. We have employed restriction endonuclease digestion of polymerase chain reaction products as an alternative to sequence analysis for rapid identification of mutant gene carriers in families in which MEN2A and FMTC are segregating. Twenty-one Australasian MEN2A and FMTC families have been screened for mutations in a cysteine-rich region of the RET proto-oncogene. Seven independent mutations were identified in key individuals in 16 of these families. We have identified a mutation in codon 620, 2053 T-->C (Cys620Arg), and two mutations in codon 634 of exon 11 of RET, 2095 T-->C (Cys634Arg) and 2096 G-->A (Cys634Tyr), all three of which were present in both MEN2A and FMTC families.

Australia↗
PubMed1994

A dynamic model of renal blood flow autoregulation.

To test whether a mathematical model combining dynamic models of the tubuloglomerular feedback (TGF) mechanism and the myogenic mechanism was sufficient to explain dynamic autoregulation of renal blood flow, we compared model simulations with experimental data. To assess the dynamic characteristics of renal autoregulation, a broad band perturbation of the arterial pressure was employed in both the simulations and the experiments. Renal blood flow and tubular pressure were used as response variables in the comparison. To better approximate the situation in vivo where a large number of individual nephrons act in parallel, each simulation was performed with 125 parallel versions of the model. The key parameters of the 125 versions of the model were chosen randomly within the physiological range. None of the constituent models, i.e., the TGF and the myogenic, could alone reproduce the experimental observations. However, in combination they reproduced most of hte features of the various transfer functions calculated from the experimental data. The major discrepancy was the presence of a bimodal distribution of the admittance phase in the simulations. This is not consistent with most of the experimental data, which shows a unimodal curve for the admittance phase. The ability of the model to reproduce the experimental data supports the hypothesis that dynamic autoregulation of renal blood flow is due to the combined action of TGF and the myogenic response.

Animals↗
PubMed1994

The effect of solution non-ideality on membrane transport in three-dimensional models of the renal concentrating mechanism.

Previous models of the renal concentrating mechanism employ ideal approximations of solution thermodynamics for membrane transport calculation. In three-dimensional models of the renal medulla, predicted urine concentrations reach levels where these idealized approximations begin to break down. In this paper we derive equations that govern membrane transport for non-dilute solutions and use these equations in a three-dimensional model of the concentrating mechanism. New numerical methods were employed that are more stable than those employed previously. Compared to ideal solution models, the urea non-ideality tends to increase predicted osmolarities, whereas NaCl non-ideality decreases predictions.

Biological Transport↗
PubMed1994

Bovine trichomoniasis: Results of a slaughter survey in Colorado and Nebraska.

A total of 2,909 bulls was cultured for the presence of Trichomonas fetus at slaughter at 4 abattoirs in Colorado and Nebraska. Samples were collected using the dry pipette preputial scraping technique and were transported to diagnostic laboratories within 24 h. Of the bulls cultured, 5 were positive. The state of the last origin for each animal was Kansas, 1 bull, Montana, 1 bull, Nebraska, 1 bull, and Utah, 2 bulls. These results indicate and incidence of less than 1% (0.172%) of trichomoniasis in the populations tested, even in the states of Colorado and Nebraska where the larger numbers of bulls were cultured.

Journal Article↗
PubMed1994

Diverse phenotypes associated with exon 10 mutations of the RET proto-oncogene.

Mutations of the RET proto-oncogene are the underlying cause of some cases of Hirschsprung disease (HSCR) and the inherited cancer syndromes multiple endocrine neoplasia types 2A (MEN 2A) and 2B (MEN 2B) and familial medullary thyroid carcinoma (FMTC). In HSCR these mutations are dispersed throughout the gene, while in MEN 2A and FMTC, they are tightly clustered in five cysteine codons of the RET extracellular domain. HSCR and MEN 2 are usually distinct but occasional families have been reported with both diseases. In each of five families with HSCR with or without MEN 2A or FMTC, we have identified a nucleotide substitution in one of the five cysteine codons previously associated with MEN 2A or FMTC. In one family, which had HSCR as its only phenotype, we detected a Cys-->Trp mutation at codon 609 which had not been previously observed. In three families, both HSCR and MEN 2A were associated with a single Cys-->Arg mutation at either codon 618 or 620 of RET. In the fifth family, FMTC and HSCR were present but we could not determine whether HSCR arose from mutation of the RET locus. We suggest that specific mutations in cysteine codons 618 and 620 result in MEN 2A or FMTC, but can also predispose to HSCR with low penetrance.

Base Sequence↗
PubMed1994

Detection of interactions between myogenic and TGF mechanisms using nonlinear analysis.

Previous studies using linear techniques have provided valuable insights into the dynamic characteristics of whole kidney autoregulation and have led to the general conclusion that the myogenic mechanism and tubuloglomerular feedback (TGF) are highly nonlinear control mechanisms. To explore further the dynamic nature of these nonlinear autoregulatory mechanisms, we introduce the technique of nonlinear modeling using Volterra-Wiener kernels. In the past several years, use of Volterra-Wiener kernels for nonlinear approximation has been most notably applied to neurophysiology. Recent advances in algorithms for computation of the kernels have made this technique more attractive for the study of the dynamics of nonlinear physiological systems, such as the system mediating renal autoregulation. In this study, the general theory and requirements for using this technique are discussed. The feasibility of using the technique on whole kidney pressure and flow data is examined, and a basis for using the Volterra-Wiener kernels to detect interactions between physiological control mechanisms is established. As a result of this method, we have identified the presence of interactions between the oscillating components of the myogenic and the TGF mechanisms at the level of the whole kidney blood flow in normotensive rats. An interaction between these oscillatory components had previously been demonstrated only at the single-nephron level.

Animals↗
PubMed1994

Renal blood flow regulation and arterial pressure fluctuations: a case study in nonlinear dynamics.

The arterial blood pressure, a physiological variable on which all renal excretory processes depend, fluctuates over a wide range of amplitudes and frequencies. Much of this variation originates in nonrenal vascular beds to support nonrenal tasks, and the fluctuations provide a noisy environment in which the kidney is obliged to operate. Were it not for renal blood flow autoregulation, it would be difficult to regulate renal excretory processes so as to maintain whole body variables within narrow bounds. Autoregulation is the noise filter on which other renal processes depend for maintaining a relatively noise-free environment in which to work. Because of the time-varying nature of the blood pressure, we have concentrated in this review on the now substantial body of work on the dynamics of renal blood flow regulation and the underlying mechanisms. Renal vascular control mechanisms are not simply reactive but have their own spontaneous dynamics. Both TGF and the myogenic mechanism oscillate autonomously. The TGF oscillation is the better understood of the two. There is an oscillation of tubular pressure, proximal tubular flow, early distal Cl- concentration, and efferent arteriolar blood flow at approximately 35 mHz; all these variables are synchronized when the measurements are made in a single tubule. The autonomous nature of the oscillation is supported by simulations of the nephron and its vasculature, which show that for a reasonable representation of the dynamics of these structures and of the parameters that govern their behavior, the solutions of the equation set are periodic at the frequency of the observed oscillation, and with the same phase relationships among its variables. The simulations also show that the critical variables for the development of the oscillation are the open-loop gain of the feedback system, and the various delays in the system of which convective transport in the axis of the thick ascending limb and signal transmission between the macula densa and the afferent arteriole are the most important. The oscillation in TGF is an example of nonlinear dynamical behavior and is yet another in a long list of oscillations and related dynamics arising in the inherently nonlinear properties of living systems. Some nonlinear systems can bifurcate to states known collectively as deterministic chaos, and TGF is a clear example of such a system. Rats with two different and unrelated forms of experimental hypertension provide tubular pressure records that pass statistical tests for ordered structure and sensitive dependence on initial conditions in the reconstructed state space, two of the hallmarks of deterministic chaos. These records also pass recent more stringent tests for chaos. The significance of deterministic chaos in the context of renal blood flow regulation is that the system regulating blood flow undergoes a physical change to a different dynamical state, and because the change is deterministic, there is every expectation that the critical change will yield itself to experimental discovery.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗