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J C Chapman

Publications and source records attributed to J C Chapman.

At least 37 records · Page 2Linked to original sources
PubMed1997

Characterization of ion channels in stimulus-secretion coupling in pancreatic islets.

The regulation of insulin secretion from beta-cells of the pancreatic islets of Langerhans is a highly integrated process involving several plasma membrane ion channels. The key to our understanding of the normal process is the hypothesis that glucose-induced closure of K+ channels leads to a depolarization of the cell membrane potential and the opening of voltage-gated Ca2+ channels. Support for this is provided by direct electrophysiological recordings of ion channel activity, and by recent data that have revealed how gene defects in ion channel subunits leads to the loss of regulated insulin secretion. Here, we review the general features of stimulus-response coupling in beta-cells, and how novel initiatives are providing key insights into beta-cell pathogenesis.

Adenosine Triphosphate↗
PubMed1995

The ovarian dysgenesis normally induced by neonatal thymectomy is prevented by the prior administration of estrogen.

PROBLEM: Neonatal thymectomy (Tx) and estrogen (E2) administration disrupt the reproductive and immune systems of female mice. The current experiment examined the combined effects of the two procedures on ovarian function, performed in sequence, and in reverse sequence. METHOD: Groups of (C57BL/6J x A/J)F1 (B6A) female mice were given four daily injections of 20 micrograms estradiol-17 beta, either from 0 days to 3 days, or from 3 days to 6 days postpartum. In some groups this regimen was combined with thymectomy performed either prior to steroid injection (TX-3), or after steroid treatment (TX-4). Animals were sacrificed between 100 and 110 days of age then ovaries evaluated via light microscopy for dysgenesis and follicular cysts. RESULTS: When E2 treatment followed Tx, the incidence of ovarian dysgenesis was unchanged (study 1, Tx + E2 = 60% ovarian dysgenesis; Tx = 63% ovarian dysgenesis) (study 2, Tx + E2 = 46% ovarian dysgenesis; Tx = 45% ovarian dysgenesis). In contrast, when E2 was given before Tx, ovarian dysgenesis did not occur (study 2, E2 + Tx = 0% ovarian dysgenesis; Tx = 46% ovarian dysgenesis). Ovaries from E2 + Tx animals were characteristic of ovaries from E2-injected animals without Tx. CONCLUSION: The results indicate that E2 injection prevents Tx-induced ovarian dysgenesis, suggesting E2-activation of an extrathymic pathway for thymus function.

Animals↗
PubMed1994

Declining incidence of paediatric burns in Scotland: a review of 1114 children with burns treated as inpatients and outpatients in a regional centre.

This retrospective study of paediatric burns in the Lothian region involved a review of 1114 case notes of children up to the age of 12 years, treated for burns as inpatients and outpatients, during a 3-year period between 1988 and 1990. There were more boys than girls and 79 per cent were below 5 years of age. 71.5 per cent were treated as outpatients only, whereas 28.5 per cent were admitted. The Lothian region had the highest incidence of burns of children in Scotland. There has been a statistically significant downward linear trend in burn rates and admissions in Scotland during the 20 years but in this hospital burns admissions have significantly diminished only since 1987. The number of flame burns has declined and a high proportion of the victims were scalded. Efforts need to be made to reduce the large number of scalds by educational and legislative measures.

Adolescent↗
PubMed1994

Topology of 3 beta-hydroxy-5-ene-steroid dehydrogenase/delta 5-delta 4-isomerase in adrenal cortex mitochondria and microsomes.

3 beta-Hydroxy-5-ene-steroid dehydrogenase/delta 5-delta 4-isomerase (3 beta HSD) is a NAD(+)-dependent membrane-bound enzyme that catalyzes the oxidation of delta 5-3 beta-hydroxysteroids to delta 4-3-keto structures during adrenal, gonadal, and placental steroidogenesis. Enzyme activity is located in both microsomes and mitochondria. In these experiments we examined the membrane topologies of 3 beta HSD in rat and calf adrenal microsomes and mitochondria by comparing access to the active sites of coenzyme and the inhibitor mersalyl, a nonpenetrant organic mercurial anion. Microsomal activity required exogenous NAD+ and was inhibited by mersalyl, indicating that the active site faced the medium in vitro and the cytoplasm in vivo. In contrast, mitochondrial 3 beta HSD used matrix space NAD+, was inhibited by reduction of intramitochondrial NAD(P)+, and was insensitive to mersalyl. Mitochondrial activity was decreased by exogenous NADH (apparent Ki, 2.8 microM) and increased by added NAD+ (apparent Ka, 2.4 microM). However, mersalyl blocked the effects of exogenous NADH and NAD+ and returned the activity to that observed before coenzyme addition. The membrane-sidedness of the NAD+ activation was examined further in submitochondrial particles prepared by sonication of pyridine nucleotide-depleted calf adrenal cortex mitochondria. Particles were prepared in the absence or presence of 10 mM NAD+ and contained none or 2.9-7.3 nmol NAD+/mg protein, respectively. Both groups of submitochondrial particles required exogenous NAD+ for 3 beta HSD activity, indicating that the active site faced the medium (the particles were everted), and the contained NAD+ was inside the particles. However, 3 beta HSD activity was increased 12-140% in particles that contained NAD+. The results suggest that mitochondrial 3 beta HSD is an integral inner membrane protein, that the active site faces the matrix space and is influenced by coenzyme availability, and that a regulatory site(s) faces the intermembrane space. Binding of NAD+ or NADH to this external site increases or decreases, respectively, the rate of catalysis at the active site. Mitochondrial 3 beta HSD activity may be enhanced by oxidation of intermembrane space NADH via an active rotenone- and antimycin-a-insensitive NADH oxidase.

Adrenal Cortex↗
PubMed1993

Radioligand exchange binding cannot directly determine the dissociation constant (Kd) of the rat ventral prostate nuclear androgen receptor: valid Kd determinations require additional uptake binding data.

Radioligand exchange was examined for its ability to derive the dissociation constant (Kd) of the rat ventral prostate nuclear androgen receptor. In one 24-h, 12 degrees C incubation, Scatchard plot analysis of [3H]dihydrotestosterone ([3H]DHT) exchange binding produced a Kd of 6.9 x 10(-9) M. Specific binding of [3H]DHT ranged from 114 to 758 pM, and the extrapolated value for the total number of binding sites (n) was 1320 pM. When aliquots from the same receptor pool were incubated with unlabeled DHT, and bound androgen was measured by radioimmunoassay, each titration point held a concentration of specifically bound unlabeled DHT little different from the preincubation value of bound endogenous ligand (1338 pM), suggesting that few, if any, unoccupied sites were created during the incubation. In a second radioligand exchange assay, unoccupied receptor sites were measured at the end of incubation. Virtually no unoccupied sites were found, though the range of predicted values was 124 to 383 pM (n = 425 pM). The data, in toto, suggest that although radioactive ligand exchanges with bound unlabeled ligand, the dynamics of the process do not include the creation of unoccupied sites. Since the Kd is determined by measuring the concentrations of unoccupied sites, free ligand, and receptor sites bound to ligand, the absence of unoccupied sites suggests that radioligand exchange cannot be used to directly determine the Kd of the prostate nuclear androgen receptor. The numerical value obtained from radioligand exchange, therefore, instead of being a Kd, is very likely the result of a graphic plot of the increase in specific activity of bound radioligand as [3H]DHT is titrated to higher levels. In the last phase of the study a technique was developed which allows for the correct determination of the Kd of the rat ventral prostate nuclear androgen receptor. For the determination, data from an experiment measuring uptake binding into unoccupied sites were combined with data obtained from radioligand exchange binding. From this, the Kd of the receptor was calculated to be 1 x 10(-12) M.

Animals↗
PubMed1992

Changes in mitochondrial and microsomal 3 beta-hydroxysteroid dehydrogenase activity in mouse ovary over the course of the estrous cycle.

3 beta-Hydroxysteroid dehydrogenase (HSD) is located in the endoplasmic reticulum and mitochondria. To determine whether the separate enzymes play different roles in steroidogenesis, the specific activity (SA) of both were measured at four different stages of the mouse estrous cycle. Microsomal HSD activity changed little throughout, averaging 8.7 +/- 0.7 nmol progesterone/min/mg protein. In contrast, mitochondrial HSD activity changed dramatically at diestrus, increasing to 14.4 nmol progesterone/min/mg protein. When measured at proestrus, estrus, and metestrus, mitochondrial HSD activity was 5.5, 7.4, and 4.5 nmol progesterone/min/mg protein, respectively. To ascertain whether the increase in mitochondrial HSD activity at diestrus could be due to a preferential induction of enzyme, its SA and the SA of a mitochondrial inner membrane enzyme, cytochrome C oxidase, were compared to the SA of a mitochondrial outer membrane enzyme, rotenone-insensitive NADH cytochrome C reductase. The SA of all three enzymes changed proportionally at diestrus, suggesting that the increase in mitochondrial HSD activity was not due to its preferential induction. Rather, we believe that the HSD activity in the mitochondrial fraction, as measured at the four stages of the estrous cycle, is a reflection of the combined contributions from an ever changing population of ovarian cells. Mitochondria from luteal cells have the highest HSD activity, and are very likely responsible for the major synthesis of progesterone during the luteal phase.

3-Hydroxysteroid Dehydrogenases↗
PubMed1992

Labyrinthine enhancement on gadolinium-enhanced magnetic resonance imaging in sudden deafness and vertigo: correlation with audiologic and electronystagmographic studies.

Sudden deafness with or without vertigo presents a difficult diagnostic problem. This article describes 12 patients with enhancement of the cochlea and/or vestibule on gadolinium-diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging (MRI), correlating the enhancement with the auditory and vestibular function. All patients were studied with T2-weighted axial images taken through the whole brain, enhanced 3-mm axial T1-weighted images taken through the temporal bone, and enhanced T1-weighted sagittal images taken through the whole brain. Cochlear enhancement on the side of hearing loss was found in all the patients. The vestibular enhancement correlated with both subjective vestibular symptoms and objective measures of vestibular function on electronystagmography. In 2 patients, the resolution of symptoms 4 to 6 months later correlated with resolution of the enhancement on MRI. No labyrinthine enhancement was seen in a series of 30 control patients studied with the same MRI protocol. Labyrinthine enhancement in patients with auditory and vestibular symptoms is a new finding and is indicative of labyrinthine disease. While abnormalities on electronystagmograms and audiograms are nonspecific and only indicate a sensorineural problem, enhanced MRI may separate patients with retrocochlear lesions, such as acoustic neuromas, from those in whom the abnormal process is in the labyrinth or the brain.

Adult↗
PubMed1989

The equivocal presence of nuclear androgen binding proteins in mammalian spermatids and spermatozoa.

The presence of nuclear androgen binding proteins measured by nuclear androgen exchange in rat spermatids and spermatozoa was re-examined. Specific binding was observed to be related to less dense contaminating particles when sonicated testes were fractionated by isopcynic centrifugation through a 40-61% Nycodenz linear gradient. No specific binding was observed in a pure preparation of epididymal spermatozoa collected by retrograde perfusion of the cauda epididymidis, even when a nuclear exchange assay of superior sensitivity was used. Contamination could easily be induced by adding prostatic tissue to epididymal spermatozoa prior to sonication. Despite this strong evidence that the measure of nuclear androgen receptors by nuclear exchange in germ cells is artefactual, the persistence of high endogenous concentrations of 5 alpha-dihydrotestosterone and 5 alpha-diols (but not testosterone) in spermatozoa of castrated rats argues for the opposite conclusion.

Androgen-Binding Protein↗
PubMed1989

The testicular response to hemicastration in the male rat cannot be maintained in vitro.

The testicular response to hemicastration (in which testicular vein testosterone from the remaining testis doubles in concentration) was studied in vitro in order to establish whether the response is maintained after testicular tissue is removed from the animal. Decapsulated testes and collagenase-dispersed cells from decapsulated testes of rats were incubated for 24 h after hemicastration and testosterone production was compared with that in tissue collected at the time of surgery. Testosterone concentration in the remaining testis 24 h after hemicastration was significantly (P less than 0.05) higher than in the testis removed at the time of hemicastration, but testosterone production in vitro was similar in both tissues. Apparently the single testis remaining in a hemicastrated rat requires extratesticular support in order to maintain its stimulated state.

Animals↗
PubMed1989

Testes are asymmetric in the testicular hemicastration response of the male rat.

An enquiry was made into variability in the testicular hemicastration response of the mature rat (doubling of testicular vein testosterone concentration from the remaining testis 24 h after hemicastration). The response was shown to be asymmetric, being more reliable and more robust when the left testis was removed first. Apparently the testicular hemicastration response, which has been shown to be neurally controlled, shares the asymmetry which has been reported recently in the neural regulation of unilateral ovariectomy.

Animals↗
PubMed1986

Medical image management: practical, legal and ethical considerations.

The data acquired by the new medical imaging techniques, in many ways, exceeded our ability to properly store, transmit and use the images produced. As diagnostic imaging procedures become progressively less invasive and traumatic, they are being applied to a much larger patient population. The decrease in memory and other instrumentation costs, along with expanded technological capability of computer systems, has provided medicine an opportunity to create network systems for the storage, processing, recall, and remote location of these diagnostic images. Therefore, problems of access and confidentiality have become increasingly important. This communication will consider certain medical, legal, and ethical aspects of these technologies of data acquisition, storage, manipulation and retrieval.

Computers↗
PubMed1986

Medical image management.

Medical image management is becoming increasingly complex as additional data are produced by equipment using digital techniques. As the requirements to store and display these images increase, the following questions become important: (a) What methods can be used to ensure that information given to the physician represents the originally acquired data? (b) What technology and methods are needed to guarantee that information is presented in a timely fashion when requested? (c) How can an image archiving and transmission system be designed to protect the patient's rights of confidentiality? The authors discuss the legal implications of digital archiving of image information and propose some approaches to designing systems that provide the most information to the physician and yet attempt to minimize infringement of the patient's rights.

Communication↗
PubMed1984

Nuclear androgen binding sites in the male rat. I. Unoccupied sites in the prostate.

A study was made of unoccupied androgen binding sites in the nuclei of ventral prostate glands of male rats. They were measured at 0 degrees C by comparing specific binding of 1 nM [3H]DHT to salt extract of purified nuclei during the first hour with specific binding during both hours. This method was dependent upon demonstrated completion of uptake into unoccupied binding sites within the first hour and linearity of exchange with occupied binding sites during both hours. Unoccupied binding sites were not artefactual. They did not increase if tissue concentration was diluted prior to homogenization, while they decreased if homogenization was delayed after the tissue was minced. They could be occupied, both in vitro (if precharged with at least 1 nM unlabeled DHT) or in vivo, by administering testosterone propionate subcutaneously or by infusing testosterone into the jugular vein. Exposure to a high concentration of unoccupied prostatic cytosolic binding sites (608.4 fmol from castrated rats) as compared to low concentration (29.3 fmol from intact rats) during homogenization had little effect upon nuclear unoccupied binding site concentrations (2.16 fmol/mg DNA vs 2.41 fmol/mg DNA, respectively). In individual rats, concentration of unoccupied nuclear androgen binding sites was 4.61 +/- 1.05 fmol/mg DNA, while total binding site concentration (measured with 10 nM [3H]DHT for 24h at 12 degrees C) was 866 +/- 103 fmol/mg DNA. Unoccupied nuclear binding sites reached their highest concentration in animals 4 months old (15.09 fmol/mg DNA) when animals 21 days through 720 days of age were studied. By use of association and dissociation rates of binding, it was determined that the apparent Kd of nuclear binding sites was 1.11 X 10(-12) M. There were no observed differences between unoccupied and occupied binding sites in steroid specificity or in sedimentation rate in an 8-24% glycerol density gradient. Although no physiological importance can be attributed as yet to unoccupied nuclear androgen binding sites in the prostate, they do provide a convenient comparison with putative androgen binding sites in the nuclei of testicular and epididymal germ cells.

Animals↗
PubMed1984

Nuclear androgen binding sites in the male rat. III. Late spermatids and spermatozoa in the testis, with an introduction to epididymal spermatozoa.

Nuclear androgen binding sites were examined in late spermatids (stages 12-19) which resisted sonication of homogenized testes of mature male rats. The measurement of unoccupied binding sites in salt extract of purified spermatid heads by nuclear exchange at -10 degrees C was developed and validated. As in the prostate, unoccupied nuclear androgen binding sites in sonicated testes were in low concentration, were not artefactual, and could be occupied both in vivo and in vitro by exogenous androgens, and uniquely in hemicastrated rats by endogenously compensated androgens in the remaining testis. The properties of occupied binding sites in salt extract of purified spermatid heads (measured by nuclear exchange at 4 degrees C for 48 or more hours with 5 nM [3H]dihydrotestosterone) were almost identical to those of occupied binding sites in nuclei of the ventral prostate, except for their concentration. However, levels of specific binding activity approaching 50 fmol/mg DNA could be expected in salt extract of spermatid pellets, by use of a sulfhydryl reducing agent (dithiothreitol) prior to salt extraction, a protease inhibitor (phenylmethylsulfonyl fluoride) in all buffers, and optimization of the sonication protocol. Nuclear androgen binding sites of sonicated epididymal spermatozoa, collected by retrograde perfusion of the cauda epididymidis, were found to be completely salt-resistant. These binding proteins could be extracted by 0.4 M KCl if dithiothreitol and dihydrotestosterone were incorporated into the sonication buffer, if phenylmethylsulfonyl fluoride was added to all buffers, and if the purified epididymal sperm pellet was treated with sarkosyl, a non-ionic detergent, just before salt extraction. The salt extract of epididymal spermatozoa which were treated as described above contained two binding components: a soluble form which was eluted from hydroxylapatite by increasing concentrations of phosphate buffers, and a non-soluble form, free of DNA, which remained in the hydroxylapatite column, and which contained most of the androgen binding sites. Affinity (Kd) of dihydrotestosterone to the soluble and insoluble fractions of the steroid-binding protein complex was determined to be 0.7 and 0.1 nM, respectively. Salt-resistance of binding proteins in germ cells was shown to develop significantly in the last stages of spermiogenesis.

Animals↗
PubMed1984

Hypophysectomy and hemivasectomy can inhibit the testicular hemicastration response of the mature rat.

Three questions were asked in an attempt to understand how testosterone (T) concentration in the veins of the remaining testis can double within 24 h after hemicastration in the mature rat without a change in plasma luteinizing hormone (LH) levels. These three questions (and their answers) were: 1) Can the testicular hemicastration response occur in hypophysectomized rats? Answer, No. 2) Does LH binding to the testis increase after hemicastration? Answer, No. 3) Is there a neural route to the testis alternate to the superior spermatic plexi? Answer, Yes, apparently there is, since hemivasectomy contralateral to the excised testis partially suppressed the testicular hemicastration response (150.4 +/- 13.2 ng/ml in hemicastrated, sham- hemivasectomized rats [n = 18] vs. 109.4 +/- 11.6 ng/ml in hemicastrated, hemivasectomized rats [n = 18], P less than 0.026). It was concluded that LH was probably necessary to the testicular hemicastration response but that its presence did not provide a mechanism. The response was mediated at least partly through the inferior spermatic nerves associated with the vas deferens. A possible reason, although highly speculative, for failure to previously block the testicular hemicastration response by bilateral denervation of the superior spermatic plexi (Mock and Frankel , 1982) was that during the 12-wk interval between denervation and hemicastration, testicular innervation functionally transferred from the superior spermatic to the inferior spermatic nerves.

Animals↗