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Biomedical subjects

M K Jones

Publications and source records attributed to M K Jones.

At least 19 recordsLinked to original sources

Nuclear bodies in the egg cells of a Gyrodactylus species (Platyhelminthes, Monogenea).

The presence and ultrastructure of distinctive nuclear bodies in a mature 'egg cell' of a Gyrodactylus sp. are described. These electron-dense granular bodies, which appear in section as open or closed rings or as a solid mass are not membrane-bound and lie in clusters close to the nucleolus. The nuclear bodies are compared with the nuclear-inclusion bodies previously reported in platyhelminths. The possible origin, significance and role of the nuclear bodies in this Gyrodactylus sp. are discussed.

Animals

Accumulation of radiocalcium from the aquatic medium via the cloaca and bucco-pharynx of Australian freshwater turtles (Chelidae).

1. The cloacal and bucco-pharyngeal regions of three species of Australian freshwater turtles were experimentally compared for their ability to take up radiocalcium directly from the aquatic medium. 2. The cloacal route was at least 4 times more important than the bucco-pharyngeal route for radiocalcium uptake, in each of the three species investigated. 3. Histological examination of anatomical regions in the cloaca showed that the cloacal bursae of three species (E. dentata, C. longicollis and E. signata) had abundant villi and infolded mucosal epithelia that increase the surface area of the epithelium exposed to the aquatic medium. 4. Electron microscopic studies on the mucosal epithelium of the cloacal bursae showed that it contained many structural characteristics indicative of an exchange function and consistent with the cloacal bursae being an important site of radiocalcium uptake within the cloaca.

Animals

Myoelectric activity of the small intestine in enterotoxin-induced diarrhea of calves.

Electrodes were surgically implanted at 15-cm intervals in the jejunum and ileum of 4 healthy neonatal calves so that myoelectric activity could be recorded on 2 consecutive days. On the first day, each calf received a control treatment, and myoelectric activity was recorded for 340 minutes. Phase I was recorded for a mean of 175.8 +/- 22.8 minutes (51.5%), phase II for 124 +/- 27.4 minutes (36.5%), and phase III for 40.3 +/- 6 minutes (11.9%). On the second day, each calf was treated with approximately 200 micrograms of heat-stable enterotoxin (STa) of Escherichia coli orally. All calves developed diarrhea after the administration of STa. Phase I was recorded for a mean of 92.5 +/- 42.3 minutes (27.2%), phase II for 227.3 +/- 52.5 minutes (66.9%), and phase III for 20.3 +/- 11.4 minutes (6.0%). Increase in phase II and decrease in phases I and III after STa administration were significant (P less than 0.05). Duration of the migrating myoelectric complex was longer after STa administration (median, 64 minutes), compared with the control treatment (median, 54 minutes). Minute rhythms, recorded on the day of toxin administration, ranged from 49 to 153 minutes. There was no difference between the number of migrating action potential complexes on the control days (range, 1 to 10), compared with those on treatment days (range, 1 to 14). These findings are suggestive that enterotoxin-induced diarrhea of calves is accompanied by increased total spiking activity and minute rhythms in the distal portion of the jejunum and ileum.

Animals

The amphipathic helix in the exchangeable apolipoproteins: a review of secondary structure and function.

Site-directed mutagenesis and other molecular biology-based techniques are now available for probing the amphipathic alpha helix structural motif in the exchangeable apolipoproteins. Here we survey the published literature on lipid-binding and functional domains in apolipoproteins A-I, A-II, A-IV, C-I, C-II, C-III, and E and compare these results with recently developed computer methods for analysis of the location and properties of amphipathic helixes. This comparison suggests that there are at least three distinct classes of amphipathic helixes (classes A, Y, and G*) in the exchangeable apolipoproteins whose distribution varies within and between the seven apolipoproteins. This comparison further suggests that lipid affinity resides largely in class A amphipathic helixes (Segrest, J. P., et al. 1990. Proteins. 8: 103) and that variations in structure and/or numbers of class A domains in individual apolipoproteins allow a range of lipid affinities from high to low. The positions of the four alpha helixes recently shown to form a 4-helix bundle globular structure in apoE (Wilson, C., et al. 1991. Science. 252: 1817) correspond closely to the four amino-terminal class G* amphipathic helixes of apoE identified by our computer analysis. It is of particular interest, therefore, that all of the exchangeable apolipoproteins except apoA-II and C-I, contain amphipathic helixes of class G*. Additional implications of amphipathic helix heterogeneity for the structure and function of the exchangeable apolipoproteins will be discussed.

Amino Acid Sequence

Computer programs to identify and classify amphipathic alpha helical domains.

The amphipathic alpha helix is an often-encountered secondary structural motif in biologically active peptides and proteins. An amphipathic helix is defined as an alpha helix with opposing polar and nonpolar faces oriented along the long axis of the helix. In a recent review article we grouped amphipathic helixes into seven distinct classes (A, H, L, G, K, C, and M) based upon a detailed analysis of their physical-chemical and structural properties (Segrest, J. P., et al. Amphipathic helix motif: classes and properties. Proteins. 1990. 8: 103-117). We have developed five computer programs that automate analysis and classification of potential amphipathic helical domains from primary amino acid sequence data. Here we describe these five programs and illustrate their usefulness by comparing two data sets of sequences representing different amphipathic alpha helical motifs from the exchangeable apolipoproteins. In a companion review article (Segrest, J. P., et al. The amphipathic helix in the exchangeable apolipoproteins: a review of secondary structure and function. J. Lipid Res. 1992. 33: 000-000) these five programs are used to localize and characterize the putative amphipathic helixes in the exchangeable apolipoproteins.

Amino Acid Sequence

Severe diabetic retinopathy at presentation in a young man.

A 22 year old man presented with a severe ischaemic diabetic retinopathy and, in spite of photocoagulation therapy, was blind in one eye 16 months after diagnosis. Four similar cases of aggressive diabetic retinopathy are reviewed. There is increasing evidence that a small group of young men with insulin dependent diabetes (IDD) may develop severe diabetic retinopathy at, or soon after, diagnosis.

Adult

US-guided fallopian tube catheterization.

Ultrasound-guided fallopian tube catheterization was performed in seven women a total of 14 times. The women had normal-appearing fallopian tubes at hysterosalpingography and received sperm via the catheter as a way to overcome their inability to conceive. Techniques similar to those used for fluoroscopically guided fallopian tube catheterization were used. Forty-three percent of fallopian tubes were successfully catheterized.

Catheterization

Subcellular composition of platelet density subpopulations prepared using continuous Percoll gradients.

Normal human platelets have been separated by density on continuous Percoll gradients and the subcellular composition of platelets of different density has been analysed. The number and concentration of dense granules increased significantly with platelet density, as did the concentrations of the dense granule constituents calcium and serotonin. The amount of serotonin per granule in the low density (LD) platelets was only two-thirds of the corresponding amount in the high density (HD) platelets. Platelets of all densities were able to sequester exogenous serotonin and release it in response to thrombin stimulation with similar efficiencies. The concentrations of the alpha-granule constituents von Willebrand factor and beta-thromboglobulin increased significantly with platelet density but the concentrations of the lysosomal enzyme beta-N-acetylglucosaminidase and total sialic acid did not differ significantly in the density subpopulations. The concentrations of the cytosolic enzymes lactate dehydrogenase and glucose-6-phosphate dehydrogenase were slightly higher in the LD population than in the other density subpopulations. The concentration of glycogen showed a marked positive relationship with platelet density and calculations suggested that glycogen was an important determinant of platelet density heterogeneity. The findings of the present study are compatible with recent suggestions that LD platelets may be slightly younger than HD platelets in normal human subjects.

Adult

Analysis of plasmid profiling as a method for rapid differentiation of food-associated Clostridium perfringens strains.

Plasmid analysis of over 120 strains of Clostridium perfringens, isolated during food-poisoning incidents and from animal carcasses and food constituents with no association with food poisoning, showed the potential of plasmid profiling as a means of differentiating epidemiologically related strains. On average 65% of freshly isolated strains contained one or more plasmids which could be used in the analysis. Comparison of profiles of strains from unrelated sources or unrelated strains from the same source showed a particularly wide variety of plasmid profiles. Thus the possibility that epidemiologically-unrelated strains might possess similar profiles appears to be very low in this organism. Analysis of serologically-related strains from the same source revealed similar plasmid profiles in all the plasmid-bearing strains examined. A high proportion (71%) of fresh and well-characterized food-poisoning strains possessed plasmids of 6.2 kb in size (compared with 19% of non-food-poisoning strains). The possible role of these plasmids is discussed, since the structural gene encoding the enterotoxin type A was not present on any of the plasmids in the food-poisoning strains tested.

Animals

Circadian alterations in prolactin, corticosterone, and thyroid hormone levels and down-regulation of prolactin receptor activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Studies were initiated to determine whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) affects circadian rhythms of serum prolactin (PRL), corticosterone, thyroxine (T4), and triiodothyronine (T3) in male Sprague-Dawley rats. In addition, the effects of TCDD on PRL receptor activity, as assessed by the ability of PRL to induce ornithine decarboxylase (ODC), were determined. The earliest effect detected following TCDD administration was a significant decrease in the serum PRL concentration compared with that of pair-fed controls within 4 hr (p less than 0.05). This was followed by a significant decrease in serum T4 by 6 hr (p less than 0.05). By 8 hr the serum peak of corticosterone was shifted to 2 hr later in the TCDD-treated rats. This temporal sequence of hormonal changes suggests that the earlier alteration in PRL may be involved in the later alterations in the concentrations of serum T4 and corticosterone. The serum PRL concentration 7 days after TCDD administration was significantly higher (p less than 0.05) in TCDD-treated animals compared with that in pair-fed controls (mean of 20.5 +/- 3.7 vs 13.6 +/- 1.8 ng/ml serum, p less than 0.05, respectively). The elevation of ODC activity in response to PRL, 2 days after TCDD, was decreased in the order of thymus greater than adrenal greater than spleen greater than heart greater than kidney greater than liver. By 7 days, liver ODC activity in response to PRL was only 12% that detected in pair-fed controls. Liver ODC activity in response to dexamethasone and aminophylline was decreased to 25 and 22% of pair-fed controls, respectively, by 7 days after TCDD administration. However, in kidney, TCDD-treated rats had an increased ODC response to aminophylline to 191% of pair-fed controls by Day 7. These results suggest that the ability of TCDD to alter receptor coupling or the receptor number for diverse hormones may play a role in TCDD toxicity.

Aminophylline

Non-adenomatous inappropriate TSH hypersecretion and euthyroidism requires no treatment.

The syndrome of inappropriate TSH secretion is described in a euthyroid girl and her father. Based on nuclear T3 binding studies in fibroblasts, generalized tissue resistance was associated with a lower binding affinity for T3 in nuclear extracts suggestive of a structurally abnormal receptor for T3. Early recognition of the syndrome and observation of the short-term response to thyroid medication prevented unnecessary trials of antithyroid medication and later radical ablative thyroid treatment.

Child, Preschool

Cimetidine versus ranitidine: single-dose, oral regimen for reducing gastric acidity and volume in ambulatory surgery patients.

This placebo-controlled trial compared the efficacy of single oral doses of cimetidine or ranitidine in maintaining intragastric pH and volume greater than 2.5 and less than 25 ml, respectively, in ambulatory surgery patients requiring general anesthesia. Patients were randomized to receive either placebo, ranitidine HCl 150 mg, or cimetidine HCl 400 mg upon rising on the morning of surgery. At induction, the cimetidine and ranitidine groups had significantly higher (p less than 0.05) gastric pH values than the placebo group. At extubation, the ranitidine group had a significantly higher (p less than 0.05) gastric pH than either the cimetidine or placebo group. Both H2-blocker groups had lower volumes when compared with the placebo group at extubation (p less than 0.05). There were more patients at risk for aspiration pneumonitis (pH less than 2.5 and/or volume greater than 25 ml) in the cimetidine group (46 percent) than in the ranitidine group (15 percent). All placebo-treated patients were at risk for aspiration pneumonitis. We did not find subjective clinical evidence of aspiration pneumonitis in our patients. We conclude that both ranitidine and cimetidine are superior to placebo, but ranitidine may be the preferred agent because of its more consistent effect on gastric pH and volume.

Adult

The circadian variation of thyrotrophin in patients with primary thyroidal disease.

We have used a highly sensitive immunochemiluminometric assay (ICMA) for human TSH to study the effect of thyroid status on the circadian variation in TSH levels. Three subjects with Graves' disease, three with toxic multinodular goitre and three with euthyroid multinodular goitre were sampled every hour for 24 h. The results obtained were compared to those from five euthyroid control subjects. It was found that some patients with hyperthyroidism and suppressed basal TSH levels exhibited a 24 h secretory pattern similar to that seen in normal subjects with peak TSH levels occurring at night. In addition two subjects with a euthyroid multinodular goitre demonstrated levels of TSH below the normal range despite being clinically and biochemically euthyroid. TSH suppression in these subjects is probably related to some degree of thyroid autonomy and possible development of hyperthyroidism in the future.

Adult

A phase I trial of dactinomycin intravenous infusion in patients with advanced malignancies.

Eighteen patients with advanced malignancies refractory to other forms of treatment were given dactinomycin (Act D) as continuous intravenous infusions. Their median age was 51 years (range, 36-67); their median performance status was 50 (range, 40-90) on the Karnofsky scale. Act D was administered continuously for 5 days, utilizing a central venous line and a perfusion pump. The starting dose was 0.1 mg/m2/24 hours X 5 days (total dose, 0.5 mg/m2) and was escalated according to a modified Fibonacci scale to 0.2, 0.33, and 0.5 mg/m2/24 hours X 5 days, respectively. Three, three, four, and eight patients were entered, respectively, in each dose level. Toxicities observed were: leukopenia in four patients (nadir leukocyte count less than 1000 cells/nm3 in one patient and 2000-3000 cells/mm3 in 3 patients); thrombocytopenia, with nadir platelet counts between 50,000 and 100,000 platelets/mm3 in 2 patients; stomatitis in four patients; and nausea in three patients. Vomiting was not observed during the infusions. Two patients may have had a radiation recall phenomenon. Blood count depression, nausea, and mucositis were transient, resolving after a few days. One patient at level IV died of sepsis, which was diagnosed on the fourth day of the infusion, before leukopenia intervened. No objective responses were seen. It was concluded that a higher dose of Act D can be given by continuous infusion than by a bolus injection; the authors recommended 0.5 mg/m2/day X 5 days (total dose, 2.5 mg/m2) for further studies.

Adult