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Biomedical subjects

D Jackson

Publications and source records attributed to D Jackson.

At least 253 records · Page 14Linked to original sources
PubMed1983

Macromolecular absorption by histologically normal and abnormal small intestinal mucosa in childhood: an in vitro study using organ culture.

Knowledge of the mechanism of macromolecular absorption in the small intestine is based largely on animal studies. We have attempted to assess qualitatively and quantitatively the amount and the mechanism of uptake of horseradish peroxidase (HRP), a model macromolecule, in human small intestine, employing biopsy material from children undergoing gastrointestinal investigations. The biopsy material was incubated in culture medium containing HRP, and a comparison was made between histologically normal and histologically abnormal biopsies. In the normal specimens HRP was detected in pinocytotic vesicles along the villous epithelium. It was also seen in multivesicular bodies and in the interepithelial cell spaces at the base and tip of the villus. These latter areas corresponded to regions where damaged and extruding enterocytes, diffusely penetrated by HRP, were seen. This demonstrates that intact macromolecules can be taken up by normal small intestine in vitro in childhood and indicates two possible routes of antigen entry: (a) by active absorption through intact enterocytes and (b) through damaged or extruding cells. In the abnormal specimens the distribution of HRP was more varied. Most specimens showed an increased presence of HRP in the interepithelial cell spaces and an increased number of enterocytes diffusely penetrated by HRP, but a decrease in pinocytosis in the most severely abnormal enterocytes. An increase in HRP was also observed in the basement membrane and, in one instance, within capillaries of the lamina propria. It was concluded that when an enteropathy is present, an increase in mucosal permeability to macromolecules may result. This is most likely due to an increase in the passive diffusion of macromolecules into the mucosa.

Adolescent↗
PubMed1982

Growth, development, and reassessment of hypothyroid infants diagnosed by screening.

Thirty]six neonates in whom hypothyroidism was diagnosed after thyroid stimulating hormone screening were reassessed at 1 year. All had grown satisfactorily and the mental development scores were normal in all except two. Treatment was withdrawn in 32 and persistent hypothyroidism was confirmed in 31 cases. Thyroid stimulating hormone concentrations were raised in one-third of cases before the withdrawal of treatment and this was associated with generally lower concentrations of serum thyroxine (T4) and smaller doses of L-thyroxine than in those cases with normal concentrations of thyroid stimulating hormone. In treating congenital hypothyroidism, serum T4 concentrations should be monitored regularly and the dose of thyroxine adjusted to maintain serum T4 in the upper part of the reference range.

Child Development↗
PubMed1982

A behavioural study of the changes in the central nervous system of mice after subchronic treatment with the selective dopamine autoreceptor agonist 3-PPP (dl-3-[3-hydroxyphenyl]-N-n-propylpiperidine).

In naive mice the selective dopamine (DA) autoreceptor agonist 3-PPP (dl-3-[3-hydroxyphenyl]-N-n-propylpiperidine) produced a dose-dependent depression of locomotor activity. The duration of action of the depression was short, with no significant depression being noted one or more hours after a dose of 23.47 mg/kg (expressed as the base). Mice, administered the drug twice daily (23.47 mg/kg, in the morning and the evening, i.p.) for 5 days, were, 15 to 25 hours after the last dose, marginally less sensitive to the locomotor depressant effects of a challenge with the same drug. There was no change in the sensitivity of postsynaptic DA and alpha-adrenergic receptors, as assessed by the locomotor stimulant effects of apomorphine and apomorphine plus clonidine, respectively, in reserpine and alpha-methyltyrosine pretreated animals. However, 3-PPP-pretreated mice were most sensitive to the activating effects of d-amphetamine, and this increased sensitivity was blocked by pretreatment with reserpine. In naive mice, a low, DA autoreceptor selective dose of haloperidol (25 micrograms/kg) potentiated the locomotor stimulant effects of d-amphetamine. One explanation for the data obtained is that subchronic pretreatment with 3-PPP produced DA autoreceptor subsensitivity with no concomitant change in postsynaptic DA or alpha-adrenergic receptor sensitivity. The increased sensitivity to d-amphetamine in the 3-PPP pretreated mice may be due to a reduction in the feedback control exerted by the DA released by the d-amphetamine due to the DA autoreceptors having become subsensitive.

Animals↗
PubMed1982

Passive diffusion in small intestinal mucosa in childhood.

The passive permeability of the small intestinal mucosa in childhood was investigated by studying the penetration of two light- and electron-dense tracer molecules (ruthenium red mol. wt = 1000 and horseradish peroxidase mol. wt = 40 000) into fixed biopsy specimens. Ruthenium red confirmed the presence of damaged and extruding epithelial cells in normal mucosa and showed a significant increase in such cells in abnormal mucosa. Horseradish peroxidase demonstrated that antigenically-sized molecules could enter a proportion of these cells and significantly more cells were penetrated in abnormal mucosa, reflecting the ruthenium red results. Thus, anatomical pathways for passive diffusion of antigen through damaged or extruding cells exist in normal and, to a greater extent, in abnormal small intestinal mucosae in childhood. Further study using living tissue may reveal the importance of this phenomenon in relation to the active uptake of antigen.

Antigens↗
PubMed1982

Structure and variation of human ribosomal DNA: the external transcribed spacer and adjacent regions.

A group of human ribosomal DNA (rDNA) recombinants that include the probable site for initiation of transcription have been examined for sequence polymorphism. A detailed restriction map of one rDNA insert was constructed using plasmid subclones and end-labeled segments. Comparison of 16 similar rDNA inserts by restriction and heteroduplex analysis demonstrated striking conservation of the external transcribed spacer and 18S gene regions, but defined a region where restriction sites for the enzymes Sma I, Hpa II, and Hha I become frequent or variable. This region extends for about 400--800 base pairs (bp) at the left end of the rDNA insert and is postulated to contain nontranscribed spacer sequences. The use of cloned rDNA segments as probes for the restriction analysis of genomic rDNA has demonstrated certain fixed sites in the nontranscribed spacer that do not vary significantly among different individuals or tumor cell lines. In contrast, restriction with the enzyme Sal I reveals several variable fragments, one of which has been found only in a retinoblastoma cell line.

Base Composition↗
PubMed1981

Hepatic collagen synthesis in a rat model of cirrhosis, and its modification by colchicine.

Carbon tetrachloride inhalation in phenobarbitone treated rats caused a rapid rise in hepatic prolyl hydroxylase activity which was followed by an increase in hepatic collagen and free proline concentrations. Colchicine in a dose of 5 micrograms/day largely prevented the increase in hepatic collagen. This effect was not mediated by impairment of prolyl hydroxylase activity. Colchicine is of potential therapeutic value in preventing the progression of chronic liver disease to cirrhosis.

Animals↗
PubMed1981

Ultrasonic angiographic and pathologic correlation of noncystic-appearing renal masses.

The ultrasonic echo pattern of renal masses is retrospectively correlated with the angiographic vascular pattern in 36 cases where a noncystic-appearing mass was identified by either study. Pathologic or cytologic correlation was available in 31 of these masses. In carcinomas the echogenicity was usually found to correlate well with the degree of neovascularity.

Adenocarcinoma↗