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Biomedical subjects

R J Leeming

Publications and source records attributed to R J Leeming.

At least 55 records · Page 3Linked to original sources
PubMed1980

The effects of pathological and normal physiological processes on biopterin derivative levels in man.

Mean serum biopterin derivative levels in adult males and females were 1.75 microgram/l and 1.53 microgram/l respectively, increased with age and followed a cyclic pattern during menstruation. Foetal brain and liver levels at 16 weeks approximated adult concentrations. Wide distribution in adult tissues and variation in concentration independent of serum levels demonstrated local synthesis. Serum levels were significantly decreased in senile dementia, lead poisoning, coeliac disease and malignant carcinoid disease. Abnormal metabolism of phenylalanine in senile dementia suggest lowered levels of tetrahydrobiopterin in tissue. Methotrexate increased serum biopterin levels by inhibition of dihydropteridine reductase; a saturation effect was noted.

Adolescent↗
PubMed1980

Biopterin defect in a normal-appearing child affected by a transient phenylketonuria.

A child diagnosed as having transient phenylketonuria was found to have reduced synthesis of tetrahydrobiopterin and an abnormal clearance of phenylalanine, but he remained clinically normal when on a normal diet. A small amount of 7,8-dihydrobiopterin was found in his serum; this distinguishes the case from that of malignant hyperphenylalaninaemia.

Biopterins↗
PubMed1979

["Transitory" phenylketonuria. A permanent deficit].

Three cases are reported with hyperphenylalaninaemia greater than 1.8 micrometer/ml-1 in the neonatal period, becoming tolerant of a normal regime (3 g protein per kg) without plasma levels of phenylalanine exceeding 0.2 to 0.3 micrometer/ml-1. Atypical kinetics (zero order) of phenylalanine clearance after intravenous perfusion were shown in the three cases at the age of one year and the persistence of the disorder was again demonstrated at the age of five years in two cases by the study of an oral load of phenylalanine. Examination of the parents showed normal fasting levels of phenylalanine and a normal phenylalanine/tyrosine ratio. The observations draw together several previous publications from diverse authors and a new defined entity, "transitory" phenylketonuria, is proposed. It does not always appear to be a homogenous condition, as a partial defect in biopterin synthesis has been shown in the one case. In retrospect no anomaly of this kind was discovered in the other two cases where the mechanism was not elucidated.

Biopterins↗
PubMed1977

Serum folates in man.

In an aseptic microbiological assay of folate compounds and their breakdown compounds, using Lactobacillus casei, Streptococcus faecalis, and Pediococcus cerevisiae, 4a-hydroxy-5methyl-4,5,6,7-tetrahydrofolate and 5-methyl-5,8-dihydrofolate were inactive under all conditions to all three organisms and 5-methyl-5,6-dihydrofolate was inactive unless ascorbate was present in the incubation medium, and then only to L. casei. 5-Methyltetrahydrofolate was active only for L. casei, and activity in purified samples to S. faecalis was due to trace amounts of folic acid. Analysis of S. faecalis values in the serum in normal subjects and in patients with various disorders showed that levels of 10-formyltetrahydrofolate are raised in coeliac disease, leukaemia, rheumatoid arthritis, and schizophrenia. 5-Methyltetrahydrofolate is readily absorbed by normal human subjects and by patients with pernicious anaemia but poorly absorbed by patients with coeliac disease or leukaemia. 5-Methyl-5,6-dihydrofolate was quickly absorbed by normal human subjects, being reflected by a considerably raised level of 5-methyltetrahydrofolate in serum when sodium bicarbonate was given by mouth before the 5-methyl-5,6-dihydrofolate. These higher levels were comparable to those in patients with pernicious anaemia after oral administration of 5-methyl-5,6-dihydrofolate. Oral 5-methyl-5,8-dihydrofolate and 4a-hydroxy-5-methyl-tetrahydrofolate did not appear as microbiologically active folates in the serum. The findings of this study suggest that the availability for biological utilisation of the major dietary folate compounds will depend on the amount of gastric acidity and of ascorbate in the intestinal chyme. Many may be unavailable for metabolic utilization in the body.

Anemia, Pernicious↗
PubMed1976

Biopterin derivatives in normal and phenylketonuric patients after oral loads of L-phenylalanine, L-tyrosine, and L-tryptophan.

Plasma biopterin derivatives studied in 10 normal and 21 phenylketonuric children showed a significantly high concentration in the latter group. Biopterin derivatives correlated with plasma phenylalanine concentration, but in normal adults given an oral phenylalanine load the rate of increase with phenylalanine differed from that in phenylketonuric patients. A patient with hyperphenylalaninaemia, not due to phenylketonuria, had an abnormal biopterin derivatives response to phenylalanine distinct from that of patients with classical phenylketonuria. This may be a useful investigation to differentiate some variants of phenylketonuria.

Administration, Oral↗
PubMed1976

Biopterin derivatives in human body fluids and tissues.

Levels of biopterin derivatives in urine, serum, milk, cerebrospinal fluid, brain, and liver have been measured with the Crithidia fasciculata assay. Normal levels in serum and urine have been given and compared with those in a number of benign and malignant proliferative disorders, phenylketonuria, kidney disease, Parkinson's disease, schizophrenia, controlled epilepsy, rheumatoid arthritis, and pernicious anaemia. The active component of Crithidia factor in serum was 7,8-dihydrobiopterin. Tissue, urine, and some serum samples contained two active materials, the principal one being 7,8-dihydrobiopterin; a minor constituent was probably tetrahydrobiopterin. Serum biopterin levels following methotrexate administration were raised and subsequent administration of folic acid and 5-formyltetrahydrofolic acid further increased serum levels of biopterin derivatives; this was in contrast to the total absence of response to oral folates without prior methotrexate and to 5-methyltetrahydrofolic acid either with or without methotrexate being given.

Adolescent↗