Biomedical subjects
Publications and source records attributed to M Whittaker.
Discriminant function analysis has been applied to the results of activity and inhibitor measurements carried out on a series of 229 specimens using benzoylcholine and butyrylthiocholine as substrate. The discriminant function was more effective in differentiating cholinesterase genotypes than either a single test or a combination of two tests.
Plasma cholinesterase activity, determined using either benzoyl choline or butyrylthiocholine as substrate, is stable for prolonged periods (greater than 12 months) when stored at -20 degrees C. Likewise, repeated freezing and thawing of plasma did not markedly affect cholinesterase activity.
A simple spectrophotometric assay of phosphoribosyl pyrophosphate synthetase from human erythrocytes is described. The kinetic properties of the enzyme have been determined and are in good agreement with published results. Conditions for storing haemolysates at -20 degrees C are described. The method is suitable for semi-automation.
Venous occlusion in healthy individuals showed no binding of urate under conditions when the expected increased levels of known bound species was demonstrated. Ultrafiltration of serum from 10 healthy controls and five gouty individuals also showed the absence of binding in all cases, as did electrophoretic and chromatographic studies.
An account is presented of a patient who developed ileus, of greater or lesser severity, after each of seven operations (including two extra-abdominal and three Caesarean sections). During her most recent pregnancy, reviewed here, her plasma cholinesterase activity was found to be decreased and it remained low until at least the 6th day post-partum. However, as the normal activity had been gained by 6 weeks after delivery, the phenomenon had evidently been pregnancy-related. Despite receiving suxamethonium by infusion to completion of her Caesarean section, she did not show an abnormally prolonged response, although she did suffer considerable suxamethonium "after-pains". The question is posed of a possible relationship between the postoperative ileus, muscle pains and the decrease in cholinesterase activity.
A patient, with a history of cretinism, who developed suxamethonium apnoea as a consequence of a reduction in plasma cholinesterase activity secondary to the concurrence of pregnancy and liver dysfunction associated with pre-eclampsia is reported. The patient had a normal phenotype for plasma cholinesterase.
For assaying plasma cholinesterase (EC 3.1.1.8) activity and phenotyping by means of dibucaine inhibition, we have compared a commercially available kit, in which butyrylthiocholine is used as substrate, with two reference methods, one using benzoylcholine and the other propionylthiocholine. With 50 different samples of three of the most common genetic variants, we could clearly differentiate the variants with benzoylcholine and dibucaine, whereas there was some overlap of the E1uE1u and E1uE1a phenotypes with the other two substrates at 30 degrees C. The phenotypes were better differentiated at 25 degrees C, and in our hands the use of butyrylthiocholine was preferable to propionylthiocholine for phenotyping with dibucaine. The affinity of the usual and atypical homozygotes for fluoride with butyrylthiocholine gave an inverted response to the affinity of these variants for the anion with benzoylcholine. We suggest that this may be explained by the role of the chromogen or its products in the assay procedure with the thiocholine substrate.
The enzymic activities of erythrocyte phosphoribosyl pyrophosphate synthetase (EC 2.7.6.1) and glutathione reductase (EC 1.6.4.2) have been measured in 54 primary gout patients, 35 individuals having hyperuricaemia and 51 healthy controls. Statistical analyses have shown a significant increase (p less than 0.01) in the enzymic activity of erythrocyte PRPP synthetase in both the hyperuricaemic and gout groups compared with the controls. No correlation between activity and age was found in any of the three clinical groups. A significant decrease (p congruent to 0.01) was found in the enzymic activity of red cell glutathione reductase in the gout group compared with the other two groups. The biochemical significance of the changes in enzymic activities of the two enzymes in primary gout is discussed.
Human erythrocyte acetylcholinesterase and the plasma cholinesterase variants are not only inhibited by propranolol but have been found to show stereospecificity for its isomers. The erythrocyte enzyme has a greater affinity for the L-isomer than either the racemate or the D-isomer. In contrast the plasma cholinesterases have greater specificity for the D-isomer than the other isomer or racemate. The usual enzyme shows greater stereospecificity than the atypical enzyme and these findings present additional evidence that these enzyme variants differ in structure at the catalytic active site. Neither Na+ + K+ -ATPase nor Mg2+-ATPase show stereo-specificity for the isomers of propranolol although both enzymes are inhibited by the drug. The action of the drug on the four enzymes in blood samples obtained from patients having Huntington's disease was found to be identical to those observed on the enzymes in blood samples from healthy controls.
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One hundred and six individuals from 33 families with a history of malignant hyperthermia have been investigated for plasma cholinesterase variants. An increased frequency of the fluoride-resistant gene has been found. Although an adequate explanation for our results is elusive, some hypotheses are discussed.
The inhibitory effect of (+/-) propranolol 1.69 x 10(-4)-1.69 x 10(-7) mol litre-1 on normal and atypical plasma cholinesterase variants was investigated. The atypical enzyme is less sensitive to inhibition by (+/-) propranolol or either of its enantiomorphs than the usual enzyme. Propranolol 8.45 x 10(-6) mol litre-1 was used as differential inhibitor of 643 plasma samples from individuals of known genotype. Although the measurement of propranolol inhibition alone is not always unambiguous for assigning a definite genotype to a given individual, the correlation of propranolol inhibition with fluoride inhibition gives clear differentiation of the E1uE1u and E1UE1f phenotypes as well as other phenotypes.
A steroid, the dibutyrate analogue of pancuronium bromide (9.8 X 10(-8)M), has been used as differential inhibitor in the study of the plasma cholinesterase variants. Pancuronium dibutyrate numbers have been measured for 190 individuals, and the mean values for six of the known genotypes, E1uE1u, E1uE1f, E1uE1a, E1fE1a, E1aE1a, and E1fE1f, have been calculated. Evidence is presented that a combination of the pancuronium dibutyrate number and the fluoride number give better resolution of the six genotypes than the combination of the pancuronium dibutyrate and the dibucaine number. This new differential inhibitor has real potential for revealing the probable existence of new genotypes.
Five differential inhibitors of plasma cholinesterase have been compared using benzoylcholine as substrate. None of the inhibitors (dibucaine, NaF, NaBr, NaCl, or pancuronium dibutyryloxy bromide) could be used singly to resolve all the variants. Better resolution was obtained when two inhibitors were used in conjunction. Clear differentiation of all six genotypes was obtained only with the combined use of pancuronium dibutyryloxy bromide and sodium fluoride. The limitations of some of the parameters are discussed.
Pancuronium bromide, a 3,17-diacetoxy-5 alpha-androstane, and three of its analogues, the 17-desoxy, the 3,17-dibutyryloxy and the 16-N-monoquaternary ammonium derivatives have been used as inhibitors of the usual and atypical plasma cholinesterase variants. In all cases the usual enzyme is more sensitive to inhibition by the substituted steroids than the dibucaine resistant enzyme. The relative affinities of the bis-quaternary ammonium compounds for either enzyme is in the order dibutyryloxy derivative > 17-desoxy derivative greater than or equal to pancuronium bromide. The monoquaternary compound has the least affinity of all the inhibitors for the usual enzyme but the greater affinity for the atypical enzyme. These observations show that the bis-quaternary compounds are very powerful differentiators of the variants. The monoquaternary derivative shows less differential inhibition, but provides additional evidence that the usual and dibucaine resistant variants differ in structure at or near their esteratic active site.
An 11-year-old boy was given halothane, nitrous oxide and oxygen, pancuronium 0.4 mg and suxamethonium 100 mg for induction of anaesthesia. In response to this a marked jaw stiffness occurred which lasted for two minutes and the anaesthesia were terminated. Four hours of apnoea ensued and he suffered generalized severe myalgia lasting for one week. He was found to have atypical plasma cholinesterase with a dibucaine number of 12, indicating homozygocity. This was verified by study of the family. The case shows that prolonged jaw rigidity and myalgia may occur after suxamethonium in patients with atypical cholinesterase despite pretreatment with pancuronium.