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Biomedical subjects

D A Walker

Publications and source records attributed to D A Walker.

At least 91 records · Page 5Linked to original sources
PubMed1983

Changes in blood pressure and renal function after parathyroidectomy in primary hyperparathyroidism.

Changes in blood pressure and renal function were investigated in 62 patients with primary hyperparathyroidism treated surgically, in an attempt to assess whether or not hypertension and renal impairment should be regarded as important indications for parathyroidectomy. 29% were hypertensive pre-operatively and the blood pressure remained elevated after parathyroidectomy in all of these patients. Hypertension developed for the first time after parathyroidectomy in 45% of those patients who were normotensive before surgery. Renal function was normal initially in 73% and mild renal impairment developed after surgery in 9% of these patients. At the end of the follow-up period, the prevalence of hypertension was higher in patients with renal impairment pre-operatively (88%) than in those with normal renal function (51%). We conclude that hypertension alone should not be regarded as an indication for parathyroidectomy in asymptomatic hyperparathyroidism. No firm conclusions can be reached about the importance of mild renal failure as an indication for surgery and the question is unlikely to be resolved without conducting a prospective controlled trial.

Blood Pressure↗
PubMed1981

Similarity of Ribulose-1,5-bisphosphate Carboxylases of Isogenic Diploid and Tetraploid Ryegrass (Lolium perenne L.) Cultivars.

Partially purified ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) was isolated from diploid and tetraploid cultivars of ryegrass (Lolium perenne L.) using two separate methods. The apparent K(m) (CO(2)) values for the enzymes prepared by either method did not differ significantly between diploid and tetraploid when assayed by two separate techniques. The unpurified enzymes from freshly lysed (and fully functional) protoplasts of both diploid and tetraploid cultivars gave virtually identical apparent K(m) (CO(2)) values. There was no indication of large differences in affinity for CO(2) of illuminated intact protoplasts from the two cultivars.

Journal Article↗
PubMed1981

Addison's disease presenting as a hypercalcemic crisis in a patient with idiopathic hypoparathyroidism.

A patient with idiopathic hypoparathyroidism complicated by Addison's disease is described. The development of adrenal insufficiency was accompanied by a hypercalcaemic crisis. The hypercalcaemia appeared to result from a reduction in the filtered load and enhanced renal tubular reabsorption of calcium. Cortisone therapy was followed by the characteristic renal tubular leak of calcium associated with hypoparathyroidism and a return of the serum calcium to normal. The possible mechanisms for these changes in calcium homeostasis are discussed.

Addison Disease↗
PubMed1981

Huntington's Chorea in South Wales. A genetic and epidemiological study.

A study of Huntington's Chorea in South Wales has shown a prevalence of 7.61 per 100,000 in the counties of Gwent and Glamorgan, with a total population of 1.7 million. Heterozygote frequency is close to 1 in 5,000. Total ascertainment within this area has been attempted, and experience since conclusion of the study has shown no patients who have been omitted apart from those originating outside the area and those new cases with no living affected relatives. Analysis of migration patterns suggests that around 20% of cases in each generation arise from outside Glamorgan and Gwent and that around 12% of first-degree relatives of indigenous cases have left the area. The survey has formed the initial phase of a long-term prospective study of the disease involving systematic genetic counselling of all high-risk individuals and regular surveillance to monitor possible trends in future prevalence.

Genetic Counseling↗
PubMed1980

Regulation of fructose-1,6-biphosphatase activity in intact chloroplasts. Studies of the mechanism of inactivation.

1. The aim of this work was to investigate the mechanism of dark inactivation of fructose-1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) in isolated intact chloroplasts of Triticum aestivum. 2. Dark inactivation of the enzyme, which was rapid under aerobic conditions, was prevented under anaerobic conditions when chloroplasts were incubated in the absence of an electron acceptor. Electron acceptors such as oxaloacetate readily brought about inactivation under anaerobic conditions whether chloroplasts were illuminated or in the dark. Inactivation of the enzyme also occurred if illuminated or darkened anaerobic chloroplasts were exposed to oxygen. 3. Pyocyanine, which catalyses a cyclic electron flow around Photosystem I, also caused inactivation of the enzyme in illuminated, anaerobic chloroplasts. 4. It is proposed that the activity of fructose-1,6-bisphosphatase is regulated by the availability of electrons, and thus by electron acceptors, and that dark inactivation may occur by a direct reversal of the activation process.

Anaerobiosis↗
PubMed1980

Light-mediated activation of stromal sedoheptulose bisphosphatase.

When isolated wheat (Triticum aestivum) chloroplasts were illuminated, the activity of sedoheptulose bisphosphatase increased severalfold. The rate of activation was limited by the size of the carbon pool, and experiments with a partially purified enzyme preparation showed that the degree of reductive activation of the enzyme is governed by the concentration of its substrate.

Chloroplasts↗
PubMed1980

Distribution of Metabolites between Chloroplast and Cytoplasm during the Induction Phase of Photosynthesis in Leaf Protoplasts.

A method for rapid separation of the chloroplast and cytoplasmic fractions from isolated leaf protoplasts of wheat and spinach has been used to determine the distribution of (14)C-labeled products during photosynthesis. In the dark, CO(2) fixation was only 1 to 2% of that in the light and the products were mainly in the cytoplasmic fraction suggesting fixation by phosphoenolpyruvate carboxylase. Label appeared rapidly in the chloroplast fraction following illumination but the amount leveled off after 4 to 5 minutes reflecting the buildup of intermediates to steady state levels. There was only a slight lag before label appeared in the cytoplasmic fraction and it continued to increase at a constant rate reflecting synthesis of neutral products. In the light, the percentage of label in the chloroplast fraction decreased rapidly in the first minute of illumination and was only 10 to 20% in the steady-state. It is suggested that the chloroplast phosphate transporter promotes a rapid transfer of sugar phosphates from the chloroplast to the cytoplasm, even during the induction phase of photosynthesis.

Journal Article↗