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Biomedical subjects

J M Kuyl

Publications and source records attributed to J M Kuyl.

At least 19 recordsLinked to original sources
PubMed2001

The influence of long-term exposure of mice to randomly varied power frequency magnetic fields on their nocturnal melatonin secretion patterns.

Disruption of the normal melatonin rhythm has many implications in health and disease. Exposure to magnetic fields is alleged to suppress nocturnal melatonin production, which could implicate magnetic fields in the development of, for example, breast cancer. Magnetic fields of overhead powerlines allegedly pose a risk in the development of childhood leukemia, and the question arises whether changed pineal function could play a role here. In this study two strains of mice were exposed to a rms 50-Hz magnetic field which varied randomly between 0.5 and 77 microT with an average of 2.75 microT and compared to sham-exposed groups. The male mice were exposed for 24 h per day from conception until adult age. Nighttime plasma melatonin values were determined using radioimmunoassay (n=9 for each time point). Statistical comparison was done by nonparametric 95% confidence intervals for median differences to determine nocturnal elevated melatonin values. Although a shortcoming of the study was the small sample size, no statistically significant difference in the nocturnal median elevated melatonin values between exposed and sham-exposed groups could be demonstrated. Long-term and continuous exposure to simulated powerline magnetic fields did not result in a decreased nocturnal melatonin secretion in mice.

Animals↗
PubMed1996

Effect of flavonoids on the outcome of myocardial mitochondrial ischemia/reperfusion injury.

There is evidence that flavonoid intake correlates inversely with coronary heart disease risk. Flavonoids are widely distributed in food and drinks and act as antioxidants and iron chelators. The aim of this study was to determine whether pycnogenol (a flavonoid extracted from the bark of Pinus pinaster) and catechin could minimise the myocardial mitochondrial damage due to ischemia/reperfusion. Using the rat heart model of ischemia/reperfusion we found that pycnogenol had no significant effect on the resultant damage, while catechin suppressed the observed elevation of low molecular weight iron during ischemia/reperfusion which might explain the significantly reduced mitochondrial injury when using catechin in the perfusate. Our results suggest that some flavonoids might be effective in minimizing ischaemic/reperfusion injury and would require further detailed investigation.

Animals↗
PubMed1994

Effects of a low-insulin-response, energy-restricted diet on weight loss and plasma insulin concentrations in hyperinsulinemic obese females.

The effects of two low-energy diets on serum insulin concentrations and weight loss in obese hyperinsulinemic females were compared during a 12-wk period. The first diet (n = 15) was designed to evoke a low insulin response (ID), and the second (n = 15) was a conventionally balanced diet (ND). After a 12-wk washout period, seven and nine subjects who had been on the ID and ND, respectively, changed to the alternative diet for 12 wk. Variables studied were basal and 30- and 120-min concentrations of blood glucose, insulin, and C-peptide after an oral glucose load; body weight; and energy intake. Mean (+/- SD) weight was significantly reduced after ID and ND (9.35 +/- 2.49 and 7.41 +/- 4.23, respectively). The mean weight loss was more after ID. Fasting insulin concentrations decreased more after ID compared with ND (91.3 +/- 61.8 vs 21.0 +/- 71.5 pmol/L; P < 0.05). We conclude that ID significantly reduces serum insulin concentrations and weight in obese hyperinsulinemic females.

Adult↗
PubMed1994

Ischemia/reperfusion injury is aggravated by an iron supplemented diet and is partly prevented by simultaneous antioxidant supplementation.

In humans high levels of storage iron as well as low iron binding capacity are considered risks for ischemic heart disease development. The aim of this study was to determine whether a diet containing iron to a concentration of the recommended upper limit alters the degree of myocardial ischemic/reperfusion injury on rats and whether simultaneous antioxidant supplementation had any effect. Results indicate that the iron supplemented diet increased the degree of oxidative injury while simultaneous antioxidant supplementation prevented much of this increase. The mechanism for this was probably an elevated hydroxyl radical production due to the enlarged transit iron pool.

Animals↗
PubMed1994

Salicylate in the perfusate during ischemia/reperfusion prevented mitochondrial injury.

Salicylate is widely used as a stable trap for the highly reactive hydroxyl radical. The purpose of this study was to determine whether the addition of salicylate to hearts subjected to ischemia and reperfusion was able to prevent some injury. Salicylate was able to inhibit mitochondrial damage, and preserved ascorbate and alpha-tocopherol depletion due to ischemia/reperfusion in rat hearts. It did not prevent the elevation of low molecular weight iron. We conclude that salicylate functions as an antioxidant and afforded protection against ischemia and reperfusion.

Animals↗
PubMed1994

Antioxidant supplementation partially protects against myocardial mitochondrial ischemia/reperfusion injury, but ascorbate in the perfusate prevented the beneficial effect.

This study was undertaken to investigate whether prior antioxidant supplementation had a beneficial effect on subsequent myocardial ischemic/reperfusion injury and whether addition of ascorbate during ischemia/reperfusion had any effect. Supplementation with antioxidants resulted in elevated concentrations of myocardial alpha-tocopherol, but not of ascorbate. Combined supplementation with alpha-tocopherol, beta-carotene and ascorbic acid gave the highest myocardial alpha-tocopherol concentration. Hearts of rats supplemented with antioxidants was partially protected to ischemia/reperfusion as indicated by the mitochondrial function. However, addition of ascorbate during ischemia/reperfusion nullified this protective effect.

Administration, Oral↗
PubMed1992

Experience with a provocative test of calcitonin release as a prospective screening for preclinical medullary thyroid carcinoma in MEN type 2A family members.

We report our experience with a provocative test of calcitonin (CT) release using a combined stimulus of intravenous 10% CaCl2 solution and pentagastrin on 34 normal adults (15 females: age 41 +/- 12.3 years and range 22-65 years; and 19 males: age 43 +/- 9.1 years and range 23-60 years) and in 44 family members of three proven multiple endocrine neoplasia type 2A syndrome (MEN 2A) patients. A commercial radioimmunoassay was used to determine the serum CT levels. Peak CT levels were reached within 2 to 5 minutes after administration of the stimulus in all subjects tested. In the group of normal subjects there was no significant difference in the mean basal CT levels between males (54.8 +/- 21.7 pg/ml) and females (56.5 +/- 34.8 pg/ml), whilst the mean peak response values for males was 146.3 +/- 120.6 pg/ml, which was significantly different from the mean value of females, namely 71.6 +/- 39.0 pg/ml. We did not find significant correlations between the basal CT level, peak CT response, and age. Of the 44 family members tested, 9 showed an exaggerated CT response to the combined stimulus and subsequently had a total thyroidectomy. Histological examination confirmed C-cell hyperplasia (CCH) in one and medullary thyroid carcinoma (MTC) in the other 8. Three of the 9 had high basal plasma CT levels. The 9 patients were retested postoperatively and all showed a flat response to the combined stimulus. Those family members with histological proof of MTC or CCH were screened for genetic linkage to the disease gene for MEN 2A using probe MCK2, and showed correlation in each instance.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Observed relationship between ratios HDL-cholesterol/total cholesterol and apolipoprotein A1/apolipoprotein B.

Epidemiological evidence suggests that the ratio HDL-cholesterol (HDL-C)/total cholesterol (TC) or apolipoprotein A1 (apo A1)/apolipoprotein B (apo B) are good indicators of coronary heart disease risk. In investigating the distribution of these ratios in the typical population served by our routine laboratory, we analysed the lipid results of 541 serum samples submitted over a 2-month period for TC, HDL-C, apo A1, and apo B. Good correlation was observed between HDL-C and apo A1 (r = 0.664), and between TC and apo B (r = 0.674). Surprisingly, the correlation between the ratios HDL-C/TC (range: 0.05-0.40) and apo A1/apo B (range: 0.27-3.71) was even higher (r = 0.822). Similar significant correlations were observed in 31 heterozygous and 20 homozygous familial hypercholesterolemic subjects, viz. the correlations between HDL-C/TC (ranges: 0.04-0.24 and 0.02-0.12, respectively) and apo A1/apo B (ranges: 0.47-1.84 and 0.15-1.12, respectively) were r = 0.951 and r = 0.972, respectively.

Apolipoprotein A-I↗
PubMed1992

Antioxidant vitamin supplementation of smoke-exposed rats partially protects against myocardial ischaemic/reperfusion injury.

Our previous studies showed that exposure of rats to limited periods of cigarette smoke resulted in more severe myocardial damage when their hearts were subjected to myocardial ischaemia/reperfusion. The aim of this study was to determine whether supplementation of rats with antioxidant vitamins alpha-tocopherol and beta-carotene was able to protect their hearts against the increase in ischaemia/reperfusion injury caused by smoke-exposure. The parameters measured were mitochondrial oxidative function, cellular levels of alpha-tocopherol and low molecular weight iron (LMWI). Supplementation with antioxidant vitamins resulted in significantly less mitochondrial functional oxidative damage compared to that observed in the controls. Supplementation did not affect the cellular LMWI content, suggesting that the generation rate of hydroxyl radicals was similar in both groups. The protective effect of alpha-tocopherol and beta-carotene supplementation on the mitochondrial function against ischaemia/reperfusion could be due to their free radical scavenging action. Supplementation with antioxidant vitamins, therefore, had a beneficial effect on the excessive myocardial ischaemia/reperfusion injury of smoke exposed rats.

Animals↗
PubMed1991

Effect of various mixtures of diethylether, halothane, nitrous oxide and oxygen on low molecular weight iron content and mitochondrial function of the rat myocardium.

Anaesthetic drugs can induce reversible as well as irreversible changes in cell membranes and intracellular proteins as well as lipid peroxidation in the liver. Low molecular weight iron species (LMWI) can by their catalytic activity contribute to the generation of free radicals (hydroxyl radicals). Free radicals are a recognisable cause of intracellular damage. Impaired mitochondrial function is also a sign of intracellular damage, which is usually irreversible. Thus, an agent may be cytotoxic when it causes a significant increase in intracellular LMWI. Whether the LMWI arise from ferritin or is released from iron containing proteins, the same reaction occurs. As long as LMWI can undergo redox cycling, hydroxyl radicals can be formed. We investigated the effect of various mixtures of diethylether, halothane, nitrous oxide and oxygen on the intracellular LMWI content and mitochondrial function of the rat myocardium. Hearts isolated from rats anaesthetised with diethylether showed an increase in the cytosolic LMWI compared to the control group. No increase in mitochondrial LMWI was demonstrated. Subsequent perfusion of the isolated hearts showed a further increase in the LMWI. On perfusion the mitochondrial LMWI increased in comparison with controls. Mitochondrial function was significantly impaired as measured by the QO2 (state 3), ADP/O ratio and oxidative phosphorylation rate (OPR). Exposure of rats to 50% nitrous oxide for 15 minutes increased the myocardial LMWI, but had no effect on mitochondrial function. Exposure to room air for 30 minutes before isolating the hearts, still showed a significant increase in LMWI with no detectable change in mitochondrial function.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Toxic cannabis psychosis is a valid entity.

One hundred black men admitted to hospital with acute psychiatric symptoms were investigated for the presence of urinary cannabis metabolites in order to delineate the psychiatric role played by 'dagga', the potent South African cannabinol, in the study population and to determine the diagnostic value of the entity 'toxic psychosis (dagga)'. Cannabinoids were present in 29% of patients, and 31% were discharged with a diagnosis of toxic psychosis (dagga). Clinical and demographic material was gathered for all patients and no consistent differences were found between dagga-positive and dagga-negative patients or toxic dagga psychotic patients and 'functional' psychotics other than a history of recent dagga use and the dagga screening test result. The latter measure was found to be both more sensitive and more specific than the history of dagga use alone. The findings support the routine use of a simple screening test for dagga in the sample population studied. The study demonstrated the heterogeneous nature of the toxic dagga psychosis syndrome by documenting a variety of different clinical presentations, which included schizophrenia (42%), paranoia (26%), maniform psychosis (16%) and organic psychosis (16%).

Adult↗
PubMed1990

Effect of desferrioxamine on reperfusion damage of rat heart mitochondria.

Ischaemia of the myocardium leads to necrosis unless oxygen supply is restored but it has only recently been realised that reperfusion is not without danger. The greatest rate of myocardial damage, as measured by mitochondrial function, occurred during the first 5 minutes of reperfusion in rat hearts subjected to normothermic ischaemic cardiac arrest. Addition of desferrioxamine to the perfusate after 5 minutes of reperfusion did not reverse the mitochondrial damage. It is therefore concluded that desferrioxamine prevents mitochondrial damage caused by ischaemia-reperfusion but does not reverse the damage already present.

Animals↗
PubMed1990

The effect of desferal on rat heart mitochondrial function, iron content, and xanthine dehydrogenase/oxidase conversion during ischemia-reperfusion.

Cardiac mitochondrial function as measured by oxidative phosphorylation is impaired by ischemia; and, this deteriorates even further on reperfusion of the heart. Free oxygen radicals, especially the formation of hydroxyl radicals via the iron-catalyzed Haber-Weiss and Fenton reactions have been implicated in the reperfusion injury. In this study, the effect of desferrioxamine (desferal) in the perfusate on mitochondrial function of isolated rat hearts during different periods of normothermic ischemic cardiac arrest (NICA), and subsequent reperfusion was investigated. Mitochondrial functions measured were the QO2 (state 3); ADP/O ratio and oxidative phosphorylation; the mitochondrial, loosely bound (chelateable) iron (LB-iron); the xanthine dehydrogenase and xanthine oxidase activities. Inclusion of desferal in the perfusion solution significantly improved mitochondrial function during the different NICA periods, and prevented the deterioration of mitochondrial function resulting from reperfusion. Desferal did not significantly affect the LB-iron content of the mitochondria or the ratio of xanthine dehydrogenase/xanthine oxidase activities in the mitochondria during NICA or reperfusion. Our experiments suggest that iron, which is free to be chelated by desferal, plays a role in this injury to the rat myocardium.

Animals↗
PubMed1990

Investigation of the effects of oral administration of vitamin E and beta-carotene on the chemiluminescence responses and the frequency of sister chromatid exchanges in circulating leukocytes from cigarette smokers.

Sixty asymptomatic cigarette smokers were randomly allocated into three treatment groups. Smokers in Group 1 received 900 international units of Vitamin E (VE) daily for 6 wk, whereas 40 mg of beta-carotene (BC) daily was administered to those in Group 2 for the same period. Subjects in Group 3 were treated with a matched placebo. Plasma levels of VE and BC as well as circulating leukocyte counts, sister chromatid exchanges (SCEs), and the luminol-enhanced chemiluminescence (LECL) responses of blood phagocytes activated with phorbol myristate acetate (PMA) and FMLP with cytochalasin B (FMLP/CB) were measured prior to the administration of the antioxidant/placebo after 4 and 6 wk of supplementation and 12 wk after cessation of treatment. SCEs and leukocyte counts remained unchanged throughout the trial in all three treatment groups. Administration of VE for 4 wk was accompanied by decreased FMLP/CB-activated (p less than 0.005) and PMA-activated (p less than 0.005) LECL responses. However, with PMA as stimulant, the inhibition of LECL was transient, with partial recovery observed after 6 wk despite continued administration of VE. Administration of BC was associated with progressive inhibition of both FMLP/CB-activated (p less than 0.05 and p less than 0.01 after 4 and 6 wk, respectively) and PMA-activated (p less than 0.025 after 6 wk) LECL. No alterations in LECL responses were observed in Group 3 (placebo). VE appeared to inhibit the generation of oxidants by activated phagocytes, whereas BC scavenged oxidants generated by the myeloperoxidase/H2O2/halide system.

Acridines↗
PubMed1987

Gallstone disease among black South Africans. A review of the Baragwanath Hospital experience.

It has been suggested that gallstone disease is rare in Africa. The 118 cholecystectomies for this condition performed at Baragwanath Hospital over the 3-year period 1983-1985 were reviewed; 100 records were available. The male: female ratio was 1:4, the mean age 51 years. Fifty-one per cent of patients presented with acute cholecystitis, 18% with obstructive jaundice, 9% with pancreatitis and only 22% with biliary colic. The incidence of complicated presentation was higher in the over 60-year-old age group (P less than 0.05). The correct diagnosis was made on admission in only 41% of cases. The mean delay in diagnosis was 5 days; however, the delay was 8 days for patients admitted to the medical wards compared with 2 days in the surgical wards (P less than 0.001). Elective operations were performed on 82% of patients and 18% had urgent surgery. The incidence of common bile duct stones was 22%. The overall mortality rate was 10%; however, the mortality rate was 3.2% for the under-60-year-old group compared with 21% for patients 60 years and older (P = 0.006). This series, which is probably the largest reported in black patients, suggests that greater awareness of acute cholecystitis is necessary in the black patient since there is a rising in-hospital incidence.

Adult↗