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Biomedical subjects

D J du Plessis

Publications and source records attributed to D J du Plessis.

At least 37 records · Page 2Linked to original sources
PubMed1991

Pathogenesis of kidney stones.

Although many risk factors and theories exist in the literature for urinary stone formation, a hypothesis is suggested for the pathogenesis of renal stones. According to the matrix theory, a protein such as uromucoid activates the initial crystallisation process by promoting the formation of calcium oxalate and calcium phosphate crystals as well as clumping in whole urine. We put forward a theory whereby one of the most important factors in the matrix theory would be the composition and concentration of the protein. In support of this hypothesis, emphasis is placed on the activities of urokinase and sialidase.

Humans↗
PubMed1990

Sialic acid concentrations in the urine of men with and without renal stones.

It has been suggested that urinary sialidase may play a role in the formation of renal stones. The present study was therefore undertaken to compare spectrophotometrically the different types of sialic acid concentrations and sialidase activities in fresh first morning urine specimens of men (21-65 years) with (13) and without (9) calcium oxalate renal stones. Although the free urinary sialic acid concentrations of the two groups of men were statistically about the same (P = 0.0614), the total (P = 0.003) and bound (P = 0.0012) urinary sialic acid concentrations differed significantly. Both the total and bound sialic acid concentrations were lower in the urine specimens of the stone patients than in their healthy counterparts. This decrease in urinary sialic acid concentrations was firstly thought to be the result of elevated breakdown enzymes of sialic acid, which would favour the production of pyruvate. However, spectrophotometric determinations of the endogenous pyruvate concentrations of the two types of urine specimens did not differ significantly (P = 0.0708). Secondly, the decrease in total urinary total sialic acid concentration of stone patients, could be attributed to less sialic acid synthesis or less renal excretion. Therefore, the same experiments were repeated using serum of 13 patients and 9 healthy men. Conversely, the total (P = 0.4425) and bound (P = 0.2850) serum sialic acid concentrations were found to be similar in the two types of subjects. However, the free serum sialic acid concentration of stone patients was significantly lower than in the healthy subjects (P = 0.0062).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Correlation between the macromolecular effects of estradiol and catecholestradiols and the total prostatic catecholestrogen concentration.

Various authors have demonstrated that estrogens stimulate both protein and DNA synthesis, as well as cell proliferation. This study was therefore undertaken to investigate the correlation between these physiological effects of estrogens and the total prostatic catecholestrogens. Either 17 beta-estradiol (5 ng), 2-hydroxyestradiol (40 ng), 4-hydroxyestradiol (17 ng), propane-1,2-diol or a saline solution was injected intraperitoneally to 22-day-old Sprague-Dawley rats daily. Regardless of the treatment, the prostate mass, the rate of DNA or protein synthesis correlates positively with the total prostatic catecholestrogen concentration. We therefore conclude that the effect of each estrogen per se should be regarded in terms of the total prostatic catecholestrogen concentration.

Animals↗
PubMed1990

Influence of sialic acid on the binding activity of estrogen receptors.

The influence of sialidase and sialyltransferase on the binding of 3H-estradiol to estrogen receptors in baboon uterus was investigated to ascertain if sialylation was involved. Specific binding capacity increased approximately 37% in the presence of sialidase, although Kd values essentially remained unchanged. 3H-Estradiol binding was correlated with free sialic acid in the presence of either sialidase or sialyltransferase. As sialidase concentrations were increased, 3H-estradiol binding and free sialic acid concentration increased linearly (r = 0.937, p less than 0.001). Incubation of 22 x 10(-5) U sialidase with its inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, decreased binding capacity and sialic acid concentration (r = 0.929, p less than 0.001). Although a decrease in binding capacity and free sialic acid concentration was observed in the presence of increasing amounts of sialyltransferase, a positive correlation was found between these two parameters (r = 0.839, p less than 0.035). A negative trend that was statistically insignificant was observed between binding capacity and sialic acid concentration when 2 x 10(-4) U sialyltransferase was incubated with the inhibitor, acetylsalicylic acid (r = -0.571, p = 0.195). The sialic acid concentration increased, while the 3H-estradiol binding capacity decreased. Collectively, these results show that both sialidase and sialyltransferase affect the binding of estradiol to its receptor in opposite directions. We suggest that biological activities of estrogen receptors in target cells may be regulated by the extent of sialylation of the receptor molecule itself. This posttranslational alteration may represent a new type of control mechanism for estrogen action.

Animals↗
PubMed1989

Seminal carnitine, epididymal function and spermatozoal motility.

The carnitine content of semen from azoospermic subjects and subjects with either impaired motility or forward progression is reported. Within the azoospermic group, the values were not significantly different between those with testicular failure or obstruction. The patients with impaired motility (less than 40%) or impaired forward progression (less than 3) had a lower mean seminal carnitine content than those with good motility and forward progression (P less than 0.05). Seminal carnitine concentration was not an index of epididymal patency and could not be regarded as useful for locating the level of obstruction in the epididymis. Since carnitine plays an important role in the maturation process when sperm acquire motility, it would seem that seminal carnitine might be an indicator of epididymal dysfunction.

Carnitine↗
PubMed1989

The relationship between total urinary testosterone and renal calculi.

It is generally known that age and sex are risk factors of urolithiasis. Therefore the total urinary testosterone concentrations of persons with and without renal stones were investigated by means of radioimmunoassay. The total testosterone level of the first morning midstream urine was comparable with 24 urine samples of 16 healthy persons (rs = 0.9618). Investigation of the total urinary testosterone confirmed that the concentration is age dependent. A distinct decrease in total testosterone was observed in elderly persons. Therefore the total testosterone concentrations of the two groups, with and without stones, were studied within the same age interval (P = 0.8292). The the testosterone level differed significantly for these two groups (P = 0.0006). In general, the testosterone level of the kidney stone patients was lower than that of their healthy counterparts. In order to determine whether this variation in testosterone concentration would affect the urinary urokinase activity, a correlation study was undertaken. A positive correlation was found between the total urinary testosterone concentrations and the activity of urokinase (rs = 0.7305). It therefore seems that the total urinary testosterone concentrations may play a role in the pathogenesis of the multifactorial disease, urolithiasis.

Age Factors↗
PubMed1989

Estradiol and catecholestradiols as possible genotoxic carcinogens.

Estradiol and other estrogens are not classified as genotoxic carcinogens, but rather as tumor promoters in the multistage process of carcinogenesis. This study is a reexamination of the carcinogenic status of estradiol and the catecholestradiols (2-OHE2 and 4-OHE2) with the recently developed bacterial assays for genotoxic carcinogens, the Chromotest. The bacterial kits revealed estradiol and catecholestradiols as biphasic and potential genotoxic carcinogens with the following SOS inducing potency values: E2 43,265 (SD 8,300); 2-OHE2 30,153 (SD 2,500), and 4-OHE2 68,939 (SD 4,500). The differences between these values are statistically highly significant (p less than 0.0005). These results were confirmed by studies on Escherichia coli, which showed an increase in cell number and a stimulation of DNA content in the presence of the estrogens. It is therefore concluded that estradiol and the catecholestradiols are possible genotoxic carcinogens which probably act as tumor inducers rather than tumor promoters.

Carcinogens↗
PubMed1988

Renal calculi-urate as a urokinase inhibitor.

The formation of renal calculi is one of the most widely studied urinary ailments. Spectrophotometric analysis of urinary inhibition on the urokinase/plasmin system revealed a significant difference between subjects with and without renal calculi (P less than 0.001). The percentage urokinase/plasmin inhibition in the two groups was 77.1% for those with, and 47.1% for those without renal calculi. Because of the significant (P less than 0.015) positive correlation (r = 0.762) between the percentage inhibition of urokinase/plasmin and urinary urate concentration, the inhibition of urate on urokinase/plasmin and on plasmin and urokinase was investigated. The urokinase/plasmin system was inhibited up to 94.4% with 0.5 mM urate. Inhibition occurred with both low and high molecular weight urokinases. In order to determine which enzyme of the complex was inhibited, each was investigated independently and a 50% inhibition of urokinase activity was obtained with 4 mM urate. It was found that the urine of stone formers contained a higher concentration of urate than the urine of healthy subjects and that at the same time there was a decrease in urinary urokinase activity in these patients.

Adult↗
PubMed1987

Renographic comparison of function in bivalved kidneys repaired using either a fibrin adhesive (Tisseel) or conventional suturing.

In 6 male baboons, the left kidney was bivalved and repaired using a fibrin adhesive (group A) or conventional suturing (group B). 99mTc diethylenetriamine penta-acetic acid (DTPA) renography was used to evaluate renal function for up to 24 weeks after surgery. No significant impairment of renal function could be detected for either of the two repair methods. It seems as though the function was less affected after suturing, but the trend could not be supported statistically. The fibrin adhesive did not prove superior to conventional suturing.

Animals↗
PubMed1986

Smoking and vascular impotence. A reason for concern.

Of the patients at an impotence clinic 39% were classified as having vasculogenic impotence. They were in a high age group and 93% smoked. The possible role of smoking in the pathogenesis of the impotence of ageing is discussed.

Adult↗