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Biomedical subjects

K D Roberts

Publications and source records attributed to K D Roberts.

At least 91 records · Page 5Linked to original sources
PubMed1979

Metabolism of sex steroids in the human and canine vas deferens.

The contribution of the vas deferens to the metabolism of steroids was investigated in the human and in the dog by perfusion experiments and in vitro incubation. Perfusion of testosterone or androstenedione through the canine vas deferens resulted in the formation of dihydrotestosterone; no significant formation of estrogens could be detected. When dihydrotestosterone was perfused, 3alpha- and 3beta-androstanediols were isolated. In vitro incubation experiments with human was deferencs have shown an active metabolism of androgens by this time and, therefore, confer a new role to the vas deferens in the male.

Androgens↗
PubMed1979

Properties of spermatozoa in relation to their elimination after vasectomy.

Sperm disposal and the formation of sperm granulomas are two related critical aspects of vasectomy which have been studied in man and several animal models. Since mammalian spermatozoa present a keratinoid quality, a comparison was made of the resistance of human and rat spermatozoa. When exposed to dithiothreitol and sodium dodecyl sulfate, human sperm decondense readily while rat sperm resist decondensation for long periods of time. A cooperative effect in the rate of decondensation was observed for human sperm but not for rat sperm. Oxidation of sulfhydryl groups renders human spermatozoa as resistant as rat spermatozoa, indicating that disulfide crosslinks are involved in this resistance. Human spermatozoa constitute a heterogeneous population with respect to sulfhydryl group content, suggesting variations in the state of maturation and/or elimination. The sulfhydryl group content of rat epididymal spermatozoa was similar from one cell to another, suggesting little sperm reabsorption in the epididymis. Human and rat spermatozoa differ in size, resistance to decondensing agents, cooperative effect during decondensation, and content and localization of sulfhydryl groups; these differences can explain why vasectomized rats invariably develop huge granulomas while this side effect is not severe in vasectomized men.

Animals↗
PubMed1978

5alpha-Cholesta-7,24-dien-3beta-ol as a major sterol of the male hamster reproductive tract.

Marked variations in the 3beta-hydroxysterol content of hamster spermatozoa were observed as they progress through the epididymis. Cholesterol is the major sterol of caputal spermatozoa while the concentration of precursors of cholesterol was higher than that of cholesterol in caudal spermatozoa. One of these precursors has been identified as desmosterol. A second sterol has now been identified as 5alpha-cholestra-7,24-dien-3beta-ol by GLC-MS and by NMR. Its concentration is approximately 3-fold higher than that of cholesterol. This 3beta-hydroxysterol is also found in epididymal tissue.

Animals↗
PubMed1978

Solubilization and partial purification of steroid sulfatase of human placenta.

Steroid sulfatase of human placenta has been solubilized by treatment of the microsomal fraction with an amphoteric surface active agent, Miranol H2M and ultrasound. Criteria of solubility include non-sedimentation of the activity following centrifugation at 160,000 x g, its retention on Sepharose 6B and a single peak of activity after polyacrylamide gel electrophoresis. Enzyme activity was located in the same gel fractions for the two substrates tested; cholesterol sulfate and dehydroisoandrosterone sulfate. The addition of dithiothreitol was found necessary to maintain the stability of the enzyme indicating the presence of sulfhydryl groups in the molecule. A molecular weight of approximately 330,000 has been estimated from the elution volume of the enzyme system on a column of Sepharose 6B. It is believed that this protein represents a sulfatase enzyme complex composed of subunits with different specificities. From kinetic studies, a Km of 6.2 x 10(-5)M for the cleavage of dehydroisoandrosterone sulfate and a Km of 2 x 10(-6)M for the cleavage of cholesterol sulfate have been calculated.

Chromatography, Ion Exchange↗
PubMed1977

Coarctation of aorta with special reference to infants. Long-term results of operation in 126 cases.

A review of 126 cases of coarctation of the aorta confirms the need for surgical resection in infants with intractable congestive cardiac failure. The high association with additional cardiovascular abnormalities in patients presenting in early infancy contributes significantly to the mortality. Patients with large ventricular septal defects and coarctation of the aorta are at risk and may require pulmonary artery banding at the time of resection of the aortic coarctation. Long-term complications included restenosis (18 cases) and persistent hypertension (10 cases). In order to prevent persistent hypertension, it is suggested that elective resection of the coarctation be done at 1 year of age.

Adolescent↗
PubMed1976

Cholesteryl sulfate and sterol sulfatase in the human reproductive tract.

Cholesteryl sulfate is a component of human seminal plasma (avg. 445 mug%) and spermatozoa (15 mug/10 (9) cells) and represents more than 85% of the sterol sulfate fraction. This conjugate is avidly bound by spermatozoa when compared to other steroids or steroid sulfates. Autoradiographic localization of CS associated with the spermatozoa revealed a greater accumulation of the radioactivity in the acrosomal region in many, but not all, of those cells examined. Semen is not a site of metabolism of the sterol sulfate but the enzyme, sterol sulfatase, is present in the human female reproductive tract. This cleavage enzyme was detected in Graafian follicles and the activity in the endometrium was ten-fold that found in the Fallopian tube. These findings lead to the proposal that cholesteryl sulfate, an amphipathic molecule ideally suited for interaction with membrane components and implicated in erythrocyte membrane stabilization, may be involved in membrane modifications of the spermatozoa during the process of fertilization.

Cervix Mucus↗
PubMed1975

Cholesterol sulfate. II. Studies on its metabolism and possible function in canine blood.

Previous in vitro studies to evaluate the possible role of cholesterol sulfate in the stabilization of the human erythrocyte membrane have been extended to the dog in vivo. Thus, following the injection of labelled cholesterol sulfate, a large fraction of the administered sterol conjugate is taken up by the membrane of the canine erythrocyte. Peak membrane levels were obtained within 30-60 min. Measurement of radioactivity associated with the plasma and red cell fractions in serial samples allowed the calculation of the half-life of cholesterol sulfate in each fraction. From the data obtained from the plasma of four dogs, the half-life was calculated to 5.8 plus or minus 0.9 h. The half-life of chlesterol sulfate associated with the erythrocyte membrane was calculated to be 6.7 plus or minus 1.2 h. In addition, following the intravenous administration of 0.2-0.7 mg of cholesterol sulfate/kg of body weight and withdrawal of serial blood samples, a significant diminution in the degree of hemolysis was observed when the red cells were exposed to hypotonic saline solutions. Maximal stabilization effects were observed at approx. 6-7 h after the administration of the sterol conjugate. Hemolytic properties returned to normal at approx. 24 h following the injection.

Animals↗
PubMed1975

Excess intravascular coagulation complicating low cardiac output.

In 42 children with congenital heart disease coagulation factor levels were studied serially during the first 20 hours following cardiopulmonary bypass surgery. The acyanotic patients, and also cyanotic patients who survived the operation, showed a progressive improvement in their coagulation profile from initial low postoperative levels. In 12 cyanotic patients who died within 72 hours, however, the coagulation factor levels either remained low, or fell further, until death. Fresh frozen plasma was administered to eight of these patients without apparent benefit. The abnormal coagulation profile correlated significantly with low skin temperature and increased blood loss and was considered to represent excess intravascular coagulation secondary to low cardiac output and poor tissue perfusion.

Blood Coagulation Disorders↗