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Biomedical subjects

A F Clark

Publications and source records attributed to A F Clark.

At least 127 records · Page 7Linked to original sources
PubMed1975

In vivo metabolism of 3H-testosterone in adult male rats: effects of estrogen administration.

The metabolism of testosterone (T) was studied in normal adult male rats using a constant infusion of trace amounts of the 3H-steroid into a tail vein for 3 h in order to attain a state of equilibrium. Samples of plasma, liver, kidney, prostate, seminal vesicles and muscle were analysed for 3H-testosterone, 3H-5alpha-dihydrotestosterone (5alphaDHT) and 3H-5alpha-androstanediol (Adiol). When compared to the 3H-T level in plasma there were high levels of 3H-T in kidney and of 3H-5alphaDHT in prostate and seminal vesicles. Intraperitoneal estradiol valerate administration (100 mug/day) for 4 days decreased and 3H-5alphaDHT levels in the prostate and seminal vesicles. The estrogen administration increased the T metabolic clearance rate from 17.5 1/24 h/100 g body wt to 22.6 1/24 h/100 g body wt.

Androstane-3,17-diol↗
PubMed1975

Nuclear 3alpha-hydroxysteroid dehydrogenase (3alphaOHD) activity for 5alpha-dihydrotestosterone in the rat prostate.

The in vitro examination of adult male rat prostatic 3alpha-hydroxysteroid dehydrogenase (3alphaOHD) activity using 5alpha-dihydrotestosterone4 as substrate indicates that significant levels of enzyme activity are associated with purified nuclei as well as with the cytosol fractions. Both the purified nuclear and the cytosol fractions exhibited higher levels of 3alphaOHD activity with NADH than with NADPH. The pH activity curves for the NADH and NADPH catalyzed reactions were different for both the nuclear and cytosol fractions. The results suggest the presence of a number of 3alphaOHD enzymes in rat prostate.

Androstane-3,17-diol↗
PubMed1975

Plasma testosterone free index: a better indicator of plasma androgen activity?

Testosterone, quantitatively the most important androgen in the circulation, must enter cells to exert an androgenic effect. It is accepted that it is that fraction of the hormone not bound to the specific, binding, beta-globulin which is available for entry into the cells. By equilibrium dialysis we obtained an in vitro measurement of the unbound fraction. The product of this fraction and the total testosterone level gave us a testosterone free index (TFI). In normal men and women, our ranges were 24.6 to 93.6 and 0.8 to 3.8 ng/100 ml, respectively. Of 54 hirsute women, 24 had an elevated TFI; 4 of these had normal plasma testosterone levels. Thirteen men with hypogonadism had a decreased TFI. Nine of ten women and two men with hyperthyroidism had a normal TFI, although there was an elevated plasma testosterone level in most instances. The calculated TFI, which reflects both the extent of binding and the total testosterone level, may therefore be a better indicator of circulating androgen activity.

Adolescent↗
PubMed1974

The problem of catheter encrustation.

Catheter encrustation was studied in a group of long-stay hospital patients using both latex and silicone catheters. Moisture accounted for 80% by weight of the encrusted material with both catheters. Of the dry weight 90% was composed of protein, calcium, phosphorus, magnesium and uric acid. No relationship was found between the amounts of these substances in the urine and in the encrusted material. High levels of calcium, phosphorus and magnesium were found in the encrusted material from patients infected with Proteus organisms. No direct relationship was found between the duration of catheter drainage and the degree of encrustation, and there was a variation in patient susceptibility to encrustation irrespective of the catheter material. There was significantly less encrustation associated with silicone catheters.

Calcium↗
PubMed1972

The Formation of beta, 1 --> 4 Glucan from UDP-alpha-d-Glucose Catalyzed by a Phaseolus aureus Enzyme.

Particulate enzyme preparations from Phaseolus aureus hypocotyls catalyze the formation of an alkali insoluble beta, 1 --> 4 linked [(14)C]-glucan using UDP-alpha-d [(14)C]-glucose as substrate. Particulate enzymes prepared from root tissue also catalyzed the production of beta, 1 --> 4 glucan. UDP-beta-d-[(14)C]-glucose would not serve as a substrate for these enzymes. The presence or absence of beta, 1 --> 4 glucan synthetase activity was independent of tissue source, substrate concentration, or homogenization method.The particulate enzyme also catalyzes the formation of a beta, 1 --> 3 linked glucan from UDP-d glucose which is usually soluble in hot alkali. The solubility of the beta, 1 --> 3[(14)C]-glucan decreased when the enzyme was obtained from hypocotyls germinated at a higher temperature. The water-soluble material resulting from the catalyzed reaction includes a large proportion of what appears to be [(14)C]-laminaribiose, and smaller proportions of [(14)C]-laminaritriose and [(14)C]-glucose. There is no detectable quantity of [(14)C]-cellobiose or [(14)C]-cellotriose in the water-soluble material.

Journal Article↗