The metabolism of 17beta-estradiol-3-glucosiduronate and estrone-3-glucosiduronate in the rabbit.

[6, 7-3H]-17beta-Estradiol-3-glucosiduronate, [6, 7-3H]-estrone-3-glucosiduronate or [6, 7-3H]-estrone was administered intravenously into the rabbit, and analysis and identification of the urinary metabolites were carried out. In either case, the major urinary metabolite was found to be a diconjugate. The sequential enzymic hydrolysis indicated that this diconjugate was glucosiduronate-N-acetyglucosaminide of 17alpha-estradiol. From these results, the conversion of the estrogen glucosiduronate into a diconjugate was thought a rather universal phenomenon in the rabbit.     

Effect of thyroid state on estradiol-17β metabolism in the rabbit

It is well known that the metabolic clearance rate (MCR) of a hormone is Influenced highly by the level of its specific binding protein. It was interesting, therefore, to study the metabolism of estradiol-17β (E₂) in an animal model such as the rabbit where there is a lack for a highly specific binding protein for the steroid. The kinetics of the hormone was studied in relation to the thyroid state, namely in rabbits receiving thyroxin or propylthiouracil.In the absence of any significant decrease of the level of the rabbit androgen binding protein (R-ABP), the accelerated MCR^E2 and the elevated conversion ratio of estradiol to estrone (CR ^E₂→E₁) observed in hyperthyroid rabbits were attributed to the important role of metabolizing enzymes in the liver and/or extrahepatic tissues. In hypothyroid rabbits, while the CR ^E₂→E₁ decreased significantly the MCR^E2 was not altered.     

The metabolism of aldosterone and 3 alpha, 5 beta-tetrahydroaldosterone in the rabbit

Analysis of urinary metabolites of [1, 2-3H]-aldosterone and [1, 2-3H]-3 alpha, 5 beta-tetrahydroaldosterone was performed in male rabbits. The preliminary separation of urinary metabolites was carried out by submitting these metabolites to countercurrent distribution. Further separation of each fraction thus obtained was achieved by means of DEAE-Sephadex A-25 column chromatography. The separated peak was then hydrolyzed with the enzyme and the free steroid released was identified on the basis of the mobilities of the steroid and its derivatives on paper chromatography. After the injection of [1, 2-3H]-aldosterone, a major urinary metabolite was characterized as monosulphate of 3 alpha, 5 beta-tetrahydroaldosterone. In addition, a small amount of the monoglucosiduronate fraction was found in the urine. 3 alpha, 5 beta-tetrahydroaldosterone and 3 beta, 5 alpha-tetrahydroaldosterone were detected as aglycones in this fraction. After the injection of [1, 2-3H]-3 alpha, 5 beta-tetrahydroaldosterone, a similar pattern of urinary radiometabolites was observed. The close similarity between the profile of urinary metabolites of [1, 2-3H]-aldosterone and that of [1, 2-3H]-3 alpha, 5 beta-tetrahydroaldosterone suggests that the conversion of aldosterone to 3 alpha, 5 beta-tetrahydroaldosterone is needed before the conjugation processes take place.     

Identification of radioactive 17beta-estradiol-17-beta-D-glucuronide and 17alpha-estradiol-17-beta-D-glucuronide in the urine of the domestic fowl after intramuscular injection of [4-14C]estrone.

Two previously uncharacterized radioactive estrogen conjugates, 17beta-estradiol-17-beta-D-glucuronide (3-hydroxyestra-1,3,5(10)-trien-17beta-D-glucopyranosiduronate) and 17alpha-estradiol-17beta-D-glucuronide (3-hydroxyestra-1,3,5(10)-trien-17alpha-yl-beta-D-glucopyranosiduronate), have been identified in small but significant amounts in avian urine and in a ratio of approximately 2:1 after intramuscular injection of [4-14C]estrone.     

3H-Benzene metabolism in rabbit bone marrow

An assay for benzene metabolism using ³H-benzene and high pressure liquid chromatography was developed. ³H-Benzene metabolism (2 pmoles benzene equivalents/mg protein/min) required the presence of a TPNH generating system and was inhibited 80% in the presence of a CO:O₂ (9:1) atmosphere. The products of ³H-benzene rabbit bone marrow microsomal metabolism were phenol and an unidentified metabolite. Cytochrome P-450 (26–51 pmoles/mg microsomal protein) and cytochrome $\text{c}$ reductase activity (7.8–21.0 nmole/mg microsomal protein/min) were detected in rabbit bone marrow.     

The distribution and metabolism of glycerol in the rabbit.

1. The effective volume of distribution of labelled glycerol was studied in conscious young adult rabbits provided with in-dwelling cannulae in the femoral blood vessels. This could be estimated after sampling arterial blood throughout an intravenous infusion of [2-3H]glycerol. The volume was calculated by using an algebraic method of graphical area analysis over 100 min of equilibration, and is symbolized 100V e or 100V e%. It occupied 34.1 +/- 2.2% (mean +/- S.E.M.; n = 13) of the body weight. The pool of endogenous glycerol occupying this space is distinguished in the present paper by calling it the transit pool, symbolized 100Me. 2. The median time of transit of glycerol through this pool was approx. 6 min in these conscious rabbits with normal (less than 0.2 mM) blood glycerol concentrations. 3. The metabolism of glycerol was also studied in rabbits while anaesthetized with urethane or while conscious. On average, half of the change in glycerol concentration that occurred on overnight starvation could be attributed to a decrease in clearance, whereas half was due to an increase in lipolysis. 4. The correlation between the reciprocal of glycerol concentration and clearance showed that in these animals about a quarter of the variation in concentration was due to an association with clearance. The remainder of the variation was attributed to variations in the rate of glycerol formation (lipolysis). 5. The regression of glycerol turnover rate on concentration implied that turnover was positive at zero glycerol concentration. This confirms previous findings from studies on other species. The explanation offered for this phenomenon is that the well-known physiological changes induced by feeding (decreased lipolysis, increased splanchnic blood flow) may independently decrease the glycerol concentration by both decreasing its release into the blood and simultaneously increasing its clearance.     

The metabolism of oxytocin during lactation in the rabbit

1. It has been suggested that changes in the concentration of hypothalamic enzymes inactivating oxytocin might be taken as an index of hormone production (Hooper, 1966). The present work describes the changes in enzyme concentration shortly after parturition and during lactation. 2. Two groups of animals were used; one consisted of lactating animals from which litters had been removed shortly after parturition. 3. Two fractions obtained from homogenized hypothalamus contained enzyme activity. In animals which had been suckled for 3 days the enzyme activity in the supernatant fraction was three times as great as that observed during pregnancy. Between the third and fifth days the activity reverted to pregnancy levels, and remained fairly constant for as long as the animals were suckled. 4. In animals whose litters were removed shortly after birth, the enzyme activity reverted to pregnancy levels by about the third day post partum, and by the sixth day non-pregnancy levels were reached. 5. The enzymes of a particulate fraction behaved somewhat differently; 6 hr. after parturition the enzyme activity was similar to that found in pregnant animals and there was no detectable activity by the tenth day in suckled animals. In non-suckled animals the enzyme activity decreased more rapidly, and non-detectable levels were reached by the fourth day post partum.     

Transport and bioactivity of cyanidin 3-glucoside into the vascular endothelium

Flavonoids are dietary components involved in decreasing oxidative stress in the vascular endothelium and thus the risk of endothelial dysfunction. However, their very low concentrations in plasma place this role in doubt. Thus, a relationship between the effective intracellular concentration of flavonoids and their bioactivity needs to be assessed. This study examined the uptake of physiological concentrations of cyanidin 3-glucoside, a widespread dietary flavonoid, into human vascular endothelial cells. Furthermore, the involvement of the membrane transporter bilitranslocase (TC No. 2.A.65.1.1) as the key underlying molecular mechanism for membrane transport was investigated by using purified anti-sequence antibodies binding at the extracellular domain of the protein. The experimental observations were carried out in isolated plasma membrane vesicles and intact endothelial cells from human endothelial cells (EA.hy926) and on an ischemia-reperfusion model in isolated rat hearts. Cyanidin 3-glucoside was transported via bilitranslocase into endothelial cells, where it acted as a powerful intracellular antioxidant and a cardioprotective agent in the reperfusion phase after ischemia. These findings suggest that dietary flavonoids, despite their limited oral bioavailability and very low postabsorption plasma concentrations, may provide protection against oxidative stress-based cardiovascular diseases. Bilitranslocase, by mediating the cellular uptake of some flavonoids, is thus a key factor in their protective activity on endothelial function.