Comparison of the metabolism in dogs of estradiol-17 beta following its intravenous and oral administration

Dehydroepiandrosterone metabolism in the female rhesus monkey: oral versus intravenous administration

Because of the biologic effects on a variety of end points reported for dehydroepiandrosterone (DHA) and its sulfate (DHAS) after oral administration, we studied the metabolism of DHA in six female rhesus monkeys after oral and after intravenous administration. We administered [4-14C]DHA p.o. and [7-3H]DHA i.v. simultaneously, drawing blood samples at increasingly longer intervals for 24 h. The mean +/- SE metabolic clearance rate of the intravenous DHA was 404 +/- 49 L/day. The mean metabolic clearance rate was 2,601 +/- 261 L/day after oral administration, and the calculated absorption was 16.3 +/- 2.5%. There was rapid conversion of p.o. DHA to DHAS, as the conversion ratio of the orally administered DHA measured in the blood as [4-14C]DHAS was 63.3 +/- 13.6, whereas the conversion ratio of intravenously administered DHA to DHAS was 9.3 +/- 2.0. Small amounts of DHA were measured in the blood as testosterone and androstenedione after both forms of administration. We conclude that there is marked metabolism in splanchnic tissue of orally administered DHA to DHAS prior to its entry into the bloodstream, and the absorption of DHA itself is minimal when administered by mouth to the rhesus monkey.

Profiles of plasma estrogens, progesterone and their metabolites after oral or vaginal administration of estradiol or progesterone

Doses of 100 mg of micronized progesterone (P) and of 0.5 mg of micronized estradiol (E2) were administered vaginally and orally, respectively, in the early follicular phase of the menstrual cycle in six premenopausal women. In the second cycle, the same doses were administered in the same subjects, orally for P and vaginally for E2. Serial blood samples were collected and the following steroids were assayed by highly reliable techniques: P, E2, estrone (E1), deoxycorticosterone (DOC), 5 alpha- and 5 beta-pregnanolone and the sulfates of E1, E2, and DOC. Circulating P and E2 levels were higher after vaginal than after oral administration, while those of E1 were similar after either route. Metabolites of P (DOC, DOCS and pregnanolone) were higher after oral administration. Concerning estrogen sulfates, E1S concentrations were similar whichever the route, while those of E2S were lower after oral than after vaginal administration. This study has confirmed that metabolism of ingested P and E2 occurs mainly in the intestine. Moreover, P was predominantly metabolized to 5 alpha-reduced derivatives, whatever the route of administration. In view of the metabolic pathways which are operative and of the peripheral plasma levels which were found, the vaginal route appears to be more adequate than the oral one for hormone replacement therapy.

Metabolites of estradiol in serum, bile, intestine and feces of the domestic cat ()

We wished to develop an efficient, noninvasive method for monitoring ovarian function in domestic and nondomestic Felidae. We hypothesized that the method could be based on measurement of one of the major excreted estrogen metabolites. To identify and characterize the major excreted metabolites, a bolus of (14)C-estradiol was administered into the femoral vein of adult female cats. We measured the amounts of total radioactivity per unit time contained in unconjugated and conjugated estradiol metabolites, in conjugated metabolites that were hydrolyzable, and in those not hydrolyzable by beta Glucuronidase / aryl sulfatase (the enzyme). Radionuclide levels were determined in voided feces and urine, in jugular vein plasma, bile, contents of the duodenum, and in the small intestine. Metabolites of (14)C-estradiol were voided preferentially in feces and in equal amounts either as unconjugated estradiol or as conjugates not hydrolyzable by the enzyme. In plasma, conjugated estrogens comprised an increasing proportion of the total radioactivity during the first 40 min after administration. Plasma pools of samples from 0.5 to 30 min and 40 to 360 min contained a monoconjugate and a diconjugate, respectively; both were hydrolyzable by the enzyme. Bile and intestinal samples were collected at 360 min after administration. In the bile, 99% of the total radioactivity was in conjugated compounds, only 20% of which were not hydrolysable by the enzyme. The proportion of unconjugated metabolites increased to 18% in the duodenum and to 45% in the small intestine. The major conjugates contained in voided feces not hydrolyzable by the enzyme were estradiol sulfate (m/z = 351.6836), distributed as the 3-sulfate (20%) and 17-sulfate (80%); of the latter, 70% were 17alpha- and 30% 17beta-estradiol sulfates. These data document the fate of estradiol in the circulation of the cat, they demonstrate that a large portion of the voided estradiol metabolites are not hydrolyzable by the enzyme, and account for those conjugates previously termed nonhydrolyzable.

Prodrugs for improved oral beta-estradiol bioavailability

Prodrugs of beta-estradiol (1) were prepared with the objective of improving its oral bioavailability. beta-Estradiol-3-acetylsalicylate (2), beta-estradiol-3-salicylate (3), and beta-estradiol-3-anthranilate (4) were synthesized. With these prodrugs the 3-phenolic hydroxy group of estradiol was protected, so that first-pass conjugative metabolism could be reduced. Prodrug hydrolysis rates in dog and human plasma in vitro were determined. Deacetylation of estradiol-3-acetylsalicylate was much more rapid than its hydrolysis to estradiol. In dogs, oral estradiol bioavailability after administration of 2 and 4 was 17-fold and 5-fold higher, respectively, than after oral 1.

Comparative metabolism of oestrone sulphate after oral and intravenous administration in post-menopausal women

Oestrone sulphate (E1S) is currently used in hormone replacement therapy in post-menopausal women. While isotope studies have demonstrated that E1S is metabolised in a similar way after administration by either the oral or intravenous route, pharmacokinetic studies point to its efficient extraction and metabolism by the liver. E1S was accordingly administered orally and intravenously at pharmacological dosages in a group of post-menopausal women and its conversion to oestrone (E1) and oestradiol (E2) was determined. We were able to demonstrate that E1S may cross the splanchnic area unaltered, since its conversion to E1 and E2 was similar after administration by each of the routes investigated.

The metabolism of estradiol; oral compared to intravenous administration

We administered [6,7-3H]estradiol p.o. and [4-14C]estradiol i.v. simultaneously to 5 women 22-35 years of age. Fourteen blood samples were collected over 480 min, and all urine was collected for 96 h. The blood samples were analyzed for radioactivity as estradiol, estrone, estrone-sulfate and estradiol glucuronide. The urine samples were analyzed for radioactivity as the glucuronide and pH 1 hydrolyzable conjugates of estradiol, estrone, estriol, 16 alpha-hydroxy-estrone, 2-hydroxy-estrone, 2-hydroxy-estradiol, 2-methoxy-estradiol and 2-methoxy-estrone. The major circulating estrogen, after either estradiol, p.o. or i.v. administration, was estrone sulfate; approximately 50% of estradiol administered by either route being converted to and measured as estrone sulfate in the blood. Following oral administration about twice as much estradiol was converted to and measured as estradiol glucuronide in the blood as after i.v. administration. Of the estradiol administered p.o., only 10% was absorbed into the blood as estradiol the rest being metabolized prior to absorption. After estradiol, p.o., the major radioactive compounds in the urine were the glucuronides of estrone and estradiol, but after estradiol, i.v., the conjugates of estrone, estradiol and estriol were present to about the same extent as the conjugates of the 2-oxygenated compounds. Following p.o., considerable metabolism of estradiol administration occurs in the splanchnic tissue, much of it in the intestinal wall.

Sites of in vivo extraction and interconversion of estrone and estradiol in the dog

The interconversion and extraction of estrone and estradiol-17beta across and within different tissues or areas have been studied in the dog by the constant infusion technique. The results were calculated estradiol obtained from afferent and efferent blood and tissues at equilibrium. From these results it is concluded that: (1) there is no significant difference between metabolic clearance rates of estrone and estradiol, (2) blood transfer constants indicates a higher conversion of estradiol to estrone than of estrone to estradiol, (3) the transtissue interconversion favors the formation of estrone while the intratissue interconversion favors the formation of estradiol, (4) no interconversion of the two estrogens is observed in adipose tissue, (5) the extraction of estradiol entering a tissue was lower than the extraction of estradiol formed in these tissues, (6) calculation of the tissue metabolic clearance rates show that 63% of the total metabolism of estrone and estradiol, respectively, occurs in the splanchnic bed, and (7) the contribution of each tissues to the total interconversion of estrone and estradiol show that more than 90% of this interconversion occurs extrahepatically.