W. Eechaute

Buccal absorption of testosterone and its esters using a bioadhesive tablet in dogs.

AbstractPurpose. As the oral bioavailability of testosterone is very low because of its high first pass effect, buccal administration might present a viable alternative. In this study a buccal bioadhesive tablet was used in order to sustain the delivery and bypass the liver. Methods. Testosterone and testosterone acetate, propionate, enanthate and decanoate were investigated. The influence of the concentration of testosterone (10–50%) and testosterone esters (30%) on in vitro bioadhesion was investigated. The absolute (IV) and relative (oral) bioavailability of 60 mg testosterone or an equivalent amount of testosterone ester was determined in castrated male dogs. Results. Both the in vitro detachment force and the work of adhesion decreased gradually with an increasing amount of testosterone and for an increasing chain length of the esters, except in the case of testosterone enanthate. The in vivo results revealed that the bioavailability of testosterone was significantly higher (p < 0.05) than that of the esters, which is probably due to the lower solubility of the esters. The mean absolute bioavailability of testosterone from the bioadhesive tablet was 14.1%, while the mean relative bioavailability was 1370%. The buccal administration of testosterone via the bioadhesive tablet allowed the maintenance of the plasma level at above 3 ng/ml for 15 to 24 h. Conclusions. Buccal absorption of testosterone was significantly higher than that of its esters.

Influence of age on the formation of 5α-androstanediol and 7α-hydroxy-testosterone by incubated rat testes

Abstract Testes from rats of different ages were incubated with or without tritiated testosterone. The exogenously-added or endogenously-produced testosterone is mainly metabolized to 7α-hydroxylated testosterone in adult animals, and to Set-reduced metabolites (especially 5α-androstanediol) in immature animals.

The biosynthesis of estrogens by cow follicles

Abstract Separated and recombined granulosa and thecal cells of ripening cow follicles were incubated in vitro in the presence of different steroid precursors involved in the Δ 4 and Δ 5 -pathways. The experiments indicate that both in the granulosa and the thecal cells the transformation of pregnenolone to androstenedione occurs predominantly through the Δ 5 -pathway. Although both cell types are able to transform androstenedione to estrogens, this capacity is very small in the thecal tissue as compared to the granulosa cells. Incubations of combined granulosa and thecal cells yielded larger amounts of estrogens than the incubations of each cell type separately, indicating a positive interaction between both cell types in the experimental conditions.

The conversion of testosterone to 7α-hydroxy-testosterone by incubated rat testes

Abstract Incubations of testes of adult rats with testosterone yield rather important amounts of a very polar metabolite which is identified as 7α-hydroxytestosterone. The identification of the metabolite is based on chromatography, spectrophotometry, fluorimetry, counter current distribution and NMR spectrometry.

Progesterone-transforming enzyme activity in the hypothalamus of the male rat.

The aim of the present study was to assess the activities of the progesterone (Pr) transforming enzyme systems 3alpha-oxidoreductase (3alpha-OR), 5alpha-reductase (5alpha-R) and 20alpha-oxidoreductase (20alpha-OR) in the hypothalamus of the male rat, at different stages of sexual maturation and following castration and adrenalectomy. Special attention was paid to transformation to 3alpha-reduced compounds previously shown to inhibit FSH synthesis and secretion. Homogenates of hypothalamic tissue were incubated with 14C-progesterone. Pr-metabolites were isolated, identified by gas chromatography/mass-spectrometry (GC/MS) and measured by liquid scintillation counting (LSC). In adult rats a ratio of 6:2.5:1 for 5alpha-R:3alpha-OR:20alpha-OR enzyme- activities was found. The hypothalamic 5alpha-R and particularly 3alpha-OR activities were considerably higher before puberty (10-20 day old rats) than in adulthood. Adrenalectomy in adult rats resulted in an increased activity of the three enzyme systems. No significant changes were seen following castration. Among the isolated metabolites, 3alpha-hydroxy-pregn-4-en-20-one (3alpha-Pr) and 3alpha-hydroxy-5alpha-pregnane-20-one (5alpha,3alpha-Pr) were identified. Conversion to both these neurosteroids was considerably higher during prepuberty than in adulthood. The finding that before puberty the hypothalamus has a markedly increased capacity to convert Pr to 3alpha-reduced compounds, such as 3alpha-Pr, known to effectively inhibit FSH release, warrants further research into the mechanisms regulating the hypothalamic formation of biologically active Pr derivatives and their role in the regulation of gonadotropin secretion.

Hypothalamic 5α-reductase and 3α-oxidoreductase activity in the male rat

Abstract The aim of the present study was to assess the progesterone (Pr) transforming 5α-reductase (5α-R) and 3α-oxidoreductase (3α-OR) activities in the hypothalamus of the male rat as a function of age and following castration and/or adrenalectomy performed at the sixth day of life. The hypothalamic activity of these enzymes was estimated from the sum of the 5α- or 3α-reduced metabolites produced from 14 C-labeled Pr incubated “in vitro” with hypothalamic tissue. Plasma levels of testosterone (T), progesterone (Pr), estrone (E1), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured simultaneously. Special attention was paid to the GC/MS analysis of the endogenous content of the hypothalamic Pr-metabolites 3α-hydroxy-pregn-4-en-20-one (3α-Pr), 5α-pregnane-3,20-dione (5α-Pr) and 3α-hydroxy-5α-pregnan-20-one (5α,3α-Pr). The high 5α-R and 3α-OR activities estimated in the hypothalamus of prepubertal rats are not related to the action of gonadal or adrenal steroids. Substantial and comparable endogenous 3α- and/or 5α-Pr-metabolites were found in hypothalami from both prepubertal and mature rats. The results of the present study do not provide evidence for a contributory role of the 3α-hydroxylated Pr derivative to the regulation of gonadotropin secretion in the male rat.

Sucrose laurate gels as a percutaneous delivery system for oestradiol in rabbits.

In this study sucrose laurate was formulated in hydrogels and investigated as a suitable transdermal penetration enhancer for oestradiol. Using rabbits as an animal model, the absolute bioavailability and the skin irritation were evaluated after single and multiple application. Three hydrogels containing 60 mg% oestradiol were evaluated: Oestrogel, and two hypromellose gels containing 5 and 15% sucrose laurate (w/w), respectively.

The influence of gonadotrophin (HCG) treatment on the steroidogenesis by incubated rat testes

Abstract The production of steroids and the metabolism of testosterone by the incubated testes from normal and HCG treated rats were studied. The production experiments show that HCG (3 UI/day for 10 days) induces an increase of testosterone and 5α-androstanediol production and a strong depression of 7α-hydroxytestosterone formation. The metabolism experiments indicate an increased transformation of testosterone to 5-reduced metabolites and a decreased conversion to 7α-hydroxytestosterone by the testes of HCG treated rats. It is concluded that HCG provokes a shift in the testicular metabolism pattern of testosterone from the 7α-hydroxylation to the 5α-reduction pathway.

[4-14C]-Testosterone metabolism and steroid production by incubated whole testes, seminiferous tubules and interstitial tissue from rats

Abstract In incubated testes of young rats (30 days old), 5α-reduction predominates over 7α-hydroxylation. This 5α-reductase activity appears to be located predominantly in the interstitial tissue. In incubated testes of mature rats (120 days old) 7α-hydroxylation is more important than 5α-reduction. This 7αzydroxylation mainly occurs in the interstitial tissue, while 5α-reduction predominates in the seminiferous tubules. During long term treatment with HCG, 7α-hydroxylation in the incubation of whole testes and of interstitial tissue decreases to low levels and the steroid metabolism shifts to 5α-reduction.

Regulation of the pituitary 5α-reductase activity by gonadotropin releasing hormone and testosterone in the adult male rat

Intact or castrated adult male rats were treated for nine days with GnRH (10 micrograms/day), the synthetic GnRH goserelin (100 micrograms/day) or the GnRH-antagonist Org 30276 (250 or 500 micrograms/day). In some series, 1 mg testosterone propionate was administered alone, or in combination with goserelin or Org 30276. The in vitro metabolism of [1 alpha,2 alpha-3H]testosterone by pituitary and hypothalamic homogenates was investigated in combination with the estimation of plasma concentrations of testosterone and gonadotropins. No qualitative or quantitative differences were observed in hypothalamic testosterone metabolism or in the pituitary 17 beta-hydroxysteroid dehydrogenase activity. Testosterone administration to intact male rats decreased the pituitary 5 alpha-reductase activity and LH, while administered to castrated rats, it was able to suppress totally the castration-induced increase of the 5 alpha-reductase activity and of the gonadotropin secretion. The drastic decrease of the plasma levels of testosterone, observed after a prolonged treatment with GnRH, goserelin or Org 30276 was not accompanied by an increased pituitary 5 alpha-reductase activity. Injected to castrated rats, it was observed that the castration-induced increase of the pituitary 5 alpha-reductase was further stimulated by GnRH, totally suppressed by goserelin and partially suppressed by Org 30276. Concomitant administration of goserelin or Org 30276 and testosterone propionate to castrated rats resulted in a further decrease of the pituitary 5 alpha-reductase activity, compared to the castrated, GnRH-analogue treated rats. These data indicate that the pituitary 5 alpha-reductase enzyme system is controlled by both direct steroidal and indirect GnRH-mediated mechanisms.