Seasonal modulation of androgen synthesis in the mink (Mustela vison) is associated with qualitative changes in testicular steroidogenesis in vitro
✍ Scribed by Tähkä, Klaus M. ;Teräväinen, Tommi ;Sundqvist, Christer
- Book ID
- 102894193
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 857 KB
- Volume
- 258
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
Annual changes in testicular weight and microsomal androgen synthesis were studied in the mink (Mustela vison). Testicular samples were taken at different phases of the annual reproductive cycle. Steroidogenesis was assessed by investigating seasonal differences in the testicular conversion of [4‐^14^C]pregnenolone (P) and [4‐^14^C]dehydroepiandrosterone (DHA) to metabolites in vitro. The steroid metabolites were identified by thin‐layer chromatography. Seasonal changes in the capacity of the testis to produce testosterone from DHA and P correlated positively with the annual reproductive cycle of the species as well as with our earlier findings on plasma testosterone levels. Although the percentage conversion to testosterone (T) from both substrates decreased (39.8% to 19%, DHA; 33% to 15.5%, P) during testicular regression, the in vitro production of androstenedione (A) was increased. The A/T ratio changed from 0.32 (DHA) and 0.42 (P) during testicular activation in November to 1.9 (DHA) and 2.52 (P) during regression in September. Both substrates were utilized efficiently throughout the reproductive cycle. During testicular regression the decreased conversion to T was associated with a marked qualitative and quantitative increase (per unit weight) in the production of unidentified metabolites. The conversion to 5α‐reduced androgens appears to be insignificant, since none of the main 5α‐reduced testicular androgens were identified at any phase of the reproductive cycle.
Our data suggest that the observed differences in testosterone production in vitro are in part due to changes in the activity of 17β‐hydroxysteroid dehydrogenase and possibly also in the enzymes catalyzing the conversion of C~21~ steroids to androgens. It would also appear that seasonal modulation of androgen synthesis in this species is associated with a prominent qualitative shift in testicular steroidogenesis rather than with a marked reduction in the microsomal capacity to use the substrates.