Androgenic and estrogenic effects of the synthetic androgen 17alpha-methyltestosterone on sexual development and reproductive performance in the fathead minnow (Pimephales promelas) determined using the gonadal recrudescence assay.
The effects of the androgen, 17alpha-methyltestosterone were assessed on sexual development and reproductive performance in the fathead minnow (Pimephales promelas) using a gonadal recrudescence assay. In this assay, mature male and female fathead minnow, previously kept under simulated winter conditions (15 degrees C; 8:16 h light:dark regime) were transferred to simulated summer conditions (25 degrees C water temperature; 16:8 h light:dark regime) to induce gonadal recrudescence. To assess sexual development fish were exposed to nominal concentrations of 0, 0.1, 1, 5 and 50 microg/L 17alpha-methyltestosterone. After 3 weeks of chemical exposure, effects on condition (condition factor, CF), plasma vitellogenin (VTG), secondary sex characteristics, gonad growth (gonadosomatic index; GSI) and gonad histology were investigated. Reproductive performance, including reproductive output (egg production), spawning behaviour, and fertilisation rate were measured over a subsequent 3-week-period in breeding adults maintained in clean water. 17alpha-Methyltestosterone had no effects on the condition of fish at any of the doses tested. 17alpha-Methyltestosterone induced both androgenic and estrogenic effects with females generally more affected by 17alpha-methyltestosterone than males: atretic follicles and male-specific sex characteristics (androgenic effect) were induced in females at > or = 0.1 and > or = 1 microg/L 17alpha-methyltestosterone, respectively. An inhibitory effect on ovary growth occurred at an exposure concentration of 50 microg/L 17alpha-methyltestosterone. In males 1 microg/L 17alpha-methyltestosterone induced a concentration-response induction of plasma vitellogenin (estrogenic effect) likely due to its conversion into 17alpha-methylestradiol, rather to the competition with endogenous steroids and their cross reactivity with the estrogen receptor. In the fish breeding studies, concentration-dependent reductions in egg number, fertilisation rate and increases in abnormal sexual behaviour in females were observed. All of these effects occurred at exposure concentrations of > or = 5 microg/L 17alpha-methyltestosterone. Thus, it could be assumed that the observed estrogenic effects in male fathead minnow were likely to the conversion of 17alpha-methyltestosterone into the estrogen 17alpha-methylestradiol, rather to the acting of 17alpha-methyltestosterone itself. In conclusion to this, showing hormonally activity of 17alpha-methyltestosterone in fish down to 100 ng/L, indicates that its potency was close to the range of several naturally occurring estrogens.
Pawlowski
S
S
Institut für Biologische Analytik und Consulting GmbH, Rossdorf, Germany. spawlows@zoo.uni-heidelberg.de
Sauer
A
A
Shears
J A
JA
Tyler
C R
CR
Braunbeck
T
T
D000704:Analysis of Variance; D000818:Animals; D003530:Cyprinidae / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000378:metabolism; D005260:Female; D005618:Fresh Water; D006066:Gonads / Q000473:pathology / Q000502:physiology*; D006652:Histological Techniques; D008297:Male; D008777:Methyltestosterone / Q000494:pharmacology*; D017440:Photoperiod; D012008:Recurrence; D012044:Regression Analysis; D012098:Reproduction / Q000187:drug effects*; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000187:drug effects; D012741:Sexual Maturation / Q000187:drug effects*; D013696:Temperature; D014819:Vitellogenins / Q000097:blood
D004967:Estrogens; D014819:Vitellogenins; D008777:Methyltestosterone