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Abstract
1. The aim of this study was to examine ganders at different stages of the reproductive season and the effect of: (1) diets with high phytoestrogen content and (2) in vitro phytoestrogen treatment on testosterone secretion by isolated Leydig cells.
2. Thirty-six male Biłgoraj geese were fed control diets with low phytoestrogen content (containing grass meal) and diets with high phytoestrogens (containing alfalfa meal and soy).
3. Testes were obtained from both groups of ganders at three different times of the breeding season: peak of reproductive activity (March), second half of reproductive activity (May) and beginning of photorefractoriness (July).
4. Isolated Leydig cells were incubated with LH as well as genistein, daidzein, equol and coumestrol and the concentration of testosterone in the medium was determined by radioimmunoassay.
5. The mean weight of testes from ganders in May and July decreased relative to their weights in March, but no significant differences among experimental groups were noted.
6. No differences were observed in basal and LH-stimulated testosterone secretion by Leydig cells of ganders fed the control diets and the diets with higher phytoestrogen content. In July, LH did not stimulate testosterone secretion in either group. In vitro treatment with genistein, daidzein and equol (5 and 50 µM) inhibited basal and LH-stimulated testosterone production by Leydig cells from both groups. Coumestrol (5 and 50 µM) inhibited basal testosterone secretion only in March in the control group.
7. Dietary exposure to phytoestrogens had a slight effect on in vitro testicular secretion in ganders. In vitro treatment with phytoestrogen inhibited testosterone production by Leydig cells. Genistein showed the strongest effect and coumestrol had the weakest influence on testicular secretion.
Acknowledgements
This study was supported by the State Committee for Scientific Research, Poland as a Solicited Project PBZ-KBN-084/P06/2002 from 2003 to 2005. We are very grateful for Dr W. Wiczkowski for his skilful HPLC-MS analysis.