Introduction
Isoflavones compounds, including formononetin, biochanin A, daidzein and genistein occurring in red clover (Trifolium pratence) may cause infertility in female sheep (Adams, 1995). Phytoestrogens mimic the actions of oestradiol and their affinity to oestrogen receptor beta is substantial (Gustafsson, 1999). The aim of the present work was to study effects of the central administration of genistein on prolactin changes in ewes during the seasonal anoestrus.
Methods
Eight ewes of Lowland Breed during the anoestrus were used in this experiment. Four out of them served as control animals. A steel guide cannulae (1.6 mm o.d.) was implanted under stereotaxic control in the third brain ventricle through a drill hole in the skull under general anaesthesia. The guide cannula was fixed to the skull with stainless steel screws and dental cement. Infusions into the third ventricle of ewes were performed with calibrated 1.0-ml gas-tight syringes and a microinjection pump. Control infusions from 12.01 to 16.01 were done with a Ringer-Locke solution at flow rate 100 ml/h. The dose of genistein was 1 mg/100 ml/h during 4-h infusions from 12.01 to 16.01. During the experiments, animals were kept in cages of comfortable sizes, in which they could lie down and have unrestrained access to hay and water. Three ml of blood samples was collected at 10-min intervals from 8.00 to 20.00 through a catheter from the jugular vein. Plasma samples were stored at -20oC until assayed for prolactin by radioimmunoassay. The hormonal observations were first log transformed and then the repeated measurement analysis of variance was performed using the MIXED procedure on the generated averages according to the SAS package. Values are expressed as LSmeans ± SEM.
Results
The plasma concentrations of prolactin in control and experimental ewes were similar before infusion either of Ringer-Locke solution or genistein (47 ± 16 mg/l vs 71 ± 11 mg/l, respectively). Infusion of Ringer-Locke solution did not changed significantly prolactin secretion and its concentration varied between 43 and 57 mg/l. Infusion of genistein into the third ventricle resulted in the significant increase of prolactin from 71 ± 11 mg/l at 12.00 to 128 ± 11 mg/l at 17.00. Afterwards, prolactin concentration gradually decreased and reached level compared to the control animals.
Conclusions
In conclusion, it seems that the centrally administered genistein may influence the secretion of prolactin in ewes during the seasonal anoestrus.
This work was supported financially by the Swedish Council for Forestry and Agricultural Research (AM). The experimental part was carried out in The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Jablonna near Warsaw, Poland (KR, TM, BB).
References
Adams, N.R. 1995. J Anim Sci 73, 1509-1515.
Gustafsson, J.A. 1999. J Endocrinol 163, 379-383.