Plasma Prolactin Concentrations in Pinealectomized Ewes Receiving Melatonin Treatment and in Pineal Intact Ewes Maintained Under a Non-24-Hour Photoperiod
Article first published online: 30 JAN 2007
Journal of Pineal Research
Volume 6, Issue 3, pages 243–252, July 1989
How to Cite
Poulton, A.L., English, J., Symons, A.M. and Arendt, J. (1989), Plasma Prolactin Concentrations in Pinealectomized Ewes Receiving Melatonin Treatment and in Pineal Intact Ewes Maintained Under a Non-24-Hour Photoperiod. Journal of Pineal Research, 6: 243–252. doi: 10.1111/j.1600-079X.1989.tb00420.x
- Issue published online: 30 JAN 2007
- Article first published online: 30 JAN 2007
- Received January 20, 1988; accepted August 5, 1988.
- breeding activity;
We have investigated the profiles of prolactin secretion in relation to onset of breeding activity in Suffolk-Cross ewes with artificially modified melatonin rhythms. With treatments commencing in midsummer, groups of ewes were 1) subjected to a 8L:16D photoperiod, 2) maintained under a “short” (6L:16D) photoperiod repeated over a 22-h cycle that induces an elevation in plasma melatonin that does not endure for the entire dark phase, 3) pinealectomized (pnx) to abolish plasma melatonin levels, and 4) pinealectomized and treated with a melatonin implant (subcutaneous) to provide a constant (no 24-h rhythm) elevation in plasma melatonin. The onset of breeding activity was significantly advanced in both the 8L:16D and pnx/implant groups compared to the 6L:16D and untreated pnx ewes. The two latter groups displayed a normal timing in seasonal breeding activity. Low and high plasma prolactin levels corresponded with short and long photoperiods during both the 24 and 22-h cycles. There was no clearcut “seasonal” rhythm in plasma prolactin in either of the pnx groups. A clear differentiation was seen between reproductive response and prolactin response, particularly in the case of ewes monitored on 22-h cycles of short photoperiod.