No abstract

No abstract

The objective of this study was to compare the effects of melatonin implants combined with intravaginal, progestagen-impregnated pessaries with the conventional treatment of progestagen pessaries followed by pregnant mare serum gonadatrophin (PMSG) on the reproductive performance of ewes during the anoestrous period.A commercial flock of 179 seasonally anoestrous Chios crossbred ewes was used. The ewes within the flock were randomly allocated to one of two groups. Ewes of group MP (melatonin + pessaries) received melatonin implants on 20 March (50 days before the target breeding date of 10 May) and were treated with intravaginal progestagen pessaries 35 days later (25 April). Ewes of group PP (pessaries + PMSG) were also treated with pessaries on 25 April. After 14 days the pessaries were removed from both groups and 500 i.u. PMSG was injected (i.m.) into ewes of group PP only. Fertile rams were introduced into both groups 24 h after sponge removal. Pregnancy rate and litter size were determined by ultrasound scanning 80 days after ram introduction.Pregnancy rate at first oestrus was significantly higher in group MP than in group PP (57 v. 40%, P < 0·05). The overall conception rate during two oestrous cycles was significantly higher in group MP than in group PP (78 v. 59%, P < 0·02). The groups did not differ significantly in the mean number of foetuses per pregnant ewe that conceived during the first or second oestrus after pessary removal (1·78 and 1·87, respectively). The total number of foetuses per treated ewe was higher in group MP than in group PP (1·39 v. 1·10) as a consequence of the difference in pregnancy rate.

Sex steroid binding protein (SBP) is a plasma protein that specifically binds sex steroids with high affinity. It is synthesized in the liver and circulates in the plasma of many species including human, monkey, cattle, dog, cat and others. SBP is a dimeric protein with a Mr ranging between 84-9Θ KDa and binds one steroid molecule per dimer. Its expression is regulated by many hormones and estradiol promotes while testosterone inhibits its expression. Its physiological role is not known completely, but it is likely to control at least the bioavailable levels of circulating steroids. Experimental evidence from our laboratory and others supports the dogma that non-bound steroids are free to enter the target cells and act. After the discovery of SBP-membrane receptor, it seems that SBP serves also other biological role except that of binding steroids. All recent reports are discussed.