1. Introduction
Ž .
Release of oxytocin OT can be elicited at oestrus by mating and presence of the Ž
. male McNeilly and Ducker, 1972; Gilbert et al., 1991 and these high concentrations of
Ž .
OT may serve to facilitate gamete transport Wathes, 1984; Gilbert et al., 1992 . The pattern of OT release at mating appears to be highly species-dependent. In some species
the physical act of coitus is thought to be a relatively minor component in stimulating Ž
. the release of OT McNeilly and Ducker, 1972 and OT peaks may be provoked by the
Ž sensory and psychic stimuli occurring at the time of mating Campbell and Petersen,
. 1953; McNeilly and Folley, 1970; McNeilly and Ducker, 1972 . In the mare, mating is a
complex combination of sensory, psychic and mechanical stimuli involving teasing, mounting, intromission and ejaculation by the stallion. It is known that teasing stimu-
Ž .
lates OT peaks in the mare at mating Alexander et al., 1995 , but there is only limited Ž
. information on the pattern of OT release Walmsley, 1963; Alexander et al., 1995 .
Ž .
Prostaglandin F PGF
release is high in late dioestrus in mares, in association
2 a 2 a
Ž .
with luteolysis Goff et al., 1984 . Release of PGF can also be stimulated at other
2 a
Ž .
stages of the cycle by OT Goff et al., 1987 and there is a positive correlation between Ž
. plasma OT concentrations and PGF
release in nonpregnant mares Sharp et al., 1997 .
2 a
Therefore, any increase in OT at mating in mares might be accompanied by release of Ž
PGF . Both PGF and OT have been implicated as ecbolic agents in mares Troedsson
2 a 2 a
. et al., 1995 . Persistent mating-induced endometritis is a major cause of subfertility in
mares. Susceptibility to this condition is associated with low myometrial contractility Ž
. Troedsson et al., 1993 . Increases in concentrations of PGF
and OT around the time
2 a
of mating may therefore be important not only in gamete transport, but in stimulating uterine contractile activity after mating, which serves to evacuate collections of inflam-
Ž matory uterine fluid and cellular debris in genitally normal mares Hughes and Loy,
. 1975 .
We hypothesised that mares susceptible to endometritis, with delayed uterine clear- ance after mating may have defective release of ecbolic hormones. However, there is no
detailed information on endocrine events occurring around the time of mating and other intrauterine interventions in genitally normal mares. Therefore, in the present study, we
measured the release patterns of the ecbolic hormones OT and PGF at the time of
2 a
mating in the mare and some hours following mating when clearance of uterine contamination may occur. We also investigated the effect of a range of stimuli
associated with mating on OT and PGF release.
2 a
2. Materials and methods
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