The increase in uterine oxytocin receptor concentrations over the late lute
al phase of the oestrous cycle in sheep is thought to play an important rol
e in the regulation of the duration of the cycle by facilitating the effect
of oxytocin on uterine prostaglandin release. Experiments indicated that o
xytocin receptor mRNA expression in the endometrium was high at oestrus com
pared with at days 2, 7 and 12 of the oestrous cycle. The amount of oxytoci
n receptor mRNA expression in the pituitary gland did not show any signific
ant differences during the oestrous cycle. Oxytocin receptor cDNA was obtai
ned and characterized from ovine uterine endometrium on day 15 of the oestr
ous cycle, using RT-PCR techniques, to study the mechanisms underlying the
resolution of oxytocin receptor expression. The cDNA sequence for the oxyto
cin receptor gene in sheep was found to be similar to that described previo
usly, except for a difference of seven nucleotides. These nucleotide differ
ences resulted in changes in four of the deduced amino acids in the oxytoci
n receptor sequence. The heterogeneity of the different sized oxytocin rece
ptor transcripts in sheep is due, at least in part, to the alternative use
of polyadenylation sites. Northern hybridization confirmed that the oxytoci
n receptor gene is expressed in ovine corpus luteum. The investigations on
oxytocin receptor gene expression indicate that the patten of oxytocin rece
ptor gene expression in sheep is not only tissue-specific, but also highly
function-related. Evidence was obtained of mRNA editing in both the coding
and the 3'-untranslated (3'UTR) regions of oxytocin receptor gene transcrip
ts in ovine endometrium; this was the first demonstration of this phenomeno
n for oxytocin receptor mRNA. The present results indicate that the observe
d differences in oxytocin receptor mRNA sequences for the different oxytoci
n receptor populations in endometrium are due to mRNA editing. mRNA editing
of oxytocin receptor transcripts may be reflected in changes in the amino
acid composition of the carboxyl terminus of the receptor, which would expl
ain the differences in the observed responses to an oxytocin challenge.