Expression of the oxytocin gene, but not the vasopressin gene, in the rat uterus during pregnancy: influence of oestradiol and progesterone.

Oxytocin (OT) and vasopressin (VP) are neurohypophyseal hormones with potent stimulatory actions on the uterus. In order to determine whether these hormones may have a paracrine action on the uterus, OT and VP gene expression was studied in myometrium from pregnant rats at gestational ages of 14 and 20 days, and from ovariectomized animals treated with oestradiol and progesterone. OT and VP mRNA concentrations were measured using real-time quantitative reverse transcription-PCR, and OT- and VP-like immunoreactivities were determined using RIA. OT mRNA was detected in the uterus from pregnant rats, but did not differ between the groups of different gestational ages. Oestradiol significantly (P<0.05) stimulated OT gene expression in ovariectomized rats. Progesterone alone was without effect on OT mRNA concentrations, but significantly (P<0.05) reduced the oestradiol-induced OT mRNA accumulation. The OT-like immunoreactivity in an extract of myometrium from pregnant rats was eluted from a reverse-phase HPLC column with a retention time identical to that of synthetic OT. Neither VP mRNA nor VP-like immunoreactivity was detected in the myometrium from pregnant or ovariectomized rats. The study demonstrates steroid-dependent expression of the OT gene in the rat uterus and processing of uterine preprooxytocin to the mature nonapeptide. The data support the theory that this peptide may act in a paracrine pathway. No evidence was found for the presence of VP in the uterus so that, if the hormone is involved in a stimulatory action on this tissue, it probably acts via an endocrine mechanism.