Circulating Immunoreactive Oxytocin During the Human Menstrual Cycle Comes From the Pituitary and Is Estradiol Dependent*

Abstract

The aims of this study were to 1) evaluate the relative contributions of hypothalamic and ovarian oxytocin (OT) to peripheral serum concentrations and 2) determine the relationship between serum OT and ovarian steroid concentrations. Four groups of women were studied: 1) women with spontaneous cycles (n = 4) and normal serum estradiol (E2), progesterone, LH, and FSH levels; 2) in vitro fertilization (IVF) patients (n = 8) undergoing ovarian hyperstimulation; 3) agonadal oocyte-recipient patients (n = 6) receiving replacement E2 and P therapy; and 4) postmenopausal women (n = 21). Peripheral serum samples were collected daily during a menstrual cycle from the normal and agonadal women and for 6 days before ovulation in the IVF group. Serum immunoreactive OT was measured by specific RIA after Sep-Pak extraction; the assay sensitivity was 0.6 pmol/L. Serum OT in the women with normal cycles increased during the follicular phase, reaching a peak 1 day after the LH surge, and decreased in the luteal phase [days 7, 16, and 21, 10.7 +/- 3.5 (mean +/- SE), 25.7 +/- 5.7, and 13.2 +/- 2.5 pmol/L, respectively; P less than 0.05]. Serum OT levels were higher in IVF patients before ovulation than in women with spontaneous cycles, but lower than those in the agonadal women, who had a peak value (49.1 +/- 9.6 pmol/L; P less than 0.05) on day 13 of E2/progesterone replacement therapy. Serum OT was positively correlated (r = 0.68, normal women; r = 0.91, oocyte recipients) with serum E2 values during the first part of the cycle (P less than 0.01). A similar positive correlation between serum OT and E2 was found in the postmenopausal women (r = 0.83). We conclude that serum OT before and around the time of ovulation comes mainly from the pituitary, and not from the ovary, and is E2 dependent.

Reproductive hormones in plasma over the menstrual cycle in primary dysmenorrhea compared with healthy subjects

“…The major finding of the present study was a significantly higher concentration of oxytocin at menstruation and an increase of FSH at the corresponding time, suggesting a regulatory mechanism. In agreement with previous results [18,19], the plasma level of oxytocin in both women with dysmenorrhea and healthy subjects increased during the follicular phase, reaching a peak at the time of ovulation, followed by a decrease in the luteal phase. The oxytocin concentrations were overall comparable in the two groups.…”

Speculations on the links between feelings, emotions and sexual behaviour: Are vasopressin and oxytocin involved?

“…Shukovski et al (1989) confirmed that oxytocin in women with normal menstrual cycles is dependent on oestradial (circulating oestrogen) and moreover peaks at the time of ovulation. Similarly, for the Carmichael et al (1994) subjects, baseline oxytocin levels were significantly higher at mid-cycle compared to the follicular phase, although at orgasm there were no differences in plasma oxytocin readings between the two groups.…”

Synthesis of oxytocin in amnion, chorion, and decidua may influence the timing of human parturition.

“…We have previously demonstrated that estradiol biosynthesis increases in human fetal membranes around the time of parturition (7). Estradiol increases synthesis and release of OT from the neurohypophyseal system (20,26,27). To determine whether estradiol can increase OT mRNA levels in chorio-decidua, we incubated full-thickness membrane explants (amnion, chorion, and decidua) in the presence of various concentrations ofestradiol for 12 h. Ribonuclease protection assays of equal amounts of total RNA isolated from these explants indicated that estradiol (0.1 and 1.0 nM) increased OT mRNA content relative to controls incubated for the same period of time with no estradiol (Fig.…”