抄録
In order to elucidate the diurnal and circadian rhythms of oxytocin secretion, and the relation of estrogen, progesterone, testosterone and LH-RH to oxytocin secretion, plasma oxytocin levels were determined before and after the administration of these hormones in normal and hypogonadal subjects. The results were as follows.
(1) In females with normal menstrual cycle, plasma oxytocin levels in the morning after overnight fasting were significantly higher (4.5 ± 2.6 pg/ml (mean ± SE)) in the follicular phase than they were (2.1 ± 1.3 pg/ml) in the luteal phase (p<0.01). Plasma oxytocin levels were higher in the follicular and ovulatory phases than they were in the luteal phase. In the luteal phase, the mean oxytocin concentration was higher during sleeping than during waking; however, in the follicular phase a variation of plasma oxytocin level was higher during waking than during sleeping.
(2) In healthy males, plasma oxytocin level in the morning after overnight fasting was 3.5 ± 1.7 pg/ml, which was higher during sleeping than during waking. But the variation of plasma oxytocin levels during waking was larger than that during sleeping. Plasma oxytocin levels did not show cyclic changes in a year, but they were higher in summer than in winter.
(3) Plasma oxytocin levels rose significantly after estradiol administration in normal females and males and did not change significantly after progesterone, and estradiol and progesterone administrations. A significant positive correlation was observed between plasma oxytocin level and the ratio of estradiol to progesterone concentrations in plasma in females and males.
Plasma oxytocin levels rose significantly after testosterone administration in normal males. A significant positive correlation was observed between oxytocin and testosterone levels in plasma after the administration of testosterone.
In the male subjects with hypogonadism, plasma oxytocin levels were elevated markedly 15 minutes after LH-RH administration.
From these findings, it is suspected that in females with normal menstrual cycle, estrogen or LH-RH stimulates oxytocin secretion which is inhibited by progesterone, and that testosterone or LH-RH stimulates oxytocin secretion in normal males. On the other hand, a transient elevation of oxytocin secretion during waking in both females and males may be attributed to stimuli other than the sex hormones.
The results also suggest that oxytocin secretion is affected by mechanism related to the hypothalamus-pituitary-gonadal system, and by mechanisms other than the system.
