Cycle dependent variations in transfer of 133xenon from vagina to uterus in rats. 
The possible existence of an oestrus cycle dependent on local transfer of 133xenon from vagina to uterus was investigated in anaesthetized rats.  133Xenon in saline was infused into the vaginal lumen of rats in oestrous (n = 7) and dioestrous (n = 10).  The uterus was removed 3 min after the infusion and the radioactivity in the organ counted, after which the remaining radioactivity in vagina was measured.  The results showed that the radioactivity increased in all uteri compared with that of the background.  The average transfer, expressed as per cent transfer, from vagina in the dioestrous group (5.5%) was significantly higher (P < 0.01, Mann-Whitney) than in the oestrous group (1.4%).  The results suggest that the rate of transfer from vagina to uterus depended on the oestrous cycle.  Vaginal treatment of women with progesterone for example, may similarly induce high local concentrations in the uterus.  Empirically this is already used after in vitro fertilisation, it may also prevent progesterone induced migraine in menopausal women.  The possible cycle dependent variations in the transfer in women should be evaluated.