| Popis: |
Rhythms have been long recognized as an important aspect of reproductive physiology, especially cycles of relatively long duration such as the oestrous cycle and seasonal variations in reproductive activity. More recently the contribution of circadian rhythms to the’organization of longer rhythms has been explored. We became interested in this general topic after reading the report of Hansen and Sodersten of a diurnal rhythm in the levels of lordosis behaviour in female rats (Hansen et al. 1979). They reported higher levels of lordosis during the dark phase of the lighting cycle, apparently vindicating behavioural endocrinologists who had been observing sex behaviour under dim red illumination for all of those years. This finding, of a rhythm of the performance of the behaviour per se, has been disconfirmed by several laboratories in America including our own, and reconfirmed an equal number of times by Sodersten’s group. This points to possible strain differences or latitude differences in the effects of the lighting cycle on the lordosis reflex. However, another finding from the same laboratory was equally interesting to us, namely that the time of administration of oestradiol within the light-dark cycle affected the degree of subsequent lordosis (Hansen et al. 1978). This finding suggested that the brain may vary in its sensitivity to hormonal stimulation. Since we had been working on the mechanisms of the initial aspects of oestrogen stimulation — namely oestrogen-binding proteins — it seemed to us that regulation of the cytoplasmic oestrogen receptor might be a way that the brain could vary its responsiveness to the hormone. There had been an earlier report of a diurnal variation in the levels of cytoplasmic oestrogen receptors in the rat uterus (Vaughan et al. 1979), but the use of ovarian-intact rats in those experiments allowed the possibility that the diurnal variation of receptors was a simple reflection of a diurnal variation in plasma oestradiol levels. |
