DIURNAL VARIATION IN RESPONSE TO GONADOTROPIN IN THE MOUSE

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Abstract
With the use of immature mice 18–20 days of age it was shown that a single injection of 0.1–10.0 i.U. chorionic gonadotropin (HCG) or pregnant mare serum gonadotropin (PMS) resulted in greater uterine and ovarian weights 24 hours later if given in the afternoon as compared with the morning. A diurnal difference in response was also observed in ovarian but not in uterine weights at48 hours after injection. The diurnal variation in response was not apparent in mice aged 14–17 days, but was significant in 6 week old mice. In the latter the period of increased responsiveness was more restricted than in mice aged 20–22 days. A study of the time-response relationships indicated that the greater response in organ weights at 24 hours was a consequence of an earlier beginning of growth rather than an increased rate of growth. Hypophysectomy and high doses of PMS and HCG (30 I.U.) prevented the diurnal variation in response, which was also not apparent in the uterine weight response to a single injection of either oestradiol, post-menopausal urine gonadotropin or a crude extract of anterior pituitary glands. It is concluded that there is a diurnal variation in pituitary function and not in ovarian or uterine function. The results are discussed in relation to the gonadotropic hormones.