THE RELATION BETWEEN NATURAL FECUNDITY AND RESPONSE TO FOLLICLE-STIMULATING HORMONE

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Abstract
SUMMARY: A study was made of the response to induced ovulation of female mice from strains in which the spontaneous ovulation rate had increased as a result of artificial selection for litter size. In response to standard doses of follicle-stimulating hormone (FSH) within the physiological range, the number of eggs shed differed significantly among the three strains tested, in the direction expected on the basis of their spontaneous ovulation rates. This indicates that the principal effect of selection has been to increase the sensitivity of the ovary to FSH. In one strain, the possibility remains open that there may also have been some increase in the amount of FSH available. In response to larger doses of FSH, females from the strain with the highest spontaneous ovulation rate shed significantly fewer eggs than the other two groups. Selection must therefore have altered the shape of the dose-response curve, increasing the ovarian response at low levels of hormone and decreasing it at high levels.

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