SOME DIFFERENCES BETWEEN TWO STRAINS OF RATS DEVELOPED BY SELECTION TO DIFFER IN THEIR RESPONSE TO EQUINE GONADOTROPHIN1

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Abstract
SOME of the causes of variation in the response of the ovaries of 21- day-old rats to a standard dose of equine gonadotrophin have been reported by Chapman (1946). Heredity was estimated on his random-bred stock as responsible for 40% of the variance in the weight of the stimulated ovaries after the variability due to body weight and to temporal factors was eliminated. Selection and inbreeding experiments have since been carried out on the descendents of this stock to develop lines that differ markedly in their quantitative response to the gonadotrophic hormone (Kyle and Chapman, 1948). The ability of a rat ovary to respond to gonadotrophic stimulation is associated with the presence of vesicular follicles (Corey, 1930 and Hargitt, 1930). It may be suspected that the larger the number of vesicular follicles present, within limits, the greater will be the response to a given amount of hormone and that differences in number of vesicular follicles might account for differences between lines in the degree of this response.