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S. A. ASDELL and G. A. SPERLING

Summary.

A result reported earlier that oestradiol sensitizes the nervous system of the male rat so that it responds to testosterone with increased motor activity could not be repeated. The male and female rat respond differently, the male only to oestradiol and the female to both oestradiol and testosterone. A few rats sometimes respond to testosterone.

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S. A. ASDELL, H. DOORNENBAL and G. A. SPERLING

Summary.

Oestrogen pellets implanted in castrated or spayed rats cause both the males and females to take a considerable amount of voluntary exercise. Testosterone pellets cause implanted spayed females to take considerable exercise but their effect on the castrated male is much less. If the male has previously been under the influence of an oestrogen pellet, the amount of activity that results when a testosterone pellet is implanted is increased. The suggestion is made that once the responsible brain centre has been exposed to oestrogen it becomes sensitive to the action of testosterone.

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S. A. ASDELL, H. DOORNENBAL, S. R. JOSHI and G. A. SPERLING

Summary.

Eleven groups of fifty rats each were kept under uniform conditions of management and their life-spans under different treatments were compared. Females lived longer than males, while ovariectomy tended to shorten the life-span of females and castration to lengthen that of males. Implantation of gonadectomized rats with oestradiol benzoate did not prolong the life-span of the females but it did tend to prolong that of males. Implantation of gonadectomized rats with testosterone propionate tended to shorten the average life-span of both sexes. Unbred females outlived bred ones, on the average, but the difference was not significant at the 5% level. Late initial breeding appeared to be more harmful than breeding for the first time at the usual age for laboratory rats. Light breeding had little or no effect upon the average longevity of males. These conclusions are tentative. The results are consistent but they mostly lack acceptable statistical significance. The most significant result statistically was that rats exposed to their own or implanted oestrogens had a longer average life-span than did those exposed to their own or to implanted testosterone.