No abstract

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 ofmales. 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.

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.

No abstract

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.Oestradiol benzoate pellets implanted beneath the skin of the gonadectomized rat cause both males and females to take large amounts of exercise in an activity drum. Testosterone propionate causes the females to take much exercise but has a small effect upon the males. Asdell, Doornenbal & Sperling (1962) have suggested that testosterone propionate is effective in males if the implant follows one of oestradiol benzoate. Therefore it was postulated that oestrogen sensitizes the nervous system to androgen. We have been unable to repeat this work and believe that the previous result was obtained because the testosterone implant was made before the direct effect of the oestrogen had disappeared.Eight male rats were castrated when about 45 days old. A week later, each was implanted subcutaneously with one pellet containing 1 mg of oestradiol benzoate. All responded with increased activity and in all but one a daily average of over 10,000 rotations of the activity drum, about 7 miles, was reached. At the end of 8 weeks, when activity had decreased to normal levels, each rat was implanted with one pellet containing 1 mg of testosterone propion¬ ate. During the following 8 weeks, no increased activity was observed in any of the rats. They were then implanted with 1-mg oestradiol pellets and all displayed increased activity but not to the degree reached in the earlier oestrogen period. After 8 weeks, another testosterone implantation was made. Activity increased slightly in two rats only.In an experiment designed to test the effect of testosterone level, eight male rats were castrated when about 45 days old. Two were implanted with single 1-mg testosterone propionate pellets. One showed a marked increase in activity; the other had a small response. With two 1-mg pellets, one rat increased markedly and the other showed a slight response. With a single 10-mg pellet, one rat responded markedly; the second with a little increased activity. With two 10-mg pellets, one rat increased markedly and the second to a small degree. After 8 weeks, 1-mg testosterone propionate pellets were 123