PITUITARY GROWTH HORMONE AND MITOSES IN IMMATURE MOUSE LIVER1

Abstract

The effect of pituitary growth hormone (STH) on liver mitoses in immature male ZBC mice was studied under conditions standardized for periodicity analysis. STH was administered to groups of animals in doses of 1 [mu]g./gm. of body weight and 10 [mu]g./gm. of body weight, for three successive days. The mitotic activity of the liver was then determined in animals sacrificed either 8 or 20 hours after the last injection, the following midnight or noon, respectively, and compared with the corresponding values for animals given,saline solution. The mean mitotic activity for the saline-treated group by day was twice the corresponding value by night. Moreover, the mitotic activity of the groups treated with STH was significantly higher than that of the corresponding saline-treated group, in livers removed at noon, but not in livers removed at midnight. The effect of STH thus was manifest at the daily time of high mitotic activity, and absent at the time of low mitotic activity. The effect of STH upon hepatic mitoses seems to be exerted indirectly by modifying some unknown metabolic process, the peak of which process precedes the daily mitotic peak.