Polyploidy in mammalian tissues occurs in the regenerating liver of t h e rat and mouse (Beams and King, 1942 ; Wilson and Leduc, 1948), and in rat decidual tissue (Krehbiel, 1937 ; Wolfe and Wright, 1942 ; Velardo et al., 1953 ; Sachs and Shelesnyak, 1955). An extensive decidual reaction, comparable to that normally associated with ovum implantation, can be produced in rats by stimulating with histamine endometrium previously sensitised by hormone treatment. Both the naturally occurring decidua of nidation and that experimentally produced with histamine (" deciduoma ") can be suppressed by local application of various antihistamines (Shelesnyak, 1952(Shelesnyak, , 1957. A histological study of histamine " deciduoma " by Sachs and Shelesnyak (1955) showed that extensive nuclear polyploidy appeared in the developing '' deciduoma " about 36 hr after stimulation of the uterus, and that the application of antihistamines a t the time of stimulation prevented polyploidy, but did not interfere with normal diploid mitosis, which occurs earlier in the decidual process.Suppression of polyploidy in " deciduomas " by antihistamines might occur in two ways-the histamine antagonists might interfere with decidua formation, with consequent failure of polyploidy, or the antihistamine might cause a general suppression of nuclear polyploidy, and thus prevent subsequent decidua formation.To decide between these two possibilities, we carried out experiments on the influence of antihistamines on the regenerative processes, and especially the polyploid activity, in mouse liver.
MATERIALS AND METHODSTwo hundred male albino T.O. strain mice were used in the experiment. They were maintained on diet 41B (Joseph Rank), and water was supplied ad libitum.Each animal was weighed, anesthetised with ether, and numbered, and then partial hepatectomy was performed. An epigastric incision (1-1.5 cm.) was made just to the left of the lower end of the xiphoid. A silk ligature, already tied, was placed on the abdomen in such a way that the incision was at its centre. The median and lateral lobes of the liver were delivered through the wound, and hence through the ligature, by gently squeezing the upper abdomen. The ligature was worked up towards the pedicles containing the hepatic artery, portal vein and bile-duct, and when it had been drawn tight the pedicle was cut. The liver removed was immediately weighed. After this operative procedure the animals recovered in a few minutes. Special precautions were taken to keep them warm. Glucose water was given. The immediate operative mortality wag 8 per cent., and anesthetic deaths 4 per cent.
