ECTOPIC AUTOGRAFTS OF BLASTOCYSTS IN MICE MAINTAINED IN DELAYED IMPLANTATION

Summary. During delayed implantation mouse blastocysts were trans- ferred from the uterus to the animal's own kidney. Under the kidney capsule the blastocystsimplanted' and developed normally, whilst those in the uterus remained in delay. The implications of these findings are discussed. Mouse eggs taken from the genital tract and transplanted to extra-uterine sites 'implant' and develop independently of the endocrine state of the host. Their development is, however, greatly influenced by the state of differentiation of the egg when transplanted (Kirby, 1962, 1965). All previous accounts have dealt with eggs taken from the oviduct or uterus of a mouse during normal pregnancy ('normal' eggs). In these experiments eggs from mice in delayed implantation ('delayed' eggs) were used. In sexually mature, randomly bred mice, eggs were prevented from im¬ planting by removal of both ovaries. This operation was performed on sixteen mice on Day 1 of pregnancy (day of copulation plug = Day 0), and a further five mice on Day 2 of pregnancy. All mice were maintained on 2 mg of pro¬ gesterone in oil (s.c.) from the day of ovariectomy until autopsy. On Day 5 of pregnancy (i.e. 1 day beyond the normal time of implantation), none of the mice showed implantation sites, and an attempt was made to extract blasto¬ cysts from the left uterine horn whilst the mouse remained anaesthetized. This was done by gently flushing with physiological saline through a fistula whilst the horn was in situ or, in a few cases, by flushing after the horn had been removed from the body. Blastocysts were found in eleven of the twenty-one mice and one (or in two cases two), blastocysts were taken up in a micropipette and transplanted to the animal's own kidney (autografi). Between 3 and 12 days later the mice were killed, and in all eleven animals a characteristic haemorrhagic nodule had developed on the kidney indicating that the extra-uterine blastocyst had implanted. The kidneys were fixed in Bouin's fluid and subsequent histological examination of the growths showed that in six of the eleven mice the blastocyst had given rise to an embryo of reasonably normal appearance (Plate 1). In