QUANTITATIVE STUDIES ON THE EFFECT OF THE SUCKLING STIMULUS ON BLASTOCYST IMPLANTATION IN THE RAT

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Abstract
Rats which were kept under conditions of controlled illumination were allowed to nurse a standardized litter of 10 young. The day on which post-partum vaginal sperm was found was considered as day 0 of lactation-pregancy. By measuring the diameter of the implantation sites and comparing this with the control data, the extent of a possible delay of implantation could be estimated. The following observations were made Lactation until the 13th hour of the third day of lactation-pregnancy does not cause a delay of implantation. Each day suckling is allowed after the third day of lactation-pregnancy, causes one day delay of implantation. Implantation could be induced at will on any of the first 5 days after the third day of lactation-pregnancy by litter removal. Spontaneous implantation in lactating rats occurred from the eighth day onwards. No special implantation periods were observed. Temporary litter removal during a period of 12 hours including the late afternoon, induced implantation. One case of incomplete implantation was noted. One single dose, or daily administration of progesterone, did not induce implantation during lactation-pregnancy.