STUDIES ON THE MECHANISM OF NIDATION. XXXIII.

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Abstract
In an extension of previous studies which had shown that decidual induction in the rat depends on the availability of histamine, the possibility that exposure of the rat uterus to semen influences the availability of histamine in the uterus was investigated. The histamine content of the rat uterus was measured following normal mating (uterus exposed to seminal plasma plus sperm), following mating with vasectomized males (uterus exposed to seminal plasma only) and following electrical induction of pseudopregnancy. Mating with vasectomized males resulted in an elevation of the histamine content of the uterus from the low level characteristic of electrically induced pseudo-pregnancy to approximately the level characteristic of pregnancy in the preimplantation period. Histamine-release, which occurs at the time of decidual induction in the pregnant rat, did not occur in the uterus of the rats mated with vasectomized males. The elevation in histamine following mating was attributed to importation by cells infiltrating the uterus in response to the stimulus of mating. The non-release of histamine was attributed to the lack of stimulating in the absence of the blastocyst.