The Elemental Composition of the Environments of the Gametes and Preimplantation Embryo During the Initiation of Pregnancy

Micropuncture and electron probe microanalysis were used to determine the concentrations of Na, Cl, K, Ca, Mg, S and P in picoliter volumes of fluid in the microenvironments of male and female gametes and zygotes in the female genital tract of the mouse. Since ejaculation occurs directly into the lumen of the uterine cornua, post-coital uterine fluid is the first microenvironment of sperm following coitus. This fluid is characterized by a high concentration of K (32 mM) but low concentrations of Na (114 mM), Cl (115 mM) and Ca (1 mM), relative to mouse serum. Elemental analyses of the liquid ejaculate and proestrous uterine fluid demonstrate that the liquid ejaculate is the main modifier of proestrous uterine fluid in the formation of postcoital uterine fluid. In passing from postcoital uterine fluid to the ampulla, the site of fertilization, spermatozoa experience changes in the concentrations of only two elements: Cl and Ca significantly increase. Bursal sac fluid and oviducal fluids in the microenvironment of the mouse ova have unique compositions. Bursal sac fluid is lower in Ca, S and P than serum but slightly higher in K. Ampulla and isthmus fluids contain high concentrations of K (23–25 mM) but low concentrations of Ca (1.7–2.0 mM). Analyses of proestrous `ampulla fluid demonstrate that high K levels in the mouse oviduct are not due to cumulus cell degeneration, but probably originate from the oviducal epithelium.