VARIATIONS IN UTERINE KALLIKREIN DURING CYCLE AND EARLY-PREGNANCY IN THE RAT

We have previously demonstrated the presence of tissue kallikrein and its mRNA in rat uterus, and an increase of the immunoreactive enzyme o n Day 7 of gestation, which suggests a hormonal regulation and a role in implantation. This study pursued the sequential variations during t he cycle and early pregnancy. During the estrous cycle, immunoreactive uterine kallikrein levels showed a recurrent pattern, with the highes t value on proestrus (12.9 +/- 1.5 ng/uterus or 0.49 +/- 0.03 ng/mg pr otein), and the lowest on metestrus (4.1 ng +/- 0.5 ng or 0.30 +/- 0.0 3 ng/mg protein); p < 0.05. During gestation, values on Day 1 (6.1 +/- 0.4 ng/uterus or 0.30 +/- 0.01 ng/mg protein) and Day 3 (4.9 +/- 0.3 ng or 0.35 +/- 0.01 ng/mg protein) were similar to levels during estru s and diestrus; a progressive rise, observed from Day 5 (8.2 +/- 1.1 n g or 0.43 +/- 0.02 ngl mg protein), attained the highest value on Day 7 (15.8 +/- 1.7 ng or 0.78 +/- 0.05 ng/mg protein); p < 0.05. The vari ations observed during the cycle and early gestation coincide with tho se described for ovarian steroids and uterine vasoactive changes, sugg est the hormonal regulation of uterine kallikrein levels, and support its role in implantation.