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 on Day 7 of gestation, which suggests a hormonal regulation and a role in implantation. This study pursued the sequential variations during the cycle and early pregnancy. During the estrous cycle, immunoreactive uterine kallikrein levels showed a recurrent pattern, with the highest value on proestrus (12.9 +/- 1.5 ng/uterus or 0.49 +/- 0.03 ng/mg protein), and the lowest on metestrus (4.1 ng +/- 0.5 ng or 0.30 +/- 0.03 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 estrus and diestrus; a progressive rise, observed from Day 5 (8.2 +/- 1.1 ng or 0.43 +/- 0.02 ng/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 variations observed during the cycle and early gestation coincide with those described for ovarian steroids and uterine vasoactive changes, suggest the hormonal regulation of uterine kallikrein levels, and support its role in implantation.