Glandular kallikrein levels in the rat anterior pituitary during the estrous cycle and pregnancy

Glandular kallikrein (a trypsin-like serine protease) is a major estrogen-induced protein in the rat anterior pituitary, which appears to be associated with lactotropes. The present study examined glandular kallikrein levels in the anterior pituitary during the rat estrous cycle and pregnancy. After trypsin treatment of anterior pituitary homogenates (to activate latent forms of the enzyme), glandular kallikrein activity was measured by using the chromogenic substrate D-val-leu-arg-p-nitroanilide: 98-95% of the enzymatic activity was immunoprecipitable with glandular kallikrein antiserum. Glandular kallikrein levels did not change significantly during the various phases of the rat estrous cycle. However, a sharp decrease was observed starting on Day 15 of pregnancy and lasting through parturition; levels had almost returned to control values by Day 5 of lactation.