Neutral aminopeptidase activity levels during the estrous cycle and the pregnancy in the hypothalamus and the pituitary of the rat.

Neutral aminopeptidase activity levels during the estrous cycle and pregnancy, in the hypothalamus and the pituitary of experimental animals, was studied in this research. The cyclic stages were the estrous, diestrous and proestrous (at morning and afternoon). The pregnancy phases were the 2nd, 7th, 14th and 20th day postinsemination. The parturition day was also studied. The higher cyclic enzyme levels were found in the proestrous stage (afternoon). No differences between estrous and diestrous were observed. During pregnancy, there was a rise at 7th and 14th day, with a decrease in the 20th day. In the hypothalamus, significant increases after parturition were shown, the latter not being observed in the pituitary. In general, the changes seem to be parallel to those of the luteinizing hormone.