Cyclic changes of exopeptidase activities in the rat brain: a regional study

The present report describes the activity of three neuropeptide-degrading enzymes, in 12 brain areas during the estrous cycle of Sprague-Dawley rats. The quantitation of the enzyme activities was performed by measuring the rate of hydrolysis of the chromogenic substrates Leu-, Lys- and Asp-2-naphthylamides, by neutral, basic and acid aminopeptidase (AP) activities, respectively. Lys- and Leu-AP activities show a significant increase during the proestrus stage in the hypothalamus and the pituitary gland. Also there is a significant increase of Leu-AP activity in the occipital cortex. No significant decreases for Asp-AP activity during the proestrus in the hypothalamus and the pituitary were observed. As the changes seem to be limited at the hypothalamic-pituitary axis, these findings could be interpreted to mean that these exopeptidase activities play a role in the hormonal changes that take place during the estrous cycle of the rat.