Membrane-bound tyrosine aminopeptidase activities in the rat brain throughout the estrous cycle.

Puromycin sensitive and insensitive membrane-bound aminopeptidase activity levels during the estrous cycle in several brain areas have been described in this research. We have found the highest aminopeptidase M activity levels during the proetrous stage in the hypothalamus, the amygdala and the pituitary gland. Since this enzyme has been involved in opioid peptide metabolism, it is suggested that aminopeptidase M could play a part in the decrease in the inhibitory influence of the endogenous opioids peptides that participate in the LH surge.