Endocrine Regulation of Rat Serum Cholinesterase Activity*

Enzymological and endocrine studies of rat serum cholinesterase (CHE) suggest that this enzyme is subject to a complex and specific form of regulation. Adult CHE activity levels are 3-fold higher in adult females than in males. Gonadectomy and/or hypophysectomy abolish these sex differences. Androgen and estrogen replacement to gonadectomized but not to hypophysectomized animals reverses this action. Adrenalectomy produces no significant changes in serum CHE levels in either male or female rats. An ectopic pituitary plus the appropriate steroid cannot reverse the effect of hypophysectomy. The catalytic properties of CHE alter concurrently with isozyme changes and are reflected in the changes in the ratio of hydrolysis of the butyryl and acetyl substrates. Androgens and estrogens, acting through the hypothalamic-hypophyseal axis, appear to modulate the synthesis of specific CHE isozymes.