The secretion of human chorionic gonadotropin as well as the α- and β-messenger ribonucleic acid levels are stimulated by exogenous gonadoliberin pulses applied to first trimester placenta in a superfusion tissue culture system - Merz,W.E.; Erlewein,C.; Licht,P.; Harbarth,P. (J Clin Endocrinol Metab, 1991)