two trials were conducted to measure the progesterone ( p ( 4 ) ) decline and luteinizing hormone ( lh ) surge in serum subsequent to administration of a short half-life ( short t ( 1 2 ) ) prostaglandin ( pgf ( 2alpha ) ) or a long half-life ( long t ( 1 2 ) ) prostaglandin analogue ( fenprostalene ) on days 6 or 11 of the estrous cycle .
C0033554
prostaglandin
C0033568
prostaglandin analogue