Differential Effects of Prostaglandins on Lordosis Behavior in Female Guinea Pigs and Rats

The facilitatory and inhibitory effects of prostaglandins PGE2 and PGF2α on lordosis behavior were compared in guinea pigs and rats. In the first part of experiment 1, PGE2 or PGF2α (500 µg) failed to facilitate significantly lordosis behavior in ovariectomized, estradiol benzoate (EB)-primed guinea pigs. However, in the second part of experiment 1, in guinea pigs treated with EB followed 44 h later by progesterone (P), PGE2 and PGF2α (500 µg) significantly inhibited lordosis responses when given at the same time as P, 5 h after P (at the onset of heat) or 8 h after P (at the time of maximal lordosis responding). Doses of 20 µg or 100 µg PGE2 or PGF2α also inhibited lordosis responding when given 5 h after P to EB-primed guinea pigs. Oxytocin treatment (100 mU or 500 mU) given 5 h after P to EB-primed guinea pigs had no effect on subsequent lordosis responding. In experiment 2, PGE2 (100 µg) significantly facilitated lordosis in EB-primed rats but, in contrast to guinea pigs, 500 µg PGE2 or PGF2α had no inhibitory effect on lordosis behavior when given 4 or 8 h after P treatment to EB-primed rats. Inhibitory effects of prostaglandins on lordosis behavior in guinea pigs and facilitatory effects of prostaglandins on lordosis behavior in rats may be indicative of differential neurochemical mechanisms for the regulation of lordosis behavior in guinea pigs and rats.