The possible mode of action of prostaglandins: X. Antagonism between prostaglandin F2a and prolactin or human chorionic gonadotropin : A comparative study

A comparative assessment of the efficacy of prolactin or HCG in reversing the luteolytic property of a single dose (2.0 mg/kg) of PGF₂a was conducted in pregnant (day 10) rats. It was found that prolactin maintained pregnancy in 90% of the test animals. HCG though found to maintain pregnancy in 70% of the PGF₂a-treated pregnants, the fetal survival rate was, however, recorded to be 62% against the control value of 98%. Conversely, prolactin replacement maintained the fetal survival rate as high as 93.4%. Moreover, the growth of the fetuses, placentae and corpus luteum in the pregnants having prolactin in conjunction with PGF₂a was also found to be greater compared to the animals which h ad a combined regimen of PGF₂a and HCG, but identical to controls. On the other hand, similar combined regimen when applied to hysterectomized pregnant rats, it was observed that though the vaginal diestrus was maintained by the prolactin or HCG in the presence of PGF₂a, the prolactin regimen was found to be superb compared to HCG in the maintenance of luteal weight and functional activity. It was concluded that the antifertility effect of PGF₂a in the rat is primarily the consequence of luteolysis and prolactin seems to be a much more appropriate hormonal replacement compared to HCG, a long-acting LH, in antagonizing the luteolytic property of PGF₂a.