Effects of prostaglandin f(2alpha) on corpora lutea formation and function in mated bitches.

Fifteen mated bitches were used to study the effects of prostaglandin F(2alpha) on ovarian endocrine function during the early and midluteal phase. Five dogs were kept as controls, five were given 250 mug/kg prostaglandin F(2alpha) twice daily between the first and fifth day of metestrus, and five were similarly treated with prostaglandin F(2alpha) between 31 and 35 days of metestrus. Function of corpora lutea was monitored by measuring serum progesterone concentrations during the first 45 days of gestation.Dogs treated with prostaglandin F(2alpha) during the early luteal phase had progesterone concentrations similar to controls and pregnancies were undisturbed in both groups. A dramatic decrease in serum progesterone concentration and abortion resulted after prostaglandin F(2alpha) administration at midpregnancy.These results indicate that prostaglandin F(2alpha) was not luteolytic during the early luteal phase and was therefore ineffective for preventing pregnancy at that time. However, at the dosage and frequency used in this study, prostaglandin F(2alpha) was luteolytic and abortifacient at midgestation.