Intra-ovarian dynamic blood flow in pseudopregnant rabbits during prostaglandin F2α-induced luteolysis

Contents In the present study, we evaluated the dynamic changes of intra-ovarian blood flow, by real-time colour-coded and pulsed Doppler ultrasonography, as well as the immunopresence of prostaglandin F2 (PGF2) receptor (FP) and peripheral plasma progesterone concentrations in pseudopregnant rabbit after PGF2 treatments at either early- (4days) and mid-luteal (9days) stages. During the pre-treatment observation interval of one hour, the ovarian blood flows showed a fluctuating pattern. Independently of luteal stage, PGF2 administration caused a fourfold decline in the blood flow within 40min that was followed 50min later by a reactive hyperaemia that lasted several hours, while the resistive index showed an opposite trend. Twenty-four hour later, the blood flow was one half that measured before PGF2 injection. At day 4 of pseudopregnancy, PGF2 did not affect peripheral plasma progesterone concentrations, but at day 9, it caused functional luteolysis as progesterone levels declined 6hr later to reach basal values after 24hr. The changes in the ovarian blood flows of pseudopregnant rabbits receiving PGF2 were accompanied by simultaneous changes in the resistance index. This biphasic response in the blood flow and vascular resistances likely reflects reactive hyperaemia following vasoconstriction. By immunohistochemistry, strong positive immune reaction for FP was detected in the cytoplasm of endothelial cells of ovarian arteries, veins and capillaries. In conclusion, these results suggest that PGF2 could acutely regulate the ovarian blood flow of pseudopregnant rabbits, even if there is no evidence of a blood flow reduction anticipating luteolysis.