The actions of prostaglandins and cyclo-oxygenase inhibition on the resistance vessels supplying the human fetal placenta.

The resistance arteries supplying individual exchange villi of the full-term human fetal placenta were examined for their reactivity to various prostaglandins (PG's) as well as for their ability to synthesize biologically active PG's. PGA1, PGF2 alpha, PGE2 and PGE1 produced dose-dependent contractions between 10(-7) and 10(-5)M. The order of potency observed was PGA1 approximately PGF2 alpha greater than PGE2 greater than PGE1. TXB2 was without activity in this preparation. Prostacyclin (PGI2) produced a dose-dependent relaxation of pre-contracted strips between 10(-8)M and 10(-5)M. Arachidonic acid (A.A.) produced stable dose-dependent contractions (10(-5) M to 10(-3)M) which were totally abolished by pretreatment with 10(-7)M meclofenamate (MF). At no concentration of A.A. was any evidence of vascular relaxation observed. Larger concentrations of MF (greater than 10(-6)M) resulted in a non-specific depression of the placental vascular smooth muscle. Meclofenamate (10(-7)M) pretreatment of strips subjected to dose-response studies using PGF2 alpha, PGE2, bradykinin (B K) and angiotensin II (AII) revealed a significant reduction in tension developed to both BK and AII. This finding suggests that the vasoactive peptides BK and AII stimulate the synthesis of vasoconstricting PG's in the fetal placental resistance arteries which relax in response to PGI2 and contract in response to the other PG's tested.