Eicosanoid production in rabbit vascular tissues and placentas

In pregnant rabbits, systemic levels of prostaglandin E₂ (PGE₂) are elevated. To evaluate the source of the rise in circulating levels of PGE₂, eicosanoid production was determined in rabbit placental cotyledons and the following vascular tissues: mesenteric arteries, main renal arteries, and intrarenal preglomerular vessels (n = 6 or 7 rabbits). Comparisons were made with vascular tissues from nonpregnant rabbits (n = 6 or 7). Freshly isolated tissues were incubated for 15 min at 37°C. Medium aliquots were analyzed for eicosanoids by radioimmunoassay. Maximal net production and release (pg/μg protein) was determined by subtraction of the quantity of eicosanoids present in medium before incubation from that present at the end of incubation. Net production and release of 6-ketoprostaglandin F(1α) (PGF(1α)), a stable metabolite of prostacyclin, and of PGE₂ was similar in vascular tissues from pregnant and nonpregnant rabbits. Thromboxane B₂ (TxB₂) generation in preglomerular vessels from pregnant rabbits was lower (P < 0.05) than that of nonpregnant rabbits. This could contribute to renal vasodilation in pregnancy. The pattern of eicosanoid production in vascular tissues was 6-keto-PGF(1α) > PGE₂ > TxB₂, and in cotyledons it was PGE₂ > 6-keto-PGF(1α) > TxB₂. In cotyledons, PGE₂ and TxB₂ production was 56-219 and 2-12 times that in maternal vascular tissues, respectively. These data suggest that physiologically significant quantities of eicosanoids may be released by rabbit placental tissue.