THE LOCAL DIFFERENTIAL EFFECT OF PROSTACYCLIN, PROSTAGLANDIN E(2) ANDPROSTAGLANDIN-F2-ALPHA ON MAMMARY BLOOD-FLOW OF LACTATING GOATS

Mammary blood flow (MBF) and Milk yield are closely related in dairy r uminants, but little is known about the regulation of MBF in vivo. The local effects on MBF of injections or continuous infusions into the m ammary artery of prostaglandins (PG) or indomethacin (an inhibitor of prostaglandins) respectively, were investigated in surgically prepared conscious goats. Prostacyclin (PGI(2)) was found to be a potent stimu lator of MBF which increased linearly over the dose range 50-1000 ng. PGE(2) was almost as potent as PGI(2) at low doses, but tachyphylaxis occurred at doses at and above 100 ng. The response to repeated inject ions of PGE(2) quickly declined depending on the dose. PGF(2 alpha) ha d no effect on MBF. During infusion of indomethacin into the mammary a rtery MBF was reduced markedly, showing that endogenous mammary prosta glandins are involved in the regulation of vasodilatation. The results indicate that PGI(2) (and to a lesser extent PGE(2)) has an important role in the local regulation of vascular tone in the mammary gland.