Responses to potential vasoactive substances of isolated mammary blood vessels from lactating sows

The purpose of the investigation was to examine the response of the milk Ve in and the mammary artery to potential vasoactive substances in lactating s ows. The response on artery and Vein segments from the same sow was measure d for the following substances: noradrenaline (NA), serotonin (5-HT), prost aglandin F-2 alpha (PGF(2 alpha)), prostacyclin (PGI(2)), histamine (Hi) an d potassium (K+). Interestingly, the contractile force in the mammary vein segments expressed per weight unit (mN/mg) was 1.5-2.5 fold larger than in the artery segments when NA, 5-HT and PGF(2 alpha) were used, but similar f or K+, Hi and PGI(2). In vein segments, the order of sensitivity to the sub stances expressed by their pD(2) values was 5-HT > NA = PGF(2 alpha) > Hi > K+. The present findings suggest that NA, 5-HT, PGF(2 alpha), PGI(2), and Hi are involved in mammary blood flow regulation in the sow, and the mammar y venous system may be as important as the mammary arterial system in this regulation. (C) 1999 Elsevier Science Inc. All rights reserved.