RESPONSES OF THE BOVINE MAMMARY ARTERY TO ANGIOTENSINS

The main objective of our study was to determine whether angiotensins cause vasoconstriction of mammary arterial segments in vitro. Once thi s action was established, its specificity was determined. Mammary arte rial sections were obtained from lactating cattle at slaughter. Vessel sections were placed in a gravity-fed, closed, perfusion apparatus, a nd flow was measured by a transit-time flow sensor mounted in-line. Tr eatments were administered by injection into a leurlock port located p roximal to the sensor. Angiotensins I, II, and III induced a dose-depe ndent vasoconstriction of arterial segments at concentrations of 5 x 1 0(-10) to 5 x 10(-6) M. Angiotensin II receptor antagonists, Saralisin and (Sarl, Thr8)-angiotensin II (5 x 10(-8) M)), inhibited vasoconstr iction induced by angiotensins I, II, and III. The angiotensin-convert ing enzyme inhibitor, Captopril (5 x 10(-8) M), inhibited angiotensin I vasoconstriction, thereby showing that the vasoconstriction by angio tensin I was mediated through its conversion to angiotensin II. These data demonstrated that the mammary artery of lactating cows is respons ive to the angiotensin family. Furthermore, mammary arteries contain a ngiotensin-converting enzyme and specific receptors for angiotensin II . This system may be important in the normal physiological regulation of mammary gland blood flow of lactating cows.