EFFECTS OF ADRENALINE, OXYTOCIN AND 2-Br-α-ERGOCRYPTINE ON MAMMARY BLOOD FLOW IN THE LACTATING EWE

Abstract

The mammary blood flow (MBF) and heart rate (HR) responses to standing, lying, suckling, adrenaline (A), oxytocin and 2-Br-α-ergocryptine were studied in four lactating ewes. Posture had a variable effect on MBF. In three of the four ewes there was an increase (P < 0.05) and in one ewe a decrease (P < 0.05) in MBF as a result of lying. Heart rate recorded while the ewes were lying was significantly lower (P < 0.01) than while standing. Suckling resulted in an average decrease in MBF of 39% (P < 0.01) compared to standing values. Continuous infusion of A at a rate of 300 ng kg−1 min−1 for 2.5 h resulted in a progressive increase in HR (P < 0.05) for 2 h of the infusion. During the A infusion MBF decreased transiently for 10–15 min and then increased thereafter (P < 0.05) throughout the A infusion in three of the ewes. In the fourth ewe, MBF increased to a peak during hour 2 of A infusion and thereafter declined. Exogenous oxytocin administered at doses [Formula: see text] had a stimulatory effect on MBF. Suckling and handmilking induced decreases in blood flow of 39 ± 6% and 54 ± 13%, respectively, after injection of 1 mU kg−1 oxytocin. Treatment of ewes with 2-Br-α-erogcryptine (a prolactin-release inhibitor) did not influence mean MBF while standing or lying but attenuated the negative effects of suckling and hand milking on MBF. Mammary blood flow in the lactating ewe is, therefore, sensitive to posture, suckling and hand milking but the response to the latter two activities could not be attributed to oxytocin on the basis of the present results. Key words: Mammary artery, suckling, milk, hormonal effect