Vandeputte-Van Messom G, Burvenich C, Peeters G
Department of Physiology, Faculty of Veterinary Medicine, University of Ghent, Belgium.
Arch Int Pharmacodyn Ther. 1987 Oct;289(2):177-88.
The activities of epinephrine (2-6 micrograms) and of norepinephrine (20-60 micrograms) on the relaxation of teat sphincter muscles were compared by measuring milk leakage from the full udder of 5 lactating cows. Substances were injected into the external pudic artery after pretreatment with an alpha-adrenoceptor blocking agent (prazosin or phentolamine). Milk leakage was induced by creating a vacuum (-30 cm of water) in a plethysmographic chamber enclosing one teat and volumes of milk loss were measured every min. In a second series of experiments the activities of the beta 2-adrenoceptor selective agonist zinterol (0.5-2.5 micrograms) and of the nonselective beta-agonist isoproterenol (3-22.5 micrograms) on sphincter muscle relaxation were compared. Epinephrine was found to be more potent than norepinephrine in inducing relaxation of sphincter muscles. Zinterol was more active than isoproterenol. It is concluded that there is a predominance of beta 2-adrenoceptors in the teat sphincters.
通过测量5头泌乳奶牛充满乳汁的乳房的乳汁渗漏情况，比较了肾上腺素（2 - 6微克）和去甲肾上腺素（20 - 60微克）对乳头括约肌松弛的作用。在用α-肾上腺素能受体阻断剂（哌唑嗪或酚妥拉明）预处理后，将药物注入阴部外动脉。通过在包围一个乳头的体积描记室中产生真空（-30厘米水柱）来诱导乳汁渗漏，每分钟测量乳汁丢失量。在第二组实验中，比较了β2 - 肾上腺素能受体选择性激动剂齐帕特罗（0.5 - 2.5微克）和非选择性β-激动剂异丙肾上腺素（3 - 22.5微克）对括约肌松弛的作用。发现肾上腺素在诱导括约肌松弛方面比去甲肾上腺素更有效。齐帕特罗比异丙肾上腺素更具活性。得出的结论是，乳头括约肌中β2 - 肾上腺素能受体占优势。
