Hammon H M, Bruckmaier R M, Honegger U E, Blum J W
Institut für Tierzucht der Universität Bern, Schweiz.
J Dairy Res. 1994 Feb;61(1):47-57. doi: 10.1017/s0022029900028041.
Radioreceptor binding studies were designed to localize and determine the number of alpha- and beta-adrenergic receptors in the mammary gland of lactating cows. 3H-prazosin, 3H-rauwolscine and 3H-dihydroalprenolol were used for the regional characterization of alpha 1-, alpha 2- and beta-adrenergic receptors by competitive inhibition of binding of 3H-ligands with unlabelled adrenergic agonists and antagonists. The alpha 1-, alpha 2- and beta 2-adrenergic receptor subtypes could thus be demonstrated in the regions of the teats, large mammary ducts and parenchyma. Tissues of the teat wall, of the large mammary ducts above the gland cistern and of the mammary parenchyma were prepared to determine the density of alpha 1-, alpha 2- and beta-receptors by saturation binding assays using 3H-prazosin, 3H-rauwolscine and 3H-dihydroalprenolol respectively. Binding to high affinity sites was reversible within minutes and saturable. Equilibrium was reached within minutes. The number of alpha 1- and alpha 2-adrenergic receptors decreased from the teat to the mammary ducts to the parenchyma. Most of the alpha 1- and alpha 2-adrenergic receptors were found in the teat wall, whereas in the parenchyma alpha-adrenergic receptors were absent or barely detectable. The density of beta-adrenergic receptors was similar in the teat wall and the large mammary ducts, but much lower in the parenchyma. Thus, alpha 1-, alpha 2- and beta-adrenergic receptors were found mainly in the milk purging system and hardly at all in mammary parenchyma. Inhibition of milk removal by alpha-adrenergic stimulation is possibly due to constriction of teat wall and to constriction of the mammary ducts, whereas enhanced milk flow after beta-adrenergic stimulation is possibly due to relaxation not only of the teat sphincter and teat wall, but probably also of the large mammary ducts.
放射性受体结合研究旨在定位并确定泌乳奶牛乳腺中α和β肾上腺素能受体的数量。通过3H-配体与未标记的肾上腺素能激动剂和拮抗剂结合的竞争性抑制作用，使用3H-哌唑嗪、3H-萝芙木碱和3H-二氢阿普洛尔对α1、α2和β肾上腺素能受体进行区域特征分析。由此可在乳头、大乳腺导管和实质区域证实α1、α2和β2肾上腺素能受体亚型。制备乳头壁、腺泡上方大乳腺导管和乳腺实质的组织，分别使用3H-哌唑嗪、3H-萝芙木碱和3H-二氢阿普洛尔通过饱和结合试验确定α1、α2和β受体的密度。与高亲和力位点的结合在数分钟内可逆且可饱和。数分钟内达到平衡。α1和α2肾上腺素能受体的数量从乳头到乳腺导管再到实质逐渐减少。大多数α1和α2肾上腺素能受体存在于乳头壁，而在实质中α肾上腺素能受体不存在或几乎检测不到。β肾上腺素能受体的密度在乳头壁和大乳腺导管中相似，但在实质中低得多。因此，α1、α2和β肾上腺素能受体主要存在于排乳系统中，在乳腺实质中几乎不存在。α肾上腺素能刺激抑制排乳可能是由于乳头壁收缩和乳腺导管收缩，而β肾上腺素能刺激后乳汁流量增加可能是由于不仅乳头括约肌和乳头壁松弛，而且大乳腺导管可能也松弛。
