Gorewit R C, Aromando M C
Proc Soc Exp Biol Med. 1985 Nov;180(2):340-7. doi: 10.3181/00379727-180-42186.
To elucidate mechanisms by which epinephrine (epi) blocks milk ejection in cattle, blood serum oxytocin (OT) concentrations were measured in four heifers before, during, and after milking following either intrajugular injection of 0.85% saline (S) or epi (3 mg). S did not affect OT concentrations. They peaked 2 min after milking-machine attachment. OT declined 3 min after milking commenced, reaching resting concentrations 10-60 min after milking. Milk yields were not altered by S. Epi did not influence significantly basal OT concentration. Yet, OT released to milking appeared less than the saline control. Peak OT concentration after epi and milking was reached 1 min after machine attachment. OT declined within 3 min after milking commenced. Milk yield was reduced 48% after epi. Jugular vein and carotid arterial OT concentrations and mammary blood flow (MBF) were measured simultaneously in four multiparous cows. Blood was collected before, during, and after milking following S or epi (50 micrograms). Jugular and carotid OT concentrations followed similar patterns for both treatments. Changes in carotid OT concentrations lagged behind those of the jugular vein by approximately 1 min. Elevated carotid OT concentrations were seen in two cows after milking and thought to be derived from non-hypothalamic-neurohypophysial sources. Epi (50 micrograms) did not reduce blood OT concentrations, but reduced MBF by 95%. Milking induced increases in MBF seen in controls, were not observed with epi, and milk yield was reduced by 56%. Our experiments suggest that epi may inhibit OT release to milking stimuli at pharmacological doses. At lower doses, epi exerts its effects peripherally by acutely reducing MFB, thus preventing physiological concentrations of hormone from reaching the myoepithelium. An intrinsic action of epi on the myoepithelial cells of cattle is unlikely, but cannot be ruled out at this time.
为阐明肾上腺素（epi）阻断奶牛排乳的机制，对4头小母牛在颈静脉注射0.85%生理盐水（S）或epi（3毫克）之前、期间和之后的血清催产素（OT）浓度进行了测量。S不影响OT浓度。OT浓度在连接挤奶机后2分钟达到峰值。挤奶开始后3分钟OT浓度下降，挤奶后10 - 60分钟达到静息浓度。S对产奶量无影响。Epi对基础OT浓度无显著影响。然而，epi注射后挤奶时释放的OT似乎少于生理盐水对照组。epi注射后挤奶时OT浓度在连接挤奶机后1分钟达到峰值。挤奶开始后3分钟内OT浓度下降。epi注射后产奶量降低了48%。在4头经产奶牛中同时测量了颈静脉和颈动脉的OT浓度以及乳腺血流量（MBF）。在注射S或epi（50微克）之前、期间和之后采集血液。两种处理的颈静脉和颈动脉OT浓度遵循相似模式。颈动脉OT浓度的变化比颈静脉滞后约1分钟。两头奶牛在挤奶后出现颈动脉OT浓度升高，认为源自非下丘脑 - 神经垂体来源。Epi（50微克）未降低血液中OT浓度，但使MBF降低了95%。对照组中观察到挤奶诱导的MBF增加，而epi处理组未观察到，且产奶量降低了56%。我们的实验表明，药理学剂量的epi可能抑制对挤奶刺激的OT释放。在较低剂量下，epi通过急性降低MFB在周围发挥作用，从而阻止激素的生理浓度到达肌上皮细胞。epi对奶牛肌上皮细胞的内在作用不太可能，但目前不能排除。
