Всероссийский научно-исследовательский институт физиологии, биохимии и питания животных – филиал Федерального государственного бюджетного научного учреждения «Федеральный научный центр животноводства – ВИЖ имени академика Л.К. Эрнста»
ABSTRACT. In experiments conducted on 6 cows under endotracheal anesthesia, simultaneous registration of arterial blood pressure (ABP) and volume blood flow (VBF) through half of the udder were performed after injection into the external pudendal artery the agonists β-adrenergic receptor agonists isoprenaline (isoproterenol) and adrenalin. Vascular resistance of the udder (VR) was evaluated by the value of the ratio ABP/VBF. β-adrenergic stimulation of the udder caused a dose-dependent biphasic change in VBF comparable with the action of oxytocin. Injections of adrenalin did not result in a change in systemic arterial blood pressure. After injection of a high dose (10 μg) of adrenalin, blood flow to the udder decreased. After injection of physiological dose of adrenalin (1 μg), there was a decrease VBF in a first reaction phase caused by the narrowing of the blood vessels, and in the second phase the decrease in VR was caused by vasodilatation effect. On this basis, the authors postulated that inhibition of milk removal, usually observed under action of adrenaline at physiological concentrations, may not be in an increase of VR due to narrowing of the blood vessels. Constant systemic blood pressure after injections of isoprenaline (isoproterenol) and adrenalin indicates the local mechanism of changes in blood supply of the udder. The presence of phase increase and decrease of blood supply of the udder after injection of β-agonists may indicate the changes in the tone of blood vessels on the background of compression and expansion of the alveoli caused by stimulation of β-adrenoreceptors in myoepithelial cells.
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