Аннотация:
ABSTRACT. The aim was to investigate the nature of the effects of impulses transmission from postganglionic neurons on vessels of the udder, and to study sensitivity of the contractile elements of the vascular wall to norepinephrine and its agonists. Two experiments were conducted on 10 cows under endotracheal anesthesia. In first experiment, it has been studied the effect of stimulation of the peripheral end of cut external semen nerve on the volume blood flow rate (VBF) in the udder. In second experiment, the response of blood vessels to the injection of noradrenaline and its agonists into udder’s bloodstream. Simultaneous recordings were carried out of blood pressure (BP), VBF through half of the udder and the values of the udder vascular resistance (CER) were calculated. Electrical stimulation of the external semen nerve is first led to a reductuion in blood supply of the udder and then to an increase over a more extended period. Local effects of norepinephrine, α1-adrenomimetic mezaton (phenylephrine) and α2-adrenomimetic clonidine caused a decrease in the VBF in the udder. The constancy of systemic blood pressure under nerve stimulation and the introduction of α-noradrenaline and adrenoagonists indicates the local mechanism of udder blood supply variations due to a change of the blood vessels vascular tone. The findings suggest the presence of α1- and α2-adrenergic receptors in the wall of the blood vessels of the udder. Vasoconstrictor response to stimulation of the external semen nerve is due to the action on the blood vessels of the udder norepinephrine released from the endings of adrenergic neurons.