Inhibitory effect of adrenaline on oxytocin release in the ewe during the milk-ejection reflex

Abstract

Milk-ejection activity was determined in the blood plasma of ewes during normal milking and during milking when adrenaline was injected intravenously before or after udder stimulation. It was found that administration of adrenaline either before or after udder washing, decreased the oxytocin concentration and milk yield but increased the yield by hand-stripping. Adrenaline also retards the average time for peak oxytocin concentration. These results and the use of a /^-receptor blocker to inhibit the effect of adrenaline at the myoepithelial cell level indicate that in ewes adrenaline can prevent the release of oxytocin from neurohypophysis.

Lactation

“…Subsequent studies indicated that the inhibitory effects of adrenaline on milk ejection were mediated by vasoconstriction ofthe mammary blood vessels, restricting access of oxytocin to the myo-epithelium, and by its ability to compete for receptor sites on the myoepithelium (see Cross, 1961;Cowie and Tindal, 1971). A recent study in the ewe, however, suggests that adrenaline may also inhibit the release of oxytocin from the neurohypophysis (Barowicz, 1979). A recent study in the ewe, however, suggests that adrenaline may also inhibit the release of oxytocin from the neurohypophysis (Barowicz, 1979).…”

Central Effects of Catecholamines upon Mammary Contractility in Rats Are Neurally Mediated

“…In parallel with these effects the same mecha nisms may respectively facilitate or inhibit the removal of milk [2,3,7,19,32,33, and present study], by regulating ductal tone within the mammary glands. Also, within this context, we may consider the recently reported central actions of prolactin upon OXY release [34] and upon mammary contractility [unpubl.…”

“…Thus at the hypothalamic level, a-adrenergic and dopa minergic mechanisms may stimulate, whereas (3-adrenergic mechanisms may inhibit the release of OXY [2,3,7,19,[31][32][33]. In parallel with these effects the same mecha nisms may respectively facilitate or inhibit the removal of milk [2,3,7,19,32,33, and present study], by regulating ductal tone within the mammary glands.…”

“…However, one implication of CAs released by suckling, is that in the lactating animal the tone of the sympathetic nervous system may be influenced by this stimulus. Thus, variations in CA re lease within the CNS [1] or actions of circulating CAs in the neural lobe [7,19] or other areas of the brain, may affect milk ejection in concert with the action of OXY.…”

Changes of blood catecholamine levels in the sheep during machine milking

“…The release of significant amounts of catecholamines in the animal economy may be shown by inhibition of milk ejection. This inhibitory effect of catecholamines is attributed either to central neural mechanisms (Cross, 1955;Denamur, 1965;Sibaja & Schmidt, 1975;Tribollet et al 1978;Barowicz, 1979) or to peripheral alterations. The peripheral inhibitory effect acts either by vasoconstriction (Linzell, 1955;Cross & Silver, 1962) or by an intrinsic action of catecholamines directly upon the myoepithelium (Chan, 1965;Bissett, Clark & Lewis, 1967;Vorherr, 1971;Ewye«aZ.…”