Year: 1967
Type: article
Abstract: Antagonism between the actions of adrenaline and oxytocin on the mammary gland was first demonstrated in 1941 by Ely & Petersen.They showed that fright or the intravenous injection of adrenaline reduced the rate of ejection of milk from the udder during machine milking in cows and that this inhibitory effect could be overcome by the injection of oxytocin.Although it is clear that adrenaline inhibits the milk-ejection response to oxytocin in many species (Braude & Mitchell, 1952; Cross, 1953; Whittle- stone, 1954; Yokoyama, 1956; Pickford, 1959; Chan, 1965; Bisset, Hilton & Poisner, 1967), the mode of action of adrenaline is uncertain.There are two possible mechanisms.Adrenaline might act indirectly by causing vasoconstriction of the mammary blood vessels, which would limit the access of oxytocin to the gland, or it might have a direct inhibitory effect on the myoepithelial cells and act as a physiological antagonist of oxytocin.Cross (1953; 1954a, b; 1955a, b; 1958) has advanced a number of arguments in favour of the vasoconstrictor hypothesis.In the first place, perfusion experiments have shown that adrenaline is an extremely potent vasoconstrictor of the mammary arteries (Hebb & Linzell, 1951).Secondly it has been observed in the rabbit (Cross, 1953) and in the sow (Whittlestone, 1954) that adrenaline causes greater inhibition when injected before, than simultaneously with oxytocin.This can be explained by supposing that after an injection of adrenaline, the mammary arteries are already constricted when oxytocin reaches the gland in the circulation.Moreover, in the rabbit, Cross & Silver (1961) have made polarographical measurements of oxygen tension (P02) as an index of capillary blood flow in the mammary gland and shown that, when adrenaline is injected before oxytocin, full inhibition of the milk-ejection response occurs only if oxytocin reaches the gland at a time when the Po2 is falling rapidly.Finally, in the rabbit the relative potencies of adrenaline and noradrenaline are similar for vasoconstric- tion and inhibition of the milk-ejection response to oxytocin (Cross, 1955a; 1958).Against the argument for a direct inhibitory action on the myoepithelial cells is the fact that adrenaline does not inhibit the milk-ejection response to mechanical tap stimuli applied to the mammary gland (Cross, 1954a, b; 1955a; Yokoyama, 1956) nor does it inhibit contraction of the alveoli when it is applied topically with oxytocin to the living gland of the mouse (Linzell, 1955).On the other hand, adrenaline has been shown to inhibit the action of oxytocin on isolated strips of mammary gland from the rabbit (Chan,
Authors: G. W. BISSET, BARBARA J. CLARK, G. P. LEWIS
Institution: National Institute for Medical Research
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2009781544