The removal of milk from the mammary gland of most species is dependent upon the neurohormonal reflex process of milk ejection.
This results from a nervous stimulus that an animal associates with the milking or suckling process, such as palpation of the teats or suckling of the young.
This stimulus reaches the central nervous system and causes the posterior lobe of the pituitary to release oxytocin.
The oxytocin travels via the blood to the mammary gland and there contracts the myoepithelial cell. The contraction process forces the milk from the alveoli into the duct system, through which it flows to the gland
Recent evidence does indicate that the milking or suckling stimulus causes a marked increase in the blood oxytocin concentrations in mammals. The amount of oxytocin in the bloodstream disappears quite rapidly after it has been released.
This is brought about either by the destruction of the hormone in the body or by the elimination from the blood. The kidneys, liver, and mammary gland are mainly involved in removing the oxytocin from the bloodstream.
The concentration of oxytocin in the blood is dependent on the time interval after release from the hypothalamus. It reaches peak concentration in the blood approximately one minute after stimulation of the animal; concentrations are generally unmeasurable after five minutes.
Half-life of oxytocin in blood is 0.55 to 3.6 minutes. Oxytocin does not appear to be eliminated in the milk.
Oxytocin is used universally in the livestock industry to increase letdown and expulsion of retained placentas after delivery, for delivery in young animals when the females have been in labour for an extended period and as an adjunct to antibiotic therapy for certain treatments.
The reports on the harmful effects of milk produced by oxytocin treated cows are quite misleading and not based on scientific facts. Whether secreted endogenously or administered exogenously, oxytocin produces the desired effect within minutes and gets metabolized rapidly leaving inactive products. It is reported that till date there is not a single report, which demonstrates the presence of this hormone in the milk.
Courtesy : The Hindu
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