Inhibition of oxytocin release and milk let-down in postpartum primiparous cows is not abolished by naloxone

Abstract

S. About 10 % of primiparous cows have no milk ejection during the first milkings after delivery. Therefore, 17 Brown Swiss dairy cows in their first lactation were used to evaluate the extent of disturbed milk let-down and the corresponding oxytocin (OT) plasma values in the 1st 5 days after delivery. The first milking was 9-22 h after parturition and served for classification of the cows to groups with inhibited (INH), bimodal (BIMO) or normal (NOR) milk let-down. The OT plasma levels before the start of manual teat stimulation and machine milking were comparably high during the first milking especially in NOR and BIMO cows. Ten minutes before the second milking (M2), 300 mg of the opioid antagonist naloxone was injected to test whether the disturbance was affected by the action of endogenous opioids on the neurohypophysis. The milk yield was not influenced by the naloxone treatment, and the INH cows had milk ejection only after a vaginal stimulation. Afterwards, the cows were milked twice every day, until the milk letdown and the OT release were unaffected (equal to control milking). Then, at the next milking, the cows were injected with 300 mg morphine 10 min before milking. The central OT release in response to manual teat stimulation and machine milking was completely blocked in all cows, but a vaginal stimulation was able to abolish this block, at least partially, in 16 cows. Thus, morphine produced a milk let-down characteristic as in the INH cows during the first three milkings. For the following milking, the cows were pre-treated with 300 mg naloxone (k15 min) plus 300 mg morphine (k10 min) before milking. The OT release and the milk yields were unaffected when compared with the control milking. This experiment demonstrates that exogenous opioids can affect the central release of OT in a naloxone-reversible manner even very soon after parturition. However, endogenous opioids are probably not the main mediators of disturbed central OT release and alveolar milk ejection in post-partum primiparous cows. K : Cow, primiparous, post-partum, oxytocin, morphine, naloxone.Complete milk removal is necessary for optimum milk quality, high performance and good health of dairy cows. Disturbed milk ejection is observed in situations like

Nonsocial Functions of Hypothalamic Oxytocin

“…Endogenous opioids likely reduce maternal behavior and increase novel exploration during lactation [134] by reducing OXT secretion [135, 136]. The inhibition of basal secretion can occur at the level of the neurosecretory terminals and at the cell bodies of magnocellular cells [137, 138], which occurs during milking but not by vaginal stimulation [139, 140]. …”

β-Phenylethylamines and the isoquinoline alkaloids

“…The analgesic properties of morphine, 206-280 its use in anaesthesia, 281-284 and its metabolism 285,286 and pharmacokinetics 287-292 have been studied, as have the effects of the alkaloid on behaviour, 293-329 on the brain, 330-347 on immune responses, [348][349][350][351][352][353][354][355][356][357][358] on the cardio-vascular system, 359-361 on neurones, 362-366 on locomotion, 367-370 on the gastro-intestinal tract, 371-375 on gene expression, 376-381 on the adrenal 382 and thymus 383 glands, on tumour growth, 384-387 on the replication of HIV, 388 on inflammation, 389-391 on platelet aggregation, 392 on respiration, 393 on nerve transmission, 394 on reflex muscle activity, 395,396 on the sphincter of Oddy, 397 on susceptibility to epileptic seizures, 398,399 on memory, 400 on intake of ethanol, 401 on the release of dopamine, 402-405 of serotonin, 406,407 of adenosine, 408 of synaptosomal ATPase, 409 of corticosterone 410 and of preprodynorphin, 411 on dopamine 412 and oestrogen 413 receptors, on G-protein function, 414 on the transport of glutamate, 415,416 on the metabolism of glucose, 417 on the degradation of endothelin-l 418 and on the effects of endomorphins 1 and 2. 419 The morphine antagonist actions of naloxone have been studied, [420][421][422][423][424][425][426][427][428] as have the effects of this compound on behaviour, 429-432 on the heart, 433 on the gastro-intestinal tract, 434 on pain, 435,436 on the intake of food 437,438 and of ethanol, 439,440 on neurones, 441 on calcium channels, 442 on the release of dopamine, 443 of oxytocin 444 and of the natriuretic peptide,…”

Effect of Restricted Suckling on Shortened Lactation Length and Performance of Sahiwal Cattle

“…Various possible reasons of short lactation can be genetic basis, absence of calf stimulus or suckling, death of calves resulting in poor milk ejection reflex, poor milk let down, incomplete milk removal (Madalena 1988) or any type of discomfort, environmental stress and novel surroundings. In primiparous cows, this problem is more and about 10% of primiparous have problem of disturbed milk ejection and complete milk ejection or removal is necessary for optimum milk production performance of cows (Kraetzl et al, 2001). W hile analysis of lactation performance of tropical zebu Effect of Restricted Suckling on Shortened Lactation Length and Performance of Sahiwal Cattle cattle, lactations shorter than 100-150 days are considered as cases of abnormal or short lactation length, so excluded from the lactation length data (Madalena 1988).…”