Breast-feeding and plasma oxytocin concentrations.

The patterns of response of oxytocin to a breast feed were studied in 10 mothers in the first week post partum. The initiation of lactation did not appear to be related to release of oxytocin. In established lactation an oxytocin response did not appear to be essential for adequate milk flow and did not occur always at the time of peak milk flow. The only factor identified that positively correlated with release of oxytocin was multiparity. In those subjects who showed a response the hormone was released in surges, some of which persisted in the circulation for less than one minute. These findings cast some doubt on the conventional view that release of oxytocin is essential for satisfactory milk flow during breast-feeding.     

Pineal peptides in the regulation of milk-ejection reflex in lactating rats

The effects of pineal peptides (mol. mass 1-4 kDa) intranasal infusions on some parameters of milk-ejection reflex were investigated. Peptides were extracted from dairy-cattle pineal glands. Pineal peptides increase body weight, levels of water intake, plasma prolactin concentration and milk yield in rats when infusing daily in dose 1 microgram/kg from the third day of lactation. On 9th and 12th days of lactation during 1-hour nursing seance the significantly greater number of reflective milk ejections were found. When 1 hour before the peptides infusion rats were intraperitoneally injected by rabbit antiserum to oxytocin (200 microliters at dilution of 1:20) the effects of pineal peptides were significantly less expressive or were absent at all. Using enzymimmunoassay it was demonstrated that there were greater increasing of oxytocin content in pineal gland in suckling-induced oxytocin release from neurohypophysial system in the chronic pineal peptides-treated female rats compared with control. This effect was absent when rats were injected by oxytocin antibodies. These data suggest that pineal peptides can participate in forming of reflect oxytocin release pattern. This pattern is initiated by suckling and is limited by oxytocin content in blood.     

Naloxone cannot abolish the lack of oxytocin release during unexperienced suckling of dairy cows

To evaluate the role of opioids for the regulation of oxytocin release in response to teat stimulation, 10 brown-Swiss dairy cows were randomized to two experiments during mid of lactation. In the first experiment, four cows without previous suckling experience were suckled by an alien calf between two normal milkings. Before and during milking or suckling, frequent blood samples were collected via a jugular cannula for determination of oxytocin and beta-endorphin. In the second experiment, six cows were treated with naloxone or saline, 10min before the start of the first or second suckling, respectively. The collected blood samples were assayed for oxytocin.In the first experiment, the plasma levels of beta-endorphin were elevated during and after the unexperienced suckling in three cows, but not in the fourth cow, and the release of oxytocin during suckling was markedly reduced, suggesting no release of alveolar milk. In the second experiment, the release of oxytocin during suckling was again significantly reduced. Pretreatment with naloxone before suckling did not completely abolish the adverse effect of suckling and the oxytocin plasma level did not increase to levels comparable with control milking.In emotional stress situations, the release of oxytocin from the pituitary is inhibited with simultaneously elevated beta-endorphin plasma levels. Although there is some evidence for a regulatory role of opioids for the release of oxytocin, other mediators are suggested to be more potent in regulating oxytocin under stress conditions.     

Minimally invasive biomarkers to detect maternal physiological status in sow saliva and milk

In this study, we aimed to validate existing plasma assays to measure biomarkers for maternal signalling in milk and saliva of lactating sows. These biological samples are minimally invasive to the animal and could give a physiological profile of maternal qualities available to their piglets. Sows were farrowed in a zero-confinement system, and their colostrum and milk samples were manually collected during naturally occurring let-downs (i.e. not induced) over the lactation period. Saliva sampling involved sows voluntarily accepting cotton buds to chew without restraint. Commercial kits designed for blood plasma were tested, and any modifications and results are given. We successfully measured total protein, cortisol, tumour necrosis factor-α (TNF-α) and oxytocin in pig milk and saliva and immunoglobulin G (IgG) in pig milk samples. We were unsuccessful at measuring relaxin and serotonin in these biological samples. We observed higher levels of biomarkers in milk than in saliva. The measurement of TNF-α in pig milk for the first time revealed increased levels with larger litters. This development will allow more detailed understanding of biomarkers in milk. There was also evidence that the minimally invasive technique of using saliva sampling did not interrupt natural oxytocin production around parturition.     

Release of oxytocin and prolactin in response to suckling.

The oxytocin and prolactin responses to suckling were measured in 10 women in early (n = 5) and established lactation (n = 5). Oxytocin was released in a pulsatile manner during suckling in all women, but the response was not related to milk volume, prolactin response, or parity of the mother. In all 10 women plasma oxytocin concentrations increased three to 10 minutes before suckling began. In five women this occurred in response to the baby crying, in three it coincided with the baby becoming restless in expectation of the feed, while in two it corresponded with the mother preparing for the feed. There was no prolactin response to stimuli other than stimulation of the nipple associated with suckling. These results clearly indicate that the milk ejection reflex, with release of oxytocin, occurs in most women before the tactile stimulus of suckling. A second release of oxytocin follows in response to the suckling stimulus itself. Thus it is important that care is taken to protect breast feeding mothers from stress not only during suckling but also immediately before nursing, when conditioned releases of oxytocin will occur.     

Effect of prostaglandins on milk ejection.

Prostaglandins (PGs) of type F2 alpha, E1, and E2 have been reported both, to inhibit or to facilitate posterior pituitary oxytocin release in lactating animals and women, and to suppress or to stimulate the mammary myoepithelium. Prostaglandin-induced milk ejection in women and cows has been attributed to central oxytocin release, but no oxytocin blood levels were determined. Moreover, for lactating cows, sows, rabbits, guinea pigs, and rats a direct PG effect on the mammary myoepithelium resulting in milk ejection has been suggested. On the other hand, PGs were found to antagonize the milk-ejection response to oxytocin in rabbits and rats. The mechanisms involved in PG synergism or antagonism of oxytocin-induced milk ejection are not understood. Studies in lactating rats showed that blood pressure active PG doses of F2 alpha, E1, and E2 largely inhibited the intramammary pressure response to oxytocin. Whereas the oxytocin-antagonistic action of PGF2 alpha was not affected by adrenergic blockers (phenoxybenzamine, propranolol), the anti-oxytocin effects of PGE1 and E2 were eliminated after alpha-receptor blockade while the activity of oxytocin increased. Under beta-receptor or alpha- plus beta-receptor blockade, the oxytocin-inhibitory effects of PGE1 and E2 were almost abolished. Mechanisms of PG-induced inhibition of the oxytocin response may involve mammary vascular changes and/or alterations in myoepithelial activity of cyclic adenosine-3,5-monophosphate (c-AMP), cyclic guanosine-3,5-monophosphate (c-GMP), and phosphodiesterase (PDE). It seems unlikely that PGs bring about significant posterior pituitary oxytocin release in rats.     

Prolactin promotes oxytocin and vasopressin release by activating neuronal nitric oxide synthase in the supraoptic and paraventricular nuclei

Prolactin (PRL) stimulates the secretion of oxytocin (OXT) and arginine AVP as part of the maternal adaptations facilitating parturition and lactation. Both neurohormones are under the regulation of nitric oxide. Here, we investigate whether the activation of neuronal nitric oxide synthase (nNOS) in the hypothalamo-neurohypophyseal system mediates the effect of PRL on OXT and AVP release and whether these effects operate in males. Plasma levels of OXT and AVP were measured in male rats after the intracerebroventricular injection of PRL or after inducing hyperprolactinemia by placing two anterior pituitary glands under the kidney capsule. NOS activity was evaluated in the paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei by NADPH-diaphorase histochemistry and in hypothalamic extracts by the phosphorylation/inactivation of nNOS at Ser(847). Elevated central and systemic PRL correlated with increased NOS activity in the PVN and SON and with higher OXT and AVP circulating levels. Notably, treatment with 7-nitroindazole, a selective inhibitor of nNOS, prevented PRL-induced stimulation of the release of both neurohormones. Also, phosphorylation of nNOS was reduced in hyperprolactinemic rats, and treatment with bromocriptine, an inhibitor of anterior pituitary PRL secretion, suppressed this effect. These findings suggest that PRL enhances nNOS activity in the PVN and SON, thereby contributing to the regulation of OXT and AVP release. This mechanism likely contributes to the regulation of processes beyond those of female reproduction.     

Increased levels of vasoactive intestinal peptide (VIP) and oxytocin during suckling in lactating dogs

The aim of the present study was to investigate how suckling influences the plasma levels of oxytocin and vasoactive intestinal peptide in lactating dogs. Blood-samples were drawn from ten lactating beagles during suckling, in week one and week three of the five week long lactation period and the levels of vasoactive intestinal peptide and oxytocin were determined by radioimmunoassay. The immunoreactive levels of vasoactive intestinal peptide and oxytocin (below referred to VIP and oxytocin) increased rapidly in response to the suckling stimulus. The rise of both peptides was significant at both suckling experiments. The origin and role of suckling-released oxytocin is well established. The origin of and function of the VIP released in response to suckling remains unknown.     

The development of nursing behaviour in swine

Certain aspects of nursing behaviour in the sow have been well documented. This literature has revealed that during parturition, nursing is asynchronous and continuous, while later in the lactation nursing is synchronous and cyclical. Fourteen Yorkshire sows and their litters were observed during the first week of lactation to study the transition from the first type of nursing to the second.The first type of nursing was termed neo-nursing and the second, cyclical nursing. Equivalent designations were assigned to suckling. The transition from neo-nursing to cyclical nursing occurred 10.7 ± 4.5 h following the birth of the first piglet. Using the video-taped behaviour of the sow and her piglets, the first cyclical nursing was defined as the first nursing of less than 30 min duration which was preceded by a period of at least 30 min in which less than one half of the litter was suckling. This transition was easily determined on the video-tapes, with little ambiguity. The transition tended to be fairly abrupt, and was probably due to the cessation of oxytocin release and the consequent cessation of continuous milk flow.     

Uterine activity, sperm transport, and the role of boar stimuli around insemination in sows

This paper describes changes in spontaneous myometrial activity around estrus, factors that affect myometrial activity, and the possible role of uterine contractions in the process of (artificial) insemination, sperm transport and fertilization. Myometrial activity in the sow increases during estrus. The activity is myogenic in origin, but several factors have been shown to affect myometrial activity. Natural mating stimulates uterine contractions through several mechanisms. The presence of a boar, rather than the act of mating, induces central oxytocin release in the sow and thus increases uterine activity. Estrogens in the ejaculate of a boar can trigger prostaglandin release by the endometrium and thus increase uterine activity. Tactile stimulation of the genital tract (cervix) or tactile stimulation of the back and flanks of the sow during artificial insemination does not cause a release of oxytocin. There is hardly any evidence for the effects of these latter stimuli on uterine activity, and if they are present at all, the effects are very small. Evidence for the effects of synthetic boar odor on oxytocin release and/or uterine activity is inconsistent. The mere presence of a boar during insemination, in contrast, clearly stimulates uterine activity through the release of oxytocin. Hormonal stimulation (intrauterine) of uterine activity with estrogens, prostaglandins, or oxytocins before, during or after insemination generally improves fertilization rate, especially in situations with reduced fertility. Therefore, uterine contractions are believed to play an important role in the transport of sperm cells to the oviducts after insemination. Whether uterine contractions are absolutely necessary for sperm transport through the uterine horns, however, is not clear. Intensive stimulation of uterine contractions using hormones can also reduce the fertilization rate, probably by increasing the reflux of sperm cells during insemination. In this respect, the presence of a boar during AI seems more adequate, as only sows with a low level of uterine activity show an increase in uterine activity in response to this stimulus.     

Pten对奶牛乳腺上皮细胞活力及乳蛋白合成的影响

Pten作为抑癌基因,参与调控细胞生长、粘附、凋亡以及其它细胞活动.目前,国内外关于Pten在奶牛乳腺发育过程中表达及调节的研究鲜有报道.为了揭示Pten的表达与奶牛乳腺发育与泌乳之间的关系,本研究应用qRT-PCR技术检测Pten在不同泌乳时期和不同乳品质的奶牛乳腺组织中的表达差异,进而应用脂质体转染方法,通过siRNA介导的RNA干扰技术改变Pten基因在奶牛乳腺上皮细胞中的表达量,CASY法检测细胞活力,用ELISA试剂盒检测细胞分泌β-酪蛋白的含量,采用qRT-PCR、Western 印迹等技术检测Pten对奶牛乳腺上皮细胞中乳蛋白相关信号通路基因表达的影响.结果显示,泌乳期高乳品质奶牛乳腺组织中Pten表达水平显著低于泌乳期低乳品质及干乳期奶牛;Pten基因沉寂后,细胞活力提高,β-酪蛋白质量浓度增加,CSN2、AKT、MTOR、STAT5表达量增加.研究表明,Pten可通过抑制细胞活力和乳蛋白分泌而影响泌乳.     

Maternal behavior in pigs

When sows kept under commercial conditions were put into crates in the early 1960s, the neuro-endocrine regulation of the maternal behavior in these domestic animals was disputed. Thus, the study of sow maternal behavior intensified and today a significant body of knowledge has accumulated to support the hormonal regulation of sow maternal behavior. The onset of nest building is associated with a periparturient decline in progesterone, an increase in prolactin and a major rise in plasma concentrations of PGF2alpha the day before parturition. Some nest building behaviors, such as pawing and gathering straw, have been found to correlate with changes in the levels of progesterone, prolactin and somatostatin. The duration of the birth process correlates negatively with peripheral oxytocin levels. During lactation, the stimuli from the piglets affect the release of several hormones which not only regulate the let down of milk but also sow metabolism and mammary milk production. The sow's nursing behavior ensures an even distribution of milk to her piglets. The piglets suckling behavior, in turn, is mainly a way to communicate their individual nutritional needs.     

Maternal nurturing is dependent on her innate anxiety: the behavioral roles of brain oxytocin and vasopressin

The maternal brain undergoes remarkable physiological and behavioral changes in the peripartum period to meet the demands of the offspring. Here, the brain neuropeptides oxytocin and vasopressin, together with prolactin, play important roles. These neuropeptides are critically involved in the regulation of maternal behavior. Furthermore, reduced anxiety in lactation is another adaptation of the maternal brain. Therefore, a link between maternal behavior and maternal anxiety has been repeatedly postulated. This is supported by our studies in rats bred for high (HAB) and low (LAB) anxiety-related behavior. While female HAB rats become less anxious in lactation, their anxiety level is still four times higher compared with LAB dams. Interestingly, HAB dams display an intense and protective mothering style including increased arched back nursing and pup retrieval whereas LAB dams display only low levels of maternal care. The amount of maternal care directed towards the pups correlates with the mother's innate anxiety. In addition to differences in maternal care, HAB dams are also more protective as they show heightened aggression against a virgin intruder compared with the less aggressive LAB dams. The level of maternal aggression correlates with both their innate anxiety level as well as with the release of oxytocin and vasopressin in hypothalamic and limbic brain areas. Importantly, manipulations of the brain oxytocin and vasopressin systems alter maternal behavior and — depending on the brain region — can also alter the dam's anxiety. Thus, the mother's innate anxiety determines her maternal performance and oxytocin and vasopressin are involved in both parameters.     

Oxytocin enhances onset of lactation among mothers delivering prematurely.

In a double-blind group sequential trial the efficiency of an oxytocin nasal spray in enhancing lactation was studied during the first five days after delivery in women who had given birth prematurely. The cumulative volume of breast milk obtained between the second and fifth days after delivery was 3.5 times greater in primiparas given oxytocin than in primiparas given placebo. There was no significant difference in the composition of the milk between the untreated women and those given oxytocin. The results of this study show that oxytocin nasal spray is an effective and safe means of enhancing lactation in women using a breast pump.     

Oxytocin response to conditioned and nonconditioned stimuli in lactating ewes

We have measured oxytocin release during lactation in the ewe in response to normal tactile sucking stimuli as well as exteroceptive stimuli emanating from the lamb. Four puerperal ewes that had indwelling catheter inserted in the femoral artery while still pregnant were used. Each nursed a single lamb. Each was studied 2 or 3 times between Days 1 and 15 of lactation during a 2.5-h experimental period that was preceded by a 2-h separation from the lamb in the early morning. Samples were taken before and after the lamb was brought within sight and sound of the ewe but without contact, and then 0.5, 1, 5, 10, 15, 30, and 60 min after suckling began. When another suckling episode intervened, the same sampling schedule was immediately restarted. Suckling occurred in an intermittent fashion; 3 to 4 episodes of 2.9 +/- 2.0 (SD)-min duration took place with variable intervals during the 2.5-h experimental period. Exteroceptive stimuli emanating from the lamb caused plasma oxytocin to rise significantly from basal levels of 10.0 +/- 4.5 to 21.8 +/- 5.7 pg/ml (mean +/- SE, n 10, p less than 0.05). This rise was not seen on Day 1 and in only half of the ewes on Day 2, but thereafter the rise occurred in every instance. A further rise in plasma oxytocin was observed in almost all instances (86%) at suckling. Peak levels were usually observed within 1 min. They were quite variable, ranging from 15 pg/ml to 287 pg/ml, and not related to the milk yield, but were significantly greater than spontaneous pulses observed in nonlactating puerperal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of ghrelin secretion during pregnancy and lactation in the rat: possible involvement of hypothalamus

We investigated the plasma concentration of ghrelin peptide during pregnancy and lactation in rats. Plasma ghrelin levels on days 10 and 15 of pregnancy were significantly lower than those of the non-pregnant rats. Thereafter, the plasma ghrelin levels on day 20 of pregnancy sharply increased to levels comparable with those in non-pregnant rats. Ghrelin peptide concentrations in the stomach did not change significantly during pregnancy. In the hypothalamus, ghrelin mRNA levels were significantly lower on day 15 of pregnancy than in the non-pregnant rats. Also, plasma ghrelin levels were significantly lower in lactating dams than non-lactating controls on days 3 and 8 of lactation. We examined the possible involvement of prolactin and oxytocin in the regulation of plasma ghrelin concentrations during lactation. Although plasma prolactin levels were decreased by the administration of bromocriptine, plasma ghrelin levels did not differ significantly between vehicle- and drug-treated lactating rats. Administration of haloperidol produced a marked increase in plasma prolactin levels as compared with the non-lactating controls. However, plasma ghrelin levels were not significantly different between vehicle- and drug-treated rats. Administration of an oxytocin antagonist into the lateral ventricle significantly inhibited the increase in the plasma oxytocin level induced by acute suckling. However, plasma ghrelin levels did not significantly between the groups. These observations indicated that the decrease in serum ghrelin is caused by a loss of the contribution of hypothalamic ghrelin. Furthermore, the present results suggested that the suckling stimulus itself, but the release of prolactin or oxytocin, is the factor most likely to be responsible for the suppression of ghrelin secretion during lactation.     

Antisense oligodeoxynucleotide effects on the hypothalamic-neurohypophysial system and the hypothalamic-pituitary-adrenal axis

The possibility of sequence-dependent, transient, and local inhibition of neuropeptide or neuropeptide receptor expression within the brain makes antisense targeting an attractive approach for those interested in the involvement of brain neuropeptide systems in behavioral and neuroendocrine regulation. Here, I describe our attempts to manipulate the synthetic activity of peptidergic systems of the hypothalamic-neurohypophysial system, i.e. , oxytocin and vasopressin, and the hypothalamic-pituitary-adrenal (HPA) axis by antisense oligodeoxynucleotides. Detailed experimental protocols including different approaches for intracerebral antisense application in anesthetized or conscious rats are provided. As a consequence of local oxytocin or vasopressin antisense treatment within the hypothalamic supraoptic nucleus, various aspects of the neuronal activity are already altered after a few hours. Thus, we monitored electrophysiological parameters of oxytocinergic and vasopressinergic neurons, stimulus-induced expression of the Fos protein in oxytocin neurons, and stimulated release of oxytocin or vasopressin into blood as well as within the hypothalamus by dendrites and cell bodies as measured by simultaneous microdialysis in blood and brain, shortly after a single acute antisense infusion. We also employed chronic antisense infusion via osmotic minipumps or by repeated local infusion into the targeted brain region; for example, septal vasopressin receptor downregulation impairs the ability of male rats to discriminate between juvenile rats. Further, reduction of the amount of available CRH, vasopressin, and oxytocin within the hypothalamic paraventricular nuclei alters the neuroendocrine stress response of the HPA axis.     

Maternal olfaction differentially modulates oxytocin and prolactin release during suckling in goats

In postparturient goats, olfactory recognition of the young allows the establishment of a selective bond between the mother and her kids. Once this bond is formed, the mother rejects alien young that attempt to suckle. We tested whether the development of the maternal selective bond in goats modulates prolactin (PRL) and oxytocin (OT) release in response to suckling. On day 37 of lactation, serial blood samples were taken during nursing of the mother's own or alien kid(s) in 10 intact/selective goats and in 10 goats rendered anosmic/nonselective through prepartum peripheral ZnSO(4) irrigation. Spontaneous nursing behavior was also studied weekly from day 7 to 30 of lactation, at which time milk production was measured. Maternal selectivity had no effect on PRL release, in contrast to OT release, which was significantly affected by this factor. Intact mothers released OT only when nursing their own kids, but not with aliens, while anosmic/nonselective dams showed an increase in OT levels regardless of the identity of the kids. In addition to these effects on maternal selectivity, the amplitude of the response of both hormones was lower in anosmic mothers than in intact mothers. Finally, nursing behavior and milk production were not significantly affected by anosmia. We conclude that maternal selective behavior in goats, which relies on the individual olfactory signature of the kid, modulates the OT, but not the PRL, response to suckling. In addition, perception of the smell of the young appears to have a general facilitatory effect, independent of the kid's identity, on the release of both hormones.     

Misexpression of wingless-related MMTV integration site 5A in mouse mammary gland inhibits the milk ejection response and regulates connexin43 phosphorylation

Wingless-related MMTV integration site 5A (Wnt5a) is a noncanonical signaling WNT that is expressed in every stage of mouse mammary gland development except lactation. Using slow release pellets containing WNT5A as well as Wnt5a-null tissue, we previously showed that WNT5A acts to limit mammary development. Here, we generated transgenic mice that overexpress WNT5A in the mammary epithelium using the mouse mammary tumor virus promoter (M5a mice). Lactation was impaired in two high WNT5A-expressing lines. Lactation defects could not be explained by differences in apoptosis, lineage differentiation, milk synthesis, or secretion. Instead, misexpression of WNT5A led to a failure in oxytocin response and milk ejection. Noting the similarity between the M5a phenotype and that of mice with a mutation in connexin43 (Cx43; official gene symbol Gja1), we examined Cx43 phosphorylation and localization in M5a mice. In wild-type mice, Cx43 switched from a phosphorylated to a more hypophosphorylated form after parturition. In contrast, the phosphorylated form of Cx43 was maintained after parturition in M5a mice. Using a nontumorigenic breast cell line, MCF10A, we showed that, in addition to increasing the levels of phosphorylation of Cx43 on serine-368, ectopic expression of WNT5A reduced or blocked the amount of dye transferred between cells. In summary, we propose that WNT5A inhibits the response to oxytocin and prevents milk ejection through regulation of Cx43 function.     

Bovine platelet-activating factor acetylhydrolase (PAF-AH) activity related to fertility

Plasma platelet-activating factor acetylhydrolase (PAF-AH), the enzyme characterized by the association with plasma lipoproteins, degrades platelet-activating factor (PAF) as well as PAF-like oxidatively fragmented phospholipids produced during oxidative stress. Apart from pro-inflammatory properties, PAF is also related to reproductive processes and successful fertility. In order to get a better insight into the involvement of PAF-AH in the fertility of cows, the aim of the study was to determine the PAF-AH activity as well as the C-reactive protein, cholesterol and high density lipoprotein-cholesterol (HDL-C) in the serum of dairy cows throughout the pregnancy and lactation, as well as in infertile cows. The results showed that serum PAF-AH activity changes throughout pregnancy and lactation with a lower level during periparturient period. It is also found higher PAF-AH activity in lactating cows with reproductive disorders compared to high lactating cows without reproductive disorders. Strong correlation between PAF-AH activity and HDL-C concentration indicates that HDL could have considerable influence on PAF-AH activity in bovine plasma. CRP concentration was also lower during transition period suggesting that lactation might stimulate CRP synthesis in bovine. A higher CRP concentration in cows with reproductive disorders compared to fertile cows at the peak of lactation, demonstrates that milk production is not the only factor influencing CRP in cows. A significant correlation between PAF-AH activity and CRP level shows that both parameters could be influenced by reproductive status of dairy cows.