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.     

Spontaneous milk ejection during lactation and its possible relevance to success of breast-feeding.

In a woman suckling twins it became apparent that both suckling-induced and precisely timed, spontaneous bursts of milk ejection were occurring. Observations on days 14, 28, 56, and 112 of lactation disclosed highly significnat increases in intervals between episodes of spontaneous milk ejection. Furthermore, at all stages of lactation the interval between a feed and the next episode of spontaneous ejection was significantly longer than the interval between spontaneous ejections. The decrease in frequency of episodes of spontaneous milk ejection during lactation may be related to the decreasing release of prolactin in response to suckling. Spontaneous milk-ejection episodes are felt only when the breast is full and may signal its readiness for a further suckling episode. Such bursts of milk ejection may stimulate the suckling response in babies, suggesting that rigid three- or four-hour feeding regimens may be unphysiological and pose a threat to the success of breast-feeding in the early postnatal period.     

Humoral and cellular immune responses in gluten-treated suckling or hand-fed rats

We analyzed the immune response to gliadin in suckling rats and rats hand-fed with an artificial milk formula, an animal model of gluten enteropathy. Animals of both groups were intragastrically given either gliadin or albumin (control animals) or gliadin from birth till day 55. When compared to the controls, spleen lymphocytes from both groups of gliadin-treated rats cultivated in vitro exhibited a significant increase of spontaneous 3H-thymidine incorporation. Moreover, the proliferation of spleen and mesenteric lymph node (MLN) lymhocytes from both groups of gliadin-treated suckling and hand-fed rats was specifically increased by the in vitro gliadin challenge. Spleen B cells from gliadin-treated rats spontaneously produced higher amounts of gliadin-specific antibodies than those from the controls, however, in vitro stimulation by gliadin caused no further increase in antibody production. Apoptotic DNA fragmentation in MLN cells was higher in gliadin-treated rats than in albumin-treated ones, independently of the milk diet during the suckling period.     

Pulsatile secretion of prolactin and oxytocin during nursing in the lactating rat

The secretory profile of prolactin and oxytocin in response to suckling stimuli by litters was studied in unanesthetized and urethane-anesthetized lactating rats. Serum prolactin levels were determined by radioimmunoassay. Oxytocin released at milk-ejection reflex was monitored by the changes in the intramammary pressure and/or the characteristic pup's reaction associated with the milk ejection. Serum prolactin concentrations began to rise earlier than the first milk ejection in unanesthetized rats, but they were never elevated without the appearance of milk ejections in urethane-anesthetized rats. Pulsatile fluctuation in serum prolactin levels at 6-15 min intervals was observed in the nursing period when 10 pups were suckling continually. The intermittent milk-ejection reflex occurred not always but preponderantly (64-91%) when the serum prolactin levels were at the nadir of the fluctuation. Injection of an estimated dose of oxytocin released at each milk ejection (1 mU) did not change the serum prolactin levels. These results indicate that the mechanism for prolactin release may be more susceptible to the effects of anesthesia than that for oxytocin release in response to the suckling stimuli and that the release of both the hormones is pulsatile in nature and be influenced by a common biological clock during the nursing period.     

Spinal pathway of the milk-ejection reflex in the rat

The effects of lesions of the spinal cord on the milk-ejection reflex evoked by suckling were studied in urethane-anesthetized lactating rats. All lesions were made between C6 and C7 vertebrae and milk ejection was monitored by recording intramammary pressure. In the first experiment on the rats with bilateral lesions, a 3-h suckling test with 5 pups on each side was performed. Eleven (84.6%) of 13 rats with the section of the dorsal funiculus (Group 2), and 12 (85.7%) of 14 rats with the combined section of the dorsal and ventral funiculi (Group 4) displayed regular milk ejection. The incidence of milk ejection in both groups was not significantly different from 81.8% (9 rats) of the 11 sham-operated rats (Group 1). In contrast, none of the 12 rats with bilateral section of the lateral funiculus (Group 3) displayed milk ejection and the incidence of milk ejection was significantly lower than that in Group 1. In the second experiment on the rats with unilateral section of the lateral funiculus, bilateral suckling with 10 pups (5 pups on each side) and unilateral suckling (both ipsilateral and contralateral to the lesion) with 5 pups were consecutively performed in the 10 rats. Milk ejection was induced in 50% by contralateral suckling and in 100% by bilateral suckling, and the incidence was significantly higher than that (0%) observed during ipsilateral suckling. A significant difference in the incidence of milk ejection was also observed between contralateral and bilateral sucklings.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Changing characteristics of the milk-ejection reflex during pregnancy, lactation and after weaning in the rat

The pattern of reflex milk ejection during suckling was investigated in anaesthetized Wistar rats at various stages of pregnancy, lactation and after weaning. Milk-ejection responses were measured using intramammary pressure recordings, and the amount of oxytocin released was estimated from log dose-response lines compiled from the mammary responses to exogenous oxytocin. The number of rats showing intramammary pressure responses to oxytocin increased on Day 22 of pregnancy (the day of parturition) and decreased at 8 days after weaning. The dose-response lines from pregnant animals were shallow, but steepened and shifted to the left during lactation and after weaning. Reflex milk-ejection responses during suckling were detectable in primigravid animals, indicating that birth of the litter and previous suckling experience are unnecessary for the immediate functioning of the reflex. Reflex milk-ejection responses improved during early lactation (such that the frequency and the amount of oxytocin released at each response were maximal at Day 10 of lactation), and subsequently declined in late lactation. Although the frequency of responses in animals 2 and 4 days after weaning was similar to that in late lactating animals, the amount of oxytocin released at each response had risen again to mid-lactation values. In animals undergoing a second pregnancy and lactation the pattern of change in the milk-ejection responses was similar to that of primiparous animals.     

Effects of different suckling systems on milk production, udder health, reproduction, calf growth and some behavioural aspects in high producing dairy cows - a review

This article discusses the consequences of different suckling systems in the industrial countries for the milk production, udder health, reproduction and behaviour of high producing dairy cows and the effects on the gain, health and behaviour of the calves. The suckling systems are divided into three different categories depending on the purpose and duration of the suckling period. Long-term suckling with or without additional milking covering the period where the calf has a nutritional need for milk, and short-term suckling, where cow and calf are kept together in the colostrum period only.Long-term suckling without additional milking in early lactation can in some situations stimulate the subsequent milk production to a greater extent than milking alone. No clear or significant differences can be found between restricted and free suckling systems. Most experiments show that suckling decreases the risk of mastitis in the suckling period and in some cases even for some time after the suckling has been terminated. Suckling and milking during the same period is not advantageous in production turns because of a very poor ejection of milk. Long-term suckling can increase the post-partum interval until first heat, in some cases until the end of the suckling period. However, as the cows appear to be more fertile, the net effect on reproduction is small. The suckled calves are usually healthy with a high daily gain. Short-term suckling have more advantages than disadvantages on production, health and behaviour of both the cow and the calf compared to an immediate separation after birth.     

Effect of calf suckling on oxytocin,prolactin, growth hormone and milk yield in crossbred Gir x Holstein cows during milking

This study evaluated the effect of different milking managements on oxytocin, prolactin and growth hormone release in Gir x Holstein cows. Six cows were suckled by their calves, before and after milking (SM group); another six cows were submitted to exclusive milking (M group). High OT levels were observed during suckling of the SM group, however both groups had similar levels of OT during milking. The SM group presented PRL levels significantly higher than the M group, however only during suckling. For GH levels, the SM group showed higher levels than the M group, however this difference was significant only during the first suckling, cleaning of the teats and at the beginning of machine milking. Despite these results, SM cows produced more milk (milking plus suckling) than M cows, however milk obtained by milking was similar for both groups.     

Nasal immunization of mice with virus-like particles protects offspring against rotavirus diarrhea

Rotavirus is the major cause of diarrhea among young infants in both humans and animals. Immune protection of newborns by vaccination is difficult to achieve since there is not enough time to mount an immune response before exposure to the virus. We have designed a vaccination strategy mediating transfer of neutralizing antibodies from the mother to the offspring during pregnancy and/or lactation. Adult female mice were nasally immunized with virus-like particles (VLPs) made of viral proteins VP2 and 6 (VLP2/6) or VP 2, 6, and 7 (VLP2/6/7) derived from the RF rotavirus strain in the presence or absence of cholera toxin. Both vaccines elicited serum and milk antibodies against the respective VPs. Four days after parturition, suckling pups were challenged orally with RF rotavirus. Pups from mothers immunized with VLP2/6/7 but not VLP2/6 were protected against rotavirus diarrhea, indicating that VP7 plays a key role in protection. Protection was mediated by milk rather than serum antibodies, and mucosal adjuvants were not required. In conclusion, VLPs containing VP7 administered nasally to mothers represent a promising vaccine candidate for the protection of suckling newborns against rotavirus-induced diarrhea, even in the absence of a mucosal adjuvant.     

Consumption of probiotic Lactobacillus rhamnosus (MTCC: 5897) containing fermented milk plays a key role in development of the immune system in newborn mice during the suckling–weaning transition

Early infancy, the period when offspring rely not only on their own immunity to combat food‐borne antigens but also acquire immunity through maternal sources (via transplacental routes and breast milk), is critical for immune system development Hence the present study was designed to evaluate the effect on offspring of administration of probiotic‐containing fermented milk (PFM) either to mothers during the suckling period or to their offspring after weaning either separately or sequentially. PFM‐fed mice showed enhanced leukocyte functionality in offspring as evidenced by significantly (P < 0.05) increased release of lysosomal enzymes (β‐galactosidase, β‐glucuronidase) in peritoneal fluid and nitric oxide production in culture supernatants of activated macrophages. Further, remarkably reduced levels (P < 0.01) of inflammatory markers (TNF‐α, monocyte chemotactic protein‐1) and allergic antibodies (total and milk specific IgE) were observed in offspring where PFM was fed either to them or to their mothers. However, considerably increased levels (P < 0.05) of SIgA were found in the guts of control and experimental groups animals irrespective of their exposure to PFM. Restoration of Th1/Th2 homeostasis further confirmed the useful effects of PFM supplementation by shifting the cytokine profile (IL‐4, IFN‐γ and IL‐10) with increased IFN‐γ/IL‐4 and reduced IgE/Ig2Ga ratios. Hence, it is logical to conclude that administration of Lactobacillus rhamnosus‐containing (MTCC:5897) fermented milk to mothers during the suckling period and to their offspring after weaning has beneficial effects on the development of newborns immune systems; this effect appears to be more pronounced when mothers are fed with it.     

Shifts in immunoglobulin (IgG,IgM and IgA) levels in the milk of southern elephant seals,at Potter Peninsula,King George Island,Antarctica

We quantified immunoglobulins (Ig) in mammary secretions of 12 female southern elephant seals ( Mirounga leonina) at King George Island, Antarctica, using single radial immunodiffusion on agarose plates. Seals were chemically immobilized for milk sample collection at four time points during the 3- to 4-week suckling period. All three major mammalian immunoglobulins (IgG, IgM, IgA) were detected in southern-elephant seal milk. Total immunoglobulin levels and the ratio of Ig subclasses varied throughout the suckling period. Total immunoglobulin levels were highest on the 1st day of lactation, when they represented over 57% of the mean total protein concentration of the milk, and declined steadily throughout lactation, representing approximately 40% of the mean total protein concentration at the end of the suckling period. IgG was the most abundant immunoglobulin class (85.93-93.78% of total milk immunoglobulins), followed by IgM (6.06-13.93%), and IgA (0.14-0.23%). There was no significant difference in IgA levels throughout the suckling period. IgG levels were significantly lower during the second stage (3-6 days post-parturition) than during the first, third or fourth stages (1, 13-15, and 19-25 days post-parturition, respectively). IgM levels were highest during the first stage of lactation; these values were significantly higher than levels measured during the second, third and fourth stages of lactation. Transfer of passive immunity from female to offspring in other mammalian species is correlated with the subclass of immunoglobulin secreted in the milk; species acquiring passive immunity in utero, via the placenta, secrete a preponderance of IgA, whereas species acquiring immunity post-partum, via lacteal secretions and gut resorption, secrete a preponderance of IgG. The Ig patterns and concentrations observed in our study of southern elephant seals are consistent with an important role of post-partum transmission of passive immunity during the pinniped lactation period.     

Interleukin-2 in human milk: a potential modulator of lymphocyte development in the breastfed infant

Development of lymphocyte subpopulations and response to antigen exposure will be influenced by the limited ability of neonates to produce cytokines. In the case of cytokines such as interleukin (IL)-2 which are potent T lymphocyte regulators but poorly produced by newborn infants, the supply of cytokines through human milk could alleviate an immunological deficit and potentially aid the maturation of the immune system. We analysed human milk from 52 mothers (15-357 days postpartum) by ELISA to determine levels of aqueous IL-2, as well as production by human milk cells. IL-2 was detectable (>8 pg/mL) in the aqueous phase of 81% of all day 1 samples with no significant difference found in the mean concentration over 3 consecutive days. IL-2 was produced constitutively at detectable levels by 57% of milk cell samples and production was significantly increased by stimulation with Con A (380%). No correlation was found between aqueous and cellular IL-2, however there was a significant correlation between milk aqueous IL-2 and serum IL-2. This is the first report of IL-2 in the aqueous phase of human milk. A supply of exogenous IL-2 in human milk may provide the suckling infant with important immunological signals during a significant stage of T cell development.     

Effect of short-term fasting/refeeding on epidermal growth factor content in the gastrointestinal tract of suckling rats.

Epidermal growth factor (EGF) is trophic for varying regions of the developing gastrointestinal tract (GIT) of suckling rats. The presence of large amounts of EGF in milk from various species, combined with low production of EGF by suckling animals, led to speculation that milk is a major source of EGF for suckling rats. We report that short-term fasting (8 hr) of 12-day-old suckling rats resulted in a significant decrease in the levels of immunoreactive EGF (irEGF) in the GIT. Pups refed by lactating mothers for 1 to 4 hr exhibited an increase in irEGF to original levels, whereas pups fed a rat milk substitute by gastric gavage did not have an increase in irEGF content. The irEGF levels in the GIT of pups that were manually fed normal rat milk, or rat milk substitute supplemented with EGF, returned to the prefasted levels. Fasted suckling rats refed 2 ml of rat milk in 2 h exhibited significantly higher level of irEGF in the GIT than did those refed with 0.5 ml in 45 min. Since rat milk irEGF exists in three distinct forms (A, B, and C; C is equal to authentic submandibular gland EGF, the irEGF forms in the GIT were characterized by native polyacrylamide gel electrophoresis. In the stomach luminal contents of the fed suckling rats, only the larger form, Peak B, was observed. Both the luminal content and the mucosa scrapings of all other segments of all groups contained only Form D (comigrating with desarginyl EGF), a metabolic derivative of EGF. All forms were immunoreactive, exhibited receptor binding, and stimulated DNA synthesis in growth-arrested fibroblasts. The rapid changes in EGF within the GIT of suckling rats suggest the EGF can acutely modify some GIT functions of suckling rats.     

Milk transfer of inorganic mercury to suckling rats

The transport of mercury into rat milk, and uptake in the suckling offspring was studied after peroral administration of inorganic mercury to lactating control rats, and to rats fed selenite in the diet. On day 8, 9, 10, or 11 of lactation, dams were administered a single oral dose of 0.1, 0.4, 0.7, 1.3, or 5.8 mg Hg/kg bw labeled with 203mercuric acetate. There was a linear relationship between mercury concentrations in dam's plasma and milk. The level of mercury in milk was approximately 25% of the level in plasma. After 3 d, milk levels were reduced to half the levels at 24 h. In the suckling offspring, exposed to mercury via milk during 3 d, the mercury level in blood was approximately 1% of the level in maternal blood. Mercury concentration in milk was linearly correlated to the levels in kidney, liver, and brain in the suckling offspring after 3 d exposure to mercury via milk. Selenite treatment of rats, 1.3 micrograms Se/g diet for 5 mo, resulted in increased transport of mercury to milk, probably because of increased plasma levels of mercury. However, selenite treatment of the dams did not cause any increased tissue levels of mercury in the suckling offspring.     

High cell-free virus load and robust autologous humoral immune responses in breast milk of simian immunodeficiency virus-infected african green monkeys

The design of immunologic interventions to prevent postnatal transmission of human immunodeficiency virus (HIV) will require identification of protective immune responses in this setting. Simian immunodeficiency virus (SIV)-infected rhesus monkeys (RMs), a species that develops an AIDS-like illness following experimental infection, transmit the virus at a high rate during breastfeeding. In contrast, postnatal transmission of SIV occurs rarely or not at all in natural, asymptomatic primate hosts of SIV. These contrasting transmission patterns provide a unique opportunity to study mechanisms that evolved to protect suckling infants from SIV infection. We compared the virologic and immunologic properties of milk of SIV-infected and uninfected natural hosts of SIV, African green monkeys (AGMs), to that of RMs. Interestingly, despite a low number of milk CD4(+) T lymphocytes in uninfected AGMs, milk virus RNA load in SIV-infected AGMs was comparable to that of SIV-infected RMs and that in AGM plasma. This observation is in contrast to the relatively low virus load in milk compared to that in plasma of SIV-infected RMs and HIV-infected women. Milk of SIV-infected AGMs also displayed robust virus-specific cellular immune responses. Importantly, an autologous challenge virus-specific neutralization response was detected in milk of five of six SIV-infected AGMs that was comparable in magnitude to that in plasma. In contrast, autologous challenge virus neutralization was not detectable in milk of SIV-infected RMs. The autologous virus-specific adaptive immune responses in breast milk of AGMs may contribute to impedance of virus transmission in the infant oral/gastrointestinal tract and the rarity of postnatal virus transmission in natural hosts of SIV.     

Preweaning feeding mechanisms in the rabbit.

Muscle contraction patterns and mandibular movements of infant rabbits during suckling and chewing were compared. Oral muscle activity was recorded by fine-wire electromyography, while jaw movements and milk bottle pressure were registered. Suckling and mastication have a comparable cycle duration and share a common pattern of oral muscle activity which consists of a succession of a jaw closer burst, during which the jaw closes and undergoes a power stroke (in mastication), a suprahyoid burst with a stationary or slightly opening jaw and a digastric burst with fast jaw opening (the power stroke of suckling). Compared to suckling, mastication shows decreased jaw opener activity, increased jaw closer activity, development of jaw closing activity in the lateral pterygoid, and increased asymmetry in the masseter by development of a new differentiated motor pattern on the working side. The study shows that the suckling motor pattern enables the infant rabbits to change to chewing with just a few modifications.     

Host-defence-related proteins in cows' milk

Milk is a source of bioactive molecules with wide-ranging functions. Among these, the immune properties have been the best characterised. In recent years, it has become apparent that besides the immunoglobulins, milk also contains a range of minor immune-related proteins that collectively form a significant first line of defence against pathogens, acting both within the mammary gland itself as well as in the digestive tract of the suckling neonate. We have used proteomics technologies to characterise the repertoire of host-defence-related milk proteins in detail, revealing more than 100 distinct gene products in milk, of which at least 15 are known host-defence-related proteins. Those having intrinsic antimicrobial activity likely function as effector proteins of the local mucosal immune defence (e.g. defensins, cathelicidins and the calgranulins). Here, we focus on the activities and biological roles of the cathelicidins and mammary serum amyloid A. The function of the immune-related milk proteins that do not have intrinsic antimicrobial activity is also discussed, notably lipopolysaccharide-binding protein, RNase4, RNase5/angiogenin and cartilage-glycoprotein 39 kDa. Evidence is shown that at least some of these facilitate recognition of microbes, resulting in the activation of innate immune signalling pathways in cells associated with the mammary and/or gut mucosal surface. Finally, the contribution of the bacteria in milk to its functionality is discussed. These investigations are elucidating how an effective first line of defence is achieved in the bovine mammary gland and how milk contributes to optimal digestive function in the suckling calf. This study will contribute to a better understanding of the health benefits of milk, as well as to the development of high-value ingredients from milk.