Subpicogram determination of oxytocin by an enzyme immunoassay using acetylcholinesterase as label

Oxytocin and cortisol release during suckling, hand-milking and machine milking in camels

This research paper addresses the hypothesis that oxytocin (OT) could be released during suckling and during milking with and without the presence of a calf and that this release could be regulated by maternal behaviour. Plasma concentration patterns of OT and cortisol (CORT) were measured in six Tunisian dromedary camels during 2 suckling episodes, 2 manual milking episodes with calves beside the mother and 2 machine milking episodes without calves present. Various patterns of OT release were observed between each camel including specific two peak release patterns. Higher plasma OT concentrations were found during the suckling and hand-milking episodes with simultaneous suckling of calves, than during the machine milking episodes without calves. Exclusive mechanical milking episodes also evoked significant mean OT release, although greatly reduced compared to suckling and hand milking. The low basal levels and classical CORT release patterns suggested non-stressful management practices were used and there were very limited differences in udder stimulation between managements. The OT release induced by exclusive suckling and suckling together with hand-milking gives a reference point for what a good milk ejection stimulation is in camels. The important and specific reduction of OT release during machine milking without the calf present could be a physiological consequence of the maternal behaviour (selectivity for the own young) and to a lesser extent explained by a lower stimulation by machine milking.

Neonatal Suckling, Oxytocin, and Early Infant Attachment to the Mother

The neuropeptide oxytocin (OT) promotes maternal care and social affiliation in adults but its importance in infant attachment still remains unknown. True animal models of infant attachment are extremely rare, and the sheep (in complement to non-human primates) is one of the few that provides the opportunity to investigate its neuroendocrinological basis. In the lamb, access to the udder has strong rewarding properties for the establishment of a preferential relationship with the mother. Therefore, the present study explored the possible involvement of OT through its release during close social contacts with the mother. The first experiment revealed that lambs having free access to the udder from birth onward developed, by 12 h of age, a clear preference for their mothers over another maternal ewe. Delaying access to the udder for six, four or even only 2 h starting at birth, by covering the ewe's udder, resulted in the lack of such a preference without affecting general activity. These effects persisted in most cases at 24 h but by 72 h of age a bond with the mother was clearly expressed. Experiment two showed that social interactions with the mother were followed by a release of OT in the plasma when lambs had the possibility to suckle. Non-nutritive interactions were without effects. Preliminary data on two subjects suggested that OT might also increase in the cerebrospinal fluid after suckling. Finally, in the third experiment, oral administration of a non-peptide OT receptor antagonist (L-368-899, Merck) over the first 4 h after birth led to decreased exploration of the mother's body compared to lambs receiving saline, and impaired the expression of a preference for the mother at 24 h. The effects were no longer observed at 48 h. Our findings demonstrate that both delayed access to the mother's udder and OT receptor antagonist alter the onset of mother preference in newborn lambs. This suggests that central OT facilitates the development of filial attachment through its release during suckling.

Oxytocin Induces Mammary Epithelium Disruption and Could Stimulate Epithelial Cell Exfoliation

Mammary epithelial cells (MEC) are exfoliated from the epithelium into milk, influencing the number of MEC present in the udder. This process is associated with epithelium integrity. The release of oxytocin (OT) induced by milking causes myoepithelial cell contraction, which, in turn, may stimulate MEC exfoliation through mechanical forces. To investigate the role of OT in MEC exfoliation, we inhibited or induced myoepithelial cell contraction by injecting the OT receptor antagonist atosiban (Ato) or a supraphysiological dose of OT, respectively. Eight cows were assigned to 2 treatments during 2 milkings according to a crossover experimental design: Control+OT (cows were first milked to collect standard milk and then received 5 IU of OT to collect residual milk through a second milking) and Ato + OT (cows were injected with Ato (50 μg/kg of body weight) and milked to collect cisternal milk, then received 5 IU of OT to collect alveolar milk through a second milking). Milk MEC were purified to determine their concentration and number in milk. Mammary epithelium integrity was assessed by measuring the kinetics of plasma lactose concentration. Inhibiting myoepithelial cell contraction by Ato injection decreased the number of exfoliated MEC in milk. In contrast, OT injection increased the concentration of MEC in the residual milk and the number of MEC in the alveolar milk. Ato injection reduced plasma lactose concentration, whereas, in both treatments, OT injections increased it. Our results suggested that myoepithelial cell contraction caused by OT could stimulate MEC exfoliation into milk and was associated with epithelium disruption.

Mammary epithelium disruption and mammary epithelial cell exfoliation during milking in dairy cows

The presence of mammary epithelial cells (MEC) in the milk of ruminants indicates that some MEC are shed from the mammary epithelium; however, the mechanisms that regulate the MEC exfoliation process are not known. Through the release of oxytocin, prolactin, and cortisol and through oxytocin-induced mechanical forces on the mammary epithelium, milking could participate in regulating the MEC exfoliation process. The aims of the present study were to determine the rate of MEC exfoliation throughout milking and to investigate its relationship to mammary epithelium integrity and milking-induced hormone release. Milk samples from 9 Holstein dairy cows producing 40.6 ± 1.36 kg of milk/d were collected at the beginning (after 1 and 2 min), in the middle, and at the end of milking. Milk MEC were purified using an immunomagnetic method. Blood samples were collected before, during, and after milking, and the oxytocin, prolactin, and cortisol concentrations in the samples were measured. Tight junction opening was assessed by plasma lactose concentration and the Na⁺:K⁺ ratio in milk. The somatic cell count in milk varied during the course of milking; it decreased at the beginning of milking and then increased, reaching the highest values at the end of milking. Exfoliated MEC were present in all milk samples collected. The presence of MEC in the milk sample collected during min 1 of milking, likely corresponding to the cisternal milk fraction, suggests that MEC were exfoliated between milkings. The observed increase in the Na⁺:K⁺ ratio in milk and in the plasma concentration of lactose indicated that disruption of mammary epithelium integrity occurred during milking. The MEC exfoliation rate at milking was not correlated with the variables describing milking-induced prolactin release but was negatively correlated with cortisol release, suggesting that cortisol may play a role in limiting exfoliation. In conclusion, milking induced a disruption of the mammary epithelial barrier. Mammary epithelial cells may be continuously exfoliated between milkings or exfoliated during milking as a consequence of the oxytocin-induced mechanical forces and the disruption of mammary epithelium integrity.

Validation of a Commercially Available Enzyme ImmunoAssay for the Determination of Oxytocin in Plasma Samples from Seven Domestic Animal Species

The neurohormone oxytocin (OT) has a broad range of behavioral effects in mammals. It modulates a multitude of social behaviors, e.g., affiliative and sexual interactions. Consequently, the OT role in various animal species is increasingly explored. However, several issues have been raised regarding the peripheral OT measurement. Indeed, various methods have been described, leading to assay discrepancies and inconsistent results. This highlights the need for a recognized and reliable method to measure peripheral OT. Our aim was to validate a method combining a pre-extraction step, previously demonstrated as essential by several authors, and a commercially available enzyme immunoassay (EIA) for OT measurement, using plasma from seven domestic species (cat, dog, horse, cow, pig, sheep, and goat). The Oxytocin EIA kit (EnzoLifeSciences) was used to assay the solid-phase extracted samples following the manufacturer's instructions with slight modifications. For all species except dogs and cats, concentration factors were applied to work above the kit's sensitivity (15 pg/ml). To validate the method, the following performance characteristics were evaluated using Validation Samples (VS) at various concentrations in each species: extraction efficiency via spiking tests and intra- and inter-assay precision, allowing for the calculation of total errors. Parallelism studies to assess matrix effects could not be performed because of too low basal concentrations. Quantification ranges and associated precision profiles were established to account for the various OT plasma concentrations in each species. According to guidelines for bioanalytical validation of immunoassays, the measurements were sufficiently precise and accurate in each species to achieve a total error ≤30% in each VS sample. In each species, the inter-assay precision after 3 runs was acceptable, except in low concentration samples. The linearity under dilution of dogs and cats' samples was verified. Although matrix effects assessments are lacking, our results indicate that OT plasma levels can reliably be measured in several domestic animal species by the method described here. Studies involving samples with low OT plasma concentrations should pay attention to reproducibility issues. This work opens new perspectives to reliably study peripheral OT in a substantial number of domestic animal species in various behavioral contexts.

Human-lamb bonding: oxytocin, cortisol and behavioural responses of lambs to human contacts and social separation

Friendly interactions between humans and animals such as gentling or petting have been shown to have positive behavioural and physiological consequences in many species. In primates, rodents and dogs, oxytocin has been associated with tactile contact and anti-stress effects that may influence bonding and responses to stress situations. However the activation of the oxytocinergic system in other human-animal interactions such as with herbivores, had not yet been studied. Sixteen female lambs were reared by artificial feeding reinforced with 3× 30 s daily stroking sessions. At 6 weeks of age, the test consisted in measuring first plasma oxytocin and cortisol responses in lambs during a first 6-min phase in the home pen where the familiar caregiver gently stroked the lamb, and then physiological and behavioural responses in a test pen during a 20-min - phase of social isolation followed by a 20-min - phase of reunion with its familiar caregiver. The lambs expressed behavioural agitation during the whole period of isolation. A strong affiliative response towards the human and a sustained reduction of the agitation behaviour were observed during reunion. Lambs' behaviours when isolated and when in contact with the human were correlated suggesting a response to social separation from the familiar caregiver more than to social isolation from congeners. No significant changes in cortisol levels were observed during the test. Oxytocin levels did not vary during human contact, but increased when the familiar caregiver left the lamb alone in the test pen. In conclusion, lambs displayed affiliative responses towards their caregiver, and the lack of cortisol response during isolation while oxytocin was released suggest an anti-stress effect of oxytocin.

Effect of the prolactin-release inhibitor quinagolide on lactating dairy cows

In most mammals, prolactin (PRL) is essential for maintaining lactation, and yet the short-term suppression of PRL during established lactation by bromocriptine has produced inconsistent effects on milk yield in cows and goats. To assess the effect of the long-term inhibition of PRL release in lactating dairy cows, 5 Holstein cows in early lactation received daily intramuscular injections of 1mg of the PRL-release inhibitor quinagolide for 9 wk. Four control cows received the vehicle (water) only. During the last week of the treatments, one udder half was milked once a day (1×) and the other twice a day (2×). Blood samples were harvested at milking in wk -1, 1, 4, and 8. The daily injections of quinagolide reduced milking-induced PRL release but not the basal PRL concentration. Quinagolide induced a faster decline in milk production, which was about 5.3 kg/d lower in the quinagolide-treated cows during the last 4 wk of treatment. During wk 9, the inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the half milked 1×. Milk production was significantly correlated with the quantity of PRL released at milking. Quinagolide did not affect the release of oxytocin at milking. Serum concentration of insulin-like growth factor-1 was not affected by treatment or correlated with milk production. Serum concentrations of leptin and the calciotropic hormone stanniocalcin were not affected by the treatment. In conclusion, the chronic administration of the PRL-release inhibitor quinagolide decreases milk production in dairy cows. The effect is likely the result of the reduced release of milking-induced PRL and is modulated at the level of the gland by milking frequency.

Clinical, biological and hormonal study of mid-pregnancy termination in cats with aglepristone

In order to evaluate the efficacy, the safety and the variation in plasma concentrations of estrogens, progesterone, PGFM, oxytocin, cortisol and prolactin after mid-pregnancy termination induced by aglepristone, 61 pregnant queens (33.3 + 4.2 days), were injected subcutaneously with 15 [corrected] mg/kg aglepristone, (Alizine) [corrected] repeated once 24 h later. Five queens served as control and received a placebo. The efficacy of aglepristone was 88.5% and termination of pregnancy was achieved in 50% of the queens within 3 days. Brief periods of depression and anorexia were noted in 9.3% of the queens before fetal expulsion (these symptoms were attributed to the phenomenon of fetal expulsions). Not one of the queens that aborted developed uterine disease. There were no changes in plasma concentrations of estrogen, prostaglandin, prolactin or oxytocin following aglepristone administration. However, there were significant increases in plasma concentrations of progesterone and cortisol 60 and 30 h, respectively, after aglepristone administration. Termination of pregnancy occurred with high plasma progesterone concentrations. Fetal expulsion was characterised by an increase in estrogen, PGFM and oxytocin concentrations, whereas prolactin and cortisol levels remained at a basal level.

Oxytocin mediates some effects of insulin-like growth factor-I on porcine ovarian follicles

The aims of the present study were (1) to investigate the influence of insulin-like growth factor-I (IGF-I) on follicular size, on the secretion of oxytocin (OT), progesterone (P), estradiol (E), IGF binding protein-3 (IGFBP-3), inhibin A, inhibin B and cAMP and on the expression of proliferation-associated peptide PCNA, ERK-related mitogen activated protein kinase (MAPK/ERK1, 2) and protein kinase A (PKA) in cultured porcine ovarian follicles; (2) to examine the effects of OT on IGF-I and on these functions; and (3) to determine whether the effects of IGF-I can be mediated by OT. To define the involvement of OT in mediating IGF-I action, we compared responses of porcine ovarian follicles to IGF-I and OT and examined whether blockade of endogenous OT by specific antiserum can affect IGF-I action. It was observed that IGF-I (1, 10 or 100 ng/ml) was able to prevent a decrease in the size of ovarian follicles during culture and caused an increase in the diameter of some follicles. It also stimulated the secretion of OT, P, IGFBP-3, inhibin A and cAMP, decreased the secretion of E and inhibin B (RIA/EIA/ELISA), and induced the expression of PCNA, PKA, MAPK/ERK1, but not MAPK/ERK2 (Western blotting). Like IGF-1, OT (100 ng/ml) prevented decrease in follicular size and increased the diameter of some follicles. It also stimulated the secretion of P and IGF-I, but not E. Antiserum against OT (1%), when given alone, did not affect the reduction of follicular size but slightly increased the percentage of follicles increasing their diameter during culture. The antiserum also inhibited secretion of OT and cAMP but not the secretion of P, E, IGFBP-3 or the expression of PKA, MAPK/ERK1 or 2. When given together with IGF-I, the antiserum prevented the stimulatory action of IGF-I on the proportion of enlarged follicles and on OT, IGFBP-3 and MAPK/ERK1. It augmented the effect of IGF-I on P, but not the effect on E, cAMP, PKA or MAPK/ERK2. These observations demonstrate the involvement of IGF-I and OT in the control of ovarian follicular size and follicular cell proliferation, progestagen, estrogen, IGFBP-3, inhibin A and B secretion and in cAMP/PKA- and MAPK/ERK1-dependent intracellular mechanisms. Furthermore, the reciprocal stimulation of IGF-I and OT and the similarity of some their effects, together with the prevention or augmentation of some IGF-I effects after OT blockade, suggest that IGF-I action can be mediated by OT.

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.

Effect of milking frequency on oxytocin release and milk production in dairy ewes

The experiment was conducted to investigate the effectiveness of milking stimulus on oxytocin release and to compare the effect of milking frequency on plasma levels of oxytocin and milk parameters. Twelve Lacaune ewes were subjected to six treatments (T1, T2, T3, T4, T5 and T7 daily milkings) during 6 days. At each milking, blood was sampled and plasma oxytocin levels were determined by enzyme immunoassay. Baseline levels of oxytocin were similar for all milking frequencies. The start of milking was followed by a significant increase in oxytocin levels for all milking frequencies. One daily milking induced significantly higher oxytocin levels than 2, 3, 4, 5 and 7 daily milkings. Milk yield was significantly increased between 4 (1787.0+/-141.5ml) and 7 (1780.0+/-53.6ml) daily milkings compared to 1 (1104.0+/-81.2ml) daily milking. Total concentration of milk protein did not change, but the total milk fat yield for 5 (73.0+/-2.0g/l) and 7 (72.8+/-1.4g/l) daily milkings were significantly higher than for 1 (58.1+/-4.3g/l) daily milking. This study confirmed milk yield gains caused by frequent milk ejection and also showed that oxytocin release was not a limiting factor for milk yield gain when daily milking frequency was increased.

Protection of immunoreactivity of dry immobilized proteins on microtitration plates in ELISA: application for detection of autoantibodies in myasthenia gravis

We show the ability of the BSA-trehalose film to convert normally fragile proteins such as mouse monoclonal antibody to the Alzheimer precursor protein A4 (APP695) and cell line TE671 acetylcholine receptor (AChRTE671) into a stable reagent, after its immobilization on microtitration plates. The remarkable property of the dry immobilized proteins are their stability under prolonged exposure to temperatures as high as 50 degrees C. Using the AChRTE671, the proposed method was applied for the measurement of anti-AChR autoantibodies in Myasthenia gravis by means of an enzyme-linked immunosorbent assay (ELISA). The test was shown to be specific and able to detect anti-AChR autoantibodies at concentrations as low as 3 nM. Using the same AchRTE671 as antigen, the results of examination of 34 serum samples for detection of anti-AChR autoantibodies by ELISA were compared with those of the conventional radioimmunoprecipitation assay (RIA). It was concluded that ELISA is another useful method for the diagnosis of M. gravis. The ELISA method offers a rapid, simple, safe and inexpensive means for mass screening of M. gravis.

Intramammary pressure and luteal oxytocin after PGF2 alpha administration in cycling and early pregnant ewes

The aim of this work was to investigate whether luteal oxytocin released after non-luteolytic prostaglandin F2 alpha (PGF2 alpha) challenge could explain the intramammary pressure (IMP) rises previously described in pregnant ewes after the normal life span of a corpus luteum. Blood oxytocin levels and IMP after challenge were measured in cycling and pregnant lactating ewes until the response ceased (approximately 55 d post oestrus). Oxytocin release was not significantly different for cycling and pregnant ewes, and fell to its lowest levels on days 16-18 post oestrus in both groups, i.e. with or without luteolysis. However, although IMP response fell with luteolysis in cycling ewes, the response persisted until day 55 in pregnant ewes. This lack of correlation between oxytocin release and IMP response raised interesting questions including: is there an unknown oxytocic compound that can be released after PGF2 alpha stimulation of the corpora lutea?