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Introduction: Oxytocin is a key hormone in breastfeeding. No recent review on plasma levels of oxytocin in response to breastfeeding is available., Materials and Methods: Systematic literature searches on breastfeeding induced oxytocin levels were conducted 2017 and 2019 in PubMed, Scopus, CINAHL, and PsycINFO. Data on oxytocin linked effects and effects of medical interventions were included if available., Results: We found 29 articles that met the inclusion criteria. All studies had an exploratory design and included 601 women. Data were extracted from the articles and summarised in tables. Breastfeeding induced an immediate and short lasting (20 minutes) release of oxytocin. The release was pulsatile early postpartum (5 pulses/10 minutes) and coalesced into a more protracted rise as lactation proceeded. Oxytocin levels were higher in multiparous versus primiparous women. The number of oxytocin pulses during early breastfeeding was associated with greater milk yield and longer duration of lactation and was reduced by stress. Breastfeeding-induced oxytocin release was associated with elevated prolactin levels; lowered ACTH and cortisol (stress hormones) and somatostatin (a gastrointestinal hormone) levels; enhanced sociability; and reduced anxiety, suggesting that oxytocin induces physiological and psychological adaptations in the mother. Mechanical breast pumping, but not bottle-feeding was associated with oxytocin and prolactin release and decreased stress levels. Emergency caesarean section reduced oxytocin and prolactin release in response to breastfeeding and also maternal mental adaptations. Epidural analgesia reduced prolactin and mental adaptation, whereas infusions of synthetic oxytocin increased prolactin and mental adaptation. Oxytocin infusion also restored negative effects induced by caesarean section and epidural analgesia., Conclusions: Oxytocin is released in response to breastfeeding to cause milk ejection, and to induce physiological changes to promote milk production and psychological adaptations to facilitate motherhood. Stress and medical interventions during birth may influence these effects and thereby adversely affect the initiation of breastfeeding., Competing Interests: The authors have no competing interests.

Objective: This study investigated possible influences of medical interventions during labor on maternal blood pressure during a breastfeed 2 days postpartum., Subjects and Methods: Sixty-six primiparae with normal deliveries were consecutively recruited. Blood pressure was measured at -5, 10, 30, and 60 minutes during a morning breastfeed 2 days postpartum. Five treatment groups were formed based on the medical interventions received during labor: Non-medicated mothers (Control group, n=21); mothers receiving epidural analgesia (EDA) with oxytocin (OT) stimulation (EDA(OT) group, n=14); mothers receiving EDA without OT stimulation (EDA(non-OT) group, n=7); mothers receiving OT stimulation only (OT intravenously [iv] group, n=9); and mothers receiving 10 IU of OT intramuscularly (im) only (OT im group, n=15)., Results: Baseline diastolic, but not systolic, blood pressure differed between the groups as displayed by significantly lower diastolic blood pressure in the EDA(non-OT) group compared with the Control group, the OT iv group, and the EDA(OT) group (p=0.045, p=0.041, and p=0.024, respectively). Both systolic and diastolic blood pressure fell significantly during the breastfeeding session in the Control group (p=0.001 and p=0.004, respectively), the OT im group (p=0.006 and p=0.001, respectively), and the EDA(OT) group (p=0.028 and p=0.002, respectively), and the fall in diastolic blood pressure tended to be significant in the OT iv group (p=0.050). The duration of skin-to-skin contact before breastfeeding correlated positively with the decrease in systolic blood pressure in the OT im group (R(s)=0.540, p=0.046)., Conclusion: Administration of EDA during labor lowers baseline diastolic blood pressure and abolishes the fall in blood pressure in response to a breastfeed 2 days after birth.

Background: Oxytocin and prolactin stimulate milk ejection and milk production during breastfeeding. The aim of the present study was to make a detailed analysis of maternal release of oxytocin and prolactin in response to breastfeeding during the second day postpartum in mothers who had received oxytocin either intravenously for stimulation of labor or intramuscularly for prevention of postpartum hemorrhage and/or epidural analgesia or those who had received no such treatment in connection with birth., Methods: In a descriptive comparative study plasma oxytocin and prolactin concentrations were measured in response to suckling during the second day postpartum in women who had received intravenous intrapartum oxytocin (n = 8), intramuscular postpartum oxytocin (n = 13), or epidural analgesia, either with (n = 14) or without (n = 6) intrapartum oxytocin infusion, and women who received none of these interventions (n = 20). Hormone levels were analyzed by enzyme immunoassay., Results: All mothers showed a pulsatile oxytocin pattern during the first 10 minutes of breastfeeding. Women who had received epidural analgesia with oxytocin infusion had the lowest endogenous median oxytocin levels. The more oxytocin infusion the mothers had received during labor, the lower their endogenous oxytocin levels were during a breastfeeding during the second day postpartum. A significant rise of prolactin was observed after 20 minutes in all women, but after 10 minutes in mothers having received oxytocin infusion during labor. In all women, oxytocin variability and the rise of prolactin levels between 0 and 20 minutes correlated significantly with median oxytocin and prolactin levels., Conclusion: Oxytocin, released in a pulsatile way, and prolactin were released by breastfeeding during the second day postpartum. Oxytocin infusion decreased endogenous oxytocin levels dose-dependently. Furthermore, oxytocin infusion facilitated the release of prolactin. Epidural analgesia in combination with oxytocin infusion influenced endogenous oxytocin levels negatively.

Women undergo physiological and psychological changes during pregnancy, labor and lactation. The psychological adaptations can be affective, cognitive and behavioral and can be measured by dimensional personality instruments. This study aims to compare (1) the personality profile in mothers after birth with a normative group of non-lactating women and to examine (2) whether the personality profile differs 2 days, 2 months and 6 months after birth between mothers who have been exposed to epidural anesthesia, oxytocin administration or neither. Sixty-nine primiparae were assigned to four groups: mothers having received oxytocin infusion during labor (OT iv group, n = 9), mothers having received epidural analgesia with/without oxytocin infusion (EDA group, n = 23), mothers having received 10 iU oxytocin intramuscularly after birth (OT im group, n = 15) and mothers having received none of these treatments (unmedicated group, n = 22). At 2 days and 2 and 6 months postpartum mothers completed the Karolinska Scales of Personality (KSP). The unmedicated, the OT iv- and OT im groups scored significantly lower on anxiety and aggression related scales and higher on the socialization subscale during the entire observation period when compared with a normative group. These differences were not observed in the EDA group 2 days postpartum. At 2 and 6 months postpartum, the scores of the EDA group had changed significantly and were almost similar to the KSP scores of the other groups. ANCOVA analysis revealed that OT infusion, over and above the effects of EDA, was associated with decreased levels of several anxiety and aggression subscales. We conclude that women who received exogenous oxytocin during labor show similar positive personality traits during breastfeeding such as reduction in anxiety and aggression and increasing socialization, including maternal behavior, that have previously been ascribed to endogenous oxytocin. More importantly, these effects were not seen at 2 days postpartum in women who received epidural anesthesia during labor.

Background and Aims: The benefits of breastfeeding for infants are well known. Recently data have started to emerge showing that breastfeeding may also induce positive effects in the mother. This study aimed to investigate the pattern of maternal blood pressure before, during, and after a breastfeed 2 days postpartum. Additionally, blood pressure during the following 25-week breastfeeding period was investigated., Methods: Sixty-six primiparae with normal deliveries were consecutively recruited. Blood pressure was measured at -5, 10, 30, and 60 minutes in connection with a morning breastfeed. Thirty-three women continued to measure blood pressure before and after breastfeeding for 25 weeks., Results: Blood pressure fell significantly in response to breastfeeding 2 days after birth. The fall in systolic and diastolic blood pressure amounted to 8.8 (SD = 11.00) and 7.7 (SD = 9.3) mm Hg, respectively. During the 25-week follow-up period a significant fall of basal blood pressure (systolic, df = 3, F = 7.843, p < 0.001; diastolic, df = 3, F = 5.453, p = 0.002) was observed. The total fall in systolic and diastolic blood pressure amounted to a mean of 15 (SD = 10.4) mm Hg and 10 (SD = 9.7) mm Hg, respectively. In addition, blood pressure fell significantly in response to individual breastfeeding sessions during the entire observation period., Conclusions: In conclusion, both systolic and diastolic blood pressures fall during a breastfeeding session, and pre-breastfeeding blood pressure decreases during at least the first 6 months of a breastfeeding period in a homelike environment. This study lends further support to the health-promoting effects of breastfeeding.

The aim of the present study was to examine how different types of early interaction between dairy cows and their calves influence milking/suckling-related hormone release in the cows and sucking/bucket-drinking related hormone release in calves. Eighteen cows of the Swedish Red and White breed were studied during the first week after parturition. The cows were machine milked twice daily, and allotted to one of three treatments: [1] cow and calf were kept together and the cow was allowed to suckle the calf for 30 min about 1 h before each milking; [2] cow and calf were kept together and the calf was bucket fed twice daily; and [3] cow and calf were separated immediately after parturition, and the calf was kept in a single box and was bucket fed twice daily. Blood samples were collected around day 7 from both cows and calves. The plasma levels of oxytocin, prolactin, cortisol, gastrin, cholecystokinin (CCK), somatostatin and insulin were analysed. In the cows the levels of oxytocin, prolactin and cortisol were influenced by all three treatments, except for the level of cortisol which did not respond to suckling. The main finding was that the release of oxytocin was as significantly greater during suckling compared with machine milking. In the calves, the hormone levels were also influenced by the different milk feeding routines. The plasma concentrations of oxytocin, gastrin, CCK and insulin increased in response to milk ingestion in all treatments. However, during sucking, the increase of oxytocin was significantly greater than during bucket drinking. In addition, a strong correlation between oxytocin and insulin was found in response to sucking. Further, significant increases in prolactin and somatostatin, and a decrease in cortisol were found during sucking. The level of somatostatin also increased in response to bucket feeding when calves were kept separately. During bucket feeding, no significant correlation was found with oxytocin, but strong correlations between the gastrointestinal hormones gastrin, CCK, somatostatin and insulin were seen. Together these data suggest that different hormonal patterns were triggered in the cows by suckling and milking and in the calves by sucking and bucket drinking. This is further supported by different correlation patterns observed in the calves in response to sucking and bucket feeding. The present findings imply that management routines for cows and calves during the first week after parturition have consequences for the physiology of the animals.

In order to study personality changes in first pregnancy and lactation, two groups of women (n = 161, mean age 26.8 years) completed the self-report inventory Karolinska Scales of Personality and a scale for emotional dependency during pregnancy and 3 or 6 months after delivery. The results were within normal limits when compared with the normative values. Analysis of variance showed that the subscales Muscular Tension, Somatic Anxiety, and Monotony Avoidance diminished significantly from pregnancy and to the test periods after delivery (all p values < 0.01). Impulsiveness showed the same trend (p = 0.1). The women who had breastfed for at least 8 weeks (91%) differed significantly from those who had not. They had lower scores on the Somatic Anxiety (p = 0.006), Muscular Tension (p = 0.003), Monotony Avoidance (p = 0.039), Suspicion (p = 0.03), Social Desirability (p = 0.045) and the Impulsiveness scale (p = 0.078) and higher scores on the Socialization scale (p = 0.001). Thus, we conclude that most personality traits are stable during first pregnancy and lactation, but some significant changes occur toward a lifestyle interpreted as more relaxed and tolerant to monotony.

Feeding during milking has been shown to influence milk production, milk flow and milking time as well as the secretion of the pituitary hormones oxytocin and prolactin, and the gastrointestinal hormone somatostatin. However, it is not known whether feeding before or after milking has any effect. The aim of the present study was to investigate how the timing of feeding relative to milking influences milk production and flow, milking time and hormone secretion. The trial was carried out over 9 weeks with 24 cows at varying stages of lactation. Each treatment period lasted for 3 weeks, including one registration week. The cows were fed ad lib. and were exposed to three treatments: feeding 1.5 h before milking (FBM), feeding at exactly the same time as milking (FDM) and feeding 1.5 h after milking (FAM). The most marked treatment effect was observed during morning milking. FDM resulted in higher milk production and higher yields of protein and lactose. FAM produced a lower fat yield and a lower fat content compared with FDM, and a lower lactose content than either FBM and FDM. Milking time was longer when cows were fed during milking, but no significant effects on milk flow were found. The amount of milk collected during the first 2 min of milking was lower when cows were fed after milking. Milking-related oxytocin and somatostatin secretion was lower in FAM than in FDM. The level of prolactin was lower when cows were fed before or after than during milking. More studies are needed to elucidate whether there is a long-term effect on milk production related to the discussed milking routines.

The aim of the present study was to investigate if personality profiles reflecting anxiety and social interaction of mothers who delivered by Cesarean section (CS) or by the vaginal route (VD) differed in early postpartum and to investigate whether these personality traits were correlated with hormonal data. Seventeen women delivered by emergency CS and 20 by the vaginal route were selected for this study. The amount of milk transferred to the baby was measured. Blood samples were collected during the second breast-feeding on the second day after delivery. The samples were analysed for oxytocin and prolactin. After breastfeeding, the mothers were asked to fill in the personality inventory, Karolinska Scales of Personality (KSP). The scores were compared between the two groups and with a normative group of women. Each scale on the personality inventory was correlated with hormonal parameters. The KSP showed significant differences between the delivered mothers and the normative group in variables related to anxiety and socialization. The VD mothers deviated more than the CS mothers from the normative group. Correlations with hormonal data indicated that anxiety was inversely related with basal levels of oxytocin and prolactin in the CS mothers, whereas the pulsatility of oxytocin was related to social desirability in both groups. Social desirability and oxytocin pulsativity were also correlated with the amount of milk transferred from the mother to the baby. The correlations indicate that central oxytocin, as reflected by basal plasma levels and patterns, may be involved in behavioral adaptations to the maternal role.

The mechanisms that regulate mammary blood flow during lactation are not fully understood. In the present study laser Doppler flowmetry (LDF) was used to measure blood flow in the cutaneous microvessels of the mammary gland of lactating rats. The effects of suckling on blood flow were examined, as were those of local injection of oxytocin (0.5-5 mU) and the vasoactive peptides calcitonin gene-related peptide (CGRP; 0.1-10 pmol), vasoactive intestinal polypeptide (VIP; 0.4-20 pmol) and neuropeptide Y (NPY; 1-40 pmol). Blood flow responses to suckling varied depending on how much time had lapsed since the previous suckling. In rats with milk in the gland, suckling caused an initial increase in blood flow. In connection with milk let-down, the blood flow decreased, but was followed by a second increase. In recently suckled rats with no milk in the gland the increase in blood flow corresponded to the number of pups suckling. Oxytocin injections also had varying effects on mammary blood flow depending on how recently suckling had taken place. In non-suckled rats with milk in the gland, oxytocin injections caused a rise in blood flow that was interrupted by a fall during milk ejection. In recently suckled rats, all doses of oxytocin caused an increase in blood flow of similar magnitude. However, the effect of the higher doses had a longer duration. CGRP and VIP injections caused a dose-dependent increase in mammary blood flow regardless of when suckling last occurred. NPY injections caused a dose-dependent decrease in blood flow.

The aim of this study was to find out whether the hormonal patterns of oxytocin, prolactin and cortisol differed between women delivered by emergency section or by the vaginal route and if these patterns show any relation to the duration of breastfeeding. Seventeen mothers with emergency section (C.S.) and 20 mothers with normal vaginal deliver (V.D.) were blood sampled in connection with breastfeeding on day 2 post partum for oxytocin, prolactin and cortisol. The number of oxytocin pulses as calculated with the PULSAR program occurring during the first 10 min of the breastfeeding session varied between 0 and 5. The V.D. mothers had significantly more pulses than the C.S. ones. Furthermore the C.S. women lacked a significant rise in prolactin levels at 20-30 min after the onset of breastfeeding. Logistic regression analysis revealed mode of delivery and infant's age at first breastfeed to be the most important, independent variables showing a relation to the release pattern of oxytocin on day 2. Correlations between oxytocin pulsatility on day 2 and the duration of the exclusive breastfeeding period in the V.D. group suggest that development of an early pulsatile oxytocin pattern is of importance for breastfeeding.

It is now well established that oxytocin, as well as stimulating uterine contractions and milk ejection, promotes the development of maternal behaviour and also bonding between mother and offspring. In addition, oxytocin exerts by way of peripheral, circulating as well as by central, neurogenic mechanisms multiple physiological, endocrine and behavioural effects in connection with milk ejection and lactation. Some effects of oxytocin in the nipple and mammary gland appear to be exerted in close collaboration with peptides released from axon collaterals of somatosensory nerves originating in this region. The distribution of peptides localized to the somatosensory afferents in the nipple and mammary gland as well as possible effects by oxytocin and/or local neurogenic peptides in connection with milk ejection and lactation are reviewed in this paper.

The magnocellular oxytocin neurons within the paraventricular and supraoptic nuclei (PVN and SON) of the hypothalamus are important relays in the milk ejection reflex in lactating animals, and are activated by suckling. It has been suggested that proto-oncogene transcription factors such as Fos/Jun act as early nuclear transducers of sensory stimuli in neurons. Therefore, we have studied with immunohistochemistry Fos-related antigens (FRAs) as a marker for neuronal activity in the PVN and SON during suckling in lactating rats. In nonlactating rats, only few cells exhibiting FRAs were observed in these nuclei. Also in lactating rats subjected to continuous suckling Fos-like activity was low. In contrast, lactating rats separated from their pups for 4 h and then exposed to suckling for 1 h expressed strong Fos-like immunoreactivity, both in vasopressin and oxytocin neurons. Using in situ hybridization and immunohistochemistry we have also investigated the expression of the mRNAs for oxytocin, dynorphin, galanin and galanin message-associated peptide and of oxytocin and dynorphin in the PVN of lactating and nonlactating rats. In lactating rats, an increase in oxytocin and dynorphin and their mRNAs was observed, whereas mRNAs for galanin and galanin message-associated peptide were downregulated. With the help of immunohistochemistry and double-staining methods, a substantial coexistence between oxytocin- and dynorphin-like immunoreactivities was shown in magnocellular neurons. These results indicate that FRAs are activated in the PVN in the beginning of a suckling period, while this response cannot be seen after continuous stimulation. Furthermore, in the PVN of lactating rats, an upregulation of oxytocin and dynorphin occurs while galanin expression decreases. Finally, the coexistence between oxytocin and dynorphin is more pronounced in lactating rats and nonlactating female rats than has previously been described in male rats.

The aim of this study was to investigate the role of vagal nerve activity for the release of oxytocin, prolactin and gastrointestinal (GI) hormones during suckling as well as for the secretion of milk in lactating rats. We have therefore performed experiments on vagotomized lactating rats. The animals were decapitated and trunk blood was collected from nonsuckling rats and from suckling rats in connection with milk ejection. Oxytocin, prolactin, vasoactive intestinal polypeptide (VIP), somatostatin, insulin, glucagon and glucose levels in plasma were measured by RIA-technique. In addition, maternal weight as well as the weight of the litters were recorded 7 d after vagotomy. As expected, oxytocin and prolactin levels rose in response to suckling in sham-operated controls. In vagotomized animals the suckling-induced increase of oxytocin was blocked and prolactin levels were significantly decreased. VIP levels in plasma increased following suckling in sham-operated animals and failed to respond after vagotomy. In contrast, somatostatin levels that rose significantly in sham-operated rats were even more significantly raised in vagotomized animals. In addition, insulin but not glucagon levels were increased by suckling. The insulin response, however, persisted after vagotomy. Interestingly, suckling was followed by a lowering of blood-glucose levels in vagotomized, but not in sham-operated animals. The vagotomized rats ate as much and increased in weight as sham-operated rats during the 7 d of vagotomy. The litters of vagotomized rats, however, gained significantly less weight in comparison with control litters. In conclusion, this study shows that vagal nerve activity is of importance for the release of oxytocin, prolactin, vasoactive intestinal polypeptide and somatostatin during suckling.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of 24 h of fasting and refeeding on the release of oxytocin, prolactin, insulin and LH in three lactating sows were investigated. The sows were starved, but supplied with water ad libitum, from 09.00 h on day 27 of lactation until 15.00 h on day 28 of lactation, when they were refed. Blood samples were collected continuously, using an automatic collection system, at a rate of 1 ml min-1 from 09.00 to 21.00 h on day 28 (P1 = 6 h period after the 24 h fast, P2 = 6 h period after refeeding). For both P1 and P2 the mean number of nursings was 7.0 +/- 1.0. Plasma insulin and glucose decreased to very low levels during fasting and increased (P < 0.001) after refeeding (insulin, 2.5 +/- 0.7 vs. 28.9 +/- 0.7 mU l-1; glucose, 2.6 +/- 0.3 vs. 6.4 +/- 0.3 mmol l-1). Following fasting, levels of prolactin were low (2.8 +/- 0.1 micrograms l-1), and sucking did not induce significant release of prolactin. However, prolactin increased rapidly after refeeding (5.4 +/- 0.1 micrograms l-1, P < 0.001). Neither the 24 h fast nor refeeding had a marked effect on basal levels of oxytocin, the percentage of sucklings with an oxytocin peak or the size of oxytocin peak. LH release (average and basal levels and number of pulses/6 h) during fasting was similar to that measured after refeeding. Plasma CCK increased significantly after feeding. The results indicate that the release of prolactin is also regulated by feed intake.(ABSTRACT TRUNCATED AT 250 WORDS)

To describe the patterns of release of oxytocin, prolactin, insulin and LH in relation to suckling and to investigate relationships between them, blood was collected continuously from four sows at a rate of 1 ml per min for 12 h (0900-2100 h) on day 10 (D10) and day 20 (D20) of lactation. The 12-h period was divided into four smaller periods: P1 (0900-1200 h), P2 (1200-1500 h), P3 (1500-1800 h) and P4 (1800-2100 h). The number of nursings occurring during a 12-h period tended to decrease between D10 (17.3 +/- 0.3) and D20 (16.0 +/- 0.3). About 40-50% of all sucklings induced a significant rise in plasma oxytocin, while prolactin gradually increased following each suckling. Decrease in the levels of oxytocin (14.1 +/- 0.4 vs 7.1 +/- 0.4 pmol/l, P < 0.001), prolactin (12.9 +/- 0.3 vs 7.9 +/- 0.1 micrograms/l, P < 0.001) and insulin (24.8 +/- 1.7 vs 14.4 +/- 1.7 mU/l, P < 0.001) were observed between D10 and D20. Average and basal levels of LH and the number of LH pulses increased (P < 0.01) between D10 and D20. A negative correlation between number of sucklings and number of LH pulses was demonstrated on D20 (r = -0.59, P = 0.07). There was a positive correlation between levels of LH and oxytocin on D10 (r = 0.54, P = 0.001) and between prolactin and insulin levels on D20 (r = 0.34, P = 0.05).

After 5 weeks of lactation 14 standard-fed primiparous sows were divided into a low weight-loss group (L-gr, loss < 25 kg, n = 7) and a high weight-loss group (H-gr, loss > or = 25 kg, n = 7). Body weights of the sows and their litters were recorded on days 2, 7, 14, 21, 28 and 35 of lactation. Blood samples were collected before the morning feeding on each weighing day. Samples were analysed to determine concentrations of insulin, glucagon, glucose, triglycerides, non-esterified fatty acids (NEFA), urea and creatinine. The H-gr sows lost weight throughout lactation, whereas the L-gr sows gained weight during the last week. Weight loss was higher in the H-gr than in the L-gr during weeks 2, 3 and 5 of lactation. Litter size and litter weight gain were higher in the H-gr than in the L-gr. Significant changes in levels of insulin, glucagon, glucose, triglycerides and creatinine were observed over lactation. No significant differences in concentrations of any of the parameters were found between the two groups, except for insulin and cholesterol which were higher in the L-gr. Catabolism of adipose tissue and muscle protein was observed in both groups during the first week of lactation. This catabolic state was more pronounced and tended to be prolonged in the H-gr. Concentrations of all parameters seemed to be stable in both groups during the last two weeks of lactation.

There is a great variation in body weight loss during lactation among primiparous sows fed a standard diet that is adjusted based on the number of piglets nursed and the maintenance requirements. Energy and protein catabolism is more pronounced during the first 1 to 3 weeks of lactation and sows with low weight loss recover earlier from their negative energy balance during lactation than sows with high weight loss. Using continuous blood collection a decrease in plasma levels of oxytocin, prolactin, and insulin, and an increase in plasma levels and no of LH pulses during lactation were demonstrated. Prolactin levels gradually increased in response to each suckling while only 40-50% of recorded sucklings induced a significant rise in plasma oxytocin. Following a 24-h fast during lactation, levels of prolactin were very low but increased rapidly after refeeding. Even plasma levels of insulin and glucose decreased to very low levels during fasting, but the release of LH was similar before and after refeeding. Weaning resulted in decrease in plasma levels of prolactin and increase in plasma levels and no. of LH pulses. Plasma levels of cortisol showed a diurnal pattern of change which disappeared on the day of weaning. In response to weaning plasma levels of glucagon and gastrin decreased, whereas insulin and somatostatin increased. At weaning sows with low weight loss during lactation had higher plasma insulin and lower plasma cortisol levels than sows with high weight loss, but no differences in levels or no. of LH pulses were observed between the two groups of sows.

Twelve conventionally fed primiparous sows with a similar number of piglets were divided into 3 groups (n = 4) according to their body weight loss after a 5-week lactation as follows: H-gr (loss greater than 25 kg), M-gr (loss 11-25 kg) and L-gr (loss less than or equal to 10 kg). Blood samples were collected at 9, 12, 15, 18 and 21 h, from 4 days before weaning until 3 days afterwards, and every 15 min for 6 h on the day before and the day after weaning. The group of sows with higher weight loss during lactation tended to have a higher farrowing weight and higher pre-weaning plasma prolactin levels. At weaning, the L-gr sows had higher plasma insulin and lower plasma cortisol concentrations, especially when compared with H-gr sows. Among the ten sows that showed oestrus within 10 days of weaning, no between-group differences were found in the length of the interval from weaning to oestrus. No significant differences between groups were observed in levels of oestradiol-17 beta and LH. The higher level of insulin in L-gr sows might relate to the higher number of corpora lutea observed in this group.

Plasma concentrations of oxytocin, prolactin, and cortisol were compared in five Swedish Red and White cows milked by hand versus machine. Cows were divided into two groups. One group was hand-milked; the other group was machine-milked. Treatments were switched every other day. The experiment was carried out for 6 d. Blood samples were taken prior to, during, and after milking and were assayed for hormones. More oxytocin and prolactin were released in hand-milked cows. There were no significant diurnal differences between the total amount of oxytocin released for the different treatments, but prolactin tended to be higher during hand-milking in the evening than in the morning milking. Cortisol concentrations were greater during hand-milking than during machine-milking. There were no significant treatment differences with regard to the total amount of cortisol released. During morning milking, cortisol concentrations were higher during hand-milking than during machine-milking. Our data show that hand-milking results in a pronounced and prolonged release of oxytocin and prolactin.

The pituitary hormones prolactin and oxytocin play important roles in the production and ejection of milk. In addition, some gastrointestinal peptides are released in response to suckling. During suckling, the piglets massage the udder of the sow both before and after let-down and the duration of suckling is correlated to the amount of milk produced by the sow. The aim of this study was to investigate whether there is a quantitative relation between the release of prolactin, gastrin, somatostatin, insulin, glucagon and vasoactive intestinal polypeptide (VIP) and the amount of stimulation of the sow's teats by the piglets. Repeated blood samples were drawn from three Swedish Landrace sows during three consecutive nursings by each sow on days 1, 3, 7 and 14 after parturition. The duration of massage by the piglets was noted, as was the number of piglets massaging. Hormone levels were quantified by radioimmunoassay. The release of prolactin, somatostatin, insulin, glucagon and VIP but not of gastrin were found to be significantly related to the amount of teat massage performed by the piglets during the first 2 weeks of lactation. The release was related to the duration of piglet massage or to the combined effect of duration and the number of piglets massaging but not to the number of piglets massaging per se. The basal level of prolactin was found to decrease during this time.

The objective of the study was to record how somatostatin levels in plasma are altered in response to breast-feeding during the lactation period and to relate somatostatin levels to the success of the lactational performance and to smoking habits. Fifty-two women were investigated 4 days post partum and 3-4 months later. Blood samples were collected and the levels of somatostatin-like immunoreactivity (below referred to as SLI) were measured with radioimmunoassay. The periods of exclusive breast-feeding and of mixed feeding were assessed as well as the milk yield. Smoking habits were noted. SLI levels were found to be significantly lower on day 4 after delivery, compared to 3-4 months later. Also the type of response to breast-feeding was different. Thus, a significant fall of SLI was seen during breast-feeding at the maternity unit, but not 3-4 months later. Smoking women breast-fed fully for a significantly shorter time than nonsmokers and had significantly higher SLI levels at onset of breast-feeding day 4 post partum. Whether the high somatostatin levels recorded in connection with breast-feeding in smokers are related to the shorter period of breast-feeding seen in this group remains to be established. In addition, the highest levels of somatostatin were seen the day after the very last breast-feeding and a possible role for somatostatin in the weaning process should be explored.

Plasma levels of cholecystokinin were increased in response to suckling in lactating rats. Efferent electrical stimulation of the vagal nerve increased the concentration of cholecystokinin in plasma. Abdominal vagotomy was found to block the suckling-induced release of cholecystokinin. Furthermore, lesions to the lateral midbrain, which disrupt the oxytocin-mediated milk-ejection reflex, were shown to inhibit the increase in plasma cholecystokinin. These results show that the suckling-induced release of cholecystokinin into plasma in lactating rats is dependent upon the vagal nerves and the central neural structures concerned with milk let-down.

The aim of the present study was to measure plasma levels of vasoactive intestinal polypeptide (VIP) and oxytocin following suckling, electrical stimulation of the mammary nerve and oxytocin infusion in lactating rats. Trunk blood was collected by decapitation after 5 and 20 min of suckling in conscious lactating rats. Repeated blood samples were drawn from the carotid artery in anesthetized rats, in connection with suckling, oxytocin infusion (0.22 nmol/l/kg/h) and electrical stimulation of the mammary nerve (5 V, 5 Hz, 2 ms). VIP and oxytocin levels were measured by radioimmunoassay. In conscious rats, VIP levels rose significantly from 18 +/- 5 to 102 +/- 30 pM after 5 min of suckling and to 123 +/- 25 pM after 20 min of suckling when milk ejection occurred. Oxytocin levels rose significantly from 90 +/- 24 to 269 +/- 45 pM during milk ejection. Suckling, oxytocin infusion and mammary nerve stimulation in anesthetized rats raised VIP levels significantly from 13 +/- 2, 18 +/- 5 and 10 +/- 2 to 43 +/- 8, 45 +/- 16 and 53 +/- 22 pM, respectively, whereas oxytocin levels rose from 111 +/- 34 to 294 +/- 66 pM after 20 min of suckling and to a peak value of 500 +/- 70 pM after oxytocin infusion. This study shows that VIP is elevated in plasma in lactating rats when the pups are suckling. The results showing that VIP levels rise following mammary nerve stimulation and oxytocin infusions indicate that both neurogenic and hormonal mechanisms can contribute to the regulation of VIP levels in plasma.

The aim of the present study was to examine suckling-related plasma levels of oxytocin and prolactin in early and established lactation and to correlate hormone profiles to success of lactation performance. Fifty-five primiparous women participated in the study. From each, 18 blood samples were drawn in connection with breast-feeding on day 4 post partum and after 3-4 months. Oxytocin and prolactin levels were determined with radio-immunoassay. Basal levels of both hormones were significantly higher 4 days post partum than 3-4 months later and after weaning. Basal prolactin levels fell significantly within 24 h of weaning. Oxytocin and prolactin levels rose in response to breast-feeding--an effect which persisted during the lactation period. The suckling-induced release of prolactin--but not that of oxytocin--was related to basal hormone levels. Basal as well as stimulated oxytocin levels obtained 4 days and 3-4 months post partum correlated significantly, indicating that each woman has an individual, characteristic level of this hormone. Milk yield did not correlate with oxytocin or prolactin levels, but prolactin levels recorded 3-4 months post partum did correlate with the remaining period of breast-feeding. In addition, mothers who breast-fed exclusively 3-4 months post partum had significantly higher oxytocin and prolactin levels than those who gave supplementary feed. There was a significant correlation between oxytocin levels at 4 days and birth weight of the infant.

The concentration of gastrin and insulin was determined in peripheral blood of 4 lactating dogs during suckling. Suckling induced an immediate rise of gastrin and insulin levels, twofold and threefold, respectively. A peak was reached at approximately 5 min after suckling was started, and basal levels were reached again within 15-20 min. The increase in gastrin and insulin levels coincided with the let-down reflex, i.e. it occurred when the puppies started to obtain milk from their mothers. Sham feeding and feeding induce a vagally mediated increase of gastrin and insulin release in dogs. We suggest that the changes in the gastrin and insulin levels observed by us in the lactating dogs, reflect a similar vagal activation induced by suckling. Possible effects of the suckling induced release of gastrin and insulin on milk ejection and secretion are discussed.

The aim of the present investigation was to study changes in insulin, glucagon and plasma glucose levels in response to suckling in lactating dogs. Blood samples were drawn from a peripheral vein during suckling in weeks 1 and 3 of lactation in 10 lactating beagles. Insulin- and glucagon-like immunoreactivity (below referred to as insulin and glucagon) were determined by radio-immunoassay, and plasma glucose levels by the glucose oxidase method. Insulin and glucagon levels rose following onset of suckling. However, only the rises recorded in week 3 of lactation were statistically significant. Plasma glucose levels were not affected. The mechanism by which suckling influences the levels of insulin and glucagon is not known. However, the release of both hormones is under vagal control and it is possible that touching of the teats reflexly elicits a vagally mediated release of these hormones. Alternatively, since oxytocin stimulates the secretion of insulin and glucagon, the effects might be secondary to the oxytocin released by suckling. The physiological function of the suckling-related release of insulin may be to stimulate milk production. Furthermore, since glucagon is also released, each suckling period may be accompanied by a transfer of glucose to the mammary glands from other maternal stores.

In monogastric animals, suckling influences the secretion of gastrointestinal hormones during lactation. The aim of the present study was to investigate whether similar effects are induced by milking in cows. Experiments were performed on four cows in midlactation. Blood samples were drawn from a chronic jugular vein catheter and gastrin, and somatostatin were determined by radioimmunoassay. Milking and feeding increased plasma gastrin. Somatostatin increased at morning milking and at feeding, but it decreased at evening milking. Atropine injected subcutaneously 30 min before milking increased resting concentrations of gastrin but decreased resting concentrations of somatostatin. Feeding-induced release of gastrin remained but the milking-induced release disappeared. The milking- and feeding-induced effect on somatostatin became more marked. We suggest that milking influences gastrin and somatostatin via activation of the vagal nerves. The gastrin release caused by milking may be mediated via a cholinergic mechanism, whereas the atropine resistant effect on gastrin caused by feeding and on somatostatin caused by both milking and feeding suggest that a noncholinergic, perhaps peptidergic, transmitter may be involved.

Plasma levels of gastrinlike, somatostatinlike, and cholecystokininlike immunoreactivity were determined by radioimmunoassay in peripheral blood from 11 beagles during pregnancy and in response to suckling during lactation. Cholecystokinin was determined in pooled and in individual plasma samples after separation of cholecystokinin and gastrin by high-performance liquid chromatography. Gastrin and somatostatin levels were significantly increased during the 8-wk-long dog pregnancy; peak values were recorded in week 7 and week 4, respectively. The cholecystokinin level rose and peaked at week 3, and remained elevated. In response to suckling, maternal gastrin levels rose significantly when tested in week 1 and 3 of lactation. Somatostatin levels did not respond significantly to suckling, but basal levels were elevated in week 1 compared to week 3 of lactation. Cholecystokinin rose in response to suckling both in week 1 and 3 of lactation. We suggest that the increased levels of gastrointestinal hormones during pregnancy and lactation may serve to increase digestive and anabolic capacity.

The levels of growth hormone, vasopressin, prolactin, calcitonin, gastrin, insulin, epinephrine, norepinephrine and dopamine were measured in six lactating women during breast feeding. Prolactin levels increased in response to suckling as expected. In addition, insulin levels rose two-fold. No consistent changes were observed in the levels of the other hormones. It is suggested that the suckling related insulin release is either secondary to a reflexly induced activation of the vagal nerves or to the increased circulating levels of prolactin. Furthermore, it is suggested that the insulin release in response to suckling participates in the stimulation of milk production.

Blood samples were collected in peripheral venous blood of seven lactating sows, when their piglets were suckling. In four of the experiments samples were also taken when the sows were fed a meal. Gastrin, insulin, somatostatin and VIP levels were measured by radioimmunoassay. Insulin levels increased by approximately 100% for about 10 min in response to suckling, in some experiments even before the suckling occurred, i.e. when the sows saw, heard and smelled their piglets. In four of the sows suckling caused a biphasic twofold increase in gastrin levels - one immediate peak which lasted for a few min and a second peak of longer duration (about 30-60 min), whereas gastrin levels remained unchanged in three animals. Somatostatin levels usually reflected gastrin levels in a reciprocal way. Thus, a biphasic decrease of somatostatin levels occurred in the high gastrin responders. In contrast, somatostatin levels increased in the experiments, in which gastrin levels did not change. Immediate and short-lasting (a few minutes long) increases of VIP levels were also induced by suckling. Large litters and long suckling periods appeared to be related to greater changes of the levels of all the peptides measured. Feeding influenced insulin, gastrin and somatostatin levels in the same way as did suckling from both a qualitative and a quantitative point of view. In contrast, VIP levels were not increased by feeding. The possible functional effects of the suckling-induced release of gastrointestinal hormones and possible mechanisms of their release are discussed.

This paper contains a discussion and presentation of evidence concerning vagal control of the release of some gastrointestinal peptides, the secretion of gastrin and somatostatin in particular. Some aspects of the regulation of vasoactive intestinal peptide (VIP), substance P, bombesin and insulin release by the vagus nerve are also reviewed. Data were obtained not only by electrical stimulation of the vagi but also by monitoring effects of feeding and suckling. The involvement of vagal afferents, transmitters, neurohormones in release of other hormones and humorally carried activators and inhibitors is analyzed. Particular attention is paid to the chains of reactions induced by physiological stimuli: feeding and suckling.

Maternal gastrin and somatostatin levels have been shown to be influenced during suckling in dogs and pigs. The present study was performed to investigate whether the levels of gastrin and somatostatin are influenced by breast feeding in lactating women. Repeated blood samples were drawn in connection with nursing in 15 females and plasma levels of gastrin and somatostatin were measured by radioimmunoassay. Gastrin levels rose significantly (P = 0.01) within two minutes after onset of suckling. Somatostatin levels either decreased or increased as an effect of breast feeding. The direction of the change was correlated to the pre-suckling somatostatin levels (P less than 0.01). The somatostatin level recorded 60 min after start of breast feeding was significantly lower than basal levels (P less than 0.01) indicating a long-term inhibitory effect on somatostatin secretion. The suckling-induced effect on somatostatin levels was correlated with the amount of milk ejected (Rs - 0.52, P less than 0.05). The mechanism by which suckling influences circulating gastrin and somatostatin levels is unknown, but we suggest that suckling leads to a reflex activation of the vagal nerves, which influence the release of these hormones from the stomach. The size of the gastrointestinal tract is increased during pregnancy and lactation, illustrating that the maternal digestive capacity is adapted to the high demand for energy intake occurring during lactation. We speculate that the suckling stimulus enhances gastric functions by influencing the release of gastrin and somatostatin, which stimulate and inhibit gastric functions and growth, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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 aim of the present study was to investigate how oxytocin, prolactin and somatostatin during nursings relate to maternal characteristics of sows. Undisturbed nursing behaviour and sow–piglet nasal contacts of 21 lactating sows were recorded on day 13 of lactation, and hormonal status was assessed during three successful nursings on day 14. Piglet and litter growth (days 8–15), sow weight loss (days 1–15) and catabolic state (measured as NEFA on day 7), as well as number of successful nursings on day 13 were used as measures of mobilisation of sow body resources. Nasal contacts and sow behaviour facilitating udder massage were used as measures of positive piglet-directed behaviours. Concentrations of oxytocin were higher, those of prolactin lower and those of somatostatin similar during nursings compared to samples taken 15 min after nursing. Oxytocin peaked during most nursings and prolactin increased gradually after nursings. Non-nursing oxytocin values were positively correlated with the proportion of sow-terminated nursings but not with other measures of piglet-directed behaviour. Non-nursing oxytocin concentrations were positively correlated with piglet weight gain and concentrations of oxytocin during nursings were correlated with NEFA and sow weight loss. Our results indicate that oxytocin might have more than merely an all-or-nothing function in triggering milk ejection. Oxytocin seems to be quantitatively related to efficiency of milk production, although the present study design does not allow for speculation on causal relationships. [Copyright &y& Elsevier]

Twenty-one sows were studied to investigate if lactating sow metabolism relates to behaviour and piglet performance. Blood samples from days 7 and 21 were analysed for NEFA, urea, glucose, insulin, somatostatin and prolactin. The behaviour parameters obtained from 24-h video recordings (days 6 and 20) included: successful and unsuccessful nursing frequency, total nursing duration, percentage and average duration of nursings terminated by the sow, and percentage of observations of sow sternal recumbency. Weight loss and catabolic state of the sows increased from day 7 to day 21; NEFA and post-feeding urea were higher and pre-feeding glucose and insulin lower on day 21. NEFA correlated strongly with sow weight loss during week 1. Prolactin correlated positively with the amount of udder stimulation in week 1 and insulin positively (week 1) or negatively (week 3) with a high incidence of massage-avoiding behaviour. High sow weight loss and NEFA during week 1 were associated with low piglet mortality. High piglet growth correlated positively with sow weight loss during week 3. We conclude that (i) catabolism increases during the first 3 weeks of lactation, (ii) there is some association between sow metabolism and behaviour and (iii) the ability of a sow to turn catabolic soon after parturition decreases piglet mortality risk. [Copyright &y& Elsevier]