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PubMed1998

Expression and immunolocalization of the oxytocin receptor in human lactating and non-lactating mammary glands.

The milk ejection reflex is mediated by the release of pituitary oxytocin and its interaction with specific receptors within the mammary gland. Although up-regulation of the oxytocin receptor during lactation has been shown for the rat mammary gland by ligand binding assay, investigation of the receptor expression in human breast at the molecular level has not yet been carried out in detail. Here we report the expression and immunolocalization of the oxytocin receptor in the human breast. It appears that the expression level of the receptor-specific mRNA is not significantly elevated during lactation and the protein remains at a relatively low level. However, this lack of increase may be only a dilution effect because of the high level of milk protein expression. Immunohistochemistry and immunoelectron microscopy using three anti-oxytocin receptor antibodies raised against different epitopes of the receptor indicated the presence of receptor immunoreactivity only to a very limited extent in the myoepithelial cells; more specific expression appeared to occur in the ductal/glandular epithelium in both the non-lactating as well as lactating breast. This finding was also confirmed in a New World monkey, the common marmoset (Callithrix jacchus). These results suggest that, at least for human and marmoset, in addition to--or even instead of--myoid cells, the ductal/glandular epithelium is also a target for oxytocin action, not only during lactation but also in the non-lactating breast. Thus, there may be other physiological effects of oxytocin besides direct myoid cell contraction in the breast.

Adult↗
PubMed1984

One cycle of reproduction consisting of pregnancy, lactation or no lactation, and recovery: effects on carcass composition in ad libitum-fed and food-restricted rats.

Groups of nine ad libitum-fed and food-restricted Osborne-Mendel rats weighing between 200 and 220 g at mating were killed on day 21 of pregnancy, day 21 of lactation and day 21 of the postweaning recovery period. Restricted rats were fed 70% of the mean daily ad libitum intake. Groups of nine ad libitum-fed animals, not permitted to suckle their young, were killed on day 21 postpartum and day 21 of the recovery period. Groups of nine nonpregnant rats of comparable initial body weight were killed at appropriate times to serve as advancing age and growth controls. Changes in carcass composition were determined in each group at the end of the pregnancy, lactation and recovery periods. Carcass fat was elevated in the nonlactating group on day 21 postpartum compared to lactating animals and nonpregnant controls. At the end of the study, carcass weight was highest in the ad libitum-fed lactating group. This was due to increased carcass water and not to increased carcass fat. In fact, carcass fat was significantly reduced in the ad libitum-fed lactating group compared to nonpregnant controls. During the recovery period, the absolute increase in carcass fat was greater in the restricted group than in the ad libitum-fed group. The data indicate that 1) pregnancy followed by no lactation results in an increase in carcass fat content and 2) the postweaning recovery period is marked by a tendency to increase carcass fat even in food-restricted rats.

Animals↗
PubMed1995

Progesterone, estradiol, and prolactin involvement in lactation, including lactation following a postpartum mating, in the Djungarian hamster (Phodopus campbelli).

The endocrinology of lactation in the Djungarian hamster was investigated through once-daily sampling of females on Days 0, 3, 6, 9, 12, 15, and 18 postpartum. Serum prolactin (PRL) was elevated during early lactation but declined with time. Serum progesterone (P4) levels were uniformly low, and serum estradiol (E2) levels increased after Day 9. New CL were formed after the postpartum ovulation and persisted throughout lactation. During the first 9 days, the CL had the high P4 content typical of pregnancy. After Day 9, each individual CL decreased in P4 content and increased in E2 content. As evidenced by the reappearance of large antral follicles, lactating females probably returned to ovulatory cycles at about that time. The Djungarian hamster has a postpartum estrus and is capable of delivering a second litter without a diapause (18 days), although the majority of second litters are delayed. Mating during the postpartum estrus had no detected effect on growth or survival of the first litter. Second pregnancies were developmentally delayed by 3 to 7 days. P4 was effectively absent from serum for the first 12 days after mating. Although CL contained high levels of P4, the CL remained small and poorly vascularized. Mated females did not have higher serum P4 levels than nonpregnant, lactating females until Day 18. In response to the competing demands of lactation and concurrent gestation, the endocrine conditions associated with pregnancy were the most affected.

Animals↗
PubMed1998

Interleukin 1alpha stimulates lactate dehydrogenase A expression and lactate production in cultured porcine sertoli cells.

By using cultured porcine Sertoli cells as a model, the action of interleukin 1alpha (IL-1alpha) on lactate production and the site of this action were studied. IL-1alpha stimulated Sertoli cell lactate production in a time- and dose-dependent manner (with a half-maximal effect [ED50] of 6 pM). Two major sites involved in IL-1alpha action were identified. First, IL-1alpha was shown to increase the uptake of glucose substrate in a time- and dose-dependent manner. The maximal effect, with an ED50 of 10 pM, was observed after 24 h of treatment. Second, IL-1alpha increased the activity of the lactate dehydrogenase (LDH) A4 isoform, which is involved in the conversion of pyruvate into lactate. This increase in LDH A4 activity was detected at 12 h and was maximal, with an ED50 of 9 pM, after 24-h treatment with IL-1alpha. The increase was related to an increase in LDH A4 expression, since IL-1alpha stimulated LDH A mRNA (size: 1.5 kilobases, evidenced through Northern blotting analysis) in a dose- and time-dependent manner. Assuming that IL-1alpha might be produced in the seminiferous tubules by both Sertoli and germ cells, which utilize lactate for their energy metabolism, we suggest that these results together show 1) that the cytokine may represent a signal in the metabolic cooperation existing between Sertoli cells and germ cells, and 2) that a redistribution of LDH isoforms in favor of LDH A4 under IL-1alpha control is a key mechanism(s) in such cooperation used by germ cells to enhance lactate production in Sertoli cells.

Animals↗
PubMed1975

Lactate, pyruvate, and excess lactate during ether and halothane anesthesia in infants and children.

Arterial blood lactate, pyruvate, and excess lactate (XL) were measured and calculated in 33 patients aged 7 months to 6 years over a period of 2 hours during repair of harelip or cleft palate. When the anesthetic was diethyl ether, lactate and pyruvate levels rose significantly 60 minutes after induction of anesthesia but did not rise thereafter. Excess lactate appeared 60 minutes after induction of ether anesthesia, but it, too, showed no further increase. When the anesthetic was halothane there was no significant change in lactate, pyruvate, or XL. Changes with ether were not age-related, nor could they be correlated with changes in rectal or skin temperature. The responses of lactate, pyruvate and XL to ether anesthesia in the present study were not significantly different from those found by others in adults.

Age Factors↗
PubMed2002

The lactate minimum test for cycling: estimation of the maximal lactate steady state.

This study evaluated the reliability and validity of the lactate minimum test (LMT), an incremental test given after lactic acidosis was induced by sprint exercise. This test is purported to accurately estimate the intensity of exercise at which the transport of lactate into and out of the blood is in equilibrium (maximal lactate steady state or MLSS) and should be a good predictor of endurance performance. Fourteen athletes (mean age 27.2 +/- 3.7 yrs) completed the following on Kreitler rollers: (a) two 20-km time-trials (35.1 +/- 3.3 and 35.7 +/- 3.5 km.hr-1, p < .05); (b) two LMTs yielding lactate minimum speeds (LMS) of 33.6 +/- 3.4 and 33.4 +/- 3.1 km.hr-1 (p > 0.6); and (c) four constant intensity rides, at speeds bracketing the LMS. At 33.5 +/- 3.1 km.hr-1 plasma lactate concentration decreased 0.4 +/- 1.6 mM from 10 to 30 min. Plasma lactate increased 1.6 +/- 0.7 mM while riding 0.9 +/- 0.9 km.hr-1 faster. The LMT is a reliable (r2 = 0.904) and valid method to predict MLSS and a good predictor of endurance performance (LMT vs. 20-km time-trial, r2 = 0.86).

Adult↗
PubMed1987

Qualitative measurements of the entry of L-lactate into single surface fibres of frog skeletal muscle using a lactate-sensitive microelectrode.

The present results demonstrate the sensitivity of the Corning chloride liquid ion exchanger 477913 to L-lactate. Microelectrodes filled with this exchanger showed responses to changes in L-lactate concentration in chloride-free solutions. In these experiments L-lactate replaced gluconate in equimolar amounts. Microelectrodes filled with this exchanger were used to qualitatively detect changes in intracellular anion in chloride-depleted frog sartorius muscle fibres during exposure to extracellular concentrations of L-lactate. The increase in intracellular anion concentration is consistent with the movement of L-lactate into the cell. This microelectrode enables one to qualitatively monitor changes in intracellular L-lactate in chloride-free experiments without incorporating selectivity coefficients.

Animals↗
PubMed1997

Tumor necrosis factor-alpha-stimulated lactate production is linked to lactate dehydrogenase A expression and activity increase in porcine cultured Sertoli cells.

By using, as a model, cultured testicular immature Sertoli cells, the action of tumor necrosis factor-alpha (TNF alpha) and the site of action of the cytokine on lactate production were studied. TNF alpha stimulated in a time- and dose-dependent manner (with an ED50 of 0.1 nM) Sertoli cell lactate production. Two major sites involved in TNF alpha action were identified. Firstly, TNF alpha was shown to increase the uptake of glucose substrate in a time- and dose-dependent manner. The maximal effect was observed after 24 h of treatment, with an ED50 of 0.1 nM. Secondly, TNF alpha increased the activity of lactate dehydrogenase (LDH) A isoform, which is involved in the conversion of pyruvate into lactate. This increase in LDH-A activity was detected at 12 h and was maximal after 24 h of treatment with TNF alpha. The stimulatory effect of the cytokine on the LDH-A isoform was observed with an ED50 of 0.05 nM. Such an increase in LDH-A activity was related to an increase in LDH-A expression, because TNF alpha stimulated LDH-A messenger RNA (size, 1.5 kilobases, determined by Northern blotting analysis). Together, assuming that in the seminiferous tubules, TNF alpha is produced by spermatids that use lactate for their energetic metabolism, we suggest that the cytokine may potentially represent a signal used by germ cells to enhance lactate production in Sertoli cells through, at least, a redistribution of LDH isoforms in favor of LDH-A.

Animals↗
PubMed1987

Suppression of luteinizing hormone secretion is removed at late lactation in ovariectomized lactating rats.

The effect of the suckling stimulus on pulsatile luteinizing hormone (LH) secretion in mid- and late lactation (days 10 and 20 of lactation) in rats was examined. Pulsatile LH secretion was strongly suppressed on either day 10 or 20 of lactation in intact rats in which the baselines of LH secretion were kept very low. In ovariectomized rats the baseline was kept as low as was observed in intact rats on day 10 of lactation, and pulsatile LH secretion was observed in 3 out of 6 rats. On day 20 the baseline secretion increased and pulsatile LH secretion was observed in 5 out of 6 rats, and the baseline for each rat showed various levels. These results clearly indicate that the pulsatile LH secretion was strongly suppressed until ovulation occurred on day 18-23 of lactation in intact rats and suggest that suppression of pulsatile LH secretion by the suckling stimulus at the hypothalamo-pituitary level is removed in late lactation and the time of the removal varies from animal to animal.

Animals↗
PubMed1983

Structure and function of L-lactate dehydrogenases from thermophilic and mesophilic bacteria. II) The primary structure of thermophilic lactate dehydrogenase from Bacillus stearothermophilus. Cyanogen bromide fragments and partial sequence.

The polypeptide chain of thermophilic lactate dehydrogenase from Bacillus stearothermophilus was split with cyanogen bromide. The 6 cyanogen bromide fragments were then separated and isolated by gel filtration (Bio-Gel P 10, Sephadex G-75) and ionic exchange chromatography (Biorex 70), respectively. Peptide fractionation was performed in 50% formic acid. Fragment yield varied between 30 and 75%. About 75% of the amino-acid sequence was determined by the automatic N-terminal sequence analysis (amino-acid sequenator) of the cyanogen bromide fragments (41-57 cycles degraded) and N-terminal region of lactate dehydrogenase (74 cycles degraded). Typical structure differences between thermophilic and mesophilic lactate dehydrogenases are already indicated by the comparison of the amino-acid composition of the thermophilic enzyme from B. stearothermophilus with the mesophilic from bacilli and higher organisms. Comparison of the N-terminal sequence reveals that sequence homology is higher (83-98%) between the thermophilic lactate dehydrogenases from B. stearothermophilus, B. caldotenax and B. caldolyticus than between the mesophilic lactate dehydrogenases of bacilli among each other or between thermophilic and mesophilic lactate dehydrogenases (about 60%). High temperature would appear to limit variation in structure.

Amino Acid Sequence↗
PubMed1983

Structure and function of L-lactate dehydrogenases from thermophilic and mesophilic bacteria. III) The primary structure of thermophilic lactate dehydrogenase from Bacillus stearothermophilus. Hydroxylamine-, o-iodosobenzoic acid- and tryptic-fragments. The complete amino-acid sequence.

Based on the partial sequence of the cyanogen bromide fragments [Tratschin, J.D., Wirz, B., Frank, G. and Zuber, H. (1983) Hoppe-Seyler's Z. Physiol. Chem. 364, 879-892], the amino-acid sequence of thermophilic lactate dehydrogenase from B. stearothermophilus was completed by the preparation and sequencing (sequenator, carboxypeptidase A and Y) of further overlapping fragments. Suitable peptide fragments were obtained by lactate dehydrogenase cleavage with hydroxylamine, o-iodosobenzoic acid and trypsin. The polypeptide chain of thermophilic lactate dehydrogenase from B. stearothermophilus consists of 317 amino-acid residues. While sequence homology with mesophilic lactate dehydrogenase of higher organisms reaches 35%, it is substantially higher with this mesophilic enzyme of bacillae (greater than 60%, B. megaterium, B. subtilis). The secondary structure elements and amino-acid residues of the active site of thermophilic lactate dehydrogenase deducted from primary structure data were compared with those from the mesophilic enzyme, the same was done for the internal sequence homology at the nucleotide-binding units. A comparative structure analysis (matrix system) based on the primary structure data of thermophilic enzyme should provide insight into the characteristic structure differences between thermophilic and mesophilic lactate dehydrogenase.

Amino Acid Sequence↗
PubMed2005

The effect of long-term storage on measured plasma lactate concentrations and prospective lactate results from a multicenter trial of antiretroviral therapy.

Plasma lactate measurements are typically performed in real time, limiting their usefulness in multicenter or longitudinal studies. To determine the stability of lactate specimens, blood was drawn in sodium fluoride/potassium oxalate tubes from 13 volunteers before and after 5 min of handgrip exercise to intentionally increase lactate concentrations. Plasma was stored at -70 degrees C. Aliquots were assayed in real time and after 1, 3, 6, 9, 12, 18, and 24 months. Real-time lactate concentrations measured at baseline ranged from 0.52 to 2.23 mmol/L before and from 2.91 to 11.04 mmol/L after handgrip exercise. Using a linear mixed model, the estimated change from baseline at month 24 was 1.67% (95% confidence interval, -0.70% to 4.03%) for pre-exercise samples and 0.39% (95% CI, -1.13% to 1.91%) for post-exercise samples. Stored serial specimens from 232 HIV-infected subjects in a multicenter trial of antiretroviral therapy were also assayed centrally. Among those, median plasma lactate increased from baseline to 64 weeks by 0.4 mmol/L with zidovudine+lamivudine treatment and by 0.6 mmol/L with didanosine+stavudine (each p<0.001 from baseline; p=0.04 for difference between groups over time). When performed as in this study, frozen storage with central batch lactate analysis is appropriate for prospectively collected samples in multicenter trials.

Acidosis, Lactic↗
PubMed1977

Influence of LH/FSH releasing hormone (LRH) on the basal secretion of gonadotrophins in relation to plasma levels of oestradiol, progesterone and prolactin during the post-partum period in lactating and in non-lactating women.

The pituitary responsiveness to LH/FSH releasing hormone (LRH) was studied in the puerperium in lactating and in non-lactating women. The response of both groups of patients to 25 mug LRH iv was tested 8-10 days, 15-17 days, and 29-32 days after a normal delivery at full term. The basal levels of FSH were low during the first 10 days after delivery. A rise was then observed, and about 4 weeks after delivery levels above or in the upper normal range of a normal follicular phase were recorded. The levels were significantly higher in the lactating group. When compared with the normal follicular phase, the relative increase in FSH basal levels was higher than the increase in LH basal levels in both groups of patients. The period of non-responsiveness of the pituitary to LRH was found to be of equal length in the two groups. In both groups the FSH response returned more rapidly than the LH response. About 2 weeks after delivery a reverse pattern of gonadotrophin response to LRH was seen with a FSH response that was greater than the LH response compared with what is generally observed in the various phases of the menstrual cycle in eumenorrhoeic women. This pattern was more pronounced in the lactating group about 4 weeks after delivery. Oestradiol levels were low and roughly equal on the three test occasions in each group, but in the non-lactating group there was a tendency to higher concentrations. Prolactin levels were highest about one week after delivery and then showed a tendency to decrease, and this was more pronounced in the non-lactating group. Progesterone levels were invariably low in both groups.

Adult↗
PubMed1982

Gonadotrophin, total oestrogen and progesterone concentrations in plasma of lactating sows with particular reference to lactational oestrus.

Plasma concentrations of LH, FSH, progesterone and total oestrogens were determined (by radioimmunoassay) throughout late pregnancy and lactation in samples taken by cardiac catheter from 10 Camborough hybrid sows. At 2-3 weeks post partum, 5 were housed individually with their litters (Group I) and 5 grouped with their litters, a boar being introduced 1 day later (Group II). Plasma progesterone fell 1-2 days per partum and oestrogens at parturition, each remaining low in early lactation. Plasma LH was undetectable in most samples in this period, but FSH fell slightly during parturition, showing signs of resurgence from Day 10 post partum. Group I sows remained in lactational anoestrus until weaning. In Group II there was increased plasma LH activity, and all Group II sows displayed oestrus during lactation. Only one farrowed to service at the lactational oestrus; of the remainder, oestrus in one was clearly anovulatory, and in two others was incomplete or atypical judged by plasma progesterone concentrations. The data suggest that whilst oestrus can be induced by appropriate lactation management, poor conception rates to service at this oestrus may be due to the absence or impairment of ovulation.

Animals↗
PubMed1987

Structural plasticity in the rat supraoptic nucleus during gestation, post-partum lactation and suckling-induced pseudogestation and lactation.

In the supraoptic nucleus (SON) of parturient and lactating rats, large portions of the surface membranes of almost all oxytocinergic neurons are directly juxtaposed with no glial interposition. A significant number of the same neurones are also contacted by the same presynaptic terminal ('double' synapses). Our present observations have revealed that direct appositions between adjacent neurons in the SON increase quite rapidly during the day before parturition. 'Double' synapses also become visible during late gestation, but they appear more progressively. Earlier studies have shown that 1 month after weaning, as in virgin rats, there are again very few appositions and 'double' synapses in the nucleus. We show here that the SON can remain structurally modified, and to the same degree, beyond normal weaning time so long as lactation is prolonged by renewing suckling litters. However, if the mothers are deprived of their pups immediately after birth, neuronal appositions disappear within 2 days and 'double' synapses by 10 days. In non-pregnant primiparous rats, continuous exposure to suckling litters leads to pseudogestation and eventually lactation (in 16-22 days). Examination of the SON in such animals revealed that the oxytocinergic system is already modified by day 12 of dioestrus; during suckling-induced lactation, the anatomical changes are identical to those seen during a normal post-partum lactation. These observations indicate that neither gestation nor suckling alone are indispensable for the anatomical reorganization of the SON apparent at lactation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Genetic and phenotypic statistics of lactation cell counts in different lactations of Holstein cows.

Between February 1977 and February 1982, 680,246 monthly test-day observations of somatic cell count were taken for Holstein cows having completed 79,124 lactations in 941 herds on the Quebec Dairy Herd Analysis Service. Data were transformed to natural log scale, and analyses were separate within five parity groups. Two lactational measures of cell count, geometric mean, and weighted (by test-day milk yield) mean of the log of monthly cell counts were calculated for each lactation. Maximum likelihood, iterative Minimum Norm Quadratic Unbiased Estimation, and multivariate Restricted Maximum Likelihood procedures were used for estimation of genetic and phenotypic parameters. Repeatabilities of log test-day cell counts and log of test-day cell counts corrected for milk yield were the same at each parity, .36, .41, .42, .42, and .42 in first, second, third, fourth, and fifth and later parities. Repeatabilities of lactational measures of cell count were .33 between first and second parities, .40 between second and third parities, .13 between first and third parities, and .27 between first, second, and third parities. Heritabilities of measures of lactational cell count were small from .06 to .14 in the five parities. Genetic correlations between measures of lactational cell count in different parities were close to unity, .90 to .97.

Animals↗
PubMed2001

Maternal prolactin concentrations and lactational behaviour in the early postpartum period in women with lactational amenorrhoea.

OBJECTIVE: To compare early postpartum differences in maternal prolactin concentrations and lactational behaviour between women who have short and long periods of lactational amenorrhoea. METHODS: Healthy lactating women resuming regular menstruation before 24 weeks [short amenorrhoea (SA) group; n = 15], and at or after 24 weeks [long amenorrhoea (LA) group; n = 15] postpartum were studied from 4 to 12 weeks postpartum. Infant feeding pattern and maternal plasma prolactin concentrations were compared between the two groups using repeated measures ANOVA. RESULTS: Breastfeeds/24 h were significantly higher and other feeds/24 h were significantly lower (p < 0.01) at 12 weeks postpartum in the LA group when expressed as a percentage of all feeds. Number of breastfeeds (total/24 h and night) significantly decreased and the number of other feeds significantly increased (p < 0.05 to 0 < 0.001) with time in both groups. Prolactin concentrations (basal, suckling stimulated and increment) were higher in the LA group, but consistent significant differences were observed mainly in the increment (p < 0.05 to p < 0.001). Prolactin concentrations significantly (p < 0.01 to < 0.001) decreased with time postpartum in the SA group, but not in the LA group. CONCLUSIONS: Women with longer periods of lactational amenorrhoea maintain higher prolactin concentrations than those with shorter periods of lactational amenorrhoea during the early postpartum period, even when the breastfeeding frequency is reduced. This could be explained by a greater sensitivity of the pituitary lactotrophe to the suckling stimulus in women who have longer periods of lactational amenorrhoea.

Adult↗
PubMed2004

[The effects of increased dietary calcium intake on bone mineral density in long-term lactating women, and recovery of bone loss caused by long-term lactation with low calcium diet].

OBJECTIVES: The purpose of this study was to examine the efficacy of an increased calcium (Ca) diet for preventing bone mineral loss in long-term lactating women, considering bone metabolism, and recovery of bone loss caused by long-term lactation with low dietary Ca intake. SUBJECTS AND METHODS: Two groups of long-term (> 12 mon.) lactating women ... one with an enhanced Ca intake (Group M, n = 22) and the other with diet feeding no cow's milk and no milk products (Group N, n = 16) ... and a control group of 21 non-lactating postpartum women (Group C) were studied. Bone mineral density (BMD) was measured by ultrasonic bone densitometry. Stiffness calculated from the combined value of speed of sound and broadband ultrasound attenuation was used as an index of BMD. BMD and bone metabolic markers in urine and serum (only M and C groups) were assessed from 1 approximately 12 weeks postpartum (initial) at six-month intervals for a maximum of two years and changes were compared among the groups. RESULTS: 1. The mean (+/- SD) dietary Ca intake was 1032 (209) mg/day in the M group. 2. After lactating for one year, the N group demonstrated significant decrease in BMD, with both 1 and 2 babies, whereas the M group had no significant change. 3. The BMD in the N group returned to initial levels at 0.5 approximately 1 year post-weaning, 4. In the N group, compared with the M group, the urinary Hydroxyproline/creatinine ratio was significantly higher at the initial measurement and half a year thereafter, while urinary Ca/ creatinine ratio was significantly lower after a year. However, there were no significant differences between the M and C groups. 5. Serum bone alkaline phosphatase was significantly higher in the M group compared with the C group. CONCLUSIONS: Bone loss during long-term lactation can be prevented with adequate dietary Ca intake. Once lost, recovery to initial levels occurs 0.5 approximately 1 year post-weaning.

Adult↗