Comparative profiles of the hexose monophosphate dehydrogenases in rat tissues over the lactation cycle

The mammary gland tissue hexose monophosphate dehydrogenase activities were low in virgin, pregnant and weaned rats, but increased at the onset of lactation. The muscle and liver glucose 6-phosphate dehydrogenase activity peaked at early and late lactation respectively. The liver 6-phosphogluconate dehydrogenase peaked in late pregnancy and remained elevated through lactation. The muscle 6-phosphogluconate dehydrogenase peaked at the onset of lactation. The adipose tissue hexose monophosphate dehydrogenases exhibited small changes during pregnancy and lactation. The spleen hexose monophosphate dehydrogenases did not respond to lactation An overshoot in both the liver and the adipose tissue hexose monophosphate dehydrogenases was observed on weaning. Serum glucose levels remained unchanged throughout pregnancy, lactation and weaning. Only liver glucose 6-phosphate dehydrogenase activity correlated with plasma insulin, which also correlated positively with food consumption. The results demonstrate that tissue-specific control of the hexose monophosphate dehydrogenases occurs in the female rat during its complete lactation cycle.     

Circadian rhythms in disaccharidases of rat small intestine and its relation to food intake.

The activities of maltase and sucrase of the small intestine were low at night and high in the daytime in rats which had been fed from 09.00 h to 15.00 h for 2 weeks. A remarkable rise of enzyme activities was observed at 08.00 h, 1 h before the start of feeding. The rhythmic changes in disaccharidase activities continued for at least 2 days after starvation, but completely disappeared after 5 days of starvation. It was suggested that the disaccharidase rhythms are not a direct consequence of food intake, but that anticipation of food intake acts as a trigger for initiation of the disaccharidase rhythms.     

The effects of pregnancy and lactation on the activities in rat liver of some enzymes associated with glucose metabolism.

1. The ratio of the combined activities of hexokinase (EC 2.7.1.1) and glucokinase (EC 2.7.1.2) to the activity of glucose-6-phosphatase (EC 3.1.3.9) changed in favour of the glycolytic enzymes during pregnancy and at peak lactation. 2. There were no important changes in the ratio of the activity of phosphofructokinase (EC 2.7.1.11) to that of fructose diphosphatase (EC 3.1.3.11). 3. The ratio of the activity of pyruvate kinase (EC 2.7.1.40) to the combined activities of phosphoenolpyruvate carboxylase (EE 4.1.1.32) and pyruvate carboxylase (EC 6.4.1.1) changed in favour of the glycolytic enzyme during pregnancy and at peak lactation, but changed in favour of the gluconeogenic enzymes immediately after parturition. 4. These changes are considered in relation to the changes in food intake and hormonal status that occur during pregnancy and lactation.     

Metabolic adaptations in goat mammary tissue during pregnancy and lactation

Metabolic adaptations of goat mammary tissue during pregnancy and lactation were monitored in serial biopsies of the tissue. Changes in the synthetic capacity of secretory cells were studied by combining measurements of enzyme activities with short-term culture of mammary explants to measure lactose, casein and total protein synthesis. By these criteria, the main phase of mammary differentiation began in late pregnancy and was essentially complete by Week 5 of lactation, coinciding with the achievement of peak milk yield. While milk yield declined after Week 5, the activities of key enzymes expressed per mg DNA and the rates of lactose and casein synthesis in mammary explants were maintained over a considerable period. The results suggest that changes in the synthetic capacity of epithelial cells may account for much of the rise in milk yield in early lactation, but are not responsible for the declining phase of milk production characteristic of lactation in ruminants.     

Cancellous and cortical bone mechanical properties and tissue dynamics during pregnancy, lactation, and postlactation in the rat

There are substantial changes in maternal skeletal dynamics during pregnancy, lactation, and after lactation. The purpose of this study was to correlate changes in cortical and cancellous bone mass, structure, and dynamics with mechanical properties during and after the first reproductive cycle in rats. Rats were mated and groups were taken at parturition, end of lactation and 8 wk after weaning, and were compared with age-matched, nulliparous controls. Measurements were taken on femoral cortical bone and lumbar vertebral body cancellous bone. At the end of pregnancy, there was an increase in cortical periosteal bone formation and an increase in cortical volume, but a suppression of turnover in cancellous bone with no change in cancellous or cortical mechanical properties. Lactation was associated with a decrease in cortical and cancellous bone strength with a decrease in bone volume, but an increase in turnover on cancellous and endocortical surfaces. After lactation, there was a partial or full restoration of mechanical properties. This study demonstrates substantial changes in bone mechanics that correlate with changes in bone structure and dynamics during the first reproductive cycle in rats. The greatest changes were observed during the lactation period with partial or full recovery in the postlactational period.     

Lactose synthetase activities in rat and mouse mammary glands

The activities of lactose synthetase (in the presence and absence of α-lactalbumin), galactosyltransferase and α-lactalbumin levels were determined in rat and mouse mammary glands during pregnancy, lactation and involution. In the rat, essentially none of the above activities were detected prior to parturition. This was followed by a sharp increase with the maximum occurring during late lactation and then by a rapid drop during involution. In the mouse, detectable levels of all the activities occurred at 15 days of pregnancy and these levels increased during pregnancy and reached a maximum level during early lactation and again sharp decreases occurred during involution. The study shows that mammary gland development occurs at an earlier date in the mouse than in the rat.     

Dynamics of antibody nuclease activity in blood of women during pregnancy and lactation

In human milk we previously found catalytic antibodies (abzymes) catalyzing hydrolysis of DNA, RNA, NMP, NDP, and NTP and also phosphorylation of proteins and lipids. In the present study we have analyzed nuclease activities of antibodies in blood of women during pregnancy and lactation. Blood of healthy male and female volunteers lacked catalytically active antibodies, whereas antibodies from blood of pregnant women hydrolyzed DNA and RNA and their relative activity varied over a wide range. Relative blood abzyme activities significantly increased after delivery and at the beginning of lactation. The highest abzyme activity was observed in blood of parturient women. Although the dynamics of changes in antibody DNase activity during pregnancy was rather individual for each woman, there was a common trend in the increase in antibody activity in the first and/or third trimester of the pregnancy. The DNase activity of IgG and IgM from blood of healthy pregnant women was 4-5 times less than that from pregnant women with pronounced autoimmune thyroiditis.     

Role of reversible phosphorylation in mediating changes in the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase during pregnancy and lactation in the rat.

1. The expressed and total (completely dephosphorylated) activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase were measured in microsomal fractions isolated from cold-clamped liver samples from female rats in various stages of the reproductive cycle. 2. There was little change in total HMG-CoA reductase activity during pregnancy and early lactation, but after 2 days post partum there was a marked increase in total activity. 3. The expressed/total activity ratio of HMG-CoA reductase showed a profound decrease during the last 2 days of pregnancy. The fraction of the enzyme in the active form increased progressively during the first 2 days of lactation. 4. The combined effect of these changes was that the expressed activity of HMG-CoA reductase changed in parallel with the known changes in the hepatic rate of cholesterogenesis during pregnancy and lactation in vivo.     

Precocious alteration of digestive enzyme activities in small intestine and pancreas by chronic oral administration of protease inhibitor in suckling rats.

1. The role of endogenous CCK in the development of digestive enzyme activities in small intestine and pancreas was investigated in suckling rats. Synthetic protease inhibitor (camostat 100 micrograms/g bwt) was orally administered twice daily for 5 days from 11 days of age. 2. Pancreatic hypertrophy and hyperplasia, and alteration of pancreatic enzyme composition, especially decreases in amylase activity and increases in trypsin and chymotrypsin activities were produced by camostat treatment. These changes were completely suppressed by simultaneous administration of the potent CCK receptor antagonist L-364,718 (1 microgram/g bwt). 3. With camostat treatment, intestinal lactase activity decreased to 41%, while maltase and sucrase activities increased 3 and 2.5 times respectively. These changes in enzyme activities were not affected by the application of L-364,718. 4. The mucosal disaccharidase and pancreatic enzyme activities could not be modified by chronic subcutaneous injection of camostat. The precocious induction of maltase and sucrase activities by camostat treatment was also observed in the adrenalectomized pups. 5. These results indicate that pancreatic growth accompanied by alteration of digestive enzyme composition in the suckling rats is regulated by endogenous CCK, but the precocious induction of disaccharidase activities is not mediated by endogenous CCK released by camostat treatment.     

Influence of pregnancy, lactation and environment on some clinical chemical reference values in Danish landrace dairy goats (Capra hircus) of different parity--I. Electrolytes and enzymes.

1. Plasma calcium, magnesium, inorganic phosphorus, sodium and potassium concentrations, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and creatine kinase activities were determined in young and adult non-pregnant non-lactating, early and late non-lactating pregnant and early, mid- and late non-pregnant lactating Danish landrace goats in five herds. The purpose was to determine the influence of pregnancy and lactation on the levels of these parameters and the effect of age and parity on the changes. 2. Calcium, phosphorus, alanine aminotransferase, alkaline phosphatase and aspartate aminotransferase decreased in late gestation. Magnesium and creatine kinase decreased in early lactating goats but increased in subsequent lactation periods. Sodium and potassium fluctuated little during pregnancy and lactation. Calcium, magnesium and potassium profiles were inversely, while phosphorus was directly, proportional to parity. 3. There were significant differences in most ions and enzymes between goats of different herds (within the same physiological state). 4. The transferases and creatine kinase were higher in young goats than in old ones, while alkaline phosphatase was unpredictably high or low in individual goats. 5. Alterations in the level of plasma electrolytes and enzyme activities occur due to pregnancy and lactation and the degree depends on age and parity, influenced also by environment.     

The effect of spermine on the disaccharidase activities in suckling rats of different age.

The influence of the age of the rat on the maturation of disaccharidase activities induced by spermine was studied. Three-day- and 9-day-old rats were used in the experiment. Spermine was administered orally or directly into the stomach using thin tubing daily for 3 days, and disaccharidase activities in the jejunum were measured. While spermine caused maturation of not only lactase activity but also maltase and sucrase activities in 9-day-old rats, it only caused maturation of lactase activity in 3-day-old rats. Histological studies showed no significant changes in the jejunum of 3-day-old rats treated with spermine.     

Localization and expression of BCAT during pregnancy and lactation in the rat mammary gland

During lactation, branched-chain aminotransferase (BCAT) gene expression increases in the mammary gland. To determine the cell type and whether this induction is present only during lactation, female rats were randomly assigned to one of three experimental groups: pregnancy, lactation, or postweaning. Mammary gland BCAT activity during the first days of pregnancy was similar to that of virgin rats, increasing significantly from day 16 to the last day of pregnancy. Maximal BCAT activity occurred on day 12 of lactation. During postweaning, BCAT activity decreased rapidly to values close to those observed in virgin rats. Analyses by Western and Northern blot revealed that changes in enzyme activity were accompanied by parallel changes in the amount of enzyme and its mRNA. Immunohistochemical studies of the mammary gland showed a progressive increase in mitochondrial BCAT (mBCAT)-specific staining of the epithelial acinar cells during lactation, reaching high levels by day 12. Immunoreactivity decreased rapidly after weaning. There was a significant correlation between total BCAT activity and milk production. These results indicate that the pattern of mBCAT gene expression follows lactogenesis stages I and II and is restricted to the milk-producing epithelial acinar cells. Furthermore, BCAT activity is associated with milk production in the mammary gland during lactation.     

Changes of the activities of adenyl cyclase and cAMP-phosphodiesterase and of the level of 3'5' cyclic adenosine monophosphate in rat mammary gland during pregnancy and lactation

The activities of adenyl cyclase, the low- and high-K_m cAMP phosphodiesterases and the tissue level of cAMP have been measured in mammary glands taken from pregnant and lactating rats. Adenyl cyclase reaches its maximum activity late in pregnancy and thereafter falls continuously throughout lactation. The high-K_m phosphodiesterase rises slowly in pregnancy but reaches a maximum late in lactation. The tissue cAMP content is maximal at the end of pregnancy and then falls progressively to its lowest level by the sixteenth day of lactation. These changes are discussed in relation to the metabolic adaptation of the gland and its responsiveness to hormonal stimulation.     

Adaptation of the small intestine during pregnancy and lactation in the rat.

During pregnancy and lactation in the rat the small intestine in general and the mucosal epithelium in particular gain weight. The specific activities of sucrase, lactate dehydrogenase and succinate-tetrazolium reductase remain constant and those of glucose 6-phosphate dehydrogenase and isocitrate dehydrogenase increase. There is no evidence that the reported decrease in absorption per unit area or weight of mucosal epithelium during pregnancy and lactation is due to decreases in enzyme activities within the epithelium. The pattern of enzyme change shows that the response of the gut to the stimuli of pregnancy and lactation must be a complex one, possibly involving increases in the specific activities of some enzymes.     

Effects of gestation and lactation on rat gastric fundus

This study evaluated the effects of gestation and lactation on stomach growth in rats. Constant increases were observed in gastric fundus weight during pregnancy and lactation, with a maximum obtained after 3 weeks of lactation. This increase in tissue weight was not associated with hyperplasia of the gastric fundus as in no instance did total DNA contents from mated females differ significantly from those of the unmated controls. Mild hypertrophy, as evidenced by significant increases in cellular mass and RNA and protein concentrations, was observed during late lactation. Gastrin might be responsible for these modest changes in the gastric fundus.     

Hepatic and intestinal formation of polar sterols in vivo in animals fed on a cholesterol-supplemented diet.

Measurements were made of the activities of the enzymes of the 'de novo' and salvage pathways of purine synthesis [phosphoribosyl pyrophosphate amidotransferase (EC 2.4.2.14), adenine phosphoribosyltransferase (EC 2.4.2.7) and hypoxanthine phosphoribosyltranferase (EC 2.4.2.8)] at different stages of the lactation cycle, and the effects of diabetes on the activity of these enzymes in lactation were studied. A distinctive pattern of enzyme change was observed, in which the 'de novo' pathway enzyme phosphoribosyl pyrophosphate amidotransferase increased sharply between days 10 and 14 of pregnancy, and then remained sensibly constant until the height of lactation, whereas the enzymes of the salvage pathway increased later in pregnancy and continued to rise during lactation. Diabetes severely depressed the activity of the enzymes of the salvage pathway, but appeared to be without effect on the 'de novo' pathway enzyme. These results are discussed in relation to the provision of purine precursors from tissues outside the mammary gland.     

Activities of some metabolic enzymes in the small intestinal mucosa during pregnancy and lactation in the rat

The food intake, gut weight, gut length, mucosal protein and mucosal activities of alkaline phosphate (EC 3.1.3.1), acid phosphate (EC 3.1.3.2), isocitric dehydrogenase (EC 1.1.1.42) and glucose-6-phosphate (EC 3.1.3.9) were measured in rats during pregnancy, lactation and after the young were weaned. In general, the quantities measured increased slightly during pregnancy and considerably during lactation, reaching maximum values during the 3rd weeks of lacation and falling more or less rapidly after the young were weaned to the same levels as those in unmated animals. However, the gut length and mucosal protein remained higher even 3 weeks after weaning, so that weight per unit length and specific enzyme activities (per mg protein) tended to be lower in mated than in unmated rats. Changes in the specific activities of enzymes indicate alterations of the metabolic function of the enterocytes during breeding similar to changes reported for digestive enzymes. It is suggested that the intestine may reflect changes that take place in the liver.     

Elevated leptin concentrations in pregnancy and lactation: possible role as a modulator of substrate utilization.

Energy needs are increased during pregnancy and lactation. These increased energy needs may be met through partitioning of nutrients for energy utilization which is under hormonal control. The objective of the present studies was to determine if changes in plasma leptin occurred during pregnancy and lactation and if the changes were related to prolactin. Plasma leptin and prolactin were measured longitudinally in 9 women through pregnancy and lactation. In a second study, leptin and prolactin were measured 4 days and 28 days postpartum in 21 lactating women. Mean plasma leptin during the three trimesters of pregnancy was significantly higher (29.3+/-2.8 ng/ml) when compared to mean leptin during the three time periods of lactation (19.3+/-3.2 ng/ml) and control groups (9.8+/-1.4 ng/ml). Plasma leptin was elevated early in pregnancy and remained elevated throughout pregnancy. In the second study, the mean plasma leptin in the lactating women was significantly higher 4 days postpartum (17.3+/-3.7 ng/ml) and 28 days postpartum (19.2+/-3.9 ng/ml) when compared to controls (11.6+/-1.2 ng/ml). Prolactin in the control subjects (24+/-4 ng/ml) was significantly lower than in the pregnant (202+/-16 ng/ml) and lactating (108+/-26 ng/ml) groups. Similar observations were made in the second study (controls 20+/-2 ng/ml; lactation 28 days 159+/-21 ng/ml). Leptin during lactation was lower than in pregnancy but higher than control subjects. Regression analysis suggested that BMI and prolactin can be used as predictors of leptin in pregnancy and lactation. The increase in leptin and prolactin early in pregnancy suggests an association between the two hormones. Results of the present studies and research done by other investigators presents a strong role for leptin during pregnancy and lactation. Leptin is regulated by factors other than adiposity especially in reproductive women leading to our hypothesis that there are leptin and prolactin mediated effects on substrates used for energy utilization during pregnancy and lactation.     

Mast cells in the mouse mammary gland--correlation with the development of lactiferous structures

Specimens of mouse mammary glands obtained from animals being in different phases of reproductive cycle were collected. After staining MCN, the total mast cell area (TMC), mean mast cell area (MMC), and lactiferous structure density index (LDI) were examined in sections, using a computer image analysis system. Statistically significant (P < 0.05) results were: 1. An increase in MCN observed in Group I (4-5 and 9-10 days of pregnancy), a decrease in MCN observed in Group II (2nd and 10th day of lactation); 2. Changes of TMC fully corresponding to changes of MCN; 3. Increase in MMC observed in Group I at mid (days 9-10) and at the end (days 18-19) of pregnancy, decrease in MMC observed in Group IIB (10th day of lactation); 4. LDI (%) higher at the end of pregnancy (Group IC) and during lactation (groups IIA, IIB), compared with control (23.5 +/- 4.12, 37.6 +/- 3.24, 71.0 +/- 4.33 vs. 3.8 +/- 0.39). The observed changes in the number and size of MC strictly correspond to physiological phenomena leading to alternation of the mouse mammary gland functional status by development/involution of the lactiferous structures.     

Co-ordinate changes in enzymes of fatty acid synthesis, activation and esterification in rabbit mammary gland druing pregnancy and lactation.

1. The activities of fatty acid synthetase, acyl-CoA synthetase, glycerol phosphate acyltransferase and phosphatidate phosphatase were measured in the mammary glands of rabbits from day 16 of pregnancy to day 15 of post partum. 2. There were significant correlations between the increases in activities of these enzymes during this period. This was the case whether the activities were expressed per mg of homogenate protein, per g wet wt. of tissue or per total wet weight of the whole glands. The only exception was the lack of correlation between the activities of fatty acid synthetase and of phosphatidate phosphatase per g wet wt. of tissue. 3. These co-ordinate increases are discussed in relation to the changes which occur in fatty acid metabolism in the mammary gland during pregnancy and lactation.