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.     

Enzymes of adenosine metabolism of sheep adipose tissue: changes in activity with season, pregnancy and lactation

Activities of enzymes involved in the synthesis and degradation of adenosine have been measured in samples of adipose tissue from unmated sheep at various times of the year between January and October and from pregnant and lactating sheep. 5'-Nucleotidase activity increased during the spring in unmated sheep but this increase was suppressed in lactating sheep. Neither adenosine kinase nor adenosine deaminase activities varied significantly between January and October in unmated sheep. Lactation resulted in a rise in adenosine deaminase activity and a small decrease in adenosine kinase activity. Pregnancy had no obvious effect on the activities of any of the three enzymes noted above. Changes in adipocyte mean cell volume and number per g tissue and the concentrations of DNA and protein of the tissue are also described. Results are discussed in relation to changes in the capacity for lipid synthesis and mobilization which occur in response to season, pregnancy and lactation in sheep.     

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.     

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.     

Enzymic changes in rabbit and rat mammary gland during the lactation cycle

1. Activities of glucose 6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), isocitrate dehydrogenase (EC 1.1.1.42), malate dehydrogenase (EC 1.1.1.37), malate dehydrogenase (decarboxylating) (EC 1.1.1.40), and pyruvate carboxylase (EC 6.4.1.1) were determined in subcellular fractions of mammary gland from rabbits during pregnancy, at different stages of lactation and during weaning. The results were compared with those obtained in similar experiments with rat mammary gland. 2. Three bases of expression of the activity of enzymes in the particle-free supernatant fraction of mammary gland were compared. During lactation, activity expressed per mg. of particle-free supernatant protein (uncorrected for milk protein) correlated well with that expressed per mug. of DNA phosphorus. The disadvantages of expressing activities per g. wet wt. are discussed. 3. The major differences between the two tissues were: (a) neither malate dehydrogenase (decarboxylating) nor a soluble form of pyruvate carboxylase could be detected in rabbit mammary gland at any stage of the lactation cycle; (b) isocitrate dehydrogenase increased in activity during lactation in rabbit mammary gland, but not in that of the rat. 4. Pyruvate carboxylase in the mitochondrial fraction of rabbit mammary gland, and in both the mitochondrial and the soluble fractions of rat mammary gland, did not change in activity during lactation. 5. For each tissue, the NADP-dependent dehydrogenases studied had a high activity at all stages of the lactation cycle compared with the rate of fatty acid synthesis at mid-lactation. The significance of these results is discussed with respect to the supply of NADPH via NADH.     

Variations in the activity of several enzymes in the mammary glands of non-pregnant, pregnant and lactating rabbits

1. The enzymes phosphofructokinase (EC 2.7.1.11), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), phosphoglucomutase (EC 2.7.5.1), ATP-citrate lyase (EC 4.1.3.8), acetyl-CoA carboxylase (EC 6.4.1.2) and acetyl-CoA synthetase (EC 6.2.1.1) were assayed in rabbit mammary glands at various stages of the pregnancy-lactation cycle. 2. The activities of all enzymes were low during pregnancy and, with the exception of phosphofructokinase, in non-pregnant animals. Two- to ten-fold increases in enzyme activities occurred over the first 20 days of lactation. Although milk yield was considerably decreased, the enzyme activities remained elevated in late lactation (45 days after parturition). 3. These findings are discussed in relation to mammary-gland metabolism and compared with similar observations previously made on ruminants and other small mammals.     

Changes in the proportion of acetyl-CoA carboxylase in the active form in rat liver. Effect of starvation, lactation and weaning

1. The activity of acetyl-CoA carboxylase (EC 6.4.1.2) in extracts of freeze-clamped liver samples from fed or 24 h-starved virgin, pregnant, lactating and weaned rats was measured (i) immediately after preparation of extracts (;I activity'), (ii) after incubation of extracts with partially purified preparations of either rabbit muscle protein phosphatase 1 [Antoniw, Nimmo, Yeaman & Cohen (1977) Biochem. J.162, 423-433] or rabbit liver phosphatase [Brandt, Capulong & Lee (1975) J. Biol. Chem.250, 8038-8044] (;A activity') and (iii) after incubation with 20mm-potassium citrate before or after incubation with phosphatases (;C activity'). 2. Incubation of liver extracts at 30 degrees C without any additions resulted in activation of acetyl-CoA carboxylase that was shown to be due to dephosphorylation of the enzyme by endogenous protein phosphatase activity. This latter activity was not stimulated by Ca(2+) and/or Mg(2+) but was stimulated by 1 mm-Mn(2+). Incubation of extracts with either of the partially purified phosphatases (0.2-0.5 unit) resulted in faster dephosphorylation and activation. The activity achieved after incubation with either of the exogenously added phosphatases was similar. 3. The A and C activities increased during late pregnancy, were lower than in the virgin rat liver during early lactation and increased by 2-fold in liver of mid-lactating rats. Weaning of mid-lactating rats for 24 h resulted in no change in A and C activities but after 48 h weaning they were significantly lower than those in livers from suckled mothers. 4. The I activity followed a similar pattern of changes as the A and C activities during pregnancy and lactation such that, although the I/A and I/C activity ratios tended to be lower during late pregnancy and early lactation, there were no significant changes in I/A and I/C ratios between lactating and virgin animals. However, these ratios were significantly higher in liver from fed 24 h-weaned animals. 5. Starvation (24 h) resulted in a marked decrease in I activity for all animals studied except early-lactating rats. This was due to a combination of a decrease in the concentration of acetyl-CoA carboxylase in liver of starved animals (A and C activities) and a decrease in the fraction of the enzyme in the active form (lower I/C and I/A ratios). The relative importance of the two forms of regulation in mediating the starvation-induced fall in I activity was about equal in livers of virgin, pregnant and lactating animals. However, the decrease in I/A and I/C ratios was of dominating importance in livers of weaned animals. The A/C activity ratios were the same for livers from all animals studied. 6. The maximal activity of fatty acid synthase was also measured in livers and was highly and positively correlated with the A and C activities of acetyl-CoA carboxylase, suggesting that the concentrations of the two enzymes in the liver were controlled coordinately. 7. It is suggested that the lack of correlation between plasma insulin levels and rates of lipogenesis in the transition from the virgin to the lactating state may be explained by different effects of insulin and prolactin on the concentration of acetyl-CoA carboxylase in the liver and on the fraction of the enzyme in the active form.     

Chronic ingestion of ethanol or glucose solutions affects hypothalamic and limbic TRH metabolism in dams and their pups

The effect of chronic ethanol consumption during pregnancy and lactation on thyrotropin releasing hormone (TRH) metabolism was investigated in the hypothalamus and limbic areas of female rats and their weaned pups. Pregnant female rats received ethanol or isocaloric glucose solution during pregnancy either alone, or also during the 3 weeks of lactation. Thyrotropin (TSH) and corticosterone levels were measured in serum; TRH and TRH-gly concentrations were determined in hypothalamus, hippocampus, n.accumbens, frontal cortex and amygdala of dams and pups at 21 days after parturition. Ethanol or glucose consumption during pregnancy and lactation produced a decrease in TSH levels compared with control animals fed at libitum; water replacement during lactation normalized TSH levels only in glucose-fed dams. Pups from ethanol or pair-fed dams showed low weight and increased TSH levels compared with normal rats. Variations in TRH metabolism were detected in limbic areas. Chronic ethanol caused a decrease in the levels of TRH in the hippocampus and frontal cortex of dams. In contrast, glucose chronic ingestion increased TRH content specifically in n.accumbens and amygdala of dams. Most of the variations in TRH content of limbic areas of pups were not specific for glucose or ethanol treatment and correlated with the deleterious effect of the mother's thyroid condition, although some differences were observed depending on pup's gender. These results support the involvement of TRHergic neurons in the limbic system of the female rat exposed to alcohol or glucose during pregnancy and lactation.     

Regulation of 6-phosphofructo-1-kinase from the epithelial cells of rat small intestine during pregnancy and lactation

The regulation of 6-phosphofructo-1-kinase (PFK) in the epithelial cells of rat small intestine was studied during pregnancy and lactation. The total activities and activity ratios (activity at 0.5 mM fructose 6-phosphate at pH 7.0/activity at pH 8.0 (nu 0.5/V] of the partially purified mucosal PFK were found to increase initially in early pregnant rats (11-12 days of gestation) and to fall back to normal in late pregnant rats (19-20 days of gestation). These changes in enzyme activity during pregnancy were associated with similar changes in the circulating levels of progesterone. The maximal activity and activity ratio (nu 0.5/V) were increased in male and female rats injected with progesterone. An increase in the total activity and activity ratio of mucosal PFK was also obtained in lactating rats. However, the enzyme was not strongly activated by inorganic phosphate, fructose 2,6-bisphosphate or glucose 1,6-bisphosphate either in early pregnant or lactating rats. These results indicate that mucosal PFK is already present as an active form during early pregnancy and lactation. Therefore, it is suggested that female sex hormones increase the circulating levels of insulin during early pregnancy which, in turn, positively affect the activity of mucosal PFK which could be also stimulated by the increased levels of fructose 2,6-bisphosphate. The increased activity of PFK in the peak lactating rats could be possible because of an increased demand for lactate production from glucose together with the stimulation of PFK by the increased concentrations of fructose 2,6-bisphosphate which therefore increases the rate of glycolysis.     

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.     

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.     

Chronic systemic treatment with epidermal growth factor in the rat increases the mucosal surface of the small intestine

We examined the effects of treatment with human recombinant epidermal growth factor (EGF) on the functioning small intestine in the rat. Male Wistar rats, 7–8 weeks old, were treated with EGF administered subcutaneously in doses of 0 (n = 7) or 150 μg/kg/day (n = 8) for 4 weeks. The histological composition and mucosal surface area of the perfusion-fixed small intestine was quantified with stereological principles. The length of the gut remained unchanged. The amount of tissue and surface area per length of gut (median (ranges)) were increased from 117 (101–131) mg/cm and 2.6 (2.1–3.5) cm²/cm in the controls to 146 (138–152) mg/cm and 3.5 (2.5–3.8) cm²/cm for the complete small intestine (both comparisons p < 0.02). The weight increase was due to mucosal growth in all parts of the intestine, whereas the surface area was only increased in proximal and middle parts. It is concluded that EGF treatment in rats increases the mucosal weight and surface area of the functioning small intestine.     

Induction of a phosphate appetite in adult male and female rats

We have reported that dietary inorganic phosphate (Pi) deprivation induces a Pi-seeking behavior in juvenile male rats. The purpose of the present study was to determine whether the Pi appetite is present in adult animals, and if so, whether it is altered during times of increased demand for Pi, such as pregnancy and lactation. Both male and female animals fed a low-phosphate diet (LPD) ingested significantly greater amounts of PiH(2)O daily than their normal phosphate diet (NPD) controls, and per 100 g of body weight (BW), the female animals fed LPD tended to ingest greater amounts of PiH(2)O than male rats fed LPD. Pregnant and lactating rats fed LPD ingested significantly more PiH(2)O than those fed NPD, however, neither group displayed a Pi appetite different than virgin females. However, lactation further reduced Pi levels in plasma and cerebral spinal fluid compared with control values. Despite the additional Pi from the PiH(2)O in the mothers fed LPD, pup birth weight was significantly lower than in NPD litters, and this was exacerbated 9 days after birth. This attenuated BW gain was associated with lower plasma Pi levels in the pups. In conclusion, a mild but consistent Pi-seeking behavior is induced in adult male and female rats after only 2 days of dietary Pi restriction. On a relative basis, the amount of PiH(2)O ingested is greater in female than in male animals, but does not increase further 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.     

Disaccharidase activities in pregnant and lactating rats

The changes in intestinal disaccharidase activities in pregnancy and lactation could be explained as a result of an adaptation to the energy demands of each reproductive stage. To examine these changes, disaccharidase activities (lactase, sucrase, maltase, and trehalase) were measured in the jejunum and ileum of virgin, pregnant and lactating Wistar rats. Minor changes in disaccharidase activities were observed in pregnancy, whereas an increase of disaccharidase activities per small intestine length normalized to body mass was observed in lactation.     

Urea synthesis in the liver and kidney of developing sheep

In order to establish if the urea found in foetal fluids in sheep could be of foetal origin and whether there are changes in the ability of ovine liver to synthesise urea during foetal and postnatal development, the rates of urea production from ammonium and bicarbonate ions have been measured in liver and kidney slices from animals aged from 50 days conceptual age to 16 weeks after birth, and in pregnant and non-pregnant ewes. The activities of five enzymes directly involved in the biosynthesis of urea have also been determined.Urea was found to be synthesised by foetal liver from at least 50 days conceptual age at rates similar to those observed in adult ewes. Highest rates of urea synthesis per unit weight of liver were found immediately after birth. In the liver there were significant positive correlations between the rates of urea synthesis by slices and the activities of carbomoyl phosphate synthase (ammonia) (EC 2.7.2.5), argininosuccinate synthetase (EC 6.3.4.5) and argininosuccinate lyase EC 4.3.2.1). Ornithine carbomoyl transferase (EC 2.1.3.3) activity was highest in the livers of ruminating animals. Hepatic arginase activity (EC 3.5.3.1) was highest during the late foetal life and in the mature foetuses the activity was ten-fold greated than that in maternal liver.Urea was not synthesised from ammonia and bicarbonate in kidney slices and neither ornithine carbomoyl transferase activity nor argininosuccinate synthetase activity could be detected. The activity of renal arginase was at least 70 times less than that found in the liver and the highest activity was found in ruminating lambs.The changes observed in the activities of the urea cycle enzymes during development have been contrasted with those reported to occur in other species. It is concluded that there is no single factor regulating the activities of the five enzymes directly concerned with urea synthesis during development. The results support the hypothesis that in mammals the ability of the liver to synthesise urea in foetal life is related to renal development.     

Body weight loss during lactation and its influence on weaning-to-service interval and ovulation rate in Landrace and Yorkshire sows in the tropical environment of Thailand

The aim of this study was to investigate the ovulation rate and the weaning-to-service interval (WSI) of sows in relation to their body weight loss during lactation in tropical climatic conditions. Effect of lactation length (LL), number of total born piglets, number of live born piglets, litter birth weight, average piglet birth weight, number of pigs weaned, litter weaning weight and average pig weaned weight on sow weight loss during lactation were also studied. This study was conducted in two commercial purebred sow herds (A, B) in the central part of Thailand from August to December 1997. The herds had both Landrace (L) and Yorkshire (Y) sows. The 123 sows (55 L and 68 Y) in herd A and 153 sows (95 L and 58 Y) in herd B, parity 1-4, were weighed within 4 days after farrowing and at weaning. Lactation length, litter size at birth and at weaning, litter weight at birth and at weaning, and WSI were recorded for each of these sows. In herd A, 52 sows (20 L and 32 Y) were examined once by laparoscopy between days 8 and 14 after AI-service. These sows had farrowed at least seven piglets in the previous parturition. The numbers of corpora lutea (CL) in both ovaries were counted, and were assumed to equal the ovulation rate. L-sows had significantly (P < 0.05) higher relative weight loss during lactation (RWL) than Y-sows. The RWL increased by 0.7% for each extra pig weaned. When LL increased by 1 day, within the interval of 17-34 days, RWL decreased by 0.6%. Sows with a high weight loss had significantly (P < 0.05) longer WSI than sows with medium or low weight loss. Weight loss had a significant (P < 0.05) effect on WSI in parity 1 and 2 sows. Y-sows had more CL than L-sows (15.7 versus 14.0) (P < 0.05). RWL, parity and regression on lactation length had no significant effect on number of CL. In conclusion, sows with higher number of pigs weaned lose more weight. Under the restricted feeding regime applied, high weight loss during lactation prolongs WSI in parity 1 and 2 sows, but has no influence on the ovulation rate at first oestrus after weaning. The ovulation rate is higher in Yorkshire than in Landrace sows. The ovulation rate is independent of parity.     

Effects of concurrent pregnancy and lactation on reproduction in four strains of mice

The influence of concurrent pregnancy until the third lactation on reproduction was studied in four strains of mice (SHN, SLN, C3H/He and GRS/A) as a possible step to evaluate the efficiency of this system on offspring production. In all strains, little difference was observed between sequential and concurrent pregnancy and lactation groups in any parameter as the index of reproductivity--delivery interval, litter size, average weight and growth rate of pups, mother weight, rearing rate, still-birth rate and rate of still-born pups. Also, no difference was seen between groups of any strain, in the number of females which had three litters. The estimated number of pups weaned per female during 50 days after first being placed with males was higher in the concurrent pregnancy groups than in the sequential pregnancy groups of all strains. Meanwhile, the incidence of spontaneous mammary tumors, the major characteristic of these strains, was consistently lower in the concurrent pregnancy group in all strains. These results have demonstrated that the concurrent pregnancy and lactation system is an efficient means of mouse production.     

Studies of mitochondrial development prior to lactogenesis in the mouse mammary gland

Studies were performed to define mitochondrial development in relation to epithelial cell proliferation and differentiation prior to lactogenesis in the mammary gland of the mouse. Gland weight, total DNA, and total protein, selected as criteria of gland growth and proliferation, and various parameters of mitochondrial development were followed throughout the period. Gland weight and total DNA started increasing about Day 5 of pregnancy and reached maximal values by parturition. Total gland protein began to increase at the same time but did not reach maximal values until Day 4 of lactation. Total mitochondrial protein and the mitochondrial marker enzyme activities, succinate oxidase, succinate-linked ATP formation, and cytochrome oxidase increased gradually during pregnancy with rapid 2- to 3-fold increases occurring during the early days of lactation. Similarly, succinate oxidase activity per unit DNA of isolated mammary parenchymal cells increased gradually from mid-pregnancy to parturition with a precipitous, 2-fold increase occurring during early lactation.