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PubMed1984

Plasma catecholamines and their effect on blood lactate and muscle lactate output.

This study was designed to test the hypothesis that epinephrine (E) and norepinephrine (NE) increase net muscle lactate output (L) of in situ gastrocnemius-plantaris muscle group during contractions. Plasma [E] and [NE] were measured before and after the surgical isolation of the muscle and at 10-min intervals during the 60-min experiments. Plasma [E] and [NE] were increased threefold by intravenous infusions of E (n = 3) or NE (n = 3) at a rate of 1.5 micrograms X kg body wt-1 X min-1. Arterial and muscle venous blood samples for O2 and lactate concentrations were also obtained. The infusions began at min 11 and repetitive isometric contractions (4 tw/s) began at min 31. The presurgery plasma [E] and [NE] averaged 0.34 and 0.52 ng/ml, respectively, and rose to 1.12 and 1.19 ng/ml 10 min after surgery. Arterial and venous lactate concentrations (CaL and CvL) increased continuously during E infusion but remained constant during NE infusion. Maximal L during the first 10 min of contractions was significantly increased compared with an identical earlier study without infusions. O2 uptake was not changed by the infusions. It is concluded that E causes CaL to rise and that both E and NE increase maximal net lactate output during contractions.

Animals↗

PubMed1995

Bioavailability of calcium from calcium carbonate, DL-calcium lactate, L-calcium lactate and powdered oyster shell calcium in vitamin D-deficient or -replete rats.

The bioavailability of calcium from various calcium sources in humans and animals has been the subject of investigation for many years and there is considerable controversy as to the relative bioavailability of different calcium salts. Most of the studies have used a calcium balance technique which has numerous problems in terms of performance and interpretation. Using a method for evaluating the efficacy of calcium from calcium salts used for plasma calcium metabolism and bone mineralization, we examined the bioavailability of calcium from four commercially available calcium salts, namely calcium carbonate, DL-calcium lactate, L-calcium lactate and powdered oyster shell-calcium in vitamin D-deficient or -replete rats. Among the calcium salts, the differences in bioavailability were small and not statistically significant as tested by analysis of variance in both groups of rats. Thus, we conclude that calcium is utilized to the same extent from calcium carbonate, DL-calcium lactate, L-calcium lactate and powered oyster shell-calcium in both vitamin D-deficient and -replete rats.

Animals↗

PubMed1985

Homeorhesis during early lactation. Euthyroid sick-like syndrome in lactating cows.

Serum levels of thyroxine (T4), triiodothyronine (T3) and reverse T3 (rT3) were studied in dry, early (first trimester) and middle (second trimester) lactating purebred Holstein cows. The study encompassed three different seasons: autumn, winter and spring. Under comfortable weather conditions (temperature 22 degrees C; relative humidity, 40%) or moderately hot (28 degrees C; 60%), January and October, respectively, cows in early lactation exhibited significantly lower levels of T4 and T3, and higher values of rT3 than dry or middle lactating animals. In contrast, during May, when environmental temperature increased (34 degrees C; 40%), a clear-cut shift in T3/rT3 ratio occurred, and animals in early lactation exhibited the highest T3 and the lowest rT3 concentrations. These findings suggest that in dairy cattle, peripheral thyroid hormone metabolism plays a major role in regulating the homeorhetic responses involved in the maintenance of high priority functions.

Adaptation, Physiological↗

PubMed1977

Metabolic clearance of rat prolactin in the lactating and non-lactating rat.

The metabolic clearance of rat prolactin, assessed by the continuous infusion to equilibrium method, increased from 0-77 to 2-15 ml/min in lactating and from 0-65 to 1-75 ml/min in non-lactating rats as the infusion rate was increased from 100 to 472 ng/min. The clearance rate of rat prolactin did not increase when large doses of ovine prolactin were infused simultaneously with rat prolactin. The clearance rates computed from equilibrium levels of immunoreactive 131I-labelled rat prolactin in plasma were highly correlated with, but were considerably greater than, those computed from unlabelled rat prolactin which was infused simultaneously. In lactating and non-lactating rats, the clearance of each prolactin tested (RP-1, B-1, Nicoll's secreted and 131I-labelled) increased and had stabilized within the 30-35 min of infusion of each new higher dose of the hormone. The ability of the rat to clear quickly greater amounts of prolactin from the circulation as the infusion rate increases implies that plasma prolactin concentrations do not necessarily mirror the rate of prolactin secretion from the pituitary.

Animals↗

PubMed1992

Lactation performance of sows injected with growth hormone-releasing factor during gestation and(or) lactation.

Fifty-two Yorkshire x Landrace gilts were equally allotted to four treatments: 1) controls, saline injections (CTL); 2) injections of 12 mg of growth hormone-releasing factor (GRF) (1-29)NH2 thrice daily (0700, 1500, and 2300) from d 100 of gestation until parturition (GEST); 3) injections of GRF thrice daily from d 3 to 29 of lactation (LACT); and 4) injections of GRF thrice daily during gestation (d 100 to parturition) and lactation (d 3 to 29) (GEST-LACT). Within 48 h of birth, litters were standardized to 9 +/- 1 pigs. Weights of the pigs were recorded weekly from birth (less than 24 h) until weaning (d 30) and on d 42 and 56. Weights of gilts at mating, d 110 of gestation, 1 d postfarrowing, and at weaning also were recorded. On d 24 of lactation, milk yield was estimated by the weigh-suckle-weigh method, and a representative milk sample was obtained the next day. Jugular vein cannulas were inserted into six sows per treatment on d 26, and a 6-h blood profile (sampling every 20 min from 0600 to 1200) was obtained on d 29. Daily feed consumption of sows was recorded throughout the study. Weights of the pigs at any one time or survival until weaning were not affected by treatments (P greater than .1). Sows injected with GRF during GEST (P = .05) and(or) LACT (P less than .01) were lighter than CTL sows at weaning; in addition, sows treated during lactation had less backfat (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2000

Lysine metabolism by the mammary gland of lactating goats at two stages of lactation.

An arteriovenous kinetics technique was used to monitor mammary gland lysine and protein metabolism in goats (n = 4) at two stages of lactation (80 +/- 17 vs. 233 +/- 14 DIM) in response to an i.v. infusion of lysine (Lys) plus methionine (Met). At each stage of lactation [2-15N] and [1-13C; 6,6-2H2] Lys kinetics were performed on the last day of 5-d i.v. infusion of saline followed by Lys (370 mg/h) plus Met (84 mg/h, LM). Milk and protein yields and dry matter intake were higher in early than in late lactation, but LM infusion did not affect these variables. Regardless of stage of lactation, the absolute and fractional oxidation rates of Lys by the mammary gland increased in response to LM infusion. When corrected for Lys oxidation, net uptake of Lys by the gland was less than milk protein Lys secretion. However, correction for the contribution of peptides (15.8%) to Lys uptake brought net Lys uptake close into balance with milk Lys secretion. The present data suggests that when Lys is in excess of requirements, the mammary gland appears to dispose of the extra supply via the oxidative mechanism.

Animals↗

PubMed2001

The effects of milk yield and stage of lactation on the partitioning of nutrients in lactating dairy cows.

The objective of the experiment was to examine, using indirect calorimetry, the effects of milk yield and stage of lactation on the response in milk and body tissue energy, and heat production, to a reduction (decrement) in nutrient intake (assessed as metabolizable energy intake). Eight lactating dairy cows, four representing each of two stages of lactation [either mean initial days in milk (DIM) 158 (SD 6.1) or 414 (SD 51.1)] were used. Each cow underwent four 17-d periods incorporating two physiological states [number of mammary glands milked: either four (periods 1 and 2), or two (periods 3 and 4)], and two levels of metabolizable energy intake within each physiological state [either sufficient to meet requirements for zero tissue balance plus 10 MJ/d (periods 1 and 3)] or these allowances reduced by 20 MJ/d in the subsequent period (periods 2 and 4, respectively). Partitioning was calculated from the changes in metabolizable energy intake, milk energy, tissue energy, and heat production between DIM groups and between four and two gland milking (milk yield) components of the study. Partitioning of the changes in metabolizable energy intake was not influenced by DIM, but milk yield response was greater in the early lactation cows compared with the late group. Cows milked in four glands (higher milk yield) partitioned a significantly greater proportion of decremental changes in metabolizable energy intake to milk energy and less to tissue energy, than when milked in only two glands (lower milk yield).

Animals↗

PubMed1982

Comparison of first lactations and all lactations of dams to predict sons' milk evaluations.

Multiple regression of genetic evaluations of about 170 Holstein bulls on sire, dam, and maternal grandsire genetic evaluations indicated that the partial regression coefficient for the sire is similar to the theoretical regression coefficient (.45 vs. .50), that the regression coefficient for the dam is much smaller than the theoretical regression coefficient when all records of the dam including her first are included in her evaluation (.12 vs. .35), although about as expected when only first records of the cow and her herdmates are used (.33 vs. .35), and that the regression for the maternal grandsire is larger than expected when his proof and all records of the dam are used in her evaluation (.07 vs. .00), although about as expected when his proof and only her first record is used (-.02 vs. .00). Preferential treatment of potential bull dams is a possible explanation for these results. Genetic correlations among lactations are not likely to be small enough to account for the differences in regression coefficients for the dam's genetic evaluations for all and first lactations. If conditions for selecting bull dams in the future will be similar to what they have been in the past, the conclusion is that genetic evaluations of cows from their first lactation records be used in preference to genetic evaluations from all lactation records for selection of dams of bulls.

Animals↗

PubMed1988

Regulation of bovine adipose tissue metabolism during lactation. 4. Dose-responsiveness to epinephrine as altered by stage of lactation.

Adaptations in adipose tissue lipolysis responsiveness to doses of epinephrine were determined in first lactation Holstein cows. Subcutaneous adipose tissue was biopsied at -30, -15, 30, 60, 120, 180, and 240 d about first calving. Glycerol and fatty acid release from tissue triglycerides were determined in vitro in the presence of 10(-8) to 10(-4) M epinephrine. Basal lipolysis increased postpartum and remained elevated through 240 d of lactation. Glycerol release in response to graded doses of epinephrine increased from 30 d prepartum to 30 d postpartum and remained elevated through 240 d. The highest net response was reached at 120 d and was maintained to 240 d. Increases during lactation were noted in actual glycerol release, net response (stimulated minus basal activity), and maximum net response (calculated from reciprocal plots). Maximal and submaximal response of fatty acid release to epinephrine increased post partum with maximal adaptation occurring by 30 d and remaining elevated through 240 d. Maximum net response of glycerol release at 30 d was related positively (r = .73) to milk energy secretion and negatively to energy intake (r = -.57) and energy balance (r = -.79). Net maximum free fatty acid response at 120 d related positively (r = .89) to milk energy secretion and negatively (r = -.81) to energy balance. The epinephrine responsiveness of adipose tissue increases during lactation in a manner consistent with whole body energy inputs and outputs.

Adipose Tissue↗

PubMed1992

Long-term effects of sometribove in lactating cows during a fourth consecutive lactation of treatment: insulin and somatotropin responses to glucose infusion.

The effect of sometribove (USAN, methionyl bST) on the endocrine pancreas and blood bST concentrations was investigated in 6 control and 6 treated Friesian cows, averaging 111 and 118 d postpartum in their fourth lactation of treatment. Each lactation the treated cows received sometribove injections (500 mg) every 2 wk (injection cycle) starting 60 +/- 3 d postpartum, increasing milk yield 3.3, 5.9, 1.9, and 4.2 kg/d in lactations 1, 2, 3, and 4, respectively. On d 8 of a fourth lactation injection cycle, blood was sampled for 390 min, starting 30 min before an intravenous glucose infusion (100 mg/kg) over a 20-min period. Preinfusion concentrations of glucose, insulin, and bST were elevated in sometribove-treated cows versus controls: 82.1 versus 74.4 mg/dl, 28.1 versus 19.7 microIU/ml, and 4.6 versus .9 ng/ml, respectively. Glucose infusion resulted in a rapid increase in blood glucose and insulin concentrations, followed by a sharp decline to preinfusion values across both treatments, resulting in similar net area under the curves for glucose and insulin. Blood bST concentrations remained unchanged. This study supports the concept that sometribove increases milk yield in dairy cows by chronically influencing homeorhetic mechanisms.

Animals↗

PubMed1999

[Effect of lactation state (1st-20th week of lactation) on dynamics of C-reactive protein (CRP) in initial quarter milk samples in relation to somatic cell count, lactose content and blood serum CRP levels].

The concentration of C-reactive protein (CRP) in milk and blood serum varies during the first half of lactation. Somatic cell count and lactose content also depend on the stage of lactation. CRP blood serum levels show a distinct tendency to increase from the 2nd to the 20th week of lactation. In contrary the milk CRP content decreases from the 1st week to the end of the 2nd month post partum and increases again from the 8th to the 20th week post partum. Somatic cells and CRP-concentrations in milk increase parallelly but the lactose content shows a contrary pattern in the first five months of lactation.

Animals↗

PubMed1984

Mineral content of colostrum and mature milk of lactating Nigerian women as influenced by stage of lactation.

380 milk samples (96 colostrum and 284 mature milk samples) collected from 240 lactating Nigerian women within the first 9 months of lactation were analyzed for zinc, copper, iron, calcium, and magnesium concentrations by atomic absorption spectrophotometry. Mean levels of zinc, copper, iron, calcium, and magnesium in colostrum were 5.83, 0.52, 0.55, 400, and 33 mcg/ml, respectively; the levels for the same minerals in mature milk collected in the 8th and 12th week of lactation were 3.08, 0.29, 0.38, 300, and 31 mcg/ml, respectively. While milk levels of all minerals decreased with increase in lactation age, zinc levels showed the fastest rate of decrease. Milk zinc levels at the 9th month were only 13% of that in colostrum. Similar percentages for copper, iron, calcium, and magnesium were 49, 60, 34, and 74%, respectively. Estimates of intake by solely breastfed infants during the first 6 months showed gross inadequacies when compared with Recommended Daily Allowances. Results suggest the need for early supplementation, especially as zinc deficiencies as well as a high incicdence of iron deficiency anemia has been reported in Nigerian infants.

Africa↗

PubMed1989

[Pathology and productivity of the lactating cow: interrelations based on the level of lactation].

The effects of sanitary problems in dairy herds on milk production have been determined using 595 cases of health problems noted in Friesian and Montbeliarde cows in a long-term feeding trial, covering over 487 lactations. Relationships between each sanitary condition and lactation characteristics were established. On a short-term basis (5 weeks), the greater milk losses were first due to lameness at turnout (56 kg) and second to winter mastitis (24 kg); the effects of lameness lasted beyond the 5th week depending on when the problem was first detected. Over the whole lactation cycle, the highest milk losses resulted from recurrent lameness: 640 kg loss for cows presenting a lameness at least three times, versus 20 kg for those presenting only one lameness. The frequency of recurrent lameness was three times higher in Friesian than in Montbeliarde cows and four times higher with grass silage-based diets as compared with hay diets. Four main types of lactation cycles were characterized on the basis of the cows' level of production, their health status, their reproduction performances and their culling rate. Cumulative differences in any of those characteristics accounted for up to a 1 800 kg difference in milk production.

Animals↗

PubMed1989

[Antipeptide antibodies to the porcine lactate dehydrogenase isoenzyme M4 active center fragment as a probe for the structural analysis of active centers of human lactate dehydrogenase isoforms].

Antipeptide antibodies (AB) to the fragment of the active center of porcine lactate dehydrogenase M4 isoform were used for the analysis of antigenic properties and structural comparison of active centers of human lactate dehydrogenase isoforms. Selective precipitation of the M-subunit-containing isoforms using an immunoadsorbent based on antipeptide AB as well as selective inhibition of the enzymic activity of the M4 isoform by antipeptide AB testify to the specific binding of isoforms to antipeptide AB. The experimental results confirm the literary data on conformational changes in the structure of the active centers of corresponding human lactate dehydrogenase isoforms. The specific interaction of antipeptide AB with human lactate dehydrogenase isoforms suggests that the site of the amino acid sequence (residues 180-214) in both human and porcine M4 isoenzymes is immunochemically identical. The data obtained suggest that antipeptide AB are convenient probes for detecting differences (including minor ones) in the primary and spatial structure of enzymes.

Animals↗

PubMed1986

Selective changes in gangliosides of human milk during lactation: a molecular indicator for the period of lactation.

Gangliosides of human milk from women at various periods of lactation were analyzed. GD3 in colostrum, particularly in the early period of lactation, was the major ganglioside, and the molar ratio of GM3 to GD3 was 0.2-0.3 in the milk at 2-6 days postpartum. In contrast, milk from women at 60-390 days postpartum contained GM3 as the major ganglioside and the molar ratio of GM3 to GD3 was more than 3. Milk at 8-40 days postpartum represented an intermediate stage in terms of the ratio of GM3 to GD3. The selective change in the molar ratio of gangliosides was observed as a phenomenon common to all human milk from different individuals at different periods of lactation, indicating that the periods of lactation can be defined on the basis of the ratio. Since glycolipids in human milk are preferentially localized in the milk fat globule membrane, which is derived from the plasma membrane of epithelial cells in the mammary gland, the changes in the ganglioside composition reported in this communication may reflect a qualitative change of the cells in the mammary gland.

Female↗

PubMed1983

The proportion of fatty acids in mammary secretion of cows lactating after calving and hormonal induction of lactation.

The changes in the proportion of fatty acids in lacteal fat of cows induced into lactation by 7-day treatment with oestradiol and progesterone were characterized by an increases in the proportion of fatty acids C6--C13: the proportions of C14, C15, C17, C19 fatty acids changed slightly if at all; the proportions of C16, C20 and C22 fatty acids decreased during the first 28 days of lactation. Similar changes in fatty acid composition were found in lacteal fat of cows lactating after calving. These results demonstrated that the hormonal induction of lactation in nonpregnant cows initiates mammary secretion similar to the fatty acid composition in normal cow milk.

Animals↗

PubMed1995

X-ray structure of two complexes of the Y143F flavocytochrome b2 mutant crystallized in the presence of lactate or phenyl lactate.

Flavocytochrome b2 is a flavohemo enzyme localized in the intermembrane space of yeast mitochondria, where it catalyzes the electron transfer from its substrate, L-lactate, to cytochrome c. We have obtained crystals of a flavocytochrome b2 mutant, Y143F, which are isostructural with those of the native recombinant enzyme [Tegoni, M., & Cambillau, C. (1994) Protein Sci.3, 303-314]. These crystals were grown under similar conditions to those used to obtain the recombinant enzyme, but in the presence of phenyl lactate or lactate. We report here on the structural analysis of the two complexes of flavocytochrome b2 with the reaction products at 2.9 A resolution. In both structures, the Phe143 phenyl ring keeps the same position as that of the phenolic ring of Tyr143 in both the native recombinant and in the native wild-type enzymes. The product of the reaction, phenyl pyruvate or pyruvate, is present at the active site of both subunits, and not only in subunit 2 as observed in the wild-type structure [Xia, Z.-X., & Mathews, F.S. (1990) J. Mol. Biol. 212, 837-863]. The number of interactions between the FMN and the heme domain is considerably lower in the Y143F mutant than in the native proteins. The latter finding strongly supports the hypothesis that the main role of Tyr143 in the native proteins. The latter findings strongly supports the hypothesis that the main role of Tyr143 in the native protein probably consists in establishing a hydrogen bond with the heme [Xia, Z.-X., & Mathews, F.S. (1990) J. Mol. Biol. 212, 837-863]. This interaction appears to be essential for the two domains to approach each other suitably so that the intramolecular electron transfer can occur.

Binding Sites↗

PubMed2005

The effect of inspiratory muscle training upon maximum lactate steady-state and blood lactate concentration.

Several studies have reported that improvements in endurance performance following respiratory muscle training (RMT) are associated with a decrease in blood lactate concentration ([Lac](B)). The present study examined whether pressure threshold inspiratory muscle training (IMT) elicits an increase in the cycling power output corresponding to the maximum lactate steady state (MLSS). Using a double-blind, placebo-controlled design, 12 healthy, non-endurance-trained male participants were assigned in equal numbers to an experimental (IMT) or sham training control (placebo) group. Cycling power output at MLSS was initially identified using a lactate minimum protocol followed by a series of constant power output rides (2.5% increments) of 29.5 min duration; MLSS was reassessed following six weeks of IMT or sham IMT. Maximum inspiratory mouth pressure increased significantly (26%) in the IMT group, but remained unchanged in the placebo group. The cycling power output corresponding to MLSS remained unchanged in both groups after the intervention. After IMT, [Lac](B) decreased significantly at MLSS power in the IMT group [-1.17 (1.01) mmol l(-1) after 29.5 min of cycling; mean (SD)], but remained unchanged in the placebo group [+0.37 (1.66) mmol l(-1)]. These data support previous observations that IMT results in a decrease in [Lac](B )at a given intensity of exercise. That such a decrease in [Lac](B) was not associated with a substantial (>2.5%) increase in MLSS power is a new finding suggesting that RMT-induced increases in exercise tolerance and reductions in [Lac](B) are not ascribable to a substantial increase in the 'lactate threshold'.

Adult↗