Regulation of blood fatty acids and glycerol in lactating cows

Metabolic and Endocrine Role of Adipose Tissue During Lactation

The adipose tissue serves an essential role for survival and reproduction in mammals, especially females. It serves primarily as an energy storage organ and is directly linked to the reproductive success of mammals. In wild animals, adipose tissue function is linked to seasonality of the food supply to support fetal growth and milk production. Adipose tissue depots in ruminants and non-ruminants can secrete many signal molecules (adipokines) that act as hormones and as pro- and anti-inflammatory cytokines. The visceral adipose tissue especially appears to be more endocrinologically active than other adipose depots. The endocrine function is important for the overall long-term regulation of energy metabolism and plays an important role in the adaptation to lactation in many mammalian species, including humans. Furthermore, endocrine signals from adipose tissue depots contribute to fertility modulation, immune function, and inflammatory response. Energy homeostasis is modulated by changes in feed intake, insulin sensitivity, and energy expenditure, processes that can be influenced by adipokines in the brain and in peripheral tissues.

Twenty-four-hour patterns of hormones and metabolites in week 9 and 19 of lactation in high-yielding dairy cows fed triglycerides and free fatty acids

Effects of feeding crystalline triglycerides (TGA), free fatty acids (FFA), and a starch-rich ration (STA) on metabolite and hormone concentrations in blood plasma were studied in high-yielding dairy cows over a 24-h period in week 9 and 19 of lactating. Energy-corrected milk production in the three groups was similar, but was lower in week 19 than in week 9. Energy and protein intakes were greater in week 9 than in week 19, but energy and protein balances in the three groups and in weeks 9 and 19 were similar. Plasma glucose and triglyceride concentrations were lower in week 9 than in week 19. In cows fed FFA, glucose concentrations were highest in week 9. Plasma triglyceride, phospholipid and cholesterol concentrations were highest, whereas beta-hydroxybutyrate concentrations were lowest in FFA-fed cows in weeks 9 and 19. Concentrations of insulin-like growth factor-I in week 19 were lower in cows fed TGA and FFA than in those fed the starch-rich ration. Post-prandial responses were usually greater following morning than afternoon meals. Fructosamine, albumin, urea, growth hormone, thyroxine, and 3,5,3'-triiodothyronine concentrations were similar in weeks 9 and 19 and were not influenced by dietary treatment or feeding times. In conclusion, there were distinct metabolic and endocrine effects of feeding TGA and FFA compared with STA and the concentrations as well as the 24-h changes of various metabolic and endocrine traits in weeks 9 and 19 of lactation were also different.

Glucose and norepinephrine challenges during abomasal infusion of cis or trans octadecenoates in Holstein cows

This experiment determined the effects of infusion of mixtures of fat containing predominantly cis-C18:1 or trans-C18:1 fatty acids into the abomasum on responses of cows to glucose and norepinephrine challenges administered i.v. Six lactating Holstein cows, each with a rumen cannula, were arranged in two Latin squares with 21-d periods. The common basal diet contained 40% forage and 60% concentrate. Treatments were the uninfused control, 750 g/d of a cis fat mixture (65% high oleic sunflower oil and 35% cocoa butter), and 750 g/d of a trans fat mixture (93% shortening and 7% corn oil) infused into the abomasum via a tube that passed through the rumen cannula. Glucose challenges (0.4 mg/kg of BW, administered i.v.) were conducted on d 18, and norepinephrine challenges (0.7 microgram/kg of BW, administered i.v.) were conducted on d 19 of each experimental period. Despite a lower percentage of fat in milk for trans than for cis treatment, disappearance rates of glucose, secretion of insulin after glucose challenge, and appearance rates of NEFA and triglycerides after norepinephrine challenge were similar between treatments. Thus, these data support the hypothesis that trans-C18:1 fatty acids affect the synthesis of milk fat in the mammary gland of lactating cows.

Duodenal rapeseed oil infusion in early and midlactation cows. 4. In vivo and in vitro adipose tissue lipolytic responses

In vitro glycerol and FFA releases from adipose tissue were studied in early (wk 3, trial 1) and midlactation (wk 19 to 26, trial 2) multiparous Holstein Friesian cows receiving a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In trial 2, in vitro basal FFA release, basal FFA: glycerol ratio, and isoproterenol-stimulated FFA and glycerol releases were higher in perirenal adipose tissue from oil-infused cows. Plasma FFA concentration also was higher in oil-infused cows before and after intravenous isoproterenol injection. In trail 1, basal and stimulated glycerol and FFA releases from perirenal (but not subcutaneous) adipose tissue tended to be lower in oil-infused cows. This was probably linked to a lower milk production potential of oil-infused than of control cows which introduced a bias in energy balance. The basal FFA:glycerol ratio tended to be higher in oil-infused cows in both adipose tissues, suggesting a lower rate of reesterification inducted by oil, as was the case in trial 2. The alpha 2-agonist clonidine decreased perirenal adipose tissue glycerol release in cows and treatments in which the responses to 4 x 10(-7) M isoproterenol were higher. In vivo and in vitro lipolytic responses were lower in trial 2 than in trial 1, except the in vitro maximally stimulated lipolytic rate, which probably reflected a long lasting teleophoretic adaptation to ensure energy needs of lactation. This study indicated that oil infusion affected both beta- and alpha 2-adrenergic responses and that postpartum lipid mobilization did not seem to be reduced by the exogenous unsaturated fatty acid supply.

Regulation of adipose tissue metabolism in support of lactation

In the dairy cow, adipose tissue lipid accumulates during pregnancy, and catabolism begins prior to parturition and increases dramatically afterward. After peak lactation, body lipid is replenished. The duration and magnitudes of these adaptations depend on milk energy secretion, net energy intake, genotype, and endocrine environment. Recent research efforts have focused on endocrine, genetic, and biochemical mechanisms underlying metabolic adaptations in cows of high production potential. Adipose tissue lipid synthesis is decreased and lipolysis is increased in early lactation. The magnitude and duration of these adaptations are increased in animals either consuming relatively less energy or producing more milk. Adipose tissue is more responsive to catecholamines in early and midlactation and in animals with higher production. This is more of an increase in maximal response than in sensitivity. In vivo and in vitro rates of adipose tissue lipolysis correlate positively with milk energy secretion, whereas lipid synthesis rates correlate with energy intake. Thus, mammary metabolic activity, within and among lactations, correlates with that in adipose tissue. Likely mechanisms include adaptations in receptors for homeostatic signals and modulation of postreceptor responses. Research is needed into neural, genetic, and hormone regulation of nutrient utilization and body fat use and recovery during lactation. Research should describe mechanistic relationships among nutrients in animals of high production as well as investigate cellular and molecular mechanisms suitable to genetic manipulation.

Regulation of bovine adipose tissue metabolism during lactation. 5. Relationships of lipid synthesis and lipolysis with energy intake and utilization

The effects of energy utilization during lactation on adipose tissue metabolism were determined in 51 first lactation Holstein heifers producing between 5950 and 10,246 kg milk in 305 d. Net energy intake ranged from 18.3 to 40.6 Mcal/d during 28 to 140 d of lactation. Milk yield ranged from 13.5 to 47.4 kg/d and fat percent from 1.49 to 4.60 during 28 to 140 d, providing a range of 8.2 to 32.6 Mcal/d milk energy secretion. Calculated energy balance ranged from -16.4 to 11.5 Mcal/d. Weight change ranged from -70 to 143 kg during that 112-d period. Subcutaneous adipose tissue was biopsied nine times from 30 d prepartum to 15 d after lactation ceased. Adipose lipid synthesis measured prepartum was negatively related to subsequent milk energy secretion. Net energy intake, body weight, and body weight change were related positively to adipose lipid synthesis rates from 28 to 56 d, but those rates were related negatively to milk energy secretion. Lipolysis was positively related to milk energy secretion and body weight and negatively related to NE intake. At d 60 of lactation, adipose tissue lipid synthesis rates were a function of body weight, weight gain, and net energy intake. However, catecholamine-stimulated lipolysis rates were a function of body weight and milk energy secretion. After 140 d, lipid synthesis and lipolysis were elevated and more closely related to the previous peak rather than to concomitant milk energy secretion. These relationships demonstrate the effects of dietary energy content and genetic selection for milk production on adipose tissue metabolism.

Nonesterified fatty acids and glucose in lactating dairy cows: diurnal variations and changes in responsiveness during fasting to epinephrine and effects of beta-adrenergic blockade

To examine whether the typical nightly rise of nonesterified fatty acids in high yielding dairy cows is due to enhanced sympathoadrenal activity, the beta-adrenergic blocker, propranolol, was infused from 1800 to 0805 h. Concentrations of nonesterified fatty acids continuously increased, whereas those of glucose and insulin decreased. Nonesterified fatty acid concentration decreased within minutes in response to concentrate feeding, starting at 0700 h, in association with an increase of insulin and glucose. In a second experiment, adrenaline (.82 mumol/kg/min) was infused from 1800 to 1810 h, 0600 to 0610 h, and 0600 to 0610 h on the 1st, 2nd and 3rd d. After the second infusion, food was withdrawn for 23 h. Concentrations of adrenaline increased similarly. Nonesterified fatty acids and glucose responses were higher during the second than the first infusion. During fasting, nonesterified fatty acid concentrations increased, whereas glucose and insulin concentrations decreased. During the third infusion nonesterified fatty acids responses were unchanged, whereas glucose responses were decreased. Thus, the nightly rise of nonesterified fatty acids was not the consequence of enhanced beta-adrenergic activity. Responses of glucose and nonesterified fatty acids to adrenaline exhibited diurnal differences. Responses of glucose to adrenaline were reduced within 1 d of fasting, whereas those of nonesterified fatty acids were not altered.

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.

Effect of amount and source of dietary nitrogen on milk fat depression in early lactation dairy cows

Twenty-four multiparous and 15 primiparous Holstein cows were fed a total mixed corn silage diet with one of three dietary treatments: 14% crude protein, 22% crude protein (all preformed), or 22% crude protein (preformed plus nonprotein N). Eight multiparous and 5 primiparous cows were randomly assigned to each treatment at calving. The diet contained 23% ADF during wk 1 to 4 postpartum and was lowered to 11% ADF for wk 5 to 12 postpartum. Treatment had no effect on the magnitude of depression in milk fat percentage or milk fat yield in multiparous cows. After fiber was lowered, changes in rumen acetate to propionate ratio, blood glucose, free fatty acids, and insulin were not influenced by treatment. Depression in milk fat percentage for primiparous cows was 19.7, 9.2, and 14.9% for low protein, high protein, and high protein with nonprotein N, respectively. When changed from high fiber to low fiber, the primiparous cows increased milk fat yield 9% for high preformed protein treatment but decreased fat yield for other treatments. Depression in acetate to propionate ratio and increase in blood glucose was least for the high preformed protein group.

Beta-adrenergic receptor involvement in lipolysis of dairy cattle subcutaneous adipose tissue during dry and lactating state

The influence of lactation on beta-adrenergic receptor kinetics was studied with adipocytes from eight Holstein cows during two physiological states, dry period 30 days prepartum and 30 days postpartum or early lactation. Physiological state had no effect on binding kinetics of (--)-hydrogen-3 labeled dihydroalprenolol. Affinity rate constants (8.2 versus 7.2 X 10(7) min-1 M-1) and equilibrium dissociation constants (7.1 versus 7.9 nM) for both prepartum and postpartum periods were similar. In contrast, the apparent number of beta-adrenergic receptors varied with lactational state (42,154 versus 72,264 sites/cell) for dry and lactating status as estimated in assays containing 5 nM (--)-hydrogen-3 dihydroalprenolol. Glycerol release and adipocyte concentrations of adenosine-3',5'-cyclic phosphoric acid were assayed with or without 10 microM epinephrine. Epinephrine elicited greater release of glycerol in adipocytes from lactating than dry cows (3.91 versus 2.1 mumol/10(6) cells/120 min). The concentration of adenosine-3',5'-cyclic phosphoric acid rose during the first 5 min of incubation in the presence of epinephrine and then fell to base after 10 min. Maximum concentrations at 5 min were not different in adipocytes from dry and lactating cows (250 versus 280 pmol/10(6) cells).

Partitioning of nutrients during pregnancy and lactation: a review of mechanisms involving homeostasis and homeorhesis

Control of metabolism during pregnancy and lactation involves two types of regulation-homeostasis and homeorhesis. Homeostasis control involves maintenance of physiological equilibrium or constancy of environmental conditions within the animal. Homeorhesis is the orchestrated or coordinated control in metabolism of body tissues necessary to support a physiological state. Regulation of nutrient partitioning during pregnancy involves homeorhetic controls arising from the conceptus. This assures growth of the conceptus (fetus and fetal membranes) and gravid uterus as well as development of the mammary gland. With the onset of lactation many--perhaps even most--maternal tissues undergo further adaptations to support rates of lipogenesis and lipolysis in adipose tissue are examples of important homeorhetic controls of nutrient partitioning that are necessary to supply mammary needs for milk synthesis. The interactions between homeorhesis and homeostasis during pregnancy and lactation and possible endocrine control are discussed. While not definitively established, roles for placental lactogen and prolactin are attractive possibilities in homeorhetic regulation of maternal tissues to support pregnancy and the initiation of lactaion, respectively.

The mechanism of activation of hormone-sensitive lipase in human adipose tissue

A partially purified hormone-sensitive triglyceride lipase of human adipose tissue was found to be activated twofold by the addition of cyclic 3',5'-AMP, ATP, and magnesium ions. Lipase activities against diolein and monoolein were not affected. Addition of protein kinase inhibitor at zero time completely inhibited activation, and this inhibition was prevented by prior addition of an excess of exogenous protein kinase (from rabbit skeletal muscle). Addition of protein kinase inhibitor during the activation step blocked the activation process without a time lag, suggesting that protein kinase operates directly on hormone-sensitive lipase. Further purification yielded a fraction free of protein kinase, and lipase activation in this fraction depended absolutely on addition of exogenous kinase. Incubation of human fat with epinephrine or isoproterenol stimulated lipolysis and caused conversion of nonactivated hormone-sensitive lipase to its activated form, as indicated by a decrease in the activation subsequently obtainable in fractions prepared from such hormone-treated tissues. These findings strongly suggest that the stimulation of lipolysis by hormonal treatment is the consequence of the activation of hormone-sensitive triglyceride lipase by cyclic 3',5'-AMP-dependent protein kinase.