Effects of pregnancy and lactation on lipolysis of ewe adipocytes induced by beta-adrenergic stimulation

Adrenergic Tone as an Intermediary in the Temperament Syndrome Associated With Flight Speed in Beef Cattle

The temperament of farm animals can influence their resilience to everyday variations within the managed production environment and has been under strong direct and indirect selection during the course of domestication. A prominent objective measure used for assessing temperament in beef cattle is the behavioral flight response to release from confinement in a crush or chute. This behavioral measure, termed flight speed (also known as escape velocity) is associated with physiological processes including body temperature, feeding behavior, growth rate, carcass composition, immune function, and health outcomes. This review examines the functional links between this suite of traits and adrenergic activity of the sympathetic nervous system and the adrenomedullary hormonal system. It is suggested that flight speed is the behavioral aspect of an underlying “flightiness” temperament syndrome, and that elevated adrenergic tone in animals with a high level of flightiness (i.e., flighty animals) tunes physiological activities toward a sustained “fight or flight” defense profile that reduces productivity and the capacity to flourish within the production environment. Nonetheless, despite a common influence of adrenergic tone on this suite of traits, variation in each trait is also influenced by other regulatory pathways and by the capacity of tissues to respond to a range of modulators in addition to adrenergic stimuli. It is suggested that tuning by adrenergic tone is an example of homeorhetic regulation that can help account for the persistent expression of behavioral and somatic traits associated with the flight speed temperament syndrome across the life of the animal. At a population level, temperament may modulate ecological fit within and across generations in the face of environmental variability and change. Associations of flight speed with the psychological affective state of the animal, and implications for welfare are also considered. The review will help advance understanding of the developmental biology and physiological regulation of temperament syndromes.

The effect of breed, parity and body fatness on the lipolytic response of dairy cows

The objective of this study was to examine the effect of breed, parity and body fatness on the lipolytic response of dairy cows. The lipolytic response was estimated as the plasma non-esterified fatty acid (NEFA) response to an adrenergic challenge. Four challenges per lactation were carried out on 124 Danish Holsteins, 101 Danish Red and 82 Jerseys through consecutive lactations. Within breed, there were two genetic lines. Cows were equally distributed across two feeding treatments, a normal and a low energy total mixed ration. Diet composition was constant throughout lactation. The lipolytic response was significantly affected by breed, parity and stage of lactation. Lipolytic response was greater in early lactation than other stages in lactation (P 0·001). The larger breeds had a higher lipolytic response than Jerseys (P 0·05), and showed an increase in lipolytic response between first and second parity (P 0·05), but not between second and third lactation. Lipolytic response in Jerseys was not significantly affected by parity. No line or feeding treatment effects were observed on the lipolytic response. Ultrasound measurement of the area of subcutaneous backfat was used to estimate effect of body fatness on the lipolytic response. There was an increase in lipolytic response with increasing body fatness (P 0·05) in mid lactation and the dry period. The slope of this was not affected by breed or parity. It was concluded that the lipolytic response of dairy cows, and by implication the responsiveness of the lipid reserves, varies according to breed, parity and physiological state.

Plasma non-esterified fatty acid response to a β-adrenergic challenge before or after feeding in energy underfed or overfed, dry or lactating cows

The effects of adrenergic challenge (in order to evaluate the adipose tissue lipolytic potential) and time of challenge relative to feeding on the response curve of plasma non-esterified fatty acids (NEFA) in four underfed or overfed non-lactating non-pregnant cows were studied. Basal NEFA and NEFA response to isoproterenol (ISO; 4 nmol/kg body weight) were higher when challenged before than after feeding and higher in underfed than overfed cows. Interaction between feeding level and time of challenge was significant (P < 0·001) for the rising part of NEFA response. Pooled NEFA response curves from several trials (no. = 63 challenges) were analysed in order to obtain a simplified procedure for the prediction of the NEFA response. High correlations were found between the response area or maximal NEFA response and NEFA response at 15 min (r = 0·95 and 0·98, respectively). This simplified procedure was applied on pooled data from 84 challenges in order to evaluate the effects of energy balance, physiological status, body condition score (BCS) and time of challenge relative to feeding. Energy balance had a significant effect on basal plasma NEFA and NEFA response at 15 min after ISO challenge (–7·6 and –14·2 μmol/l when the daily energy balance increased by 1 MJ, respectively). Time of ISO injection relative to feeding had a greater effect on stimulated NEFA than on basal NEFA (308 v. 239 μmol/l). There was a significant effect of BCS (41 μmol/l per unit of BCS) on the basal plasma NEFA level. The NEFA response at 15 min after ISO challenge was lower (387 μmol/l) in lactating cows than in dry cows. The NEFA response to ISO at 15 min could provide an efficient method of studying the adipose tissue lipolytic potential of cattle in vivo.

Pregnancy Effects on Rat Adipose Tissue Lipolytic Capacity are Dependent on Anatomical Location

Pregnancy is characterized by changes in maternal adiposity. The aim of this study was to carry out a detailed analysis of the different steps of the adrenergic pathway, lipoprotein lipase (LPL) levels and adipocyte size, in order to evaluate the response of white adipose tissue (WAT) to the metabolic changes during pregnancy depending on the anatomical location. In general, the levels of the proteins of the lipolytic pathway decreased with pregnancy. In retroperitoneal WAT adenylate cyclase (AC) levels decreased from 100% in controls to 44% by day 13 and 11% by day 20. In mesenteric WAT the alpha (2A)/beta (3)-adrenergic receptor balance seemed to be one of the main regulatory points of the lipolytic pathway and the reduction in the postreceptor element levels was clearly lower than for the other two depots (PKA levels reduced from 100% in controls to 72% by day 20, while in the other two depots it decreased to 30%, and AC and HSL levels did not show statistically significant changes in this depot). In contrast, the LPL-to-HSL ratio may be a major regulatory point in gonadal WAT. In summary, we describe regional differences in the regulation of WAT metabolism throughout pregnancy, which may be of great importance to determine the role of the different fat depots during late pregnancy. Thus, gonadal and mesenteric WAT changed to a lipolytic state to sustain the rapid foetal growth, although with differences between them in the main regulatory points, while retroperitoneal WAT could have a role later on, during lactation.

Fat accumulation in the rat during early pregnancy is modulated by enhanced insulin responsiveness

Insulin sensitivity has been implicated in the variation of fat accumulation in early gestation by as-yet-unknown mechanisms. In the present study, we analyzed the insulin sensitivity of lipolysis and lipogenesis in lumbar adipocytes from rats at 0, 7, 14, and 20 days of gestation. In adipocytes of 7-day pregnant rats, we found a twofold decrease in both beta-agonist (isoproterenol and BRL-37344)-stimulated lipolysis and beta3-adrenoceptor protein but not in lipolysis initiated by forskolin or isobutylmethylxanthine, suggesting a modification of the lipolytic pathway at the receptor level. Whereas adipocytes from 7-day pregnant rats showed a twofold increase in fatty acid synthesis from glucose, those from 20-day pregnant animals displayed a decreased lipogenic activity. Insulin responsiveness of the lipolytic and lipogenic pathways was analyzed by dose-response experiments, giving evidence for the involvement of improved insulin responsiveness in the enhanced lipogenic and reduced lipolytic activities of adipocytes in early pregnancy. In contrast, insulin resistance is responsible for lower antilipolytic and lipogenic actions of insulin in late pregnant animals. In conclusion, the present study shows that enhanced adipose tissue insulin responsiveness during early pregnancy contributes to maternal fat accumulation, whereas decreased insulin responsiveness during late gestation modulates fat breakdown.

Serum concentrations of insulin-like growth factors and placental lactogen during gestation in cattle. II. Maternal profiles

This study was designed to examine the effects of fetal growth potential on maternal hormones and lipid metabolism. Sixty beef heifers were inseminated with semen from sires with high (H) or low (L) expected progeny differences for birth weight. Maternal serum was collected at 21-d intervals from Day 85 to Day 274 of gestation. Serum concentrations of insulin-like growth factor (IGF)-I, IGF-II, placental lactogen (PL), and nonesterified fatty acids (NEFA) were determined and correlated to fetal and maternal characteristics. Maternal serum IGF-I declined throughout pregnancy, whereas IGF-II was relatively constant and PL tended to increase. Maternal serum NEFA was low and invariant through Day 211 of gestation when it rose 3.5 times to peak levels at Day 253 and declined at Day 274. PL was positively correlated to NEFA (r = 0.37, P < 0.01), IGF-I was negatively correlated (P < 0.01) to NEFA and PL (r = -0.59, and -0.35, respectively), and IGF-II was negatively correlated to NEFA (r = -0.35, P < 0.01). Dams pregnant with H fetuses had lower (P = 0.02) serum IGF-I and tended to have higher (P = 0.09) serum PL concentrations than dams carrying L fetuses. Additionally, dams pregnant with L fetuses had higher (P < 0.03) serum IGF-II concentrations than dams with H fetuses (175.6 vs. 145.0 ng/ml) during the third trimester. Fetal sex had no effect on any maternal serum parameter. Fetal weight and instantaneous growth rate (IGR) were positively correlated to maternal NEFA and PL and negatively correlated to maternal IGF-I and IGF-II. Independent IGR effects were detected for PL (P < 0.06) and IGF-I (P < 0.0005) concentrations. Maternal hip height was negatively related to serum IGF-I and positively related to serum PL concentrations. Maternal body weight and body condition score were correlated with several serum parameters but were confounded by day of gestation. Correlation analysis of serum concentrations of IGF-I, IGF-II, and PL did not support the hypothesis that PL regulates IGF concentrations.

Effects of breed and adipose depot location on responsiveness and sensitivity to adrenergic stimulation in ovine adipose tissue

Karakul tail adipose tissue had the smallest adipocytes, and this tissue was also the least lipolytically responsive. However, lipolytic responsiveness did not vary with breed or depot when expressed per gram of tissue. Sensitivity to isoproterenol and epinephrine was higher in tissues of the Karakul than of the Outaouais breed of sheep. As well, there was evidence for alpha-antilipolytic action in Karakul but not Outaouais adipose tissue. The Karakul breed is a unique model for the study of adipocyte metabolism in that a wide range of adipocyte volumes exist within an individual, and the Karakul adipose tissue appears to be particularly sensitive to adrenergic regulation.

Insulin-like growth factors-I and -II, somatotropin, prolactin, and placental lactogen are not acute effectors of lipolysis in ruminants

The acute regulation of lipolysis in the adipose tissue of ruminants was evaluated with lactating cows (n = 4) and growing ewe lambs (n = 11). Subcutaneous adipose tissue was obtained by biopsy or at slaughter and was incubated with varying concentrations of biologically active insulin-like growth factors-I and -II (IGF-I, IGF-II), somatotropin (ST), prolactin (PRL), or placental lactogen (PL) to determine the effect of these hormones on lipolysis. Complimentary studies were conducted to examine the effects of IGF-I and IGF-II on the acute regulation of lipolysis in adipose tissue from lactating ewes and wethers under a variety of incubation conditions. Isoproterenol (ISO), a beta-adrenergic agonist known to rapidly stimulate lipolysis, was used as a positive control. Incubation with ISO for 3 hr resulted in a significant increase in the rates of lipolysis. However, there was no stimulation of lipolysis over the 3-hr incubation at any concentration or under any conditions for IGF-I or IGF-II. Furthermore, ST, PRL, or PL had no acute effects on the rates of lipolysis in adipose tissue. These data demonstrate that IGF-I, IGF-II, ST, PRL, and PL are not acute effectors of the lipolytic rate in the adipose tissue of ruminants.

Effect of somatotropin treatment on lipogenesis, lipolysis, and related cellular mechanisms in adipose tissue of lactating cows

The effect of bST on the metabolism of lipid in adipose tissue was studied using tissue biopsies from lactating cows treated with bST for 8 d. Cows responded to treatment by increasing daily milk yield by 10.9 kg, although net energy intake was not changed. Thus, net energy balance was changed from highly positive to slightly negative (+7.7 to -1.1 Mcal/d). Consistent with these changes in net energy balance, lipogenesis rates were dramatically reduced (97%) in adipose tissue from bST-treated cows. Activities of acetyl-coenzyme A carboxylase (initial and total) and fatty acid synthase were also dramatically decreased. Therefore, for cows in positive energy balance, reduced lipid synthesis in adipose tissue represents a major mechanism whereby bST alters nutrient partitioning to support greater milk synthesis. Treatment with bST had no effect on beta-adrenergic-stimulated lipolysis in adipose tissue explants incubated in vitro with adenosine deaminase. However, bST treatment reduced the ability of adenosine to inhibit lipolysis in adipose tissue, which involved changes in both sensitivity and responsiveness to adenosine. Therefore, the enhanced lipolytic response to catecholamine in vivo with bST treatment relates to relief in the adenosine inhibitory signaling cascade rather than to a direct effect on the stimulatory signaling pathway.

Effects of lactation on the signal transduction systems regulating lipolysis in sheep subcutaneous and omental adipose tissue

The effect of lactation on the regulation of lipolysis by beta- and alpha 2-adrenergic agents and by adenosine has been investigated. When changes in adipocyte mean cell volume (which decreases with lactation) are allowed for, lactation increased the maximum response both to beta-adrenergic agents and to the adenosine analogue N6-phenylisopropyladenosine, but had no apparent effect on the responsiveness of the alpha 2-adrenergic system in both subcutaneous and omental adipocytes. For subcutaneous adipocytes, there was no significant change in the number of beta-adrenergic or alpha 2-adrenergic receptors, but the amount of Gs and the maximum (forskolin-stimulated) adenylate cyclase activity were increased by lactation. In contrast, in omental adipocytes, the number of beta- (but not alpha 2-) adrenergic receptors and the amount of Gs were increased, whereas forskolin-stimulated adenylate cyclase activity was unchanged by lactation. In both types of adipocyte, cyclic AMP phosphodiesterase and total protein kinase A activities were unchanged. Lactation had no effect on the number of adenosine receptors but increased the amounts of the Gi isoforms expressed in both types of adipocyte. These various adaptations differ markedly in a number of respects from those described previously in the rat. Lactation, then, while having a similar overall effect on the response to beta-adrenergic agonists of adipocytes, achieves this by depot-specific mechanisms. In contrast, changes in response to adenosine appear to involve the same mechanism in the two depots investigated.

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.

Adenosine and the control of adrenergic regulation of adipose tissue lipolysis during lactation

Adenosine is a locally active factor that is produced intracellularly and extracellularly in adipose tissue. Adenosine binds to receptors in the plasma membrane of adipocytes; this activates a guanine triphosphate binding protein that inhibits adenylate cyclase activity and, hence, lipolysis. Lactation results in an enhanced responsiveness of adipocytes to beta-agonists, which stimulate lipolysis, and, paradoxically, to adenosine, which inhibits lipolysis. These adaptations are partly due to increases in ligand binding and to changes in postreceptor components of the signal transduction systems. Somatotropin is implicated in the chronic adaptations of the beta-adrenergic system, whereas insulin, somatotropin, glucocorticoids, and at least one unidentified factor have a role in the chronic control of the adenosine system of adipocytes.

Chronic control of the beta- and alpha 2-adrenergic systems of sheep adipose tissue by growth hormone and insulin

1. Sheep adipose tissue retained responsiveness to catecholamines when maintained in tissue culture for 48 h; both the rate of basal lipolysis and sensitivity to beta-agonists were increased after tissue culture. 2. Tissue culture in the presence of growth hormone resulted in an increased maximum response and sensitivity to the beta-agonist isoprenaline, but had no effect on basal lipolysis. 3. Tissue culture in the presence of insulin increased the basal rate of lipolysis and increased the ratio of the rate of noradrenaline-stimulated/isoprenaline-stimulated lipolysis, indicating a decrease in the 2-adrenergic effect of noradrenaline. 4. Tissue culture in the presence of growth hormone increased ligand binding to beta-adrenergic receptors. 5. Tissue culture in the absence of exogenous hormones increased ligand binding to alpha 2-adrenergic receptors; this was prevented by actinomycin D and partly prevented by insulin. 6. These studies show that both growth hormone and insulin chronically modulate the adrenergic system of sheep adipose tissue; the effects of growth hormone are primarily on the beta-adrenergic system, whereas insulin modulates the alpha 2-adrenergic system.

Sensitivity of freshly isolated ovine adipocytes to inhibition of lipolysis by insulin

1. Ovine adipocytes were isolated in the presence of adenosine to minimize cell damage and were incubated at a low cell concentration. 2. Insulin sensitivity of lipid metabolism was retained. 3. Insulin inhibited basal lipolysis by 61% and isoproterenol- and adenosine deaminase-stimulated lipolysis by 84%. 4. Insulin increased glucose conversion to cell lipid by 3-fold.

Lipolytic response of bovine adipose tissue to alpha and beta adrenergic agents 30 days pre- and 120 days postpartum

1. The beta adrenergic agonists isoproterenol and epinephrine stimulated in vitro lipolysis in adipose tissue removed from heifers 30 days pre- and 120 days postpartum. 2. Propranolol, a beta antagonist, blocked isoproterenol stimulated lipolysis pre- and postpartum. 3. Epinephrine co-incubated with propranolol resulted in a suppression of lipolysis similar to that produced by clonidine, an alpha agonist, both pre- and postpartum. 4. Bovine adipose tissue lipolysis was more responsive to isoproterenol and isoproterenol + propranolol at 120 days of lactation than 30 days prepartum. 5. Adipose tissue sensitivity to clonidine, epinephrine and epinephrine + propranolol did not differ 30 days pre- and 120 days postpartum.

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.