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Results for “adipocyte lipolysis”

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At least 19 recordsLinked to original sources
PubMed1976

Lipolytic activity of swine adipocytes.

Lipolysis in isolated swine adipocytes was stimulated by epinephrine, dibutyryl cyclic AMP, and weakly by adrenocorticotropin but not by glucagon or cyclic AMP. Theophylline, a phosphodiesterase inhibitor, stimulated lipolysis and greatly enhanced the activity of adrenocorticotropin. The epinephrine-stimulated lipolytic activity, expressed on a tissue or cell volume basis, was greatest at 25 days postpartum, whereas, expressed on a cell basis, the activity was maximal at day 80. Regardless of the mode of expression, the activity at day 150 was low. Cells from younger animals were more sensitive to epinephrine than cells from older animals.

Adipose Tissue↗
PubMed1976

The role of calcium ion in epinephrine activation of lipolysis.

Adipocytes were prepared by collagenase digestion of rat epididymal adipose tissue and incubated for 5, 15 or 30 minutes in Krebs-Ringer bicarbonate buffer containing albumin (40 mg/ml), glucose (1 mg/ml) and epinephrine. Calcium ion was present in some incubations at concentration of 2.5 mM and omitted from others; media with no added calcium contained 1.0 mM EGTA thereby producing a final calcium concentration of less than 10(-7) M. Glycerol release and accumulation of cyclic AMP were measured. Basal lipolysis and cell cyclic AMP levels were increased slightly but not significantly when adipocytes were incubated in calcium free media. Lipolysis could be activated with epinephrine in the absence of calcium but the sensitivity of the lipolytic response was greatly reduced; however, the maximum lipolytic response to epinephrine was not decreased in calcium free media. Similarly, incubation of adipocytes in calcium free media resulted in decreased accumulation of cyclic AMP in response to epinephrine but only when sub-maximum concentrations of the catecholamine were present. Varying the extracellular calcium concentration showed that a concentration of at least 10(-5) M was optimal for epinephrine activation of lipolysis. These observations are considered in accord with the view that activation of adenylate cyclase is facilitated by calcium ion.

Adipose Tissue↗
PubMed1979

Adenosine, thyroid status and regulation of lipolysis.

Adipocytes from hypothyroid rats do not respond to adrenaline with increased glycerol release. Adenosine deaminase largely restores lipolytic sensitivity. This effect is reversed by 2-deoxycoformycin, an inhibitor of the enzyme, and by N6-(phenylisopropyl)adenosine, which is not deaminated. Lipolytic response of normal cells to adrenaline is only 50% inhibited by phenylisopropyladenosine, whereas in cells from hypothyroid rats blockage is total. Inhibition of 50% was seen at 100 and 1 nM concentrations respectively. Insensitivity to adrenaline of hypothyroid-rat adipocytes can, at least partly, be explained by increased sensitivity to adenosine.

Adenosine↗
PubMed1978

The correlation of cyclic AMP and protein kinase activity in adipocytes with lipolysis stimulated by ACTH: the effect of adenosine deaminase and actinomycin D.

ACTH at levels as low as 0.05 mU/ml stimulated lipolysis, protein kinase and cyclic AMP accumulation in isolated fat cells from fed and fasted rats. Changes in cyclic AMP levels and in the protein kinase activity ratio were well correlated temporally. The protein kinase activity ratio was potentiated by adenosine deaminase. A sudden increase or decrease in either ACTH or dibutyryl cyclic AMP concentration was associated with a rapid and corresponding change in the rate of glycerol production. With ACTH, the changes in glycerol production were accompanied by appropriate changes in cyclic AMP levels. Actinomycin-D (10 UM) did not affect lipolysis or cyclic AMP accumulation activated by ACTH in fat cells.

Adenosine↗
PubMed2026

Lipidomic Profiling Reveals Differential Behaviors of Individual Free Fatty Acids During Altered Metabolic States in Rats.

We used lipidomic analyses to investigate how individual free fatty acids (FFAs) behave differently in metabolic states altered by diet and by antibiotic treatment (ABX) that depletes gut bacteria. Wistar rats were fed either a low-fat or high-fat purified diet, or standard chow with or without antibiotics for two weeks (n = 8-10). Blood samples were then collected before and after meals. Individual FFAs were quantified and grouped based on distinct postprandial response patterns across dietary and treatment conditions. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), key ω-3 FFAs, exhibited postprandial shifts suggestive of suppressed adipocyte lipolysis following meals. Fatty acids in the high-fat diet (HFD) elevated postprandial FFA levels, masking the meal-induced suppression of lipolysis observed with chow or low-fat diet (LFD). Some FFAs, including medium-chain saturated species, remained unaffected by meals. We further evaluated the impact of diet and ABX on baseline (pre-meal) concentrations of FFAs. Certain FFAs were altered by purified diets compared to standard chow. Notably, EPA and DHA were selectively depleted under HFD conditions, likely due to enhanced catabolic activity. In conclusion, lipidomic profiling revealed divergent behaviors among individual FFAs, reflecting distinct metabolic processes and regulatory mechanisms under altered metabolic states.

Animals↗
PubMed1978

[Absence of lipolytic action of adrenaline on a human subcutaneous adipose tissue. Role of alpha-adrenergic receptors].

Epinephrine cannot stimulate adipocytes' lipolysis of human subcutaneous adipose tissue (lateral part of the thigh) while a clear lipolytic action can be shown on the omental tissue. However, at the same concentrations, isoproterenol (a beta-agonist) exerts a strong adipokinetic effect on adipocytes of the both types of adipose tissue. An alpha-adrenolytic (phentolamine) enhances the lipolytic action of epinephrine on the omental adipose tissue and unmasks a lipolytic action of epinephrine on the subcutaneous. Epinephrine antagonizes the lipolysis induced by theophyline on the subscutaneous adipocytes, this action is increased by propranolol (a beta-adrenergic blocking agent). The unresponsiveness to epinephrine of the subcutaneous adipose tissue studied here could be linked to a strong antilipolytic alpha-adrenergic effect.

Adipose Tissue↗
PubMed1978

Influence of genetic obesity in mice on the lipolytic response of isolated adipocytes to isoproterenol and ACTH-(1-24).

The lipolytic response of isolated adipocytes from genetic obese (C57/BL/64 ob/ob) and lean (C57BL/6J +/?) mice to ACTH-(1-24), isoproterenol and glucagon has been studied. The mean cell idameter of adipocytes form ob/ob mice was approximately twice that of lean controls. The adipocytes from obese mice contained on the average approximately six times the amount of triacylglycerol present in the smaller lean mouse adipocyte. Lipolysis was calculated both on a per cell basis (10(5) cells) and per mu mole of triacylglycerol and when expressed on a cell number basis, the larger adipocytes from obese mice showed an ACTH-(1-24) stimulated glycerol release which was quantitatively similar to that of smaller adipocytes from lean mice. When expressed per mu mole of triacylglycerol, the smaller cells from lean animals appeared to be dramatically more responsive to either isoproterenol or ACTH-(1-24). On either basis, ACTH-(1-24) stimulated glycerol release from obese mouse cells was greater than the isoproterenol response. The obese mouse of adipocyte showed selective loss of response to isoproterenol compared to its lean control.

Adipose Tissue↗
PubMed1979

Inhibition of lipolysis in hamster adipocytes by the cation ionophor X537A.

The present study reports the effects of the lipophylic ionophore X537A on lipolysis and accumulation of cAMP in isolated hamster epidiymal adipocytes. X537A inhibited lipolysis activated with norepinephrine, isoproterenol, dibutyryl cAMP or theophylline but failed to influence basal lipolysis. The minimum effective concentration of X537A required to inhibit lipolysis was between 1 and 3 micrograms/ml; at a concentration of 10 micrograms/ml, X537A inhibited lipolysis by approximately 50%. The antilipolytic effect of X537A does not result from decreased formation of cAMP because the accumulation of cAMP in response to isoproterenol or theophylline was significantly potentiated in the presence of the ionophore. Most of the additional cAMP that accumulated in the presence of X537A was found to be intracellelular, the distribution of cAMP between cells and incubation medium not being influenced by X537A. Neither the basal activity of cAMP dependent protein kinase nor the activity in the presence of isoproterenol or theophylline was influenced by X537A. The effects of X537A on lipolysis and on accumulation of cAMP were found to persist in the absence of extracellular calcium, but adipocytes that were preincubated in a calcium free media containing 4.0 mM EGTA failed to respond to X537A with an increase in cAMP levels. It is concluded that X537A inhibits lipolysis by uncoupling cAMP accumulation from activation of triglyceride lipase by a mechanism unrelated to activation of protein kinase.

Adipose Tissue↗
PubMedDate not supplied

[Glucocorticoids and gluco-lipidic metabolism].

Glucocorticoids increase the stocks of carbohydrate and the supra-hepatic flow of glucose. Their excess produces a centripetal redistribtution of adipose stocks and potentialises adipocyte lipolysis. Although their role of glucose and lipid metabolism is evident, the mechanisms and sites of action of glucocorticoids are multiple and not entirely clear. The actions of glucocorticoids become clear in cases of insulin deficiency, especially when the deficiency is marked, which is of great interest in current medical practice.

Adipose Tissue↗
PubMed1979

Sensitivity of glucose uptake and lipolysis of white adipocytes of the rat to insulin and effects of some metabolites.

1. Insulin increased glucose uptake and inhibited lipolysis in white adipocytes of the rat over the same concentration range of the hormone: the half-maximal effects were observed at approx. 10 microunits of insulin/ml. Thus, contrary to previous reports, no difference in sensitivity of the two processes to insulin could be found, which suggests that both these effects of insulin are important in increasing the rate of glucose utilization after a meal. 2. Adenosine deaminase, which lowers the concentration of adenosine in the incubation medium, decreased the sensitivity of both processes (lipolysis and glucose uptake) to insulin: this suggests that adenosine increases the sensitivity of both processes. Similarly, lactate and 3-hydroxybutyrate increased the sensitivity of both processes (to the same extent) to insulin. It is suggested that this increased sensitivity will improve the response (of adipose tissue) to insulin on refeeding after a prolonged period of starvation (when the hydroxybutyrate concentration is high), and after a short burst of exercise, when the blood lactate concentration is high and when large amounts of glucose are produced from lactate via gluconeogenesis in the liver.

Adenosine Deaminase↗
PubMed1979

Insulin inhibition of lipolysis of human adipocytes: the role of cyclic adenosine monophosphate.

To gain information on the manner in which insulin suppresses lipolysis in man, isolated adipocytes, prepared from subcutaneous adipose tissue, were incubated with insulin (100 microunits/ml) alone and in combination with isoproterenol (10(-7) M or 10(-8) M). Cyclic AMP concentration was measured at 60 min; glycerol release, used as an index of lipolysis, was determined at 45 and 75 min. Insulin consistently reduced both basal and stimulated cyclic AMP and glycerol release: the degree of suppression of each was comparable. In subsequent experiments, the ability of insulin to suppress glycerol release stimulated by isoproterenol, theophylline, and dibutyryl cyclic AMP (dbcAMP), respectively, was compared. Insulin substantially reduced the raised levels of cyclic AMP and glycerol release prompted by isoproterenol and theophylline, but it had little effect on increases caused by dbcAMP. These findings support the view that reduction in cyclic AMP is an important component in the regulation of fat mobilization by insulin.

Adipose Tissue↗
PubMed1976

Effects of hyperosmolarity on the cyclic AMP concentration and lipolysis of the adipocyte stimulated by adrenocorticotropic hormone.

The effects of ACTH on 3',5'-cyclic AMP (cAMP) levels and lipolysis were examined on isolated adipocytes incubated in either isosmolar or hyperosmolar media. The ability of ACTH to induce intracellular cAMP accumulation was greatly enhanced by incubating cells in hyperosmolar sucrose (100 to 400 mM) solutions. Hyperosmolar solutions prepared by the addition of either NaCL, glucose or mannitol enhanced the ACTH effect on cAMP to the same extent as did the hyperosmolar sucrose solution, but hyperosmolar urea solutions did not have such an effect. The effect of hyperosmolarity was shown only in cells stimulated by lipolytic hormones, and the effects were still evident in the presence of high concentrations of theophylline, indicating the effect of hyperosmolarity is to facilitate hormone action on the receptor-coupler system of the adipocyte membrane. The action of glucagon on cAMP was augmented much less than the actions of ACTH and isoproterenol. Basal as well as ACTH or exogenous cAMP stimulated lipolysis was lower in hyperosmolar sucrose solutions. Some mechanism by which hyperosmolarity interferes with the metabolic sequence beyond the accumulation of cAMP was suggested.

Adipose Tissue↗
PubMed1978

Thyroid hormone modulation of epinephrine-induced lipolysis in rat adipocytes: a possible role of calcium.

Adipocytes isolated from normal, hypothyroid, and hyperthyroid rats were characterized with respect to their lipolytic activity (assessed by glycerol release) and beta-adrenergic receptors (assessed by binding of (--) [3H]alprenolol). Fat cells from hypo- and hyperthyroid rats showed the same affinity (K = 1.4 X 10(10) M(-1) and binding capacity (N = 1.21 X 10(-13) mol/microgram DNA) toward alprenolol as those from normal animals. Adipocytes from hypothyroid rats were unresponsive to epinephrine in a concentration range of 0.1-10 micron, with moderate responses at higher concentrations; injection of T3 in hypothyroid rats restored lipolytic responsiveness of the adipocytes to normal levels. Quabain (1 mM) inhibited lipolytic responses to epinephrine by 40--45% in normal and hyperthyroid rats; the lipolytic increment due to the hyperthyroid state was uninfluenced by ouabain. The lipolytic refractoriness to epinephrine of hypothyroid adipocytes was restored to normal levels by theophylline (1 mM) or EGTA (1 mM); the theophylline and EGTA effects were not additive, suggesting that they stimulated lipolysis via a common mechanism. Epinephrine-induced lipolysis in all groups was progressively inhibited by increasing concentrations of Ca2+ in the medium. The Ca ionophore, A23187, showed a concentration-dependent inhibitory action. Theophylline (1mM) almost completely overcame the inhibitory action of the ionophore; in the presence of lower concentrations of theophylline, the inhibitory effect of the ionophore was least in hypothyroid and greatest in hyperthyroid fat cells. The findings suggest that the differences in the lipolytic response to epinephrine observed in hyperthyroid, euthyroid, and hypothyroid adipocytes are not due to alterations in the number or affinity of beta-adrenergic receptors nor to a membrane mechanism that might show differential ouabain sensitivity, but may be related to altered cellular Ca2+ concentrations which may indirectly alter cellular phosphodiesterase activity.

Adipose Tissue↗
PubMed1975

Site of free-fatty-acid inhibition of lipolysis by human adipocytes.

When human adipocytes were incubated in albumin-free buffer, isoproterenol failed to stimulate an increase in either cyclic AMP or glycerol release. Cells incubated for 1/2 hr with 4% albumin and isoproterenol had a striking increase in cyclic AMP; this effect was markedly reduced when FFA concentration was increased by the addition of sodium oleate. When incubation was prolonged to 4 hr, the cyclic AMP concentration of stimulated cells fell towards the basal level. This decline in the level of cyclic AMP was prevented by frequent change in buffer. The ability of epinephrine and sodium fluoride to stimulate the adenylyl cyclase of human adipocyte membranes was not affected by the addition of sodium oleate. However, when intact cells were preincubated for 1 hr with added sodium oleate, the responsiveness to epinephrine of membranes derived from the cells was reduced. No such alternation in responsiveness to sodium fluoride occurred. These results indicate that the inhibitory effect of FFA on lipolysis is associated with a reduced production of cyclic AMP; the latter effect may be the consequence of FFA inhibition of adenylyl cyclase.

Adenylyl Cyclases↗
PubMed1978

ACTH-induced lipolysis in rat adipocytes: structure-activity relationships.

The lipolytic action of natural porcine ACTH1(-39) and of a number of highly purified synthetic ACTH peptide fragments was studied using rat adipocytes. Of the analogues tested, only ACTH1(-24) exhibited full lipolytic activity with respect to intrinsic activity and affinity. Several shorter fragments appeared to be full agonists but had lower affinity. Fragments ACTH5(-10) and ACTH7(-10) were inactive. No antagonistic effects against the lipolytic action of ACTH could be demonstrated with substimulatory doses of ACTH1(-16), ACTH1(-10), ACTH7(-24) and ACTH11(-24). Based on the relative potency derived from dose-response curves, a more refined model with respect to the active centers being encoded in various sequences of the hormone, is proposed.

Adipose Tissue↗