Showing papers by "Peter Arner published in 1990"

Adrenergic regulation of lipolysis in situ at rest and during exercise.

Abstract: The adrenergic regulation of lipolysis was investigated in situ at rest and during standardized bicycle exercise in nonobese healthy subjects, using microdialysis of the extracellular space in subcutaneous adipose tissue. The glycerol concentration was about two times greater in adipose tissue than in venous blood. At rest, the glycerol concentration in adipose tissue was rapidly increased by 100% (P less than 0.01) after the addition of phentolamine to the ingoing perfusate, whereas addition of propranolol did not alter the adipose tissue glycerol level. Glycerol in adipose tissue and plasma increased during exercise and decreased in the postexercise period. Propranolol in the perfusate almost completely inhibited the increase in the tissue dialysate glycerol during the exercise-postexercise period. Phentolamine, however, was completely ineffective in this respect. During exercise, the lipolytic activity was significantly more marked in abdominal than in gluteal adipose tissue; this was much more apparent in women than in men. Thus, in vivo lipolysis in subcutaneous adipose tissue is regulated by different adrenergic mechanisms at rest and during exercise. Alpha-adrenergic inhibitory effects modulate lipolysis at rest, whereas beta-adrenergic stimulatory effects modulate lipolysis during exercise. In addition, regional differences in lipolysis are present in vivo during exercise, which seem governed by factors relating to sex.

Beta-adrenoceptor expression in human fat cells from different regions.

Abstract: The expression of beta-adrenoceptors (BAR) was investigated in abdominal and gluteal fat cells of 32 nonobese men and women using radioligand binding and RNA excess solution hybridization. In both sexes the number of BAR binding sites was about twice as high in abdominal as in gluteal fat cells (P less than 0.01). Northern blot analysis of total RNA from adipose tissue showed hybridization of the BAR1 probe to an mRNA species of about 2.5 kb and of the BAR2 probe to an mRNA species of approximately 2.2 kb. The steady-state mRNA levels of BAR 1 and BAR 2 were also about twice as high in abdominal as in gluteal adipocytes of men and women (P less than 0.01). In abdominal fat cells the mRNA levels were approximately 45 and 30 molecules/cell for BAR1 and BAR2, respectively. There were no regional or sex variations in BAR 1 and BAR 2 mRNA stability. The apparent half-life of mRNA for both receptor subtypes was approximately 6 h in both regions. The mRNA levels for beta actin did not differ between the two regions in either sex. Thus, differences in expression of the genes encoding for BAR 1 and BAR 2 can explain why abdominal fat cells have more BAR than gluteal fat cells. This variation in gene expression may be a molecular mechanism underlying the well known regional differences in catecholamine-induced lipolysis activity between central and peripheral adipose tissue.

Catecholamine-induced lipolysis in adipose tissue of the elderly.

Abstract: Age-dependent alterations in the effects of catecholamines on lipolysis were investigated in 25 young (21-35 yr) and 10 elderly (58-72 yr) healthy, nonobese subjects using isolated adipocytes obtained from abdominal subcutaneous tissue. Basal lipolysis was not affected by aging, while the rate of catecholamine-stimulated lipolysis was reduced by 50% in the elderly subjects (P less than 0.005). To elucidate the mechanisms behind this phenomenon lipolysis was stimulated with agents that act at well-defined steps in the lipolytic cascade, from the receptor down to the final step: the activation of the protein kinase/hormone-sensitive lipase complex. All agents stimulated lipolysis at a 50% lower rate in elderly as compared with young subjects (P less than 0.05 or less). However, half-maximum effective concentrations of the lipolytic agents were similar in both groups. The antilipolytic effects of alpha 2-adrenoceptor agonists were also the same in young and old subjects. Moreover, the stoichiometric properties of the beta- and alpha 2-receptors did not change with increasing age. In vivo studies performed on the same individuals likewise demonstrated an impaired lipolytic responsiveness, with 50% lower plasma glycerol concentrations during exercise in the elderly subjects (P less than 0.05), in spite of a normal rise in plasma norepinephrine. The plasma glycerol levels correlated strongly to the glycerol release caused by catecholamine-stimulated lipolysis in vitro in both young and elderly subjects (r = 0.8-0.9, P less than 0.001). In conclusion, a decreased activation of the hormone-sensitive lipase complex appears to be the mechanism underlying a blunted lipolytic response of fat cells to catecholamine stimulation in elderly subjects. This finding may, explain the age-dependent decreased lipolytic response to exercise in vivo.

Subcutaneous adipose tissue: a source of lactate production after glucose ingestion in humans.

Abstract: The in vivo kinetics of lactate and pyruvate in the extracellular space of subcutaneous adipose tissue after glucose ingestion were investigated in healthy volunteers by the use of a microdialysis ...

Glucocorticoid Receptor Messenger Ribonucleic Acid in Different Regions of Human Adipose Tissue

Abstract: The expression of glucocorticoid receptor (GR) messenger RNA (mRNA) was investigated in sc adipose tissue and isolated adipocytes from the abdominal and gluteal regions in men and women using a human GR complementary RNA probe. GR mRNA levels were 2-fold higher in female than in male abdominal tissue or adipocytes, whereas in gluteal tissue or adipocytes no sex differences were observed. GR mRNA levels in female abdominal adipocytes were 50% higher than in corresponding female gluteal adipocytes; the opposite was observed corresponding in males. Northern blot analysis of total cellular RNA isolated from abdominal and gluteal adipocytes showed hybridization of the human GR probe to an RNA species of approximately 7.1 kilobases in both regions. No sex or regional differences in GR mRNA stability were observed. The human metallothionein II (hMTII) mRNA, which is regulated by glucocorticoids at the transcriptional level, showed an opposite sex and regional pattern as GR mRNA. However, in gluteal adipose tissue no sex differences were observed in hMTII mRNA levels. The expression of beta-actin mRNA, which is not regulated by glucocorticoids, showed no sex or regional variation. By immunocytochemistry, using an anti-GR-monoclonal antibody, cytoplasmic as well as nuclear staining for GR was demonstrated in both sexes and both regions. In conclusion, variations in GR mRNA levels between sexes and body regions may explain the well known sex and tissue differences in effects of glucocorticoids on human adipose tissue.

In situ studies of catecholamine-induced lipolysis in human adipose tissue using microdialysis.

Abstract: The effects of catecholamines on lipolysis in situ were investigated in humans. Subcutaneous adipose tissue was microdialyzed with solvents containing adrenergic agents. Norepinephrine caused a rapid increase in the glycerol level in adipose tissue (lipolysis index) that was further increased by the alpha adrenoreceptor blocker phentolamine. At 10(-11) mol/l of norepinephrine caused a 100% stimulation of lipolysis (P less than .025). In the presence of phentolamine the lipolytic effects of catecholamines at 10(-12) mol/l was isoproterenol greater than epinephrine greater than norepinephrine. All these three lipolytic catecholamines caused a transient increase in the adipose tissue dialysate glycerol level, which peaked after 20 to 30 min of catecholamine exposure and then declined. The apparent tachyphylaxia could not be overcome by a gradual increase of the catecholamine concentration from 10(-12) to 10(-8) mol/l. However, the selective alpha-2 adrenoreceptor agonist clonidine caused a continuous and dose-dependent decrease in the dialysate glycerol level; the minimum effective concentration was 10(-9) mol/l. In conclusion, catecholamines have a lipolytic effect in situ at much lower concentrations than those in the circulation. This effect is transient and is related to beta adrenoreceptors. In additio, catecholamines have alpha adrenoreceptor-mediated effects on lipolysis in situ.

β-Adrenoreceptor Subtype Expression in Human Liver*

Abstract: The pharmacological and gene expressions ofβ1-and β2-adrenoceptor subtypes (BAR1 and BAR2) were investigated in human liver by radioligand binding assays, adenylate cyclase experiments, and RNA excess solution hybridization. [125I]Cyanopindolol, nonlabeled adrenergic agents, and BAR1/ BAR2 cRNA were used as probes. The relationship between binding sites for BAR1 and BAR2 was markedly different from that between the basal mRNA expression for the two receptor subtypes. Plasma membranes as well as a microsomel-enriched fraction contained binding sites only for BAR2. The potency of BAR agonists and antagonists in stimulating adenylate cyclase activity of plasma membranes was typical of a BAR2 response. Northern blot analysis of total cellular RNA isolated from liver tissue showed hybridization of the BAR1 probe to a mRNA species of 2.5–2.6 kilobases and of the BAR2 probe to a mRNA species of 2.2–2.3 kilobases. The basal level of BAR1 mRNA was 5-fold higher than of BAR2 mRNA, as assayed by solution hybridizati...

In vivo subcutaneous adipose tissue glucose kinetics after glucose ingestion in obesity and fasting.

Abstract: The kinetic pattern of subcutaneous adipose tissue extracellular glucose following glucose ingestion was investigated in vivo with a microdialysis technique in normal-weight (n = 21) and obese subjects (n = 18) before and after a 7-day fast (n = 9). A dialysis probe (4 x 0.5 mm) was implanted subcutaneously, and was continuously perfused (5 microliters/min). The tissue dialysate glucose concentration was determined in 15-min samples before and during a period of 180 min after a 75-g oral glucose load. A comparison was made between the tissue dialysate concentrations and the venous blood glucose levels. In all study groups the increase in subcutaneous tissue dialysate glucose following glucose ingestion paralleled that in blood, with a time-lag of up to 15 min. In the normal-weight subjects the maximum relative increase in abdominal adipose tissue dialysate glucose was 25% higher (p less than 0.005) than the corresponding blood glucose level, and the total relative glucose level (area under curve, AUC) in abdominal fat was 20% (p less than 0.01) higher than in blood. In contrast, the kinetics of gluteal subcutaneous tissue dialysate and blood glucose levels were similar. In the obese patients before the fasting period the maximum relative glucose level in abdominal fat was almost twice as high as in blood (p less than 0.005), and the total glucose level (AUC) was 50% higher than the blood glucose AUC (p less than 0.005). After the fast, on the other hand, almost identical relative dynamics of abdominal subcutaneous tissue and blood glucose levels were found.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased lipolytic sensitivity to catecholamines in diabetic patients with severe autonomic neuropathy.

Abstract: Lipolytic sensitivity to catecholamines was studied in gluteal adipocytes from diabetic subjects with severe (n = 3), mild (n = 6) or no autonomic neuropathy (n = 8). Two of the three patients with severe autonomic neuropathy had a completely abolished plasma epinephrine response to insulin-induced hypoglycaemia, whereas the third patient showed a reduced and delayed plasma epinephrine response. Lipolytic sensitivity to isoprenaline (P less than 0.05), and to epinephrine in the presence of yohimbine (P less than 0.0001), was significantly increased in the diabetic subjects with severe autonomic neuropathy, compared to the other study groups. Moreover, the specific binding of the beta-adrenoceptor antagonist (+-)-4-(3-butylamino-2-hydroxypropoxyl)-(5.7-3H)-benzimidazole- -2-one-hydrochloride (3H-CGP) was markedly exaggerated (P less than 0.05) in the patients with severe autonomic neuropathy. These findings demonstrate that the lipolytic sensitivity to catecholamines in adipose tissue was increased only in patients with severe autonomic neuropathy and impaired epinephrine response to insulin-induced hypoglycaemia. This increased beta-adrenergic sensitivity could, at least in part, be attributed to an increased density of beta-adrenergic receptors in the adipocytes.