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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The methods utilized in our laboratory for a biochemical approach of obesity include dietary manipulations, fatty acid analysis of tissue lipids, in vivo lipogenesis from [3H H2O and [1-14C] acetate, in vitro utilization of [3H] H2O, [U-14C] glucose, [U-14C] fructose, [U-14C] alanine and [1-14C] acetate by adipose tissue fragments, hormone sensitivity (to insulin and catecholamines), and the activity of enzymes such as fatty acid synthetase and adenylate cyclase in adipose tissue extracts. With these methods at hand, it is possible to estimate the major biochemical factors responsible for fat accumulation in adipose tissue. As an example, the case of obese (ob/ob) homozygotic animals of the C57BL/6J strain of Bar Harbor, which suffer from an autosomal recessive obese-hyperglycemic (O-H) syndrome, is compared to that of control nonobese (ob+/ob+) mice from the same strain. The hereditary O-H syndrome in ob/ob mice is characterized by obesity, resistance to the action of insulin, and hyperinsulinism. The development of obesity depends on high lipogenesis in fat depots. Contribute also to obesity a large influx of fatty acids of hepatic and dietary origin, and reduced lipolysis. In these mice, a high fat diet is more propitious to fat accretion than a high-carbohydrate diet.
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PMID:Experimental basis of obesity. 62 36

1. Fatty acid synthesis, measured in the perfused liver of genetically obese (ob/ob) mice with 3H2O or [14C]actate, did not show the inhibition by [8-arginine]vasopressin (antidiuretic hormone) that is observed in livers from normal mice. 2. Hepatic glycogen breakdown in obese mice was stimuulated by vasopressin, but not as extensively as in lean mice. 3. If obese mice received a restricted amount of food, then fatty acid synthesis still did not respond to vasopressin, but glycogen breakdown was fully stimulated. 4. Cholesterol synthesis was not inhibited by vasopressin in livers from obese mice. 5. Vasopressin inhibited fatty acid synthesis in intact lean mice, but not in obese animals. 6. These results suggest that genetic obesity could be due to an inborn error within the mechanisms (other than adenylate cyclase) which mediate responses to extracellular effectors.
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PMID:Resistance to hepatic action of vasopressin in genetically obese (ob/ob) mice. 100 43

Insulin, proinsulin and glucagon extracted from lean rat pancreases were studied in radioimmunoassay, radioreceptorassay and bioassay systems. Extracted insulin behaved identically to a rat insulin used as a reference standard in radioimmunoassay. On the basis of its immunoreactivity, extracted insulin was slightly less potent (about 70%) than the rat standard insulin in competing with the binding of 125I-insulin to rat liver membranes (radioreceptorassay) and in stimulating glucose oxidation by rat fat cells (bioassay). Extracted glucagon and a pork glucagon used as a reference standard were indistinguishable in two radioimmunoassay systems for glucagon, in competing with the binding of 125I-glucagon to rat liver membranes (radioreceptorassay) and in stimulating adenylate cyclase in rat liver membranes (bioassay). Genetically obese rats (Zucker, "fatty") were compared to their lean littermates with respect to insulin, proinsulin and glucagon extracted from their pancreases. Proinsulin represented the same proportion of total immunoreactive insulin in both types of rats. In the radioimmunoassays, the radioreceptorassays and the bioassays, insulin, proinsulin and glucagon from obese rats were indistinguishable from insulin, proinsulin and glucagon from lean rats. It is concluded that the pancreatic hormones of obese ("fatty") rats possess the same immunoreactivity and biological potency as those of nonobese rats. This excludes the possibility that some alteration in the biological properties of pancreas insulin and/or glucagon of fatty rats could explain the metabolic abnormalities observed in this type of obesity.
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PMID:Glucagon and insulin from lean rats and genetically obese fatty rats: studies by radioimmunoassay, radioreceptorassay and bioassay. 120 22

We have investigated beta-adrenergic regulation of adenylate cyclase activity in heart tissue membranes from the genetically obese Zucker rat, the genetically obese CBA mouse and the genetically obese diabetic (db/db) mouse. Responsiveness to beta-adrenergic stimulation was impaired in membranes from the obese Zucker rat, but not in the other models. The membranes from obese Zucker rats showed both decreased beta-adrenergic-receptor number and altered coupling between beta-adrenergic receptors and the stimulatory guanine-nucleotide-binding protein, Gs. In contrast, no alterations in either the levels of Gs or the functional interaction between this protein and the catalytic moiety of adenylate cyclase were observed. In these three genetic models of obesity we observe dissimilar alterations in the control of adenylate cyclase.
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PMID:Regulation of cardiac adenylate cyclase activity in rodent models of obesity. 134 26

Fat-cells were isolated from patients of body-mass indices (BMIs) ranging from 17.9 to 83.9 kg/m2. Isoprenaline-stimulated cyclic AMP accumulation in cells prepared from obese subjects as compared with normal-weight subjects, was less sensitive to inhibition by the adenosine agonist N6-(phenylisopropyl)adenosine (PIA) (P = 0.047). The inhibition of 7 beta-desacetyl-7 beta-[gamma-(N-methylpiperazino) butyryl]-forskolin-stimulated adenylate cyclase by PIA in the presence of adenosine deaminase was also much attenuated in crude plasma membranes of adipocytes prepared from massively obese patients as compared with lean controls (P = 0.0143). This difference was probably not due to different cell size, because adenylate cyclase of crude plasma membranes of large adipocytes was actually more sensitive to PIA than was adenylate cyclase of membranes of smaller fat-cells co-isolated from the same individual. The stimulatory effect of PIA on glucose uptake in the presence of adenosine deaminase was depressed in adipocytes prepared from obese subjects and correlated with BMI at r = -0.626 (P = 0.007) at 100 nM-PIA. The adenosine receptors were studied by using the adenosine antagonist 1,3-[3H]dipropyl-8-cyclopentylxanthine. The binding was rapid and proportional to protein concentration. There was no difference in the affinities of receptors in membranes of obese and normal-weight subjects; Kd values of all patients averaged 3.3 nM. Bmax values were 54 and 130 fmol/mg of protein in membranes prepared from seven obese and five control patients respectively. The Bmax values calculated per mg of protein correlated with BMI at r = -0.539 (P = 0.047). The adenosine content of adipose tissue was higher in obese than in control subjects. These results demonstrate an attenuated response of cyclic AMP accumulation, adenylate cyclase and glucose uptake to adenosine in fat-cells prepared from obese subjects, and suggest that this change is at least partly due to changes in the amount of adenosine receptors, but not their affinity. The decreased receptor number could be due to higher adenosine content. A higher adenosine concentration in adipose tissue could explain why lipolysis is inhibited in situ in obesity, and the desensitization could explain the diminished response to adenosine analogues in isolated fat-cells.
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PMID:Attenuated adenosine-sensitivity and decreased adenosine-receptor number in adipocyte plasma membranes in human obesity. 165 38

Studies examining animal models of genetic obesity have identified defects in adipocyte hormone-stimulated lipolysis that involve the adenylate cyclase transmembrane signaling system, specifically those components that decrease adenylate cyclase activity. To determine whether obese people demonstrate alterations in adenylate cyclase activity that could contribute to the maintenance of obesity by inhibiting lipolysis, we examined human adipocytes from patients who were lean, obese, or formerly obese. Fat samples were obtained from the lower abdomen of 14 women who were morbidly obese (obese group), from 10 women who were formerly morbidly obese and had lost weight after gastric stapling (postobese group), and from 10 similarly aged women of normal weight (controls). Adipocyte adenylate cyclase activity was determined under ligand-free (no stimulatory or inhibitory influences present), hormone-stimulated (isoproterenol, 10(-6) mmol/L), and maximal (cells stimulated with 10 mumol/L forskolin) conditions by measuring cyclic adenosine monophosphate (cAMP) levels by radioimmunoassay. The activity of adenylate cyclase was significantly different (p less than 0.01) in the three groups. Adipocytes from obese women had lower levels of cyclase activity under both ligand-free (5% vs 16% of maximal) and hormone-stimulated conditions (76% vs 100% of maximal) than adipocytes from normal women. Postobese women had levels of hormone-stimulated cAMP identical to those of normal women but still had abnormal ligand-free levels (under 5%). These results suggest the presence of an alteration in adipocyte adenylate cyclase regulation in morbidly obese women that is not entirely corrected when weight is lost after food intake is reduced by gastric stapling. This alteration in ligand-free cAMP activity may contribute to the development and maintenance of obesity.
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PMID:Alterations in adipocyte adenylate cyclase activity in morbidly obese and formerly morbidly obese humans. 216 54

Adenylate cyclase activity was determined in membranes of liver, muscle, white adipose tissue, and brown adipose tissue (BAT) of lean (Fa/) and obese (fa/fa) Zucker rats. Responses were monitored following beta-adrenergic receptor stimulation and addition of GTP, GTP gamma S, or forskolin. beta-Adrenergic responses in liver, white adipose tissue, and BAT were lower in obese than in lean animals. No such difference was observed in muscle membranes. Production of cAMP after addition of guanine nucleotides was lower in liver and white adipose tissue membranes from obese rats compared with their lean littermates. Synthesis of cAMP in muscle membranes of obese animals after addition of GTP was either not different, or slightly higher, than that observed in muscle membranes from lean animals. Furthermore, production of cAMP after forskolin addition to muscle membranes of obese rats was significantly higher than that observed from lean rats under the same conditions. Interestingly, BAT membranes of obese rats were significantly more sensitive to guanine nucleotide activation than those of lean animals. The results confirm recent findings indicating inferior function of G proteins in liver plasma membranes of obese Zucker rats, and extend this observation to adipose tissue. The present results further suggest that the "nonreceptor" components (e.g., G proteins) responsible for the activation of adenylate cyclase in BAT membranes of obese rats are more responsive to stimulation than those of lean animals. Such sensitivity may be related to and perhaps compensate for the reduced thermogenic activity in the obese Zucker rat during the development of obesity.
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PMID:Nonreceptor-mediated responses of adenylate cyclase in membranes from liver, muscle, and white and brown adipose tissue of obese (fa/fa) and lean (Fa/) Zucker rats. 217 38

Periodic hormonogenesis has been described in patients with ACTH-dependent hypercorticism, and fluctuations of cortisol secretion have also been observed in patients with adrenal tumors. In this report, we studied a 41-year-old white male who presented with hypertension, central obesity, and muscle weakness of 2-years duration. His plasma cortisol was low (4.5 micrograms) in the morning and high in the evening (29.3 micrograms). Urinary free cortisol was 750 micrograms/day. A 24-hour cycle demonstrated highest values at noon and in late afternoon. This pattern was not suppressed by dexamethasone. When the patient was kept fasting, plasma cortisol remained low all day, and became elevated immediately after meal administration overnight. A left-sided adrenal mass was demonstrated and removed. In vitro, the adenylate cyclase activity of tumor tissue demonstrated more significant response to vasopressin than to ACTH; other tested peptides were inactive. We propose that a humoral factor induced by eating was responsible for the periodic hormonogenesis, directly stimulating the adrenal secretion of cortisol.
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PMID:Cushing syndrome with food-dependent periodic hormonogenesis. 283 Oct 1

Adenylate cyclase activity and its modulation by guanine nucleotides and isoproterenol were assessed in adipocyte membranes of mice with mutations causing different genetic obesity syndromes. The object was to determine whether the defect in inhibitory modulation observed in the obese (ob/ob) mouse was also present in the diabetes (db/db) mouse. The data show that adipocyte adenylate cyclase in both the ob/ob and the db/db mouse is resistant to activation by isoproterenol. The response to guanosine triphosphate (GTP) differed between the two mutants, such that an inhibitory phase was visible in the db/db but not in the ob/ob membranes. Moreover, pertussis toxin attenuated the inhibitory effect of GTP and significantly stimulated cyclase activity in the db/db but not in the ob/ob membranes. The data show that the two mutations affect the expression of adenylate cyclase activity via different mechanisms.
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PMID:Effect of the genetic background and specific mutation on adenylate cyclase activity in obesity syndromes. 318 20

We have assessed the presence of VIP/PHI/secretin receptors in heart by: (1) testing the ability of the corresponding peptides to activate adenylate cyclase in cardiac membranes from rat, dog, Cynomolgus monkey and man, and (2) examining the ability of the same peptides to exert inotropic and chronotropic effects on heart preparations from rat and Cynomolgus monkey in vitro. Based on their affinity for natural peptides and synthetic analogs, two types of VIP/PHI/secretin receptors were characterized: the relatively nonspecific "secretin/VIP receptor" of rat heart (that is "secretin-preferring" only in that secretin was more efficient than VIP in stimulating adenylate cyclase), and the "VIP/PHI-preferring" receptor of man, monkey and dog heart. Four physiopathological situations affecting secretin/VIP receptors in rat heart were explored: In male rats from the Okamoto strain and the Lyon strain, two strains presenting spontaneous hypertension, heart membranes exhibited a markedly decreased response of adenylate cyclase to secretin/VIP, with lesser alterations in the responses to isoproterenol and glucagon. This impairment developed in parallel with the occurrence of hypertension and was reproduced in normotensive rats submitted to chronic isoproterenol treatment (but not in Goldblatt hypertensive rats). These findings are consistent with a hyperactivity of norepinephrine pathways in spontaneously hypertensive rats, leading to a reduced number of cardiac post-junctional secretin/VIP receptors bound to adenylate cyclase. Heart membranes from genetically obese (fa/fa) Zucker rats also exhibited severely decreased responses to secretin/VIP with lesser alterations in the responses to glucagon and isoproterenol. These anomalies were specific for the heart, and developed in concomitance with obesity. The first anomaly could not be corrected by severe food restriction. Secretin stimulation of heart adenylate cyclase was also selectively altered in streptozotocin-diabetic rats. Thus, two types of diabetic cardiomyopathy were characterized by a severe local alteration of secretin/VIP receptors coupled to adenylate cyclase. Hypothyroidism, provoked in rat by thyroidectomy or propylthiouracil treatment, again induced a marked decrease in secretin-stimulated cardiac adenylate cyclase activity. In rat papillary muscle electrically stimulated in vitro, secretin exerted a positive inotropic effect. This effect was reduced in obese (fa/fa) Zucker rats. In rat right atrium, secretin also exerted a positive chronotropic effects.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Heart receptors for VIP, PHI and secretin are able to activate adenylate cyclase and to mediate inotropic and chronotropic effects. Species variations and physiopathology. 608 34


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