Enzymes involved in adenosine metabolism in rat white and brown adipocytes. Effects of streptozotocin-diabetes, hypothyroidism, age and sex differences

Adenosine Deaminase Activity in the Serum of Type 2 Diabetic Patients

Adenosine deaminase (ADA) is suggested to be an important enzyme for modulating the bioactivity of insulin, but its clinical significance in diabetes mellitus (DM) is not yet characterized. We measured the serum level of ADA in healthy controls (C, n=29) and type 2 diabetic patients (n=42). The mean serum level of ADA in C, and type 2 diabetic patients were 29.81±9.15 and. 20.73±8.42 U/L, respectively (P<0.006 vs. C). ADA levels of patients were significantly correlated with HbA1c (r=0.45, p<0.01). Our findings suggest that ADA may play a role in insulin effect and glycamic control. On the other hand, increased activity of ADA in type 2 DM might be a marker for insulin indication. However, further studies are required for the pathogenic role of elevated ADA activity in type 2 DM.

Predictive metabolic signatures for the occurrence and development of diabetic nephropathy and the intervention of Ginkgo biloba leaves extract based on gas or liquid chromatography with mass spectrometry

Diabetic nephropathy (DN) is one of the leading causes of death in diabetes mellitus (DM). Early warning and therapy has significant clinical value for DN. This research sought to find biomarkers to predict the occurrence and development of DN and the intervention of Ginkgo biloba leaves extract (GBE) by quantifying fatty acids, amino acids, and nucleosides and nucleobases in rat plasma. Samples were respectively collected at the weekend of 5-10 weeks after diabetic rats induced by streptozotocin were defined. Plasma fasting blood-glucose, kidney index, blood urea nitrogen, creatinine, urine albumin excretion and ultrastructural morphology of kidney were measured or observed. Fatty acids, amino acids and nucleosides and nucleobases in rat plasma were analyzed by gas chromatography or liquid phase chromatography and mass spectrometry, respectively. From the biochemical index and morphological change of kidney, the rats from the 5th to 7th week were in the stage of DM while from the begin of 8th week the rats were suggested in the early stage of DN. The results of quantitative metabolomics showed that 16 differential metabolites were related to the progression of DN, and oleic acid, glutamate and guanosine might be the potential biomarkers of kidney injury. 14 differential metabolites were related to GBE against the progression of DN, while oleic acid and glutamate might be the potential biomarkers of GBE against kidney injury. Those findings potentially promote the understanding of the pathogenic progression of DN and reveal the therapeutic mechanism of GBE against DN.

The extracellular cAMP-adenosine pathway regulates expression of renal D1 dopamine receptors in diabetic rats

Activation of D1 dopamine receptors expressed in the kidneys promotes the excretion of sodium and regulates sodium levels during increases in dietary sodium intake. A decrease in the expression or function of D1 receptors results in increased sodium retention which can potentially lead to the development of hypertension. Studies have shown that in the absence of functional D1 receptors, in null mice, the systolic, diastolic, and mean arterial pressures are higher. Previous studies have shown that the expression and function of D1 receptors in the kidneys are decreased in animal models of diabetes. The mechanisms that down-regulate the expression of renal D1 receptor gene in diabetes are not well understood. Using primary renal cells and acutely isolated kidneys from the streptozotocin-induced rat diabetic model, we demonstrate that the renal D1 receptor expression is down-regulated by the extracellular cAMP-adenosine pathway in vitro and in vivo. In cultures of primary renal cells, a 3 mm, 60-h cAMP treatment down-regulated the expression of D1 receptors. In vivo, we determined that the plasma and urine cAMP levels as well as the expression of 5'-ectonucleotidase, tissue-nonspecific alkaline phosphatase, and adenosine A2a receptors are significantly increased in diabetic rats. Inhibitors of 5'-ectonucleotidase and tissue-nonspecific alkaline phosphatase, α,β-methyleneadenosine 5'-diphosphate, and levamisole, respectively, blocked the down-regulation of D1 receptors in the primary renal cells and in the kidney of diabetic animals. The results suggest that inhibitors of the extracellular cAMP-adenosine pathway reverse the down-regulation of renal D1 receptor in diabetes.

Pleiotropic effects of thyroid hormones: learning from hypothyroidism

Hypothyroidism induces several metabolic changes that allow understanding some physiopathological mechanisms. Under experimental hypothyroid conditions in rats, heart and kidney are protected against oxidative damage induced by ischemia reperfusion. An increased resistance to opening of the permeability transition pore seems to be at the basis of such protection. Moreover, glomerular filtration rate of hypothyroid kidney is low as a result of adenosine receptors-induced renal vasoconstriction. The vascular tone of aorta is also regulated by adenosine in hypothyroid conditions. In other context, thyroid hormones regulate lipoprotein metabolism. High plasma level of LDL cholesterol is a common feature in hypothyroidism, due to a low expression of the hepatic LDL receptor. In contrast, HDL-cholesterol plasma levels are variable in hypothyroidism; several proteins involved in HDL metabolism and structure are expressed at lower levels in experimental hypothyroidism. Based on the positive influence of thyroid hormones on lipoprotein metabolism, thyromimetic drugs are promising for the treatment of dyslipidemias. In summary, hypothyroid status has been useful to understand molecular mechanisms involved in ischemia reperfusion, regulation of vascular function and intravascular metabolism of lipoproteins.

Syzygium cumini inhibits adenosine deaminase activity and reduces glucose levels in hyperglycemic patients

Syzigium cumini (L.) Skeels from the Myrtaceae family is among the most common medicinal plants used to treat diabetes in Brazil. Leaves, fruits, and barks of S. cumini have been used for their hypoglycemic activity. Adenosine deaminase (ADA) is an important enzyme that plays a relevant role in purine and DNA metabolism, immune responses, and peptidase activity. ADA is suggested to be an important enzyme for modulating the bioactivity of insulin, but its clinical significance in diabetes mellitus (DM) has not yet been proven. In this study, we examined the effect of aqueous leaf extracts of S. cumini (L.) (ASC) on ADA activity of hyperglycemic subjects and the activity of total ADA, and its isoenzymes in serum and erythrocytes. The present study indicates that: (i) the ADA activity in hyperglycemic serum was higher than normoglycemic serum and ADA activity was higher when the blood glucose level was more elevated; (ii) ASC (60-1000 microg/mL) in vitro caused a concentration-dependent inhibition of total ADA activity and a decrease in the blood glucose level in serum; (iii) ADA1 and 2 were reduced both in erythrocytes and in hyperglycemic serum. These results suggest that the decrease of ADA activity provoked by ASC may contribute to control adenosine levels and the antioxidant defense system of red cells and could be related to the complex ADA/DPP-IV-CD26 and the properties of dipeptidyl peptidase IV (DPP-IV) inhibitors which serve as important regulators of blood glucose.

Serum adenosine deaminase activity in gestational diabetes mellitus and normal pregnancy

PURPOSE

To our knowledge, there is no report regarding adenosine deaminase activity (ADA) in gestational diabetes mellitus (GDM). The aim of the present study was to investigate the level of serum ADA activity in normal pregnancy, GDM and normal non-pregnant women.

METHODS

The serum catalytic concentration of ADA was measured in samples of 20 GDM, 40 normal pregnant and 20 non-pregnant healthy women.

RESULTS

Adenosine deaminase activity was significantly higher in GDM (24.30 +/- 8.04 IU/L) and pregnant women (23.88 +/- 8.66 IU/L) than those of normal non-pregnant individuals (11.85 +/- 3.23 IU/L) (P < 0.0001), but the ADA level was not significantly different from GDM and normal pregnant women (P = 0.97).

CONCLUSIONS

Adenosine deaminase activity was significantly higher in GDM and pregnant individuals than normal group in this study. Previous reports in this field are contentious; therefore, ADA activity could be regulated in different population by immunologic and genetic factors.

Purine nucleotides and their metabolites in erythrocytes of streptozotocin diabetic rats

OBJECTIVES

In the present study it was tried to obtain a complete overview of purine nucleotide metabolism in erythrocytes of streptozotocin (STZ) induced diabetes mellitus rats.

METHODS

Erythrocyte levels of the main nucleotides (ATP, ADP, AMP, GTP, GDP, GMP, IMP, NAD+, NADP+), nucleosides (Ado, Guo, Ino) and the base Hyp were measured using the HPLC method. The parameters that can be deduced from their concentrations: TAN, TGN and AEC, GEC expressed by the ratio of high/low energy nucleoside phosphates were calculated. The effects of streptozotocin-induced diabetes on the concentration and metabolism of rat erythrocyte purine and pyridine nucleotides and the activity of Na+, K+-ATPase as well as Ca2+-ATPase were investigated.

RESULTS

Increased dephosphorylation of adenine nucleotides (found as the increased concentration of Ado and Hyp and the decrease in AEC value) and the decrease in ATP and TAN and the changes in the concentrations of NAD+ and NADP+ suggest serious purine and pyridine metabolism disruptions in diabetic erythrocytes and decrease in ATPases activity.

CONCLUSION

The observations suggest that purine nucleotide degradation is markedly accelerated in erythrocytes of STZ diabetic rats.

Experimental hypothyroidism modifies specific binding of A1 and A2A analogues to adenosine receptors in the rat kidney

1 Binding kinetic studies with the adenosine analogues [3H]CPA (0.250-50 nm) and [3H]CGS21680 (0.1-100 nm) were performed in renal tissue from control (NL) and thyroidectomised (HTX) rats. We propose that the low renal adenosine content reported in hypothyroid rats may induce changes in the density and/or affinity of adenosine receptor, distributed in the cortex (C), outer medulla (OM), and inner medulla (IM) of the kidney. 2 [3H]CPA and [3H]CGS21680 binding saturation isotherms were fitted by nonlinear regression analysis and evaluated by Furchgott's method. These results revealed high (KH) and low (KL) affinity (KD) sites for both compounds. As expected, a heterogeneous pattern was observed for Bmax and KD values. 3 Bound [3H]CPA and [3H]CGS21680 were displaced by increasing concentrations of nonlabelled DPCPX and NECA, respectively, indicating the presence of A1 and A2A adenosine receptors distributed in the renal segments studied. 4 The relative intrinsic efficacy (epsilon) for [3H]CPA and [3H]CGS21680 showed extreme values (far from 1.0), 0.5 in IM NL and 2.70 in IM HTX for [3H]CGS21680. 5 Our results indicate that A2A adenosine receptor is predominant in IM from HTX, but A1 receptors are expressed preferentially in C in NL. 6 We conclude that the changes observed in number, affinity, and epsilon for the A2A receptor in IM from HTX might be responsible from alterations in medullary function, that is, incapacity for urine concentration as observed in the hypothyroid kidney.

Adenosine regulates renal nitric oxide production in hypothyroid rats

In the hypothyroid kidney, exogenous adenosine (ADO) produces vasodilation and restores renal function to near-normal values. This study evaluates whether this response is mediated by nitric oxide synthesis stimulated by adenosine. GFR and urinary excretion of NO2-/NO3- (UNO2-/NO3-) were measured in normal (NL) and hypothyroid (HTX) rats under basal conditions and during infusion of: intra-aortic ADO, intravenously, 1,3-dipropyl-8p-sulfophenylxanthine (DPSPX), 8-cyclopentyl-1,3-dipropyl xanthine (DPCPX), N(omega)-nitro-L-arginine methylester (L-NAME) + ADO, L-NAME + PSPX, L-NAME + DPCPX, and intrarenal (IR) ADO or DPCPX + IR ADO. Intra-aortic ADO induced a fall in GFR and increased UNO2-/NO3- slightly in NL rats; in HTX rats, both GFR and UNO2-/NO3- increased significantly. DPSPX and DPCPX increased UNO2-/NO3- excretion in NL animals with minor changes in GFR; the blockers increased both GFR and UNO2-/ NO3- in HTX rats. L-NAME completely blocked the increase in NO2-/NO3- induced by ADO, DPSPX, and DPCPX. The intrarenal infusion of ADO at 1, 10, and 35 nmol/kg per min progressively decreased GFR with a slight increase in UNO2-/ NO3- in NL rats; in the HTX, GFR increased with the highest dose and UNO2-/NO3- progressively increased. DPCPX prevented the fall in GFR induced by intrarenal ADO in NL rats, with no further changes in UNO2-/NO3-; in HTX rats, intrarenal ADO under A1 blockade further increased GFR and UNO2-/NO3-. Arterial and venous ADO concentrations were lower in the HTX rats. In the HTX kidney, NO production was stimulated by ADO, most likely through activation of A2 or A3 receptors, whereas A1 receptors had an inhibitory effect. Thus, ADO receptors are involved in the regulation of kidney function in pathophysiologic conditions.

Increased responses to adenosine in isolated left atria from streptozotocin-diabetic rats: evidence for the involvement of hypothyroidism

Direct and indirect (antiadrenergic) inotropic effects of adenosine in the isolated left atrial preparations from streptozotocin-induced diabetic rats were examined by comparing with those from propylthiouracil-induced hypothyroid rats. Experimental diabetes was induced by a single i.v. injection of streptozotocin (45 mg/kg). Subsets of diabetic rats were treated daily with either insulin (6-8 units/kg) or triiodothyronine (T3; 8-10 micrograms/kg). After 10 weeks, negative inotropic and antiadrenergic effects of adenosine were assessed in the atria from nondiabetic, diabetic, insulin- or T3-treated diabetic and hypothyroid rats. Diabetic rats exhibited a significant increase in negative inotropic and antiadrenergic effects of adenosine, as well as signs of hypothyroidism such as decreased thyroid hormone levels. The same changes in the adenosine effects also were noticed in the hypothyroid rats. In our study, the influence of T3 treatment on the hyperreactivity of diabetic rat atria to adenosine also was examined by comparing with that of insulin treatment. Both insulin and T3 treatments restored the hyperreactivity to adenosine, with the exception of adenosine receptor affinity (pD2 value) calculated for the negative inotropic effect of adenosine. These findings suggest that thyroid hormone deficiency is likely to be involved in the inotropic and antiadrenergic effects of adenosine on the left atria from rats with experimental diabetes for 10 weeks.

Elevated adenosine deaminase activity in the serum of patients with diabetes mellitus

Adenosine deaminase (ADA) is suggested to be an important enzyme for modulating the bioactivity of insulin, but its clinical significance in diabetes mellitus (DM) is not yet characterized. We measured the serum levels of ADA isoenzymes (ADA1 and ADA2) in healthy donors (HD, n = 52), insulin-dependent diabetes mellitus (IDDM, n = 53) patients and non-insulin-dependent diabetes mellitus (NIDDM, n = 65) patients. The mean serum level of ADA1 in HD, IDDM or NIDDM patients was, respectively 6.5, 8.1 or 9.5 units/l (P < 0.001 vs. HD) and that of ADA2 in HD, IDDM or NIDDM patients was 7.0, 14.9 (P < 0.001 vs. HD) or 11.2 units/l (P < 0.001 vs. HD), respectively. Normalization of the blood glucose level by the hospitalization was associated with the decrease in ADA2 (but not ADA1) activity in 6 of 8 IDDM or 11 of 12 NIDDM poorly controlled patients. ADA2 (but not ADA1) activity in the poorly controlled NIDDM patients directly correlated with the hemoglobin A1c level (P < 0.002). Measurement of serum ADA2 activity may be important to better understand the clinical aspects of both IDDM and NIDDM. The pathogenic role of elevated ADA activity in the sera of DM patients was addressed.

Increased alpha 1-adrenoceptor density in brown adipose tissue indicates recruitment drive in hypothyroid rats

The effects of hypothyroidism on whole body thermogenesis, brown adipose tissue recruitment state, and alpha 1-adrenergic receptor density were investigated. Treatment of rats with methimazole for 4-5 wk led, as expected, to reduction of growth and resting metabolic rate. The thermogenic response to norepinephrine injection was practically abolished. Generally, only small effects of hypothyroidism on brown adipose tissue were observed: total protein content, mitochondrial GDP binding capacity, and total content of the uncoupling protein thermogenin were not altered. The density of beta-adrenergic receptors (estimated with [3H]CGP-12177 as a ligand) was also unchanged. However, the density of alpha 1-adrenergic receptors (estimated with [3H]prazosin) was markedly increased; in other physiological conditions, such an increase has been associated with an increased degree of recruitment of the tissue. These data indicate that brown adipose tissue in the subthermoneutral hypothyroid animal, probably due to homeostatic mechanisms, is exposed to an increased sympathetic stimulation, leading to an increased alpha 1-adrenoceptor density. However, other features of recruitment are only poorly induced, probably due to attenuation of the beta-adrenergic signaling mechanism. The increased alpha 1-adrenergic receptor density may be responsible for certain altered features of brown adipose tissue in hypothyroid animals, such as peroxisomal recruitment and perhaps also for maintenance of the thermogenin content. The results also indicate that the increased alpha 1-adrenergic density generally seen in recruitment would not result from chronic beta-adrenergic stimulation of the tissue but may be controlled via another regulatory pathway, e.g., via the alpha 1-adrenergic pathway itself.

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.

Soluble 5'-nucleotidase activities in rat brain

5'-Nucleotidase activity was assayed in 105,000-g supernatants from rat brain by following conversion of [3H]AMP into adenosine. The effect of ATP on this process was complex and suggested the presence of at least two soluble 5'-nucleotidase activities: one inhibited by ATP and another activated by ATP. The relative proportions of these activities differed considerably among brain regions. Activity changes induced by hypothyroidism also suggested that these activities may be regulated independently. These findings may have consequences for the regional regulation of adenosine formation in the brain.

Diabetes decreases sensitivity of adipocyte lipolysis to inhibition by Gi-linked receptor agonists

(1) Streptozotocin-diabetes decreased the responsiveness of noradrenaline- or forskolin-stimulated lipolysis to inhibition by phenylisopropyladenosine (PIA), prostaglandin E1 (PGE1) and nicotinate in rat adipocytes. (2) Diabetes had no effect on high affinity binding of [3H]PIA to adipocyte plasma membranes. (3) Plasma membranes from diabetic animals had increased abundance of alpha-subunits of Gi1 and Gi2. The effect of pertussis toxin in overcoming inhibition of lipolysis by PIA was delayed in adipocytes from diabetic rats. (4) Diabetes decreased the GTP-dependent right-wards shift in the dose-curve for displacement of the antagonist [3H]DPCPX by PIA in adipocyte plasma membranes. (5) It is concluded that, despite increased abundance of Gi in diabetic adipocytes, less of this is functional. This may contribute to reduced sensitivity to PIA, PGE1 and nicotinate and explains some of the loss of control of lipolysis in insulin-dependent diabetes.

Changes in the activities of adenosine-metabolizing enzymes in six regions of the rat brain on chemical induction of hypothyroidism

1. Rats (4 weeks old) were made hypothyroid by treatment with propylthiouracil and a low-iodine diet for a further period of 4 weeks. Synaptosomal membranes, myelin and 105,000 g soluble fractions were obtained from six regions of the brain. 2. Hypothyroidism resulted in 2-5-fold increases in membrane-bound 5'-nucleotidase activity in synaptosomal fractions obtained from cerebellum, cortex, striatum and hippocampus. By contrast, myelin 5'-nucleotidase activity was slightly increased only in the medulla oblongata. 3. Hypothyroidism did not change adenosine deaminase activity, but decreased adenosine kinase activity by approx. 40% in soluble fractions obtained from cerebellum, hippocampus, striatum and hypothalamus. 4. It is suggested that these changes in hypothyroidism, in particular the increases in 5'-nucleotidase activity, could enhance the neuromodulatory effect of adenosine to decrease neurotransmitter release.

A novel assay for 5'-nucleotidase using 1,N6-etheno-AMP as substrate, and comments on the properties of the reaction product, ethenoadenosine

A novel assay for 5'-nucleotidase is described in which 1,N6-etheno-AMP is converted into ethenoadenosine. The product ethenoadenosine is neither a substrate for nor an inhibitor of adenosine deaminase. Ethenoadenosine appears to have little effect at adenosine receptors on adipose-tissue cells.

Comparison of triacylglycerol synthesis in rat brown and white adipocytes. Effects of hypothyroidism and streptozotocin-diabetes on enzyme activities and metabolic fluxes

1. Adipocytes were isolated from the interscapular brown fat and the epididymal white fat of normal, streptozotocin-diabetic and hypothyroid rats. 2. Measurements were made of the maximum rate of triacylglycerol synthesis by monitoring the incorporation of [U-14C]glucose into acylglycerol glycerol in the presence of palmitate (1 mM) and insulin (4 nM) and of the activities of the following triacylglycerol-synthesizing enzymes: fatty acyl-CoA synthetase (FAS), mitochondrial and microsomal forms of glycerolphosphate acyltransferase (GPAT), dihydroxyacetonephosphate acyltransferase (DHAPAT), monoacylglycerol phosphate acyltransferase (MGPAT), Mg2+-dependent phosphatidate phosphohydrolase (PPH) and diacylglycerol acyltransferase (DGAT). 3. FAS activity in brown adipocytes was predominantly localized in the mitochondrial fraction, whereas a microsomal localization of this enzyme predominated in white adipocytes. Subcellular distributions of the other enzyme activities in brown adipocytes were similar to those shown previously with white adipocytes [Saggerson, Carpenter, Cheng & Sooranna (1980) Biochem. J. 190, 183-189]. 4. Relative to cell DNA, brown adipocytes had lower activities of triacylglycerol-synthesizing enzymes and showed lower rates of metabolic flux into acylglycerols than did white adipocytes isolated from the same animals. 5. Diabetes decreased both metabolic flux into acylglycerols and the activities of triacylglycerol-synthesizing enzymes in white adipocytes. By contrast, although diabetes decreased metabolic flux into brown-adipocyte acylglycerols by 80%, there were no decreases in the activities of triacylglycerol-synthesizing enzymes, and the activity of PPH was significantly increased. 6. Hypothyroidism increased metabolic flux into acylglycerols in both cell types, and increased activities of all triacylglycerol-synthesizing enzymes in brown adipocytes. By contrast, in white adipocytes, although hypothyroidism increased the activities of FAS, microsomal GPAT and DGAT, this condition decreased the activities of mitochondrial GPAT and PPH. 7. It was calculated that the maximum capabilities for fatty acid oxidation and esterification are approximately equal in brown adipocytes. In white adipocytes esterification is predominant by approx. 100-fold. 8. Diabetes almost abolished incorporation of [U-14C]glucose into fatty acids in both adipocyte types. Hypothyroidism increased fatty acid synthesis in white and brown adipocytes by 50% and 1000% respectively.

Factors influencing the altered thermogenic response of rat brown adipose tissue in streptozotocin-diabetes

1. Adipocytes were isolated from the interscapular brown fat of male rats maintained at 21 degrees C. These animals were controls, streptozotocin-diabetics or 2-day insulin-treated diabetics. 2. With adipocytes from diabetic animals, maximum rates of noradrenaline-stimulated O2 uptake were decreased by 58%, and the Bmax. of [3H]GDP binding to mitochondria was decreased by 55%. Insulin administration reversed both of these changes. 3. Streptozotocin-diabetes increased basal lipolysis in adipocytes incubated with adenosine deaminase (1 unit/ml), decreased the EC50 (concn. giving 50% of maximum effect) for noradrenaline, but did not change the maximum rate of noradrenaline-stimulated lipolysis. Except for some small differences at very low concentrations (10-100 pM), diabetes or insulin treatment did not alter the sensitivity of noradrenaline-stimulated lipolysis or O2 uptake to the inhibitory effect of N6-phenylisopropyladenosine. It is therefore concluded that the lesion(s) in thermogenesis in diabetes are not attributable to any changes in lipolysis. 4. Blood flow through interscapular brown fat, measured by accumulation of [14C]DDT [14C-labelled 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] was increased by 2.3-fold 70 min after a single administration of insulin to diabetic rats. This treatment decreased blood flow through epididymal white fat by 58%. 5. Propranolol treatment of diabetic rats muted the ability of insulin treatment to increase the maximum rate of noradrenaline-stimulated O2 uptake, suggesting that this action of insulin may be a secondary one rather than a direct effect of the hormone on the adipocytes.

Chemically induced hypothyroidism produces elevated amounts of the alpha subunit of the inhibitory guanine nucleotide binding protein (Gi) and the beta subunit common to all G-proteins

Adipocytes of hypothyroid rats display an increased responsiveness to agents which function by inhibiting the production of cyclic AMP. Anti-peptide antisera which selectively recognise the alpha subunit of the inhibitory guanine nucleotide binding protein (Gi) detected a 40 kDa polypeptide in adipocyte plasma membranes of both euthyroid and hypothyroid rats. Amounts of the alpha subunit of Gi were elevated some 2-fold in the hypothyroid preparations in comparison with the euthyroid controls, when equal amounts of membrane protein of the two treatments were examined. As cells from the hypothyroid animals contained 2.7 times as much membrane protein as those from the control animals, the amounts of alpha subunit of Gi are elevated some 5.6-fold per cell in adipocytes of the hypothyroid animals compared with the euthyroid controls. Amounts of the 36 kDa beta subunit of G-proteins were also elevated in plasma membranes of adipocytes of hypothyroid animals, in this case by some 50% when compared on a protein basis. These results provide direct evidence for alterations in the amounts of the subunits of Gi caused by the hypothyroid state.