Coupling between the beta-adrenergic receptor and the adenylate cyclase--pathophysiological implications

Most beta-adrenergic effects are mediated by activation of the enzyme adenylate cyclase. Hormone binds to the receptor leading to an accelarated binding of GTP to the coupling protein, the N-protein, which is activated. This causes an activation of the adenylate cyclase and an increased formation of cAMP, the intracellular second messenger. The same principles hold good for other hormones coupled to adenylate cyclase. The sensitivity of the adenylate cyclase may be altered in different clinical and experimental conditions. An increased sensitivity is seen in hyperthyroidism in man and in the rat, and during starvation in rats. A decreased sensitivity is seen in hypothyroidism, in patients with pheochromocytoma, pseudohypoparathyroidism type I or multiple symmetric lipomatosis. Several reasons for the altered sensitivity have been suggested. The number of hormone receptors, the coupling between receptor and N-protein, the amount or function of the N-protein or the PDE activity may all vary in different conditions.

Brain death activates donor organs and is associated with a worse I/R injury after liver transplantation

The majority of transplants are derived from donors who suffered from brain injury. There is evidence that brain death causes inflammatory changes in the donor. To define the impact of brain death, we evaluated the gene expression of cytokines in human brain dead and ideal living donors and compared these data to organ function following transplantation. Hepatic tissues from brain dead (n = 32) and living donors (n = 26) were collected at the time of donor laparotomy. Additional biopsies were performed before organ preservation, at the time of transplantation and one hour after reperfusion. Cytokines were assessed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and cytometric bead array. Additionally, immunohistological analysis of tissue specimens was performed. Inflammatory cytokines including IL-6, IL-10, TNF-alpha, TGF-beta and MIP-1alpha were significantly higher in brain dead donors immediately after laparotomy compared to living donors. Cellular infiltrates significantly increased in parallel to the soluble cytokines IL-6 and IL-10. Enhanced immune activation in brain dead donors was reflected by a deteriorated I/R injury proven by elevated alanin-amino-transferase (ALT), aspartat-amino-transferase (AST) and bilirubin levels, increased rates of acute rejection and primary nonfunction. Based on our clinical data, we demonstrate that brain death and the events that precede it are associated with a significant upregulation of inflammatory cytokines and lead to a worse ischemia/reperfusion injury after transplantation.

Pathogenesis and treatment of diabetic vascular disease - illustrated by two cases

This publication is a summary of the presentations given at the First JIM Grand Round held at the Sahlgrenska University Hospital on 15 March 2006. The Grand Round was based on two case reports; a patient with type 2 diabetes and pronounced macrovascular disease and another patient with early microvascular disease combined with the macrovascular complications. The pathogenesis of the vascular complications and the current treatment regimens were discussed in relation to the history and examinations performed in these patients.

Routine Screening of Donor Hearts by Coronary Angiography Is Feasible

BACKGROUND

Because of the shortage of donor hearts, the criteria for acceptance have been considerably extended. Meanwhile every fourth heart donor in Europe is over 50 years old. As we have previously demonstrated, transmission of preexisting coronary atherosclerosis (CAS) by means of transplantation is not rare. Transmitted CAS results in a 2- to 3-fold increased risk for early graft failure after heart transplantation (HTX). Nevertheless, in most cases donor angiograms are not considered feasible.

METHODS

In May 2003 in the northeast region of the Deutsche Stiftung Organtransplantation (DSO-NO), we introduced the guideline that every donor over 40 years old must be screened by angiography.

RESULTS

Up to May 2003, fewer than 5% of donors had been screened by angiography; this situation is the rule in most Eurotransplant regions at present. Since May 2003 in the DSO-NO region, 85% of all donors over 40 years old were screened by angiography. Seventy percent of all donor hospitals--offering 90% of all donors--had an angiography facility. The additional costs of approximately euro 800 per donor angiogram were compensated by fewer fruitless airplane missions when CAS was diagnosed by the surgeon on the spot, which cost on average about euro 5,000 each. In conclusion, from a logistical as well as from a financial point of view, almost comprehensive angiographic donor screening is feasible. It reduces the risk of a recipient suffering from early graft failure.

Does Contrast Medium Administration in Organ Donors Affect Early Kidney Graft Function?

Since the upper age for organ donors has been raised, a higher incidence of preexistent organ damage and functional impairment is to be expected. Coronary artery sclerosis increases with age. It can only be diagnosed with certainty by coronary angiography. Since contrast medium administration may cause renal damage when risk factors are present, this study sought to establish whether angiography negatively influenced the early postoperative function of kidney grafts. We compared the clinical courses of 36 recipients of kidneys from donors in whom coronary angiography or levography had been performed with 36 recipients of kidneys from donors who had not been subjected to contrast medium. The results showed that the administration of contrast medium had no influence on renal function at 3 or 6 months after transplantation. In conclusion, fears that donor kidneys might be harmed by contrast medium appeared to therefore be unfounded.

Significant reduction of proinflammatory cytokines by treatment of the brain-dead donor

INTRODUCTION

Experimental studies suggest that brain death in the donor has a significant impact on graft quality; however, there are no data correlating organ-specific cytokine expression and the corresponding serum protein levels in human organ donors. Furthermore, it is unknown whether donor treatment can reduce the up-regulation of proinflammatory cytokines and thereby optimize organ quality.

METHODS

We investigated the expression pattern of cytokines comparing serum (n = 53) and tissue expression (n = 25) in brain-dead human donors. The controls were living donors (n = 25). Additionally 41 deceased donors were treated with steroids before organ harvest (250 mg initial, afterward 100 mg/h until laparotomy). Hepatic tissue samples were obtained immediately after donor laparotomy to assess transcription rates of tissue cytokines (IL-6, IL-10, CD3, TGFb, TNFa, BAG, HO-1, Mipla) by RT-PCR. Serum samples were obtained after declaration of brain death and before laparotomy.

RESULTS

Transcription of proinflammatory cytokines was significantly increased in brain-dead compared to living donor grafts (P < .005). Donor treatment with steroids led to significantly decreased tissue and serum expression of proinflammatory cytokines (P < .01), which were comparable to living donors. Tissue levels of cytokines (IL-6, IL-10) correlated strongly with serum levels of the corresponding proteins.

CONCLUSIONS

Serum protein levels of proinflammatory cytokines proffer a valuable, easy accessible marker to define the immunological status of a graft. Our data suggest a beneficial effect of anti-inflammatory treatment of brain-dead organ donors.

Reduced expression of PGC-1 and insulin-signaling molecules in adipose tissue is associated with insulin resistance

Peroxisome proliferator-activated receptor gamma (PPAR gamma) co-activator 1 (PGC-1) regulates glucose metabolism and energy expenditure and, thus, potentially insulin sensitivity. We examined the expression of PGC-1, PPAR gamma, insulin receptor substrate-1 (IRS-1), glucose transporter isoform-4 (GLUT-4), and mitochondrial uncoupling protein-1 (UCP-1) in adipose tissue and skeletal muscle from non-obese, non-diabetic insulin-resistant, and insulin-sensitive individuals. PGC-1, both mRNA and protein, was expressed in human adipose tissue and the expression was significantly reduced in insulin-resistant subjects. The expression of PGC-1 correlated with the mRNA levels of IRS-1, GLUT-4, and UCP-1 in adipose tissue. Furthermore, the adipose tissue expression of PGC-1 and IRS-1 correlated with insulin action in vivo. In contrast, no differential expression of PGC-1, GLUT-4, or IRS-1 was found in the skeletal muscle of insulin-resistant vs insulin-sensitive subjects. The findings suggest that PGC-1 may be involved in the differential gene expression and regulation between adipose tissue and skeletal muscle. The combined reduction of PGC-1 and insulin signaling molecules in adipose tissue implicates adipose tissue dysfunction which, in turn, can impair the systemic insulin response in the insulin-resistant subjects.

Tactile directional sensibility and diabetic neuropathy

Five different procedures used to diagnose neuropathy were compared in a "blind" study with diabetic patients. The aim was to evaluate tests of tactile directional sensibility. Three matched groups were examined, two groups with type I diabetes, either with or without suspected neuropathy, and one of healthy controls. Testing consisted of: (1) examination by a specialist in neurology, (2) electrophysiologic measurement of nerve conduction velocity and determination of cool sensitivity, and (3) determination of directional sensibility in two stages, with categorical and quantitative techniques. Abnormal test results were obtained for both groups of diabetic patients. Quantitatively measured directional sensibility had the highest sensitivity (89%) and specificity (85%) when calculated for patients who had received a diagnosis of neuropathy from the neurologist, despite one case of abnormal directional sensibility among the healthy controls. Conduction velocity testing was almost comparably sensitive (80%) and cool sensitivity, comparably specific (85%) when calculated in the same manner.

Impaired phosphorylation and insulin-stimulated translocation to the plasma membrane of protein kinase B/Akt in adipocytes from Type II diabetic subjects

AIMS/HYPOTHESIS

To examine protein kinase B/Akt distribution and phosphorylation in response to insulin in different subcellular fractions of human fat cells from healthy subjects and subjects with Type II (non-insulin-dependent) diabetes mellitus.

METHODS

We prepared subcellular fractions of plasma membranes (PM), low density microsomes and cytosol and examined gene and protein expression as well as serine and threonine phosphorylation in response to insulin.

RESULTS

Protein kinase B/Akt mRNA as well as total protein kinase B/Akt protein in whole-cell lysate and cytosol were similar in both groups. Insulin increased protein kinase B/Akt translocation to the the plasma membrane about twofold [(p < 0.03) in non-diabetic cells but this effect was impaired in diabetic cells (approximately 30%; p > 0.1)]. In both groups, protein kinase B/Akt threonine phosphorylation considerably increased in low density microsomes and cytosol whereas serine phosphorylation was predominant in the plasma membrane. Phosphatidylinositol-dependent kinase 1, which partially activates and phosphorylates protein kinase B/Akt on the specific threonine site, was predominant in cytosol but it was also recovered in low density microsomes. Serine phosphorylation in response to insulin was considerably reduced (50-70 %; p < 0.05) in diabetic cells but threonine phosphorylation was less reduced (approximately 20%). Wortmannin inhibited these effects of insulin supporting a role for PI3-kinase activation.

CONCLUSION/INTERPRETATION

Insulin stimulates a differential subcellular pattern of phosphorylation of protein kinase B/Akt. Furthermore, insulin-stimulated translocation of protein kinase B/Akt to the plasma membrane, where serine phosphorylation and full activation occurs, is impaired in Type II diabetes. Threonine phosphorylation was much less reduced. This discrepancy may be related to differential activation of phosphatidylinositol 3-kinase in the different subcellular compartments and phosphatidylinositol-dependent kinase 1 having high affinity for phosphatidylinositol phosphate 3.

Insulin signaling and action in fat cells: associations with insulin resistance and type 2 diabetes

Adipose tissue only accounts for a relatively small proportion (< 10%) of the peripheral glucose utilization in response to insulin. However, the fat cells may still play an important role in insulin resistance and Syndrome X through, for instance, its endocrine functions (production of leptin, TNF alpha, PAI-1, etc.) and involvement in lipid metabolism (FFA release and hydrolysis of triglycerides). The fat cells are also highly sensitive to insulin and may thus be used to elucidate molecular mechanisms for insulin resistance in man. Examinations of the intracellular signaling mechanisms for insulin in fat cells from individuals with Type 2 diabetes revealed markedly lower insulin-stimulated PI3-kinase activity. This was due to a pronounced reduction in the cellular expression of the docking protein, IRS 1, whereas expression of IRS 2 was normal. However, IRS 2-associated PI3-kinase activity was only approximately one-third of that found to be associated with IRS 1 in normal cells. Downstream activation and serine phosphorylation of PKB/Akt by insulin were also markedly reduced in Type 2 diabetes. Furthermore, the dose-response curve for this effect of insulin was similar to that for glucose transport in both normal and Type 2 diabetic cells. Thus, these data show that both PI3-kinase and PKB activation by insulin are markedly reduced in Type 2 diabetes. We also examined whether an attenuated activation of PI3-kinase by insulin can be seen in non-diabetic insulin-resistant states. Approximately 30% of healthy subjects with at least two first-degree relatives with Type 2 diabetes exhibited perturbations in IRS-1 expression and signaling. These individuals were characterized by insulin resistance as well as other markers of Syndrome X. Thus, impaired IRS-1 expression and downstream signaling events in fat cells in response to insulin are associated with insulin resistance and Syndrome X.

Impaired glucose transport and protein kinase B activation by insulin, but not okadaic acid, in adipocytes from subjects with Type II diabetes mellitus

AIMS/HYPOTHESIS

To study the effects of insulin and okadaic acid, a serine/threonine phosphatase inhibitor which does not increase PI3-kinase activity, on the rate of glucose transport and protein kinase B activation in adipocytes from healthy subjects and subjects with Type II (non-insulin-dependent) diabetes mellitus.

METHODS

Adipocytes were incubated with or without insulin or okadaic acid or both and glucose transport, protein kinase B activity, phosphorylation and protein expression measured.

RESULTS

Insulin and okadaic acid alone increased glucose uptake to a similar degree in adipocytes from healthy subjects and, when combined, exerted a partial additive effect. The effect of insulin was reduced by about 60% in adipocytes from Type II diabetic patients, whereas the effect of okadaic acid was essentially unchanged and no further increase was seen when okadaic acid and insulin were combined. Okadaic acid increased protein kinase B activity to a greater extent (two to threefold) than insulin but only slightly increased the serine phosphorylation of protein kinase B. Adipocytes from Type II diabetic subjects exhibited both an impaired sensitivity as well as a reduced total serine phosphorylation and activation of protein kinase B in response to insulin but protein kinase B activity in response to okadaic acid was intact.

CONCLUSION/INTERPRETATION

These results show that the ability of insulin to increase glucose transport and activate protein kinase B is reduced in fat cells from Type II diabetic subjects. Protein kinase B can, however, be activated by agents like okadaic acid which bypass the upstream defects in the insulin signalling pathway in Type II diabetic cells and, thus, increase glucose uptake.

Bedtime uncooked cornstarch supplement prevents nocturnal hypoglycaemia in intensively treated type 1 diabetes subjects

OBJECTIVES

The present study tests two interrelated hypotheses: (1) that bedtime ingestion of uncooked cornstarch exerts a lower and delayed nocturnal blood glucose peak compared with a conventional snack; (2) that bedtime carbohydrate supplement, administered as uncooked cornstarch, prevents nocturnal hypoglycaemia without altering metabolic control in intensively treated type 1 diabetes (IDDM) patients.

DESIGN AND SUBJECTS

The above hypotheses were tested separately (1) by pooling and analysing data from two overnight studies of comparable groups of patients with non-insulin dependent diabetes mellitus (NIDDM) (14 and 10 patients, respectively), and (2) by a double-blind, randomized 4-week cross-over study in 12 intensively treated IDDM patients.

SETTING

Sahlgrenska University Hospital, Göteborg. Sweden.

INTERVENTIONS

(1) Ingestion of uncooked cornstarch and wholemeal bread (0.6 g of carbohydrates kg-1 body weight) and carbohydrate-free placebo at 22.00 h. (2) Intake of uncooked cornstarch (0.3 g kg-1 body weight) and carbohydrate-free placebo at 23.00 h.

MAIN OUTCOME MEASURES

(1) Nocturnal glucose and insulin levels; (2) frequency of self-estimated hypoglycaemia (blood glucose [BG] levels < 3.0 mmol L-1) at 03.00 h, HbA1c and fasting lipids.

RESULTS

Bedtime uncooked cornstarch ingestion led to a lower (2.9 +/- 0.5 vs. 5.2 +/- 0.6 mM, P = 0.01) and delayed (4.3 +/- 0.6 vs. 2.0 +/- 0.0 h, P < 0.01) BG peak, compared with a conventional snack, in NIDDM patients. Four weeks of bedtime uncooked cornstarch supplement, as compared with placebo, led to a 70% reduction in the frequency of self-estimated hypoglycaemia at 03.00 h (P < 0.05), without affecting HbA1c or fasting lipids in IDDM patients.

CONCLUSIONS

Uncooked cornstarch, ingested at bedtime, mimicked the nocturnal glucose utilization profile following insulin replacement, with a peak in blood glucose after 4 h. In IDDM patients, bedtime uncooked cornstarch supplement diminished the number of self-estimated hypoglycaemic episodes, without adversely affecting HbA1c and lipid levels. Hence, bedtime uncooked cornstarch ingestion may be feasible to prevent a mid-nocturnal glycaemic decline following insulin replacement in IDDM and, based on the nocturnal blood glucose profile, may also be preferable compared with conventional snacks.

Insulin receptor substrate (IRS) 1 is reduced and IRS-2 is the main docking protein for phosphatidylinositol 3-kinase in adipocytes from subjects with non-insulin-dependent diabetes mellitus

The large docking protein IRS-1 is a major substrate for the insulin receptor and other tyrosine kinases. It plays a key role in eliciting many of insulin's actions, including binding and activation of phosphatidylinositol (PI) 3-kinase and the subsequent increase in glucose transport. Gene disruption of IRS-1 in mice is associated with an impaired insulin-stimulated glucose disposal in vivo and glucose transport in vitro, but the survival of the animals and residual insulin sensitivity is dependent on the presence of the alternative docking protein IRS-2. We examined the expression and function of IRS-1 and IRS-2 in adipocytes from healthy and diabetic individuals. Cells from subjects with non-insulin-dependent diabetes mellitus (NIDDM), but not with insulin-dependent diabetes mellitus, had an impaired insulin effect and a marked reduction (70 +/- 6%) in the expression of IRS-1 protein, whereas IRS-2 was unchanged. In normal cells, IRS-1 was the main docking protein for the binding and activation of insulin-stimulated PI 3-kinase; IRS-2 was also functional but required a higher insulin concentration for a similar binding and activation of PI 3-kinase. In contrast in NIDDM cells with a low IRS-1 content, IRS-2 became the main docking protein. These findings may provide important reasons for the insulin resistance in NIDDM.

Insulin promotes and cyclic adenosine 3',5'-monophosphate impairs functional insertion of insulin receptors in the plasma membrane of rat adipocytes: evidence for opposing effects of tyrosine and serine/threonine phosphorylation

The aim of the present study was to elucidate events in the plasma membrane (PM) associated with the previously described effect of insulin to rapidly enhance the number of cell surface insulin binding sites in rat adipocytes. [125I]insulin was cross-linked to cell surface insulin receptors of intact cells that had been preincubated with or without insulin. Subsequently prepared PM displayed a approximately 3-fold increase in bound [125I]insulin when cells had been pretreated with 6 nM insulin for 20 min compared to membranes from control cells, and SDS-PAGE with autoradiography showed that this occurred at the insulin receptor alpha-subunit. The magnitude of the effect was similar to that found for insulin binding to intact cells that had been preincubated with insulin. In contrast, the insulin binding capacity in the PM was not affected by prior treatment of cells with insulin when assessed with the addition of [125I]insulin directly to solubilized PM; this suggests an unchanged total number of PM receptors. Thus, the enhancement of cell surface insulin binding capacity produced by insulin is not due to the translocation of receptors, but instead appears to be confined to receptors already present in the PM. The addition of phospholipase C (from Clostridium perfringens), which cleaves PM phospholipids, mimicked the effect of insulin to enhance cell surface binding in adipocytes, and this suggests a pool of cryptic PM receptors. Both the nonmetabolizable cAMP analog N6-monobutyryl cAMP (N6-mbcAMP) and the serine/threonine phosphatase inhibitor okadaic acid abolished the effect of concomitant insulin treatment to increase binding capacity. In contrast, the tyrosine phosphatase inhibitor vanadate increased insulin binding even in the presence of okadaic acid or N6-mbcAMP. The effect of N6-mbcAMP to impair cell surface insulin binding was also evident in the presence of a peptide derived from the major histocompatibility complex type I that effectively impairs receptor internalization, but the amount of PM receptors assessed by immunoblot was unaltered. Taken together, the data suggest that insulin exposure leads to the uncovering of cryptic receptors associated with the PM. It is also suggested that tyrosine phosphorylation promotes this process, whereas enhanced serine phosphorylation, e.g. produced by cAMP, impairs the functional insertion of the receptors, rendering them unable to bind insulin.

A stable peroxovanadium compound with insulin-like action in human fat cells

Aqueous solutions of peroxovanadium (pV) compounds are potent insulin-mimics in various types of cell. Since chemical instability is a problem with these agents, we studied the insulin-like action in human fat cells of a stable pV complex, bpV(pic). It enhanced 14C-U-glucose uptake in a dose-dependent manner by approximately twofold which was slightly less than the effect of insulin (approximately threefold). The pV complex did not alter cell-surface insulin binding and submaximal concentrations did not influence cellular sensitivity to insulin action on glucose uptake. The bpV(pic) inhibited the lipolytic effect of isoprenaline to the same extent as insulin; however, when the cGMP-inhibitable low-K(m) phosphodiesterase (cGI-PDE) was blocked with the specific inhibitor OPC 3911, the antilipolytic effect of insulin, but not that of bpV(pic), was completely prevented. Moreover, when lipolysis was stimulated by the non-hydrolysable cAMP analogue N6-monobutyryl cAMP, bpV(pic), in contrast to insulin, maintained an antilipolytic effect. These findings indicate that bpV(pic) exerts its antilipolytic effect not only through cGI-PDE activation, similar to the effect of insulin, but also by means of other mechanisms. The tyrosine kinase activity of insulin receptors from human placenta was not altered by the pV compound itself, whereas bpV(pic) clearly enhanced insulin-stimulated activity. In contrast, in situ tyrosine phosphorylation of the insulin receptor beta-subunit as well as that of several other proteins was clearly increased in cells which were treated with bpV(pic), whereas vanadate only amplified insulin-stimulated tyrosine phosphorylation. In conclusion, bpV(pic) exerts powerful insulin-like effects in human fat cells and may be a new and potentially useful agent in the management of insulin-resistant states.

The cGMP-inhibitable phosphodiesterase modulates glucose transport activation by insulin

To assess the role of the cGMP-inhibitable phosphodiesterase (cGI-PDE) in the action of insulin on glucose transport, adipocytes from young, lean rats were preincubated for 20 min at 37 degrees C with and without OPC 3911, a specific inhibitor of cGI-PDE, and 3-O-methylglucose uptake was measured. Insulin-stimulated glucose transport was impaired by OPC 3911 (approximately 15%) and this impairment became more pronounced in the presence of the degradable cAMP-analogue 8-bromo-cAMP (approximately 45%). This analogue alone did not significantly decrease glucose transport. Furthermore, insulin sensitivity was impaired by the combination of OPC 3911 and 8-bromo-cAMP. Maximal insulin-stimulated glucose transport in adipocytes from aging, obese rats was affected similarly by OPC 3911 and 8-bromo-cAMP, suggesting that cGI-PDE activity is not markedly altered in this insulin-resistant state. In conclusion, cGI-PDE exerts a modulating effect on the stimulatory action of insulin on glucose transport. This effect is particularly pronounced when the cellular cAMP levels are elevated.

Cellular cyclic AMP levels modulate insulin sensitivity and responsiveness--evidence against a significant role of Gi in insulin signal transduction

Treating rats with pertussis toxin (PTX) both elevated the adipocyte cAMP levels and impaired sensitivity and responsiveness to the antilipolytic effect of insulin in the presence of different beta-adrenergic agonists. However, in the presence of a fixed medium concentration of the degradable cAMP analogue, 8-bromo-cAMP, the effect of insulin was similar in PTX- and control cells. Elevating the cAMP levels in control cells either through different concentrations of the cAMP analogue or addition of adenosine deaminase impaired both insulin sensitivity and responsiveness to a similar extent as that seen in PTX-treated cells. The antilipolytic effect of insulin was exerted through the activation of the cGMP-inhibitable phosphodiesterase (cGI-PDE) as it was dose-dependently impaired by the specific cGI-PDE inhibitor OPC 3911. The results show the importance of the cellular cAMP levels in modulating insulin sensitivity and action. Gi plays a minor role, if any, for the signal transduction of the antilipolytic effect of insulin.

The inhibitory GTP-binding protein (Gi) regulates the agonistic property of beta-adrenergic ligands in isolated rat adipocytes. Evidence for a priming effect of cyclic AMP

Prenalterol, an allegedly beta 1-selective adrenergic agonist with high intrinsic sympathomimetic activity (ISA), was shown to be weakly lipolytic in rat adipocytes. However, in pertussis-toxin-treated adipocytes, the ISA of prenalterol was markedly increased (from 10-20% to approx. 100% of that of isoprenaline). The cellular sensitivity was also increased (EC50 approx. 60 nM and approx. 3 microM in pertussis-toxin-treated and control cells respectively). A similar effect was seen for other partial agonists such as the beta 2-selective agonist terbutaline and for beta-adrenergic antagonists with some intrinsic activity (metoprolol, pindolol). There was no clear change in sensitivity to isoprenaline's ability to stimulate adenylate cyclase in adipocyte membranes from pertussis-toxin-treated animals but the cyclase activity was increased approx. 4-fold in the presence of 1 microM-GTP. Prenalterol stimulated lipolysis by only small increases in intracellular cyclic AMP (cAMP) levels (less than 10% of that seen with isoprenaline). Basal lipolysis was increased in cells from pertussis-toxin-treated rats and the cellular sensitivity to the non-degradable cAMP analogue, N6-monobutyryl-cAMP, was increased. In control cells, a submaximal concentration of prenalterol (0.1 microM) increased the sensitivity to the cAMP analogues, N6-monobutyryl-cAMP and 8-bromo-cAMP. A low concentration (1 mM) of 8-bromo-cAMP also increased the effect of prenalterol. Similar effects were seen when the phosphodiesterase was inhibited. Thus (1) lipolysis is extremely sensitive to small increases in intracellular cAMP; (2) the degree of activation of adenylate cyclase and thus cAMP formation is the rate-limiting step for the biological response of partial agonists; (3) the inhibitory GTP-binding protein, Gi, is an important modulator ('tissue factor') of the beta-adrenergic agonistic property; (4) low levels of cAMP exert a priming effect on protein kinase A.

Human small intestine facilitative fructose/glucose transporter (GLUT5) is also present in insulin-responsive tissues and brain. Investigation of biochemical characteristics and translocation

A recent study by C.F. Burant et al. (13) demonstrates that GLUT5 is a high-affinity fructose transporter with a much lower capacity to transport glucose. To characterize the potential role of GLUT5 in fructose and glucose transport in insulin-sensitive tissues, we investigated the distribution and insulin-stimulated translocation of the GLUT5 protein in human tissues by immunoblotting with an antibody to the COOH-terminus of the human GLUT5 sequence. GLUT5 was detected in postnuclear membranes from the small intestine, kidney, heart, four different skeletal muscle groups, and the brain, and in plasma membranes from adipocytes. Cytochalasin-B photolabeled a 53,000-M(r) protein in small intestine membranes that was immunoprecipitated by the GLUT5 antibody; labeling was inhibited by D- but not L-glucose. N-glycanase treatment resulted in a band of 45,000 M(r) in all tissues. Plasma membranes were prepared from isolated adipocytes from 5 nonobese and 4 obese subjects. Incubation of adipocytes from either group with 7 nM insulin did not recruit GLUT5 to the plasma membrane, in spite of a 54% insulin-stimulated increase in GLUT4 in nonobese subjects. Thus, GLUT5 appears to be a constitutive sugar transporter that is expressed in many tissues. Further studies are needed to define its overall contribution to fructose and glucose transport in insulin-responsive tissues and brain.

Amiloride inhibits insulin sensitivity and responsiveness in rat adipocytes through different mechanisms

To investigate the mechanisms by which amiloride inhibits insulin action rat adipocytes were treated with insulin and with amiloride added before or after energy depleting the cells with 2 mM KCN. Amiloride decreased the insulin response on 3-0-methylglucose transport, IGF-II- and insulin binding in both intact and energy depleted cells. In contrast, the sensitivity to insulin was inhibited by amiloride only when it was added before KCN. The effect of amiloride on insulin sensitivity was probably exerted through the impaired activation of the insulin receptor tyrosine kinase and the decreased insulin binding. However, insulin responsiveness was probably impaired through a direct effect on the plasma membrane proteins. In contrast to a recent report with pituitary cells, amiloride did not affect the activation of the inhibitory GTP-binding protein (Gi) in rat adipocytes.

[Procurement of organ donors--initial results of the Berlin-Potsdam-Frankfurt model]

The shortage of donor kidneys is the main cause of the even insufficient supply of patients suffering from end stage renal disease. In 1987 a transplant coordinator to the districts Berlin, Frankfurt and Potsdam with 3.1 Mio inhabitants was introduced. The functions of the coordinator and the approach to organ procurement are described in detail. In comparison with 1986 the number of explanted kidneys could doubled in 1988 (68 vs 143). The number of 46.3 explanted kidneys per million inhabitants is comparable with other areas or countries with excellent organ procurement system.

Elevated aminotransferases and alkaline phosphatases in unstable diabetes mellitus without ketoacidosis or hypoglycemia

Four patients with unstable diabetes mellitus and pronounced elevations of serum aminotransferases and alkaline phosphatases are reported. Thorough investigations revealed no cause for the abnormalities. The enzyme elevations were associated with hepatomegaly, and in some instances, abdominal pain and leg edema. Liver biopsies in all patients showed only marked accumulation of glycogen in the hepatocytes.

Insulin-induced subcellular redistribution of insulin-like growth factor II receptors in the rat adipose cell. Counterregulatory effects of isoproterenol, adenosine, and cAMP analogues

Insulin shifts the steady-state subcellular distribution of insulin-like growth factor II (IGF-II) receptors from a large intracellular pool to the plasma membrane in the rat adipose cell (Wardzala, L. J., Simpson, I. A., Rechler, M. M., and Cushman, S. W. (1984) J. Biol. Chem. 259, 8378-8383). In the present study, the counterregulatory effects of adrenergic stimulation, adenosine deaminase, and cAMP on this process were studied. Both isoproterenol (10(-6) M) and adenosine deaminase reduced insulin sensitivity and also rapidly (t1/2 approximately 1.5 min) decreased the effect of a maximal insulin concentration on the number of cell surface IGF-II receptors by 35-50%, and by 70% when added together. The marked reduction in binding was retained in isolated and solubilized plasma membranes. Both isoproterenol and adenosine deaminase alone increased the EC50 for insulin from 0.06 to 0.17 nM and, when combined, to 0.6 nM. N6-Monobutyryl-cAMP and 8-bromo-cAMP were equally potent in reducing IGF-II binding in the absence of insulin and inhibited maximal insulin-stimulated IGF-II binding by 60 and 30%, respectively. However, only the nonhydrolyzable cAMP analogue, N6-monobutyryl-cAMP, reduced the insulin sensitivity (EC50 0.7 nM). An important stimulatory role for Gi (guanine nucleotide-binding regulatory protein that inhibits adenylate cyclase) was indicated by the altered activities of cells from pertussis toxin-treated animals. The results suggest that beta-adrenergic stimulation through a cAMP-dependent mechanism markedly alters the insulin-stimulated redistribution of IGF-II receptors. This effect is additional to the potent antagonistic action of cAMP on insulin's signalling mechanism.

[Comparison of inulin and creatinine clearance determinations in anesthesized and conscious rats]

Two investigation methods of the renal function by means of the inulin and the endogenous creatinine clearance in narcotized and conscious rats are described in detail. The inulin clearance was 0.84 +/- 0.16 ml/min/100 g BW. The results of the creatinine clearance obtained by 6 various methods are widely different due to co-determination of foreign chromogens. Therefore, it is important to compare these results with the results of other analytical methods determining only the "true" creatinine.

Specific creatinine determination in laboratory animals using the new enzymatic test kit "Creatinine-PAP"

The new Creatinine-PAP test kit from Boehringer Mannheim GmbH was evaluated for the determination of creatinine in dogs, rabbits, guinea pigs, rats, and mice. In comparison with methods based on the reaction with alkaline picrate, the enzymatic method gave the lowest serum creatinine values. The differences are caused by serum substances (non-creatinine chromogens) reacting with picric acid. Noticeable differences between the standard inulin clearance and creatinine clearance (e. g., in rats) arise because the non-creatinine chromogens interfere differently in the picric acid methods, and serum and urine contain different concentrations of interfering substances. The concentrations of non-creatinine chromogens are different in the various laboratory animals. Since these substances cannot be entirely removed (e. g., in rats, dogs) by the adsorption procedure with Fuller's earth, we recommend the peroxidase-coupled enzymatic test as a practical and specific method for routine measurements of creatinine in laboratory animals.

Regional adipose tissue metabolism in men and postmenopausal women

The metabolism of subcutaneous abdominal and femoral fat cells was studied in postmenopausal women and matched men of similar age and weight index. Lipoprotein lipase (LPL) activity was similar in both regions in the postmenopausal women. However, a group of women who underwent treatment with estrogen and progestins had considerably higher LPL activity in the femoral cells. Testosterone treatment for 7 days did not change LPL in either region in middle-aged men. Femoral adipocytes from both men and postmenopausal women were markedly unresponsive to catecholamine in comparison with abdominal cells. No clear effect of the sex hormones was seen on lipolysis in the women. Treating men with testosterone increased basal lipolysis in the abdominal cells. Abdominal fat cells were more responsive to the antilipolytic effect of insulin. Both responsiveness and sensitivity to insulin were somewhat greater in the abdominal fat cells from men (ED50 approximately 0.02 nm) than from women (ED50 approximately 0.17 nm). Insulin binding, however, was similar in fat cells from the abdominal and the femoral regions when the results were expressed per unit surface area. Thus, regional differences in fat cell metabolism are seen in both postmenopausal women and elderly men. LPL activity in the femoral region seems to be under the control of female sex hormones while lipolysis appears to be less influenced by sex hormones.

Reduced insulin binding to human fat cells following beta-adrenergic stimulation--experimental evidence and studies in patients with a phaeochromocytoma

The effect of beta-adrenergic stimulation on insulin binding was studied in human fat cells in vitro. Isoproterenol rapidly (approximately 5 min) reduced insulin binding through a beta-adrenergic and dose-dependent mechanism. The reduced binding was enhanced by the addition of adenosine deaminase and was also elicited by the addition of dibutyryl cAMP. This effect was due to a decreased number of binding sites. The reduction was rapidly reversed by propranolol (t1/2 approximately 10 min) and other beta-adrenoreceptor blocking agents. Insulin binding was also measured in fat cells from 6 patients with a phaeochromocytoma. A significant negative correlation between tracer binding and the log value of total urinary catecholamine excretion was found (r = -0.821, p less than 0.05). Mean tracer insulin binding was reduced about 30% as compared to cells from 16 carefully matched control subjects. Decreased insulin binding was again mainly attributable to a decreased number of binding sites. Thus, beta-adrenergic stimulation, both in vitro and in vivo, leads to a decreased number of binding sites for insulin in human fat cells.

[Hepatic coma in fulminating viral hepatitis--treatment results in 1981 in a district hospital]

n the basis of clinical case reports on liver disintegration comata in foudroyant virus hepatitis the coma therapy was explained which was performed in the clinic for infectious and tropic diseases of the County Hospital St. Georg Leipzig in 1981 and this therapy was compared with the possibilities mentioned in literature. The aim of the article was to determine the present position of a county hospital in the great number of forms of therapy proposed. The basic therapy aimed at the reduction of neurotoxic protein metabolites and the application of intensive-medical therapeutic methods in interdisciplinary cooperation of internal specialist, specialist in dialysis and haemostaseologist are valuated as successful. The combined haemoperfusion/haemodialysis--two out of three patients treated survived--as a constituent of the present concept of therapy is assessed positively.

[Hemoperfusion therapy in severe suicidal digoxin poisoning]

Severe digoxin intoxications have a mortality rate of about 20%. Clinical course of intoxication, electrocardiographic changes as well as the behaviour of the plasma-digoxin concentration could closely be controlled on 4 patients after suicidal ingestion of potentially lethal dilanacin -new doses. In 3 patients a haemoperfusion treatment lasting 4 to 6 hours was performed. Clinical symptoms and existing disturbances of cardiac rhythm were clearly positively influenced under perfusion. The earlier the treatment was begun the more favourably appear the effects on the course of intoxication. After an at first benign picture of intoxication in the non-perfused female patient a comparatively distinct prolonged clinical and electrocardiographic symptomatology developed. Though the digoxin extraction established by computation fairly slightly imposes, this eliminated free digoxin fraction seems, nevertheless, to possess a considerable pharmacological and clinical importance. The adsorber material used showed well reproducible high clearance performances. During the haemoperfusion treatment in no case clinical complications were observed.

Distinction between two subpopulations of beta 1-adrenergic receptors in human adipose cells

The beta-adrenergic receptors in human adipose membranes were identified by the specific and saturable binding of the beta-adrenergic antagonist (--)-[3H]dihydroalprenolol. The total number of sites in control membranes was 0.32 +/- 0.03 pmol/mg protein and the equilibrium dissociation constant for binding (Kd) was 2.6 nM and 2.5 nM as determined by Scatchard analysis of experiments on equilibrium binding and kinetics, respectively. The beta 1-adrenergic nature of the receptors was derived from the order of potencies of beta-adrenergic agonists (isoproterenol greater than norepinephrine greater than epinephrine) to complete with (--)-[3H]dihydroalprenolol for binding. Studies of saturation binding, kinetics and competition binding revealed the presence of a single class of beta 1-adrenergic receptors. Prolonged incubation of human adipose cells in the presence of (--)-norepinephrine decreases the lipolytic response to beta-adrenergic agonists, and reduces by 50% the concentration of beta-adrenergic receptors. The Kd values for (--)-[3H]dihydroalprenolol and the beta-adrenergic agonists remain unchanged. Catecholamines also produce a rapid conformational change of approximatively 50% of the receptors in control membranes as revealed by their increased sensitivity towards inactivation by the alkylating agent N-ethylmaleimide. This inactivation process is not observed in desensitized membranes, which indicates that desensitization and inactivation by agonists plus N-ethylmaleimide affect the same receptor population. The beta 1-adrenergic receptors in human adipocytes can thus be divided into two subpopulations on the basis of the different consequences of their interaction wtih agonist molecules.