Association between hemodialysis and patient characteristics, microbiological etiology, cardiac surgery, and mortality in patients with infective endocarditis: a nationwide study

Background

Hemodialysis and infective endocarditis are both associated with poor patient outcome. However, despite high mortality rates for each disease entity, little attention is given to patients on hemodialysis who develop infective endocarditis.

Purpose

To examine patient characteristics, microbiological etiology, cardiac surgery, and outcome among patients on hemodialysis with infective endocarditis compared with patients with infective endocarditis without hemodialysis treatment.

Methods

With Danish nationwide registries, we identified patients with infective endocarditis between 2010–2018 and linked them to microbiological data from a nationwide microbiological registry with complete blood culture data. We included patients in the hemodialysis group if they received hemodialysis treatment within 6 months prior to their first-time infective endocarditis admission. Patients not meeting this criteria were put in the non-hemodialysis group. We used Kaplan-Meier estimates for difference in mortality and Cox regression for adjusted analysis.

Results

We included 4,106 patients with infective endocarditis of which 265 (6.5%) patients were also in hemodialysis treatment (66.8% men). Patients on hemodialysis were younger (median age 66 years [IQR=54.2–74.9] vs. 72.3 years [IQR=62.3–80.4]) and had a higher burden of comorbidities including hypertension (68.7 vs. 56.9%), diabetes (47.2% vs. 18.8%), and ischemic heart disease (41.1% vs. 32.2%) compared to patients without hemodialysis treatment, all p-values <0.01. Cardiac surgery was less frequently performed in patients in the hemodialysis group than in the non-hemodialysis group (11.9% vs. 19.4%, respectively, p<0.001) and Staphylococcus aureus was more frequently the microbiological etiology of infective endocarditis in the hemodialysis group than in the non-hemodialysis group (57.0% vs. 25.3%, respectively, p<0.0001). No statistically significant difference for in-hospital mortality was found. Figure 1 shows difference in mortality between the two groups. 1- and 5-year mortality were significantly higher in the hemodialysis group than in the non-hemodialysis group (34.3% vs. 17.2% and 50.5% vs. 33.9%, respectively, p<0.00001) and in adjusted analysis hemodialysis was associated with higher 1- and 5-year mortality (hazard ratio of 2.41, 95% CI 1.85–3.13 and 2.50, 95% CI 2.05–3.05, respectively), as compared with patients in the non-hemodialysis group.

Conclusion

Patients on hemodialysis with infective endocarditis are younger, sicker and have Staphylococcus aureus as causing agent more than twice as often as patients with infective endocarditis without hemodialysis treatment. This patient group have a higher mortality and by 5 years, 75% of patients in our hemodialysis group were dead.

Funding Acknowledgement

Type of funding sources: None.

P3661Two-fold increase in incidence of infective endocarditis in the period 1997–2016: a Danish nationwide study

Background

Infective Endocarditis (IE) is a disease with high mortality. Previous studies have shown considerable differences and contradicting trends in overall incidence and mortality why data from an unselected nationwide cohort is needed.

Purpose

We investigated temporal trends in the incidence rate and in-hospital mortality of IE in Denmark in the period of 1997–2016.

Methods

We included cases of first-time IE (1997–2016) using Danish nationwide registries. Crude incidence rates were given for each calendar year. Further, incidence rates were reported for subgroups of age and sex. For the analysis of patient characteristics and in-hospital mortality, the study cohort was grouped into four 5-year intervals (1997–2001, 2002–2006, 2007–2011, 2012–2016). Multivariable adjusted Cox proportional hazard model was used to compare in-hospital mortality between groups.

Results

A total of 8,147 patients with IE were identified in the period of 1997–2016. The median age and proportion of males increased from 64.3 years (P25-P75: 48–75.5) and 59.1% to 71.8 years (P25-P75: 62.1–79.9) and 67.1% in 1997–2001 and 2012–2016, respectively. The overall incidence rate (Figure 1) increased from 4.68/100.000-person-years (PY) (CI95: 4.17–5.26) to 8.23/100.000 PY (CI95: 7.53–8.99) in 1997 and 2016, respectively. Male incidence increased from 5.35/100.000 PY (CI95: 4.59–6.23) to 11.03/100.000 PY (CI95: 9.9–12.29) and female incidence increased from 4.03/100.000 PY (CI95: 3.38–4.8) to 5.44/100.000 PY (CI95: 4.67–6.35) in 1997 and 2016 respectively. Incidence rates increased more than seven-fold for the oldest age group (≥80 years) from 1997 to 2016 (6.95/100.000 PY [CI95: 5.32–9.08] to 51.19/100.000 PY [CI95: 43.41–60.38], respectively). In-hospital mortality was significantly lower for patients with IE in the period of 2011–2016 compared with 1997–2001 HR: 0.8 (CI95: 0.69–0.92).

Figure 1

Conclusion

Infective endocarditis incidences are increasing mostly among men and elderly patients. In order to prevent this disease as best as possible, we need more knowledge on causes for this increasing incidence.

P3665Prevalence of infective endocarditis in patients with positive blood cultures: a Danish nationwide study

Background

Increasing attention has been given to the risk of infective endocarditis (IE) in patients with certain blood stream infections (BSI). Previous studies have been conducted on selected patient cohorts, yet unselected data are sparse.

Purpose

To investigate the nationwide prevalence of diagnosed IE in BSIs with bacteria typically associated with IE.

Methods

By crosslinking nationwide registries from 2010–2016, we identified patients with BSIs typically associated with IE: Enterococcus faecalis, Staphylococcus, Streptococcus spp., and coagulase negative staphylococci (CoNS) and examined the concurrent IE prevalence. A trend test was used to examine temporal changes in the prevalence of IE.

Results

In total 60,119 BSIs, distributed with 15,407, 16,790, and 27,922 BSIs were identified in the periods of 2010–2011, 2012–2013, and 2014–2016, respectively.

Patients with E. Faecalis had the highest prevalence of diagnosed IE (16.3%) followed by S. aureus (10.2%), Streptococcus spp. (7.3%), and CoNS (1.6%) (Figure). During the study period, the prevalence of IE among patients with E. faecalis increased significantly (p=0.003), Male patients had higher prevalence of IE for all microorganisms investigated compared with females. A significant increase in the prevalence of IE was seen for E. faecalis, Streptococcus spp., and CoNS with increasing age.

Percent with endocarditis

Conclusion

For E. faecalis BSI, 1 in 6 had IE, for S. aureus BSI 1 in 10 had IE, and for Streptococcus spp. 1 in 14 had IE. Our results support screening for IE in patients with E. faecalis, S. aureus, or Streptococcus spp. BSI in order to offer appropriate therapy.

P3663Prevalence of infective endocarditis in patients with a left-sided heart valve prosthesis: a nationwide study

Background

Increasing attention has been given to patients with blood stream infection (BSI) and the concurrent prevalence of infective endocarditis (IE). However, there exist a gap in knowledge on the prevalence of IE among patients with a left-sided heart valve prosthesis and BSI.

Purpose

To examine the prevalence between different BSI and IE in patients with a left-sided heart valve prosthesis.

Methods

By linking Danish nationwide registries, we were able to identify patients with a left-sided prosthetic heart valve and first-time BSI of interest (Enterococcus faecalis, Staphylococcsus aureus, streptococci species (spp.), and coagulase negative staphylococci [CoNS]) in the period of 2010–2016. Concurrent admission for IE was identified from the Danish National Patient Registry in a period of up to 14 days after the BSI.

Results

A total of 1,465 patients with BSI were included (1,319 patients with an aortic valve prosthesis [82.6% bioprosthetic] and 146 patients with a mitral valve prosthesis [48.6% bioprosthetic]). Among the included patients, 244 had E. faecalis (median age: 78.3 years, 77.0% male), 301 had S. aureus (median age: 76.9 years, 69.1% male), 401 had streptococci spp. (median age: 78.0 years, 69.1% male) and 519 had CoNS (median age: 76.4 years, 64.2% male). The percentage of patients with a diagnosis of IE in relation to the BSI was 44.3%, 33.6%, 34.4%, and 7.9% for E. faecalis, S. aureus, streptococci spp., and CoNS, respectively. No difference in the overall results was seen by type of valve prosthesis, sex, or age group.

Percentage of patients with endocarditis

Conclusion

In patients with a left-sided heart valve prosthesis, IE was diagnosed in almost half of the patients with E. faecalis, in 1/3 with S. aureus or streptococci spp. and in 1 in 12 with CoNS BSI. Future studies may try to explain why some microbes are more likely to cause prosthetic heart valve endocarditis, than others are.

P2754Streptococcal infective endocarditis: distribution of species and their prognosis

Background

Infective endocarditis (IE) is frequently caused by streptococcal species. However, there is limited knowledge about the relationship between different streptococcal species and IE, and their associated outcomes.

Purpose

To examine the prevalence of streptococci at species level in IE, and to relate these different species to outcomes.

Methods

From 2002–2012 we prospectively collected consecutive patients with IE admitted to two tertiary heart centres covering a catchment area of 2.4 million people. The registry comprises 915 IE patients, 366 (40%) with streptococcal IE. Based on phylogenetic relationship, streptococcal species were classified into seven main groups: Mitis, Bovis, Mutans, Anginosus, Salivarius, Pyogenic and Nutritionally Variant Streptococcus (NVS). Classification at species level was not possible in 51 patients, who were excluded. Complications and prognosis of streptococcal IE were compared between the subgroups, and at species level.

Results

We included 315 patients with streptococcal IE. Mean age was 63 (IQR 52–76) years, and most were men (67%). A total of 115 patients (37%) had a previous heart valve disease, 58 (18%) had a prosthetic valve, 22 (7%) had previously had IE and 29 (9%) had a cardiac electronic device. With 148 episodes (47%) the Mitis group was the most common cause of IE. Other frequent groups were the Pyogenic group and the Bovis group, accounting for 66 (21%) and 51 (16%) of the cases, respectively. Surgery was carried out in 55% (n=173) of all cases. Patients infected with S. pneumoniae or S. agalactiae had a significantly higher rate of surgery, 72.2% (n=13) and 71.9% (n=23) respectively, whereas the Bovis group had a significantly lower rate, 35.5% (n=18) (p=0.048). The aortic valve was infected in 137 patients (43.5%), mitral valve in 105 patients (33.3%) and both valves were infected in 53 patients (16.8%). Twenty patients (6.3%) had right-sided IE, including pacemaker lead IE. There was no significant difference between the species subgroups regarding type of infected valve. Embolization and osteitis were observed in 76 (24.1%) and 30 (9.5%) patients, respectively. There was no significant difference between the species groups, as was the case with mortality: 23 patients (7.3%) died in-hospital and the one-year mortality was 16% (n=50).

Distribution of streptococcal IE

Conclusion

Species of the Mitis group were the most frequent Streptococci causing IE. Patients infected with S. pneumonia or S. agalactiae had significantly higher rate of surgery, and patients infected with S. bovis group had lower rate of surgery. There was no significant difference in rate of complications such as abscesses, embolization, osteitis or mortality between the streptococcal species.

Acknowledgement/Funding

Supported by grants from Herlev-Gentofte University Hospital Research Foundation

Improving national surveillance of Lyme neuroborreliosis in Denmark through electronic reporting of specific antibody index testing from 2010 to 2012

Our aim was to evaluate the results of automated surveillance of Lyme neuroborreliosis (LNB) in Denmark using the national microbiology database (MiBa), and to describe the epidemiology of laboratory-confirmed LNB at a national level. MiBa-based surveillance includes electronic transfer of laboratory results, in contrast to the statutory surveillance based on manually processed notifications. Antibody index (AI) testing is the recommend laboratory test to support the diagnosis of LNB in Denmark. In the period from 2010 to 2012, 217 clinical cases of LNB were notified to the statutory surveillance system, while 533 cases were reported AI positive by the MiBa system. Thirty-five unconfirmed cases (29 AI-negative and 6 not tested) were notified, but not captured by MiBa. Using MiBa, the number of reported cases was increased almost 2.5 times. Furthermore, the reporting was timelier (median lag time: 6 vs 58 days). Average annual incidence of AI-confirmed LNB in Denmark was 3.2/100,000 population and incidences stratified by municipality ranged from none to above 10/100,000. This is the first study reporting nationwide incidence of LNB using objective laboratory criteria. Laboratory-based surveillance with electronic data-transfer was more accurate, complete and timely compared to the surveillance based on manually processed notifications. We propose using AI test results for LNB surveillance instead of clinical reporting.

The Danish Microbiology Database (MiBa) 2010 to 2013

The Danish Microbiology Database (MiBa) is a national database that receives copies of reports from all Danish departments of clinical microbiology. The database was launched in order to provide healthcare personnel with nationwide access to microbiology reports and to enable real-time surveillance of communicable diseases and microorganisms. The establishment and management of MiBa has been a collaborative process among stakeholders, and the present paper summarises lessons learned from this nationwide endeavour which may be relevant to similar projects in the rapidly changing landscape of health informatics.

Low vaccine effectiveness against influenza A(H3N2) virus among elderly people in Denmark in 2012/13 – a rapid epidemiological and virological assessment

Binary file ES_Abstracts_Final_ECDC.txt matches

Low vaccine effectiveness against influenza A(H3N2) virus among elderly people in Denmark in 2012/13--a rapid epidemiological and virological assessment

In Denmark, the 2012/13 influenza season has been dominated by influenza A(H3N2). We estimated the vaccine effectiveness (VE) of the trivalent influenza vaccine by linking national registers in a test-negative case-control study of patients tested for influenza aged ≥65 years. The adjusted VE against laboratory-confirmed influenza A and B was -11% (95% CI: -41 to 14) and 69% (95% CI: 26 to 87), respectively. Genetic characterisation of the influenza A(H3N2) viruses indicated genetic drift, with seven substitutions at key antigenic sites.

Increased incidence of Mycoplasma pneumoniae infections detected by laboratory-based surveillance in Denmark in 2010

In Denmark recurrent epidemics of Mycoplasma pneumoniae infections have been described since the 1950s at intervals of approximately four to six years. The latest epidemic occurred in 2004/05 followed by two years of high incidence and more than three years of low incidence. Due to a recent increase in diagnosed cases since late summer 2010, we conducted a survey of positive M. pneumoniae PCR tests performed by clinical microbiology departments in Denmark, which indicated that a new epidemic may be underway.

Increased incidence of Mycoplasma pneumoniae infections detected by laboratory-based surveillance in Denmark in 2010

In Denmark recurrent epidemics of Mycoplasma pneumoniae infections have been described since the 1950s at intervals of approximately four to six years. The latest epidemic occurred in 2004/05 followed by two years of high incidence and more than three years of low incidence. Due to a recent increase in diagnosed cases since late summer 2010, we conducted a survey of positive M. pneumoniae PCR tests performed by clinical microbiology departments in Denmark, which indicated that a new epidemic may be underway.

Caveolae, caveolin and cav-p60 in smooth muscle and renin-producing cells in the rat kidney

AIMS

In vascular smooth muscle cells caveolae are important for signalling mechanisms regulating vascular contraction. In smooth muscle layer of the renal afferent arteriole juxtaglomerular cells (JG cells) are non-contractile renin producing cells that have the capacity to change their phenotype into smooth muscle cells and back again by metaplastic transformation. Signalling mechanisms in JG cells are not fully understood and we therefore investigated if caveolae were present, and thereby could be involved as integrators of cellular signalling in both of these phenotypes of smooth muscle cells.

METHODS

Using electron microscopy we compared the number of caveolae in JG cells and smooth muscle cells in the afferent arteriole of the rat kidney. The expression of caveolin and cav-p60 was examined using a combination of immunogold electron microscopy and immunofluorescence microscopy.

RESULTS

We found that JG cells have sixfold less caveolae per cell surface sectional length than smooth muscle cells. The expression of cavolin-1 and cav-p60 correlated with the number of caveolae. An examination of the general distribution of caveolae, cav-p60 and caveolins in the rat kidney showed that cav-p60, like caveolin-1, is a specific maker of caveolae.

CONCLUSION

The number of caveolae in JG cells is very low, and this makes it unlikely that caveolae are of major importance for the renin secretion specific for JG cells.

cav-p60 expression in rat muscle tissues. Distribution of caveolar proteins

Caveolae are plasmalemmal invaginations of uncertain function. In view of the large number of hypotheses on caveolar functions, it is important to identify which components of caveolae are tissue specific and which are general. The only well-characterized major protein of caveolae is caveolin, which exists in three tissue-specific isoforms: caveolin-1, -2, and -3. Recently cav-p60 was characterized as a 60-kDa caveola-specific protein in adipocytes. The distributions of cav-p60 and caveolin isoforms in different rat muscle tissues were examined by immunofluorescence and immunoelectron microscopy. Cav-p60 was present in caveolae of skeletal and heart muscle, in vascular and intestinal smooth muscle, and in adipocyte caveolae. Furthermore cav-p60 was present in endothelial cells and cells of perineural sheaths. Caveolin-1 and -2 were present in adipocytes, endothelial cells, and cells of perineural sheaths. In all kinds of vascular and intestinal smooth muscle, caveolin-1 and -2 were present at high levels, whereas caveolin-3 expression was low or undetectable, depending on the specific smooth muscle subtype. High levels of caveolin-3 were found only in caveolae and T tubules of skeletal and heart muscle. We conclude that cav-p60 is a highly specific marker of caveolae in many if not all cell types having caveolae.

A 60-kDa protein abundant in adipocyte caveolae

To search for caveolar proteins, mice were immunised with rat adipocyte membranes. Hybridoma supernatants were screened for antibodies to proteins on the cytosolic face of caveolae by indirect immunoelectron microscopy of immunogold-labelled adipocyte plasma membrane sheets adsorbed on electron-microscope (EM) grids. One of the hybridoma supernatants (2F11) produced a specific labelling of caveolae which was much more intense than that obtained with caveolin-1 antibodies. In Western blots of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) separated proteins in crude membrane fractions from different rat tissues, 2F11 labelled a band corresponding to 60 kDa. The intensity of 2F11 labelling was high in adipose tissue and in other tissues varied in parallel to caveolin- labelling. In blots of plasma membrane (PM) and light-microsomal (LM) fractions from a homogenate of adipocytes, prior insulin stimulation of the adipocytes translocated GLUT-4 from the LM to the PM fraction, but was without effect on the distribution of the 60-kDa protein labelled by 2F11. Digestion with endoproteinase lys-C produced the same pattern of immunoreactive fragments of the protein in the vesicular PM and LM fractions, indicating similar membrane topology of the 2F11-reactive, 60-kDa protein in vesicles of PM and LM fractions.

Human neutrophils are devoid of the integral membrane protein caveolin

The secretory vesicles of human neutrophils are rapidly mobilizable vesicles that contain several GPI-linked proteins, a characteristic feature of caveolae in other cells. To investigate whether secretory vesicles are structurally related to caveolae, we examined human neutrophils for the presence of caveolin, a major constituent of caveolae, by immunoblotting using monoclonal and polyclonal antibodies. Caveolin was not detected in lysates of human neutrophils nor in isolated plasma membrane/light membrane fractions in which secretory vesicles localize. In contrast, caveolin was readily detected in isolated membranes of adipose cells. We conclude that human neutrophils are devoid of caveolin and that secretory vesicles are not related to caveolae nor dependent on caveolae for mobilization.

Expression of GLUT1 in stratified squamous epithelia and oral carcinoma from humans and rats

Most cells express facilitative glucose transporters. Four isoforms (GLUT1-4) transporting D-glucose across the plasma membrane show a specific tissue distribution, which is the basis for tissue-specific patterns in glucose metabolism. GLUT1 is expressed at high levels in tissue barriers such as the blood-brain barrier, and this isoform has been suggested as an indicator of such barriers. GLUT1 has been found in basal layers of human epidermis where no such tissue barrier is present. To further clarify these issues, we examined the distribution of GLUT1 and GLUT4 in skin, different types of oral mucosa from rat and man, and a human oral carcinoma by indirect immunofluorescence microscopy. The results showed that GLUT1 was expressed in the basal and parabasal layers of the different stratified squamous epithelia, with some variations between keratinized and non-keratinized subtypes. GLUT1 was also expressed in ductal- and myoepithelial cells of minor salivary glands and perineural sheath located in the lamina propra, and furthermore in the cells of an oral carcinoma. GLUT4 was not expressed in any of the tissues examined. This distribution of GLUT1 does not fit with the idea of GLUT1 as a general indicator of tissue barriers. In contrast, our results support the prevailing, but limited knowledge of glucose metabolism in squamous stratified epithelia, a metabolism believed to depend mostly on glycolysis, especially in the basal layers. High-level expression seemed to be confined to keratinocytes without glycogen stores.

Quantity of Na/K-ATPase and glucose transporters in the plasma membrane of rat adipocytes is reduced by in vivo triiodothyronine

The expression of sodium-potassium pumps and glucose transporters in pure adipocyte plasma membranes from a hyperthyroid animal model was studied. Hyperthyroidism was induced by enteral administration of five doses of 90 micrograms of triiodothyronine every second day to 8-week-old rats. Following isolation of epididymal adipocytes, 3-O-methylglucose transport was measured and the number of Na/K-ATPase-(alpha 1- and alpha 2-isoforms) and glucose transporter (GLUT1 and GLUT4) molecules in sheets of adipocyte plasma membrane were determined by quantitative immunoelectron microscopy, using gold labelling. Maximal in vitro insulin stimulation of adipocytes increased the glucose transport rate and the amount of GLUT4 in the plasma membrane 15-fold, whereas the amount of alpha 2 was unaffected. In adipocytes from hyperthyroid rats, mean adipocyte volume was decreased by 18% and the quantities of GLUT4 per unit area of plasma membrane (maximal insulin stimulation) and of alpha 2 were decreased by 19% and 15%, respectively. Thus, hypotrophia of fat tissue in the hyperthyroid state is associated with a decreased expression in the plasma membrane of the glucose transporter GLUT4 and the alpha 2-isoform of Na/K-ATPase.

Quantitation of Na+/K(+)-ATPase and glucose transporter isoforms in rat adipocyte plasma membrane by immunogold labeling

We have quantitated and studied the topology of isoforms of the Na+/K(+)-ATPase and of the glucose transporter in rat adipocyte plasma membranes. Adipocytes were incubated with or without insulin for 15 min. Sheets of native plasma membrane, with the cytoplasmic face exposed, were prepared by adsorption to EM grids. Grids were incubated in parallel with monoclonal antibodies against the Na+/K(+)-ATPase isoforms alpha 1 and alpha 2, and the glucose transporter isoforms GLUT1 and GLUT4, followed by immunogold labeling, negative staining and quantitation by counting of the gold particles in electron micrographs. In addition, the distribution of glucose transporters and Na+/K(+)-ATPase isoforms in subcellular membrane fractions prepared by an established fractionation procedure was monitored by Western blotting. We found that the Na+/K(+)-ATPases and the glucose transporters were confined to the planar part of the plasma membrane, without association to caveolar invaginations. The vast majority of the Na+/K(+)-ATPase molecules in the adipocyte plasma membrane were of the alpha 2 isoform; GLUT4 was the dominating glucose transporter isoform. The total number of Na+/K(+)-ATPase molecules labeled in the plasma membrane was 3.5 x 10(5) per cell, independent of insulin stimulation. Concomitantly, insulin increased GLUT4 labeling sevenfold to a value of 3.5 x 10(5) per cell.

Metformin ameliorates diabetes but does not normalize the decreased GLUT 4 content in skeletal muscle of obese (fa/fa) Zucker rats

We studied the expression of the glucose transporter GLUT 4 in the soleus and red gastrocnemius muscles from obese, diabetic (fa/fa) Zucker rats compared to their lean littermates (Fa/-), with and without treatment with the antidiabetic drug metformin. In the untreated groups of rats, the GLUT 4 content in a crude membrane fraction of both the soleus and the red gastrocnemius muscles were significantly lower in the obese (fa/fa) rats (3.46 +/- 0.28 vs. 6.04 +/- 0.41, p < 0.001 and 6.0 +/- 0.24 vs. 9.1 +/- 0.48, p < 0.0001, respectively). Differences in GLUT 4 expression in soleus muscle from the same rats were confirmed by quantitative immunofluorescence microscopy, and the results were significantly correlated with the results obtained from quantitative immunoblotting (rho = 0.70, p < 0.0005). The decreased expression of GLUT 4 in fa/fa rats could contribute to the well-established insulin resistance in skeletal muscle of these animals. After 4 weeks of treatment with metformin, weight gain was not affected in either the diabetic (fa/fa) rats or the lean (Fa/-) rats. Improvement of glucose homeostasis by metformin was not associated with normalization of the GLUT 4 expression in the skeletal muscles studied, indicating (1) that the decreased GLUT 4 expression is not directly related to hyperinsulinaemia and diabetes mellitus and (2) that metformin does not normalize the expression of GLUT 4 in skeletal muscle of the diabetic (fa/fa) Zucker rats.