Effects of empagliflozin on progression of chronic kidney disease: a prespecified secondary analysis from the empa-kidney trial

BACKGROUND

Sodium-glucose co-transporter-2 (SGLT2) inhibitors reduce progression of chronic kidney disease and the risk of cardiovascular morbidity and mortality in a wide range of patients. However, their effects on kidney disease progression in some patients with chronic kidney disease are unclear because few clinical kidney outcomes occurred among such patients in the completed trials. In particular, some guidelines stratify their level of recommendation about who should be treated with SGLT2 inhibitors based on diabetes status and albuminuria. We aimed to assess the effects of empagliflozin on progression of chronic kidney disease both overall and among specific types of participants in the EMPA-KIDNEY trial.

METHODS

EMPA-KIDNEY, a randomised, controlled, phase 3 trial, was conducted at 241 centres in eight countries (Canada, China, Germany, Italy, Japan, Malaysia, the UK, and the USA), and included individuals aged 18 years or older with an estimated glomerular filtration rate (eGFR) of 20 to less than 45 mL/min per 1·73 m2, or with an eGFR of 45 to less than 90 mL/min per 1·73 m2 with a urinary albumin-to-creatinine ratio (uACR) of 200 mg/g or higher. We explored the effects of 10 mg oral empagliflozin once daily versus placebo on the annualised rate of change in estimated glomerular filtration rate (eGFR slope), a tertiary outcome. We studied the acute slope (from randomisation to 2 months) and chronic slope (from 2 months onwards) separately, using shared parameter models to estimate the latter. Analyses were done in all randomly assigned participants by intention to treat. EMPA-KIDNEY is registered at ClinicalTrials.gov, NCT03594110.

FINDINGS

Between May 15, 2019, and April 16, 2021, 6609 participants were randomly assigned and then followed up for a median of 2·0 years (IQR 1·5-2·4). Prespecified subgroups of eGFR included 2282 (34·5%) participants with an eGFR of less than 30 mL/min per 1·73 m2, 2928 (44·3%) with an eGFR of 30 to less than 45 mL/min per 1·73 m2, and 1399 (21·2%) with an eGFR 45 mL/min per 1·73 m2 or higher. Prespecified subgroups of uACR included 1328 (20·1%) with a uACR of less than 30 mg/g, 1864 (28·2%) with a uACR of 30 to 300 mg/g, and 3417 (51·7%) with a uACR of more than 300 mg/g. Overall, allocation to empagliflozin caused an acute 2·12 mL/min per 1·73 m2 (95% CI 1·83-2·41) reduction in eGFR, equivalent to a 6% (5-6) dip in the first 2 months. After this, it halved the chronic slope from -2·75 to -1·37 mL/min per 1·73 m2 per year (relative difference 50%, 95% CI 42-58). The absolute and relative benefits of empagliflozin on the magnitude of the chronic slope varied significantly depending on diabetes status and baseline levels of eGFR and uACR. In particular, the absolute difference in chronic slopes was lower in patients with lower baseline uACR, but because this group progressed more slowly than those with higher uACR, this translated to a larger relative difference in chronic slopes in this group (86% [36-136] reduction in the chronic slope among those with baseline uACR <30 mg/g compared with a 29% [19-38] reduction for those with baseline uACR ≥2000 mg/g; ptrend<0·0001).

INTERPRETATION

Empagliflozin slowed the rate of progression of chronic kidney disease among all types of participant in the EMPA-KIDNEY trial, including those with little albuminuria. Albuminuria alone should not be used to determine whether to treat with an SGLT2 inhibitor.

FUNDING

Boehringer Ingelheim and Eli Lilly.

Impact of primary kidney disease on the effects of empagliflozin in patients with chronic kidney disease: secondary analyses of the EMPA-KIDNEY trial

BACKGROUND

The EMPA-KIDNEY trial showed that empagliflozin reduced the risk of the primary composite outcome of kidney disease progression or cardiovascular death in patients with chronic kidney disease mainly through slowing progression. We aimed to assess how effects of empagliflozin might differ by primary kidney disease across its broad population.

METHODS

EMPA-KIDNEY, a randomised, controlled, phase 3 trial, was conducted at 241 centres in eight countries (Canada, China, Germany, Italy, Japan, Malaysia, the UK, and the USA). Patients were eligible if their estimated glomerular filtration rate (eGFR) was 20 to less than 45 mL/min per 1·73 m2, or 45 to less than 90 mL/min per 1·73 m2 with a urinary albumin-to-creatinine ratio (uACR) of 200 mg/g or higher at screening. They were randomly assigned (1:1) to 10 mg oral empagliflozin once daily or matching placebo. Effects on kidney disease progression (defined as a sustained ≥40% eGFR decline from randomisation, end-stage kidney disease, a sustained eGFR below 10 mL/min per 1·73 m2, or death from kidney failure) were assessed using prespecified Cox models, and eGFR slope analyses used shared parameter models. Subgroup comparisons were performed by including relevant interaction terms in models. EMPA-KIDNEY is registered with ClinicalTrials.gov, NCT03594110.

FINDINGS

Between May 15, 2019, and April 16, 2021, 6609 participants were randomly assigned and followed up for a median of 2·0 years (IQR 1·5-2·4). Prespecified subgroupings by primary kidney disease included 2057 (31·1%) participants with diabetic kidney disease, 1669 (25·3%) with glomerular disease, 1445 (21·9%) with hypertensive or renovascular disease, and 1438 (21·8%) with other or unknown causes. Kidney disease progression occurred in 384 (11·6%) of 3304 patients in the empagliflozin group and 504 (15·2%) of 3305 patients in the placebo group (hazard ratio 0·71 [95% CI 0·62-0·81]), with no evidence that the relative effect size varied significantly by primary kidney disease (pheterogeneity=0·62). The between-group difference in chronic eGFR slopes (ie, from 2 months to final follow-up) was 1·37 mL/min per 1·73 m2 per year (95% CI 1·16-1·59), representing a 50% (42-58) reduction in the rate of chronic eGFR decline. This relative effect of empagliflozin on chronic eGFR slope was similar in analyses by different primary kidney diseases, including in explorations by type of glomerular disease and diabetes (p values for heterogeneity all >0·1).

INTERPRETATION

In a broad range of patients with chronic kidney disease at risk of progression, including a wide range of non-diabetic causes of chronic kidney disease, empagliflozin reduced risk of kidney disease progression. Relative effect sizes were broadly similar irrespective of the cause of primary kidney disease, suggesting that SGLT2 inhibitors should be part of a standard of care to minimise risk of kidney failure in chronic kidney disease.

FUNDING

Boehringer Ingelheim, Eli Lilly, and UK Medical Research Council.

Abstract P542: Classifying COVID-19 Related Hospitalizations and Deaths in the Collaborative Cohort of Cohorts for COVID-19 Research (C4R) Study

Objectives: Administrative criteria are often used to define COVID-19 outcomes despite challenges in differentiating hospitalization “for” vs “with” COVID-19 and unknown reliability for identifying COVID-related cardiopulmonary complications. We implemented a protocol to adjudicate COVID-related events across 14 studies participating in C4R.

Methods: C4R cohorts ascertained COVID-related hospitalizations and deaths via questionnaires or ongoing surveillance. Medical records were reviewed by C4R physicians using a standardized protocol to assign COVID-related diagnoses as definite or probable. C4R diagnoses were compared against ICD codes assigned to the events. This report includes data from events centrally adjudicated by C4R as of September 2022.

Results: Among 144 events ascertained across 7 cohorts as potentially COVID-related, SARS-CoV-2 infection was confirmed in 107/117 (91%) non-fatal hospitalizations and 26/27 (96%) deaths. Of confirmed infections, COVID-19 illness was diagnosed as the cause of 101/107 (94%) hospitalizations and 24/26 (92%) deaths ( Table ). Of non-fatal hospitalizations with infection, 72% were diagnosed with severe or critical COVID-19, 78% with COVID-associated pneumonia, and 29% with renal failure; other complications were less common. C4R review did not validate diagnoses indicated by ICD codes for 1 COVID-19 infection, 5 pneumonias, 1 stroke, and 7 renal failure cases. C4R review did identify diagnoses that were not ICD-coded for 13 infections, 31 pneumonias, 6 myocardial infarctions, 5 venous thromboses, and 21 renal failure cases.

Conclusions: Protocolized medical records review by C4R confirmed COVID-19 as the cause of hospitalization or death in 87% of events ascertained as potentially COVID-related and 94% of those in which SARS-CoV-2 infection was confirmed. Both false-positive and false-negative misclassification by ICD criteria was observed. Protocolized review may be useful to identify and validate COVID-related events for epidemiologic research.

Shielding commissioning factors in nuclear medicine facilities

This article reviews the essential considerations in planning and designing nuclear medicine departments. There are four proposed categories to consider as 'shielding commissioning factors' (SCF). The first SCF: 'Patient flow optimisation and workload' emphasises the importance of carefully considering patient flow in the departmental design, which would impact the cost of the shielding and the management of radioactive patients. The second SCF: 'Equipment and space allocation' discusses the principles of space allocations in the department for cost-effective designs. The third SCF: 'Shielding calculation methods' reviews the methodologies of shielding calculations in nuclear medicine to offer a standardised approach. The fourth SCF: 'Shielding integrity' reviews the plan to inspect, eyewitness and verify shielding integrity. All discussions were supplemented by practical examples. Overall, this article aims to be a practical manual which health or medical physicists can use when providing counsels to the design committee.

Position paper: recommendations for a digital mammography quality assurance program V4.0

In 2001 the ACPSEM published a position paper on quality assurance in screen film mammography which was subsequently adopted as a basis for the quality assurance programs of both the Royal Australian and New Zealand College of Radiologists (RANZCR) and of BreastScreen Australia. Since then the clinical implementation of digital mammography has been realised and it has become evident that existing screen-film protocols were not appropriate to assure the required image quality needed for reliable diagnosis or to address the new dose implications resulting from digital technology. In addition, the advantages and responsibilities inherent in teleradiology are most critical in mammography and also need to be addressed. The current document is the result of a review of current overseas practice and local experience in these areas. At this time the technology of digital imaging is undergoing significant development and there is still a lack of full international consensus about some of the detailed quality control (QC) tests that should be included in quality assurance (QA) programs. This document describes the current status in digital mammography QA and recommends test procedures that may be suitable in the Australasian environment. For completeness, this document also includes a review of the QA programs required for the various types of digital biopsy units used in mammography. In the future, international harmonisation of digital quality assurance in mammography and changes in the technology may require a review of this document. Version 2.0 represented the first of these updates and key changes related to image quality evaluation, ghost image evaluation and interpretation of signal to noise ratio measurements. In Version 3.0 some significant changes, made in light of further experience gained in testing digital mammography equipment were introduced. In Version 4.0, further changes have been made, most notably digital breast tomosynthesis (DBT) testing and QC have been addressed. Some additional testing for conventional projection imaging has been added in order that sites may have the capability to undertake dose surveys to confirm compliance with diagnostic reference levels (DRLs) that may be established at the National or State level. A key recommendation is that dosimetry calculations are now to be undertaken using the methodology of Dance et al. Some minor changes to existing facility QC tests have been made to ensure the suggested procedures align with those most recently adopted by the Royal Australian and New Zealand College of Radiologists and BreastScreen Australia. Future updates of this document may be provided as deemed necessary in electronic format on the ACPSEM's website ( https://www.acpsem.org.au/whatacpsemdoes/standards-position-papers and see also http://www.ranzcr.edu.au/quality-a-safety/radiology/practice-quality-activities/mqap ).

Novel characterization of bEnd.3 cells that express lymphatic vessel endothelial hyaluronan receptor-1

Murine bEnd.3 endothelioma cell line has been widely used in vascular research and here we report the novel finding that bEnd.3 cells express lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) and vascular endothelial growth factor receptor-3 (VEGFR-3). Moreover, these cells express progenitor cell markers of Sca-1 and CD133. Upon stimulation with tumor necrosis factor-alpha (TNF-alpha), the bEnd.3 cells demonstrate enhanced formation of capillary-type tubes, which express LYVE-1. As the bEnd.3 cell line is derived from murine endothelioma, we further examined human tissues of endothelioma and identified lymphatic vessels in the tumor samples which express both LYVE-1 and podoplanin. Moreover, a significantly higher number of lymphatic vessels were detected in the endothelioma samples compared with normal control. Taken together, this study not only redefines bEnd.3 cells for vascular research, but also indicates a broader category of human diseases that are associated with lymphatics, such as endothelioma.

How accurate is the electronic health record? - a pilot study evaluating information accuracy in a primary care setting

BACKGROUND

Electronic health records (EHR) are increasingly used for both administrative and clinical tasks with major implications for patient safety and quality of care. This study aims to determine a baseline EHR level of accuracy present on measurable information fields within an Australian general practice.

METHODS

Quantitative and descriptive pilot study of patients attending a private general practice. Patients who consented to participate in the study had their patient records reviewed to determine how many items were correct, incorrect or not recorded in each EHR information field. Statistical analysis was performed on the data collected.

RESULTS

A total of 33 patients gave consent to participate in this study. High levels of accuracy were found in the area of demographic details (94%). Moderately high levels of accuracy were reported for allergies (61%) but also a considerable percentage of non-recorded information was present (36%). Inaccuracies in medication lists were reported in 51% of records reviewed with 32.1% of all medications being inaccurately recorded. While over 91% of participants had a history summary with eight or less items present, omissions were reported for one in every five participants. There were no significant associations present between inaccurate data and frequency of practice visits or those with more than five past medical conditions listed in the EHR.

CONCLUSION

The study has confirmed that errors and inaccuracies exist in EHR in our Australian pilot study. The pilot study has also allowed us to complete a trial ensuring that a study of this type can be done safely and with correct methodology. As health informatics plays an increasingly important role in health care, studies of this type will better inform practitioners/ researchers in designing systems to ensure quality electronic patient information.

Fetoscopy under gas amniodistension: pressure-dependent influence of helium vs nitrous oxide on fetal goats

PURPOSE

Recently, gas amniodistension has been advocated for fetoscopic surgery to employ ergonomics similar to laparoscopy. However, neither the optimal type of gas nor its physiological influence on the fetus have been clearly outlined yet. This study investigates the impact of helium (HE) vs nitrous oxide (N2O) on fetal goats during fetoscopy.

METHODS

We insufflated either HE or N2O in 12 pregnant goats (15 fetuses; HE = 7, N2O = 8), then increased the pressures from 0, 4, 7, to 10 mm Hg in 30-minute intervals and recorded the fetal and maternal vital parameters. Finally, whole-body computed tomography to asses for intracorporeal gas was performed.

RESULTS

All fetuses survived. Mean fetal vital signs showed no significant differences between HE or N2O at specific pressure levels. In detail, HE/N2O at 0 vs 10 mm Hg caused a fetal temperature decrease (32.9 degrees C/33.2 degrees C vs 32 degrees C/32.5 degrees C), heart rate increase in the N2O group (100/102 vs 102/121 beats per minute), and no significant change in arterial pressure (45.8/48.3 vs 53.7/46.7 mm Hg). The PO2 was adequate (3.7/3.3 vs 3.7/2.9 kPa), whereas the pH remained unchanged (7.4/7.3 vs 7.3/7.3). However, fetal pCO2 was elevated in the N2O group before insufflation (5.5/7.2 vs 6.8/8.0 kPa) owing to maternal hypoventilation (maternal PCO2: 4.9/5.8 vs 5.0/5.4 kPa), correction of which was slower in the fetus than in the maternal animal. Computed tomography ruled out intracorporeal gas accumulation.

CONCLUSION

Neither HE nor N2O impose significant physiological harm for the fetus. Heating of the gas and maternal anesthesia seem essential. Considering the potential teratogenicity of N2O, however, HE could be the favorable environment for fetoscopic procedures under gas amniodistension.

Towards a circular bis-peptide nucleic acid

En route to a circular bis-PNA molecule, we have synthesized and characterized the DNA binding of several "clamp"-type bis-PNAs. In order to incorporate charge into a circular PNA, a new linker based on the achiral 2-aminoethylglycine has been used.

Nucleobase modified peptide nucleic acid

The Pd0/Cu1 catalyzed cross-coupling of terminal alkynes onto peptide nucleic acid monomers or submonomers bearing iodinated nucleobases has been utilized as a route to base-modified oligomers. Both 5-iodouracil and 5-iodocytosine derivatives undergo the cross-coupling to give the expected products in moderate to good yields. However, depending on the particular substrates and reaction conditions, the cross-coupling may be followed by a ring closing reaction to give the fluorescent furano- and pyrrolo-fused uracil and cytosine derivatives, respectively.

The type IV phosphodiesterase specific inhibitor mesopram inhibits experimental autoimmune encephalomyelitis in rodents

Experimental autoimmune encephalomyelitis (EAE) is an autoimmune disease with pathological features reminiscent of those seen in multiple sclerosis and thus serves as an animal model for this disease. Inhibition of type IV phosphodiesterase (PDE IV) in animals with this disease has been shown to result in amelioration of disease symptoms. Here we describe the immunomodulatory activity of the novel potent and selective PDE IV inhibitor mesopram. In vitro, mesopram selectively inhibits the activity of type 1 helper T (Th1) cells without affecting cytokine production or proliferation of type 2 helper T (Th2) cells. Administration of mesopram to rodents inhibits EAE in various models. Clinically, EAE is completely suppressed by mesopram in Lewis rats. This is accompanied by a reduction of inflammatory lesions in spinal cord and brain. RT-PCR analysis revealed a marked reduction in the expression of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in the brains of these animals. Furthermore, the ex vivo production of Th1 cytokines by activated spleen cells derived from mesopram-treated animals is significantly reduced compared to vehicle-treated controls. Amelioration of the clinical symptoms is also observed during chronic EAE in mesopram-treated SJL mice as well as in relapsing-remitting EAE in SWXJ mice using a therapeutic treatment regimen. These data demonstrate the anti-inflammatory activity of mesopram and provide a rationale for its clinical development.

Effects of beta-adrenoceptor stimulation on pacing-induced failure of dog hypertrophic hearts

1. We tested the hypothesis that the transition to pacing-induced failure in hypertrophic hearts would result in reduced functional and metabolic responses to beta-adrenoceptor stimulation. 2. Isoproterenol (ISO; 0.1 microg/kg per min) was infused into a coronary artery in five anaesthetized open-chest control, five aortic stenosis-induced left ventricular hypertrophy (LVH) and five LVH pacing-induced failure dogs. 3. In both control and LVH dogs, but not in failure dogs, ISO significantly increased local regional work (1,923+/-665 vs 2,656+/-715, 1,185+/-286 vs 1,906+/-562 and 835+/-106 vs 849+/-216g.mm/min, respectively), force (11.1+/-1.4 vs 16.9+/-2.6, 8.6+/-1.5 vs 13.7+/-2.3 and 12.2+/-1.1 vs 11.0+/-1.8g, respectively) and myocardial O2 consumption (7.3+/-2.0 vs 10.0+/-1.5, 8.2+/-1.6 vs 11.6+/-2.6 and 4.4+/-1.5 vs 5.5+/-1.8 mL O2/min per 100 g, respectively). 4. Isoproterenol also significantly increased cAMP in control and LVH dogs (474+/-67 vs 600+/-91 and 473+/-34 vs 619+/-53 pmol/g, respectively). In heart failure, cAMP was significantly lower and there was no significant increase in cAMP in response to ISO (245+/-43 vs 314+/-40pmol/g, respectively). 5. We conclude that there were no significant myocardial functional, O2 consumption or cAMP responses to ISO after the transition from hypertrophy to cardiac failure.

Down regulation of myocardial beta1-adrenoceptor signal transduction system in pacing-induced failure in dogs with aortic stenosis-induced left ventricular hypertrophy

We recently demonstrated that rapid ventricular pacing caused cardiac failure (Failure) in dogs with aortic stenosis-induced left ventricular hypertrophy (Hypertrophy) and isoproterenol caused no significant increases in function, O2 consumption and intracellular cyclic AMP level in the failing hypertrophied hearts. We tested the hypothesis that alterations in the beta1-adrenoceptor-signal transduction pathway would correlate with the reduced functional and metabolic responses to beta-adrenergic stimulation during the transition from the compensated hypertrophy to failure. Pressure overload-induced left ventricular hypertrophy was created using aortic valve plication in 10 dogs over a 6-month period. Five months after aortic valve plication, congestive heart failure was induced in 5 dogs by rapid ventricular pacing at 240 bpm for 4 weeks. The density of myocardial beta1-adrenoceptors (fmoles/mg membrane protein; fmoles/g wet tissue) was significantly reduced in the Failure dogs (176+/-19; 755+/-136) when compared to those of the Control (344+/-51; 1,551+/-203) and the Hypertrophy (298+/-33; 1,721+/-162) dogs. The receptor affinities were not significantly different among all groups. There was a small but significant decrease in the percentage of beta1-adrenoceptors of the failing hypertrophied hearts (62+/-3%) when compared to that of the hypertrophied hearts (77+/-5%). The basal myocardial adenylyl cyclase activity (pmoles/mg protein/min) was significantly lower in the Failure dogs (45+/-4) than in the Control (116+/-14) and Hypertrophy (86+/-6) dogs. The forskolin (0.1 mM)-stimulated adenylyl cyclase activity was also significantly lower in the Failure dogs (158+/-17) than in the Control dogs (296+/-35) and slightly lower than in the Hypertrophy dogs (215+/-10). There were no significant differences in low Km cyclic AMP-phosphodiesterase activities among all groups. We conclude that down regulation of beta1-adrenoceptors and reduced adenylyl cyclase activities contribute to the decreases in myocardial functions and beta-adrenergic responses in the failing hypertrophied hearts induced by rapid ventricular pacing.

Pacing-induced cardiac failure of hypertrophic hearts: effects of cyclic GMP reduction

BACKGROUND

We tested the hypothesis that pacing-induced cardiac failure of hypertrophic hearts would reduce the functional and metabolic responses of these hearts to guanylate cyclase inhibition and this was associated with alterations in cyclic GMP.

MATERIALS AND METHODS

Methylene blue (MB, 2 mg/kg/min, guanylate cyclase inhibitor) was infused into the left anterior descending coronary artery in 5 control, 5 left ventricular hypertrophy (LVH), and 5 LVH pacing-induced failure dogs. Regional myocardial work was calculated as the integrated product of force and segment shortening and regional myocardial O(2) consumption (VO(2)) from coronary blood flow and O(2) extraction measurements. Cyclic GMP was determined by radioimmunoassay.

RESULTS

MB increased regional work (635 +/- 169 vs 1649 +/- 500, 781 +/- 184 vs 1569 +/- 203 g * mm/min) and VO(2) (8.3 +/- 1.4 vs 10.9 +/- 1.4, 7.3 +/- 0.7 vs 9.1 +/- 0.7 ml O(2)/min/100 g) in both control and LVH dogs but not in failure dogs (536 +/- 234 vs 623 +/- 193, 3.6 +/- 1.1 vs 4.7 +/- 1.9). MB also decreased cyclic GMP in control dogs (1170 +/- 142 vs 812 +/- 105 pmol/g). LVH dogs had elevated baseline cyclic GMP (5875 +/- 949) compared to control dogs but also demonstrated decreased cyclic GMP in response to MB (2820 +/- 372). In failure dogs, basal cyclic GMP was also elevated (4650 +/- 613) compared to control dogs but there was a lack of response to MB (3670 +/- 640).

CONCLUSIONS

We conclude that the myocardial function, VO(2) and cyclic GMP responses to methylene blue are diminished in the transition from hypertrophy to cardiac failure.

Cyclic GMP and cyclic AMP induced changes in control and hypertrophic cardiac myocyte function interact through cyclic GMP affected cyclic-AMP phosphodiesterases

We tested the hypothesis that the negative functional effects of cyclic GMP (cGMP) would be greater after increasing cyclic AMP (cAMP), because of the action of cGMP-affected cAMP phosphodiesterases in cardiac myocytes and that this effect would be altered in left ventricular hypertrophy (LVH) produced by aortic valve plication. Myocyte shortening data were collected using a video edge detector, and O2 consumption was measured by O2 electrodes during stimulation (5 ms, 1 Hz, in 2 mM Ca2+) from control (n = 7) and LVH (n = 7) dog ventricular myocytes. cAMP and cGMP were determined by a competitive binding assay. cAMP was increased by forskolin and milrinone (10(-6) M). cGMP was increased with zaprinast and decreased by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxilin-1-one (ODQ) both at 10(-6) and 10(-4) M, with and without forskolin or forskolin + milrinone. Zaprinast significantly decreased percent shortening in control (9 +/- 1 to 7 +/- 1%) and LVH (10 +/- 1 to 7 +/- 1%) myocytes. It increased cGMP in control (36 +/- 5 to 52 +/- 7 fmol/10(5) myocytes) and from the significantly higher baseline value in LVH (71 +/- 12 to 104 +/- 18 fmol/10(5) myocytes). ODQ increased myocyte function and decreased cGMP levels in control and LVH myocytes. Forskolin + milrinone increased cAMP levels in control (6 +/- 1 to 15 +/- 2 pmol/10(5) myocytes) and LVH (8 +/- 1 to 18 +/- 2 pmol/10(5) myocytes) myocytes, as did forskolin alone. They also significantly increased percent shortening. There were significant negative functional effects of zaprinast after forskolin + milrinone in control (15 +/- 2 to 9 +/- 1%), which were greater than zaprinast alone, and LVH (12 +/- 1 to 9 +/- 1%). This was associated with an increase in cGMP and a reduction in the increased cAMP induced by forskolin or milrinone. ODQ did not further increase function after forskolin or milrinone in control myocytes, despite lowering cGMP. However, it prevented the forskolin and milrinone induced increase in cAMP. In hypertrophy, ODQ lowered cGMP and increased function after forskolin. ODQ did not affect cAMP after forskolin and milrinone in LVH. Thus, the level of cGMP was inversely correlated with myocyte function. When cAMP levels were elevated, cGMP was still inversely correlated with myocyte function. This was, in part, related to alterations in cAMP. The interaction between cGMP and cAMP was altered in LVH myocytes.

Accelerated atherosclerosis and premature calcified cartilaginous metaplasia in the aorta of diabetic male Apo E knockout mice can be prevented by chronic treatment with 17 beta-estradiol

Epidemiological data indicate that estrogens significantly reduce the risk of morbidity and mortality due to cardiovascular diseases in postmenopausal women. Although numerous animal studies demonstrated inhibition of early atheromatous lesion formation by estrogen treatment in several species, information about the potential benefits of estrogens on complex, advanced atherosclerotic lesions is still lacking. The present study was designed to test whether chronic treatment with 17 beta-estradiol affects hyperglycemia-induced premature advanced lesion formation in 40-week-old male apolipoprotein E-deficient (Apo E-KO) mice. In order to accelerate advanced lesion formation, we treated male Apo E-KO mice with streptozotocin (STZ) at the age of 6 weeks. Two weeks later the STZ-treated mice received a slow release pellet containing either 17 beta-estradiol or placebo. STZ treatment caused sustained hyperglycemia without changes in serum total cholesterol or triglyceride levels compared to citrate control mice. STZ-treated Apo E-KO mice developed significantly more lesions in some (but not all) parts of the aorta and its main branches, and caused premature calcified cartilaginous metaplasia in the lesions of the proximal aorta. Chronic treatment with 17 beta-estradiol lead to a significant decrease in blood glucose and triglyceride levels, reduced the lesion area in all vascular segments studied and prevented cartilaginous metaplasia in STZ-treated Apo E-KO mice. The results of this study show that STZ treatment leads to significant acceleration of atherosclerotic lesion formation and premature occurrence of calcified cartilaginous areas in Apo E-KO mice, which could be effectively prevented by chronic estrogen treatment.

Altered effects of acetylcholine on cyclic AMP and GMP induced changes in O2 consumption of hypertrophic dog cardiac myocytes

1. We hypothesized that acetylcholine would attenuate the metabolic effect of increasing cAMP and decreasing cGMP on cardiac myocyte O2 consumption (VO2) in dog, and this effect would be altered in left ventricular hypertrophy (LVH) produced by aortic valve placation. 2. Steady-state VO2 of a suspension of ventricular myocytes from control (n = 7) and LVH (n = 6) dogs was measured by Clark O2 electrodes during electrical stimulation (5 ms, 1 Hz, in 2 mm Ca2+). Cyclic AMP and cyclic GMP were determined by radioimmunoassay. Cellular cAMP was increased by forskolin (adenylate cyclase stimulator) and cGMP was decreased by LY83583 (guanylate cyclase inhibitor) both at 10(-7,-6,-5,-4) M with and without 10(-6) M acetylcholine. 3. Baseline cGMP level in LVH (62 +/- 10 fmol 10(-5) myocytes) was significantly greater than that in control (20 +/- 3), although the myocyte VO2 (356 +/- 39 nL O2 min(-1) 10(-5) myocytes) and cAMP levels (3.9 +/- 0.6 nmol 10(5-1) myocytes) were similar to control (312 +/- 23 and 6.9 +/- 3.1). 4. Forskolin increased myocyte cAMP in both control and LVH myocytes and increased VO2 by 51 +/- 13 in control and 91 +/- 65 in LVH myocytes. LY83583 decreased myocyte cGMP levels in control and LVH myocytes and increased VO2 by 128 +/- 57 in control and 43 +/- 26 in LVH myocytes. 5. Acetylcholine altered the cAMP, cGMP, and VO2 levels in control to 2.4 +/- 0.4, 30 +/- 3 and 213 +/- 27 and LVH to 2.5 +/- 0.3, 85 +/- 9 and 261 +/- 32. Acetylcholine attenuated the maximal effects of forskolin on VO2 to 32 +/- 27 in control and 66 +/- 56 in LVH myocytes. Acetylcholine also decreased the maximal effects of LY83583 to 82 +/- 50 in control and 19 +/- 19 in LVH myocytes. 6. The positive metabolic effects of both increases in myocyte cAMP and decreases in cGMP were blunted by acetylcholine. There was a significant increase in myocyte cGMP with forskolin in LVH myocytes. Acetylcholine decreased the increased myocyte VO2 caused by elevated cAMP or decreased cGMP in both control and LVH myocytes, although the absolute decrease in cAMP was reduced and the absolute values of cGMP were higher in LVH myocytes.

Relationship between decreased function and O2 consumption caused by cyclic GMP in cardiac myocytes and L-type calcium channels

We tested the hypothesis that part of the decreased function and metabolism caused by cyclic guanosine monophosphate (GMP) in beating cardiac myocytes is related to inhibition of L-type calcium channels. The steady state oxygen consumption (VO2) of a suspension of ventricular myocytes isolated from hearts of New Zealand white rabbits was measured using oxygen electrodes. Cellular cyclic GMP levels were determined by radioimmunoassay. Cell shortening was measured with a video edge detector. The VO2 was obtained after: (1) adding sodium nitroprusside (NP 10(-8),(-6),(-4) M), (2) pretreatment by BAY K8644 10(-5) M (BAY, L-type calcium channel activator), nifedipine 10(-4) M (NF, L-type calcium channel blocker) or forskolin 10(-7) M (FK, adenylate cyclase activator), then adding NP 10(-8),(-6),(-4) M, (3) pretreatment with both FK 10(-7) M and NF 10(-4) M and subsequently adding NP 10(-8),(-6),(-4) M. NP 10(-4) M decreased VO2 from 707 +/- 34 to 410 +/- 13 (nl O2/min per 10(5) myocytes), decreased the percentage of shortening (Pcs) from 5.7 +/- 0.6 to 3.7 +/- 0.5 and the rate of shortening (Rs) from 65.5 +/- 4.5 (microns/s) to 46.2 +/- 5.5. NP 10(-4) M also increased cyclic GMP from 264 +/- 70 (fmol/10(5) myocytes) to 760 +/- 283. Both BAY and FK increased VO2, Pcs and Rs without changing cyclic GMP. NF decreased Pcs, Rs and VO2. Similar metabolic and functional effects of NP were observed with pretreatment with these agents separately, compared to NP alone, and the elevation of cyclic GMP level was not different from the control group. With FK alone, NP 10(-4) M decreased VO2 by 51%, Pcs by 44% and Rs by 39%. In the presence of both FK and NF, the negative effects of NP were diminished significantly. NP 10(-4) M decreased VO2 by 37%, Pcs by 25% and Rs 20%. Thus, in beating cardiac myocytes, the negative metabolic and functional effects of cyclic GMP were related to inhibition on L-type calcium channels only when adenylate cyclase was stimulated.

Negative metabolic effects of cyclic GMP in quiescent cardiomyocytes are not related to L-type calcium channel activity

We tested the hypothesis that the negative metabolic effects of elevating cyclic GMP act through inhibition of L-type calcium channels in quiescent cardiac myocytes. The steady state O2 consumption (VO2) of ventricular myocytes, isolated from hearts of New Zealand white rabbits, was measured in a glass chamber using Clark-type oxygen electrodes. The cellular cyclic GMP levels were determined by radioimmunoassay at baseline with either 0.5 mM or 2.0 mM of Ca2+, sodium nitroprusside at increasing concentration (10(-8),(-6),(-4) M) with and without pretreatment by BAY K8644 10(-5) M (L-type Ca2+ channel activator) in 0.5 mM Ca2+, or nitroprusside with and without pretreatment with nifedipine 10(-4) M (L-type Ca2+ channel blocker) in 2.0 mM Ca2+. In the 0.5 mM Ca2+ medium, basal VO2 was 459 +/- 104 (nl O2/min per 10(5) myocytes) with a corresponding cyclic GMP level of 112 +/- 23 (fmol/10(5) myocytes). With nitroprusside 10(-4) M, VO2 was decreased to 285 +/- 39 and cyclic GMP level was significantly elevated to 425 +/- 128. In the same medium, VO2 was slightly increased by BAY K8644 10(-5) M while the cyclic GMP level did not change. With BAY K8644 10(-5) M, nitroprusside 10(-4) M decreased VO2 and increased cyclic GMP to a level which was similar to cells treated with nitroprusside alone. In the 2.0 mM Ca2+ medium, the basal VO2 and cyclic GMP were 518 +/- 121 and 137 +/- 24. In the presence of nitroprusside 10(-4) M, VO2 was decreased to 295 +/- 49 and cyclic GMP was increased to 454 +/- 116. In the same medium, nifedipine 10(-4) M significantly decreased VO2, while the cyclic GMP level was comparable to the baseline. After nifedipine 10(-4) M, nitroprusside 10(-4) M decreased VO2 and increased cyclic GMP to levels which were similar to control. Therefore, in quiescent cardiac myocytes, the negative metabolic effects associated with cyclic GMP were not primarily mediated through inhibition of L-type Ca2+ channels.

Altered relationship between cyclic GMP and myocardial O2 consumption in renal hypertension-induced cardiac hypertrophy

We tested the hypothesis that preventing cyclic GMP degradation with zaprinast, (a selective cyclic GMP-phosphodiesterase inhibitor) would produce a blunted reduction in myocardial O2 consumption in renal hypertension (One Kidney-One Clip, 1K1C)-induced cardiac hypertrophy. Four groups of anesthetized open-chest New Zealand white rabbits (n = 26) were utilized. Either vehicle or zaprinast (3 x 10(-3) M) was applied topically to the left ventricular surface of control or 1K1C rabbits. Coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption. Myocardial cyclic GMP levels were determined by radioimmunoassay. The 1K1C rabbits had a greater heart weight-to-body weight ratio (2.94 +/- 0.08 g/kg) than controls (2.58 +/- 0.17). Systolic blood pressure was higher in 1K1C (102 +/- 9 mm Hg) than in controls (86 +/- 3). Zaprinast significantly and similarly increased cyclic GMP in both control (3.90 +/- 0.47 to 4.66 +/- 0.89 pmol/g) subepicardium (EPI) and (5.08 +/- 0.69 to 7.06 +/- 1.36) subendocardium (ENDO) and 1K1C hearts (5.53 +/- 0.61 to 7.48 +/- 1.51 EPI and 6.48 +/- 0.42 to 8.88 +/- 1.08 ENDO). Myocardial O2 consumption (ml O2/min/ 100 g) was significantly lower in controls treated with zaprinast (EPI: 8.8 +/- 0.1; ENDO: 9.5 +/- 1.9) than in controls treated with vehicle (EPI: 13.6 +/- 1.3; ENDO: 16.2 +/- 2.9). This effect was diminished in 1K1C rabbits treated with zaprinast (EPI: 10.3 +/- 2.4; ENDO: 11.2 +/- 2.6) compared with the vehicle-treated 1K1C group (EPI: 13.3 +/- 1.2; ENDO: 14.5 +/- 2.4). There was a similar increase in myocardial cyclic GMP after treatment with zaprinast, but a greater depression of myocardial O2 consumption in control animals than in 1K1C after treatment with zaprinast. This suggested that the reduction in myocardial O2 consumption, related to increases in cyclic GMP caused by cyclic GMP-phosphodiesterase blockade, was less in 1K1C cardiac hypertrophy.

A survey of physicians' acceptance of telemedicine

Physicians' acceptance of telemedicine is an important managerial issue facing health-care organizations that have adopted, or are about to adopt, telemedicine. Most previous investigations of the acceptance of telemedicine have lacked theoretical foundation and been of limited scope. We examined technology acceptance and usage among physicians and specialists from 49 clinical departments at eight public tertiary hospitals in Hong Kong. Out of the 1021 questionnaires distributed, 310 were completed and returned, a 30% response rate. The preliminary findings suggested that use of telemedicine among clinicians in Hong Kong was moderate. While 18% of the respondents were using some form of telemedicine for patient care and management, it accounted for only 6.3% of the services provided. The intensity of their technology usage was also low, accounting for only 6.8% of a typical telemedicine-assisted service. These preliminary findings have managerial implications.

Polyclonal antibody directed against human RANTES ameliorates disease in the Lewis rat adjuvant-induced arthritis model

Adjuvant-induced arthritis (AIA) is one of many animal models of rheumatoid arthritis, a disease characterized by a T-lymphocyte and macrophage cellular infiltrate. We have characterized the development of this disease model with respect to chemokine expression. Increased levels of two chemokines, RANTES, a T-lymphocyte and monocyte chemo-attractant, and KC a chemoattractant for neutrophils, were found in whole blood and in the joint. Surprisingly, levels of MIP-1alpha, another T-lymphocyte and monocyte chemoattractant, were unchanged throughout the course of the disease in whole blood and only slightly elevated in the joint. RANTES expression plays an important role in the disease since a polyclonal antibody to RANTES greatly ameliorated symptoms in animals induced for AIA and was found to be as efficacious as treatment with indomethacin, a non-steroidal anti inflammatory. Polyclonal antibodies to either MIP-1alpha or KC were ineffective. This is the first report to show the importance of RANTES in the development of AIA.

Positive inotropy due to lowering cyclic GMP is also mediated by increases in cyclic AMP in control and hypertrophic hearts

The aim of the current study was to determine if lowering myocardial cyclic GMP by guanylate cyclase inhibition would add independently to the positive inotropic effects caused by raising cyclic AMP and if these effects are modified in left ventricular hypertrophy (LVH) produced by aortic valve plication. Isoproterenol (ISO) (0.1 mg x kg(-1) x min(-1)) was infused into a branch of the left anterior descending coronary artery of seven control and eight hypertrophy open-chest anesthetized dogs. After 10 min, simultaneous infusion of methylene blue (MB) (2 mg x kg(-1) x min(-1)) was initiated at the same site. Hypertrophy increased heart weight and heart weight/body weight ratio. While both drugs increased left ventricular dP/dt(max), no additional global effects were observed in either group. Changes in regional variables followed the same pattern in both groups, i.e., ISO produced an increase that was enhanced by the addition of MB. ISO increased segment shortening, with a significant change in the control group. ISO increased regional force in both groups. The addition of MB increased force above ISO levels, with a significant change in the LVH group. ISO increased regional minute work (g x mm x min(-1)) (control, 1779 +/- 428 to 2541 +/- 500; LVH, 1157 +/- 253 to 1839 +/- 404) and O2 consumption. MB further increased regional work (control, 2993 +/- 952; LVH, 2416 +/- 853) and O2 consumption. ISO raised cyclic AMP (pmoles x g(-1)) (control, 468 +/- 41 to 580 +/- 84; LVH, 445 +/- 43 to 562 +/- 71) and had no effect on cyclic GMP (pmoles x g(-1)) (control, baseline 3.27 +/- 0.22, ISO 2.87 +/- 0.23; LVH, baseline 6.84 +/- 1.12, ISO 5.66 +/- 0.54). The addition of MB lowered cyclic GMP (control, 2.41 +/- 0.26; LVH, 3.68 +/- 0.35), but also increased cyclic AMP (control, 1021 +/- 121; LVH, 1107 +/- 134). Similar results were observed in control hearts using a specific soluble guanylate cyclase inhibitor (ODQ) in terms of changes in local work, O2 consumption, and cyclic nucleotides. Thus, at least part of the positive inotropic response to lowering cyclic GMP was mediated by changes in cyclic AMP in the current model. This was true in both control and LVH animals, although baseline cyclic GMP levels were higher, and a larger reduction in cyclic GMP was observed with MB in the LVH group.

Targeted radiotherapy of multicell neuroblastoma spheroids with high specific activity [125I]meta-iodobenzylguanidine

PURPOSE

Iodine-125 induces cell death by a mechanism similar to that of high linear energy transfer (high-LET) radiation. This study investigates the cytotoxicity of high-specific-activity [125I]meta-iodobenzylguanidine (125I-mIBG) in human SK-N-MC neuroblastoma cells grown as three-dimensional multicellular spheroids.

MATERIALS AND METHODS

Spheroids were incubated with high-specific-activity 125I-mIBG (6 mCi/microg, 1000 times that of the conventional specific activity used for autoradiography). Cytotoxicity was assessed by fluorescence viability markers and confocal microscopy for intact spheroids, fluorescence-activated cell sorting and clonogenic assay, and clonogenic assays for dispersed whole spheroids. Distribution of radioactive mIBG was determined by quantitative light-microscope autoradiography of spheroid cryostat sections. Dose estimation was based on temporal knowledge of the retained radioactivity inside spheroids, and of the radiolabel's emission characteristics. Findings were compared with those of spheroids treated under the same conditions with 131I-mIBG, cold mIBG, and free iodine-125.

RESULTS

125I-mIBG exerted significant cell killing. Complete spheroids were eradicated when they were treated with 500 microCi of 125I-mIBG, while those treated with 500 microCi or 1000 microCi of 131I-mIBG were not. The observed difference in cytotoxicity between treatments with 125I- and 131I-mIBG could not be accounted for by the absorbed dose of spheroid alone. The peripheral, proliferating cell layer of the spheroids remained viable at the moderate radioactivity of 100 microCi for both isotopes. Cytotoxicity induced by 125I-mIBG was quantitatively comparable by the peripheral rim thickness to that of 131I-mIBG at the dose of 100 microCi. The peripheral rim thickness decreased most significantly in the first 17 hours after initial treatment. There was no statistical decrease in the rim thickness identified afterwards for the second, third, and fourth days of incubation.

CONCLUSION

The cytotoxic effect of high-specific-activity 125I-mIBG appears to be comparable to, if not more efficient than that of conventionally used 131I-mIBG at the same level of total radioactivity. 125I-mIBG may improve the therapeutic index over that of 131I-mIBG in the clinical management of metastatic neuroblastoma due to the short range of Auger electrons.

Exogenous nitric oxide reduces oxygen consumption of isolated ventricular myocytes less than other forms of guanylate cyclase stimulation

We tested the hypothesis that increasing cyclic GMP with nitric oxide (NO) would reduce cardiac myocyte metabolism less than other forms of guanylate cyclase stimulation. The steady state O2 consumption (VO2) of a suspension of ventricular myocytes in 2.0 mM Ca2+ isolated from hearts of New Zealand white rabbits was measured in a glass chamber using Clark-type oxygen electrode. The cellular cyclic GMP levels, determined by radioimmunoassay, were increased by (1) adding 3-morpholinosydnonimine (SIN-1, 10(-8)-10(-5) M) and nitroprusside (10(-8)-10(-5) M), NO donors-soluble guanylate cyclase stimulators; (2) carbon monoxide (CO, 1.5 x 10(-8)-1.5 x 10(-6) M), soluble guanylate cyclase stimulator and (3) guanylin (10(-8)-10(-5) M), particulate guanylate cyclase stimulator. The baseline myocyte cyclic GMP level was 86 +/- 13 fmol/10(5) myocytes with a corresponding VO2 of 268 +/- 21 nl O2/min per 10(5) myocytes. An inverse relationship between cellular cyclic GMP levels and VO2 existed in these myocytes. The regression equations for the four treatments were: VO2 = -0.45 x [cyclic GMP] + 294.4, r = 0.94 for SIN-1; VO2 = -1.46 x [cyclic GMP] + 444.7, r = 0.96 for CO; VO2 = -1.25 x [cyclic GMP] + 389.1, r = 0.84 for guanylin and VO2 = -0.55 x [cyclic GMP] + 322.8. r = 0.79 for nitroprusside. The regression lines of the two NO donors were parallel. A similar result was also evident for the regressions of CO and guanylin. However, the slopes of both the SIN-1 and nitroprusside regression line were significantly less steep than that of either the CO or guanylin lines. Therefore, VO2 is reduced less for a similar increase in cyclic GMP with NO donors compared to direct stimulation with CO or guanylin. These results suggest that NO has metabolic effects on myocytes in addition to its stimulatory effects on cellular cyclic GMP.

Guanylyl cyclase inhibition reduces contractility and decreases cGMP and cAMP in isolated rat hearts

OBJECTIVE

Several studies have shown that increasing cGMP in the heart reduces contractility, however, decreasing basal cGMP levels have also been shown in some studies to reduce contractility. This study was designed to evaluate the hypothesis that decreasing basal levels of cGMP decreases ventricular contractility, and that this depressed function is associated with a decrease in cAMP.

METHODS

Using paced, constant flow, buffer-perfused rat hearts, we determined the effects of intracoronary infusions of the guanylyl cyclase inhibitor, LY83583 (10(-5) M), on ventricular function, oxygen consumption, and ventricular content of cGMP and cAMP. These experiments were conducted in the absence and presence of isoproterenol (ISO) to increase baseline left ventricular developed pressure (LVDP) and cAMP.

RESULTS

LY83583, infused for 25 min, decreased LVDP by 44 +/- 3 (SE), 77 +/- 20 and 120 +/- 38 mmHg, in control, 10(-9) M, and 10(-8) M ISO-stimulated hearts, respectively. Regardless of the level of ISO stimulation, LY83583 reduced LVDP to the same sub-basal level. Oxygen consumption also decreased, but proportionately less than LVDP. ISO increased cAMP without changing cGMP. LY83583 decreased cGMP by about 25% at all levels of ISO, and decreased cAMP by 22% in the 10(-8) M ISO-stimulated group.

CONCLUSION

Guanylyl cyclase inhibition by LY83583 decreased cGMP, cAMP and ventricular contractility. However, LY83583 depression of contractility was not always associated with a reduction in cAMP, suggesting that LY83583 can depress contractility by both cAMP-dependent and independent mechanisms.

Chemokine receptor regulation and HIV type 1 tropism in monocyte-macrophages

Monocyte-macrophages can be productively infected by CCR5-specific, but not CXCR4-specific, HIV-1. This could be due either to the absence of this chemokine receptor in this cell lineage or to other, yet undefined cellular cofactors that modulate the coreceptor activity of the CXCR4 in these cells. To investigate the basis of macrophage tropism, we studied the expression of CCR5 and CXCR4, as well as several of the other CC chemokine receptors, on monocyte-macrophages at different stages of differentiation. We found that on fresh monocytes, CXCR4 was relatively abundant, but it fell to barely detectable levels in culture over 24 hr and maintained this low level of expression during differentiation in vitro. Some donor macrophages appeared to express CXCR4 at levels comparable to CCR5. In contrast, CCR5 expression was low on fresh monocytes but increased on in vitro differentiation. Taken together, the results show that monocyte-macrophage differentiation is associated with a differential expression of chemokine receptors that may contribute to, but does not fully account for, the selectivity of these cells to HIV entry. GM-CSF, a cytokine that induces macrophage differentiation, caused a rapid decrease in CXCR4 and CCR5 mRNA and was correlated with decreased ability to support HIV entry.

Reduced myocardial cyclic GMP increases myocardial O2 consumption in control but not renal hypertension-induced cardiac hypertrophy

OBJECTIVES

We tested the hypothesis that a reduction in myocardial cyclic GMP would increase myocardial O2 consumption and that renal hypertension (One Kidney-One Clip, 1K1C)-induced cardiac hypertrophy would change this relationship.

METHODS

Either vehicle or LY83583 (10(-3) M, a guanylate cyclase inhibitor) was topically applied to the left ventricular surface of control of 1K1C anesthetized open-chest New Zealand white rabbits (N = 38). Coronary blood flow (radioactive microspheres) and O2 extraction (microspectrophotometry) were used to determine subepicardial (EPI) and subendocardial (ENDO) O2 consumption and myocardial cyclic GMP was determined by radioimmunoassay.

RESULTS

The heart weight/body weight ratio was greater in the 1K1C rabbits (3.16 +/- 0.20) than controls (2.58 +/- 0.08 g/kg). Systolic blood pressure was higher in 1K1C rabbits (116 +/- 8 mm Hg) than controls (80 +/- 6), but topical LY83583 had no significant hemodynamic effects. LY83583 significantly and similarly decreased EPI cyclic GMP in both control (7.9 +/- 1.2 to 6.0 +/- 1.0 pmol/g) and 1K1C (7.7 +/- 1.2 to 5.3 +/- 0.9) hearts and control ENDO (8.7 +/- 1.7 to 7.2 +/- 1.2) but not 1K1C ENDO (6.7 +/- 0.5 to 5.7 +/- 1.1). Myocardial O2 consumption was significantly increased in control with LY83583 (EPI 6.6 +/- 1.1 to 15.6 +/- 1.4 and ENDO 7.2 +/- 0.9 to 14.2 +/- 0.7 ml O2/min/100 g), but not in 1K1C hearts (EPI 12.1 +/- 1.0 to 12.9 +/- 1.2 or ENDO 11.4 +/- 0.7 to 12.9 +/- 0.9).

CONCLUSIONS

Thus myocardial O2 consumption was only increased by LY83583 in control hearts, but LY83583 decreased cyclic GMP similarly in both the control and 1K1C EPI. This indicated, at least in the EPI, a dissociation of the inverse relationship between the myocardial level of cyclic GMP and O2 consumption in the 1K1C rabbit heart.

The negative functional and metabolic effects of muscarinic stimulation are enhanced by beta-adrenergic activation in control and hypertrophic dog hearts in vivo

The aim of the current study was to determine if the effects of muscarinic stimulation on left ventricular function and metabolism are greater during beta-adrenergic activation, whether a cyclic GMP-mediated mechanism is responsible, and if this is altered by left ventricular hypertrophy (LVH) induced by aortic valve stenosis. Acetylcholine (Ach) (5 micrograms/kg/min) and/or isoproterenol (Iso) (0.1 micrograms/kg/min) was infused into a branch of the left anterior descending (LAD) artery in 8 control and 8 LVH open-chest anesthetized dogs. LVH increased heart weight, heart-to-body weight ratio and systolic left ventricular pressure. LVH reduced muscarinic receptor density (fmol/mg protein) (control: 149.2+/-18.6; LVH: 77.8+/-8.6), but not affinity. Alone, Ach had no effect on regional force, work or metabolism. Iso increased peak force (g) (control: baseline-7.4+/-0.4; Iso-12.4+/-2.2; LVH: baseline-6.7+/-0.8; Iso-16.3+/-2.7, regional work (g mm/min)) (control: baseline-1250+/-186; Iso-1813+/-409; LVH: baseline-927+/-235; Iso-1244+/-222), and O2 consumption (ml O2/min/100 g) (control: baseline-3.3+/-0.2; Iso-8.1+/-2.0; LVH: baseline-4.8+/-1.0; Iso-8.3+/-1.1). During Iso, Ach reduced segment shortening (control: Iso-14.5+/-1.2; Iso+Ach-10.5+/-1.8; LVH: Iso-10.4+/-1.5; Iso+Ach-7.6+/-1.3) and peak force (control: Iso+Ach-7.7+/-1.0; LVH: Iso+Ach-10.5+/-1.4). Ach also reduced work (control: Iso+Ach-875+/-217; LVH: Iso+Ach-776+/-180) and O2 consumption (control: Iso+Ach-3.4+/-0.7; LVH: Iso+Ach-3.6+/-0.6) in the presence of Iso. Cyclic GMP was higher in the LVH animals during all treatments and was elevated from baseline by Ach in both groups. Neither Iso nor Iso+Ach had a significant effect on cyclic GMP. Thus, the negative functional and metabolic effects of muscarinic stimulation are enhanced during beta-adrenergic activation. This does not, however, appear to be dependent on a cyclic GMP-mediated mechanism. Despite reduced number of muscarinic receptors, this response was not altered by pressure-induced cardiac hypertrophy.

Cyclic GMP decreases cardiac myocyte oxygen consumption to a greater extent under conditions of increased metabolism

We tested the hypothesis that the negative effects of intracellular guanosine 3',5'-cyclic monophosphate (cyclic GMP) were more profound on cardiac myocyte oxygen consumption (VO2) during increased metabolism of the myocytes. The steady state VO2 of a suspension of single myocytes isolated from hearts of New Zealand White rabbits was measured in a glass chamber by using a Clark-type oxygen electrode, and cyclic GMP was determined by using a radioimmunoassay. The cellular cyclic GMP levels were increased either by adding 3-morpholino-sydnonimine (SIN-1), a guanylate cyclase stimulator, or zaprinast (ZAP), a cyclic GMP-phosphodiesterase inhibitor, at various doses. In 0.5 mM Ca2+ medium, average VO2 was 123 +/- 8 nl/min/100,000 cells, and cyclic GMP was 35.4 +/- 9.3 fmol/100,000 cells, and these increased significantly to 182 +/- 9 nl/min/100,000 cells and 78.2 +/- 7.3 fmol/100,000 cells in 2.0 mM Ca2+. There were dose-dependent responses of the VO2 and cellular cyclic GMP levels in responding to both SIN-1 and ZAP. An inverse relation between cellular cyclic GMP level and VO2 existed in the myocytes. The regression equations for the four treatments were log(VO2) = -0.002[cyclic GMP] + 2.19, r = 0.96 for SIN-1 in low (0.5 mM) Ca2+; log(VO2) = 0.005[cyclic GMP] + 1.80, r = 0.38 for ZAP in low Ca2+; log(VO2) = -0.001 [cyclic GMP] + 2.24, r = 0.82 for SIN-1 in high (2.0 mM) Ca2+; and log(VO2) = -0.004[cyclic GMP] + 2.56, r = 0.93 for ZAP in high Ca2+. The slope of ZAP regression line was significantly more negative than that of SIN-1 with high calcium. At any given level of cyclic GMP, ZAP decreased the VO2 to a greater extent than did SIN-1 although the latter caused the maximal increase in cyclic GMP level. The reduction in VO2 caused by a corresponding increase in cellular cyclic GMP was greater in myocytes incubated with high-Ca2+ medium.

Basal muscarinic activity does not impede beta-adrenergic activation in rabbit hearts in controls or thyroxine-induced cardiac hypertrophy

We tested the hypothesis that basal myocardial muscarinic receptor activity acts as a "brake" on beta-adrenergic activation and that this effect would be greater in hearts subjected to thyroxine (T4)-induced (0.5 mg/kg for 16 days) hypertrophy due to an increase in muscarinic receptor density. Twenty control and 20 T4-treated open-chest anesthetized New Zealand white rabbits were given isoproterenol (0.5 microg/kg/min, 10 min i.v.) and/or atropine (3 mg/kg bolus). Coronary blood flow (radioactive microspheres), aortic and left ventricular (LV) pressure, and wall thickening of the LV free wall were recorded. Hearts were quickly excised and stored in liquid nitrogen. Cyclic guanosine monophosphate (GMP) and cyclic adenosine monophosphate (AMP) were determined by radioimmunoassay. T4 increased heart weight/body weight ratio, blood pressures, and the first derivative of the maximal rate of increase of LV systolic pressure (dP/dt[max]). Isoproterenol increased heart rate in both groups. Atropine had no effects on hemodynamic parameters either alone or after stimulation with isoproterenol. At this dose, atropine completely blocked the depressant effects of acetylcholine (10 microg/kg). Isoproterenol increased the maximal time derivative of wall thickening (dWT/dt[max]) in control (from 11.0 +/- 1.0 to 16.4 +/- 1.5 mm/s) but not in T4 animals. T4 increased subepicardial (EPI) and subendocardial (ENDO) coronary blood flow. Isoproterenol increased coronary flow (control: EPI, from 173 +/- 11 to 346 +/- 28 ml/min/100 g; ENDO, from 197 +/- 15 to 364 +/- 30 ml/min/100 g; T4: EPI, from 314 +/- 45 to 459 +/- 43 ml/min/100 g; ENDO, from 339 +/- 48 to 458 +/- 43 ml/min/100 g). Cyclic AMP levels were higher in T4 animals. Isoproterenol increased cyclic AMP (control: EPI, from 540 +/- 82 pmol/g to 1,096 +/- 110; ENDO, 596 +/- 58 to 1,050 +/- 145 pmol/g; T4: EPI, from 882 +/- 107 pmol/g to 1,319 +/- 222; ENDO, from 954 +/- 134 to 1 ,409 +/- 261 pmol/g). Atropine, alone or after stimulation with isoproterenol, had no effect on coronary flow or cyclic AMP in either group. Cyclic GMP levels were unaffected by T4-induced hypertrophy or by any of the treatments in either group. Thus it appears that basal muscarinic activity does not significantly influence function or signal transduction either at baseline or during beta-adrenergic stimulation in controls or in T4-induced hypertrophy.

cGMP level that reduces cardiac myocyte O2 consumption is altered in renal hypertension

We tested the hypothesis that cardiac myocytes from hypertensive (one kidney, one clip; 1K,1C) cardiac-hypertrophied rabbits require higher guanosine 3',5'-cyclic monophosphate (cGMP) to similarly lower O2 consumption than control myocytes and that this effect is caused by differences in guanylate cyclase activity. Using isolated myocytes from control and 1K,1C New Zealand White rabbits, we obtained O2 consumption (nl O2 x min(-1) x 10(5) cells) and cGMP (fmol/10(5) cells) levels after stimulation of guanylate cyclase with nitroprusside, CO, or guanylin (10(-8)-10(-5) M). Soluble guanylate cyclase activity was also determined. Basal cGMP was elevated in 1K,1C vs. control (176 +/- 28 vs. 85 +/- 13) myocytes. cGMP increased in 1K,1C and control myocytes after stimulation with nitroprusside, CO, and guanylin. Guanylate cyclase activity in 1K,1C vs. control myocytes was not statistically different. Basal O2 consumption in 1K,1C vs. control myocytes was comparable (307 +/- 1 vs. 299 +/- 22). O2 consumption was similarly decreased when guanylate cyclase was stimulated. Control regression equations correlating cGMP and O2 consumption were O2 consumption = -1.46 x [cGMP] + 444.65 (r = 0.96) for CO, O2 consumption = -0.58 x [cGMP] + 328.48 (r = 0.82) for nitroprusside, and O2 consumption = -1.25 x [cGMP] + 389.15 (r = 0.88) for guanylin. The 1K,1C regression equations were O2 consumption = -1.36 x [cGMP] + 537.81 (r = 0.97) for CO, O2 consumption = -0.23 x [cGMP] + 307.30 (r = 0.88) for nitroprusside, and O2 consumption = -1.27 x [cGMP] + 502.91 (r = 0.89) for guanylin. These data indicate that 1K,1C hypertrophic myocytes had higher cGMP than controls at every level of O2 consumption. This effect was not caused by differences in basal or maximal guanylate cyclase activity.