Ischemic inactivation of G protein-coupled receptor kinase and altered desensitization of canine cardiac beta-adrenergic receptors.

BACKGROUND: G protein-coupled receptor kinases (GRKs) modulate myocardial beta-adrenergic receptor (betaAR) signaling. We examined whether GRK activity was altered 6, 24, and 96 hours after left anterior descending coronary artery ligation (LAD CAL) in the dog. METHODS AND RESULTS: GRK activity was measured in arrhythmogenic subepicardial border zone (EBZ) tissue overlying the infarct and from nonischemic remote-site (RS) subepicardial tissue from the same animal. GRK activity in the ischemic EBZ was 15% of RS (P:=0.03, n=6) 24 hours after CAL and appeared to start as early as 6 hours through 96 hours. GRK activity and immunoblot data demonstrated a marked decrease of GRK2 but not GRK5 at 24 hours. EBZ tissue exhibited high-affinity binding for (-)-isoproterenol (K:(i) of 0. 076+/-0.026 nmol/L [SEM]) at 24 hours, which was not significantly different from control tissue from nonoperated animals (1.2+/-0.8 nmol/L, P:>0.05, n=6). A significantly lower K:(i) of 13.8+/-2.8 nmol/L (P:<0.001, n=6) was observed for RS taken from the ischemic animals. This was reflected by a 4-fold increase in the EC(50) of isoproterenol-stimulated adenylyl cyclase activity from 18 nmol/L in EBZ tissue to 73 nmol/L in RS (P:<0.05, n=4). CONCLUSIONS: There is a selective decrease in GRK2 activity and a loss of the ability of the arrhythmia-prone EBZ tissue to desensitize to beta-adrenergic stimulation 24 hours after CAL. This correlates temporally with a second (late) peak in sudden cardiac death previously observed between 6 and 24 hours in dog and rat models of myocardial infarction.

The mechanism of polyethylene glycol-induced natriuresis in rats: role of atrial natriuretic hormone.

A putative role of atrial natriuretic hormone (ANH) in a polyethylene glycol (PEG) 200-induced natriuresis was examined in conscious Wistar rats. Low molecular weight PEG 200 (0.5 or 1.0 ml/100g body weight) was orally administered to rats by gavage. Urine was collected during a 3 hr test period and blood was obtained at the end of each experiment for measurement of ANH, PRA, clearance studies and for indirect indices of plasma volume. Urinary excretion of sodium and volume increased while plasma ANH concentrations were markedly decreased in a dose-related manner following PEG 200 administration. The osmotic clearance was also elevated following PEG 200 administration. No significant change was observed in any of the parameters following high molecular weight PEG 8000. The observed decrease in ANH was associated with an apparent contraction of plasma volume despite the increased serum osmolality. These data indicate that the ANH inhibitory influence of the decreased plasma volume takes precedence over the stimulatory effect of the hyperosmolality and the latter is primarily responsible for the increased osmotic clearance and natriuresis observed in this model.

Colonoscopy by a family physician: a 9-year experience of 1048 procedures.

BACKGROUND: In the last 15 years, family physicians and general internists have adopted flexible fiberoptic endoscopy as a procedure to screen patients at risk of premature death from colorectal cancer. There has been controversy regarding the ability of non-fellowship-trained primary care physicians to extend this experience to full colonoscopy. METHODS: The results of 1048 consecutive colonoscopy examinations performed by a family physician over a 9-year period were tabulated. Outcomes measured included the reach-the-cecum rate (RCR), use of medication, complication rate, and diagnostic yield. In a convenience sample of 110 cases, the effectiveness of the non-narcotic analgesic ketorolac was assessed by the RCR. Outcomes of cases in which ketorolac was used were compared with cases in which traditional sedation and analgesia were used. RESULT: A high diagnostic yield without significant complications was noted. The RCR for nonmedicated patients was 36%. Among all medicated cases, the RCR was 93%. In patients who were given the non-narcotic analgesic ketorolac, the RCR was 96%, compared with 95% in patients not given ketorolac. CONCLUSIONS: A family physician in rural practice was able to attain and sustain a state-of-the-art, reach-the-cecum rate over a 9-year period. This service resulted in a high diagnostic yield, high degree of safety, and satisfactory results for the community. Ketorolac is an effective alternative for patients who may be hypersensitive to narcotic analgesia/sedation.

Template-driven gene selection procedure.

The hierarchical clustering and statistical techniques usually used to analyse microarray data do not inherently represent the underlying biology. Herein, a hybrid approach involving characteristics of both supervised and unsupervised learning is presented. This approach is based on template matching in which the interaction of the variables of inherent malignancy and the ability to express the malignant phenotype are modelled. Immortalised normal urothelial cells and bladder cancer cells of different malignancy were grown in conventional two-dimensional tissue culture and in three dimensions on extracellular matrices (ECMs) that were either permissive or restrictive for expression of the malignant phenotype. The transcriptome represents the effects of two variables--inherent malignancy and the modulatory effect of ECM. By assigning values to each of the biological variables of inherent malignancy and the ability to express the malignant phenotype, a template was constructed, which encapsulated the interaction between them. Gene expression correlating both positively and negatively with the template was observed, but when iterative correlations were carried out, the different models for the template converged on the same actual template. A subset of 21 genes was identified, which correlated with two a priori models or an optimised model above the 95% confidence limits identified in a bootstrap resampling with 5000 permutations of the data set. The correlation coefficients of expression of several genes were > 0.8. Analysis of upstream transcriptional regulatory elements (TREs) confirmed that these genes were not a randomly selected set of genes. Several TREs were identified as significantly over-expressed in the sample of 20 genes for which TREs were identified, and the high correlations of several genes were consistent with transcriptional co-regulation. The authors suggest that the template method can be used to identify a unique set of genes for further investigation.

Infusion of atrial natriuretic hormone in DOCA/salt and spontaneously hypertensive rats.

The effects of a 6-day infusion of atrial natriuretic hormone (ANH) on blood pressure and urinary sodium excretion were determined in conscious DOCA/salt and spontaneously hypertensive rats. The DOCA/salt rats were randomly divided into two groups after 4 weeks and either infused by osmotic minipump with 32.5 pmol/h of ANH in 0.1% gelatin vehicle or sham operated with emplacement of a blind cannula. Thirteen-week-old spontaneously hypertensive rats were studied in a similar fashion. The baseline systolic blood pressure prior to the infusion was 176 +/- 7 mmHg (x +/- SEM) in the ANH group and 169 +/- 5 mmHg in the sham group of DOCA/salt animals. The ANH infusion in the DOCA/salt animals dropped their blood pressure to 160 +/- 10 mmHg (p less than 0.01) compared to that in the sham controls which continued to rise to 200 +/- 7 mmHg. The blood pressure response to ANH infusion in the spontaneously hypertensive rats was slightly greater, with a blood pressure of 192 +/- 5 mmHg in the sham group and 132 +/- 3 mmHg in the ANH-infused animals. ANH infusion produces a qualitatively similar blood pressure response in the DOCA/salt rat as well as the other hypertensive models. This response is relatively less on a quantitative basis than that observed in the spontaneously hypertensive rats and is not related to changes in sodium balance or volume contraction.