Lumen perfusion experiments have been widely employed for the evaluation of gastric acid secretion in rats. The advantage of the lumen perfusion models is the simplicity in evaluating the effectiveness of secretagogues and antisecretagogues. There is, however, no efficient methodology for biostatistical modeling of gastric acid secretion in lumen-perfused rats. In order to optimize methodology, we applied a linear regression model after splitting the time-effect curves obtained from histamine-induced gastric acid secretion in rats.
β 3 -adrenoceptors mediate negative inotropic effect in contrast to classical β 1 -and β 2adrenoceptors.Cardiac β 3 -adrenoceptors are upregulated in experimental diabetes.Thus, cardiodepressant effect mediated by β3-adrenoceptors has been proposed to contribute to the impaired cardiac function in this pathology.In our study, we investigated the influence of streptozotocindiabetes on cardiac contractility to β 3 -adrenoceptors stimulation by using Langendorff-perfused rat hearts.BRL 37344, a selective β 3 -adrenoceptor agonist, induced dose-dependent decreases in left ventricular developed pressure (LVDP) in hearts from control rats.BRL 37344 also dose-dependently decreased +dP/dt and -dP/dt values.Effects of BRL 37344 were abolished by SR 59230, but not altered by nadolol pre-treatment.On the other hand, these effects of BRL 37344 were all significantly increased in hearts from diabetic rats.We also observed that diabetes significantly increased the mRNA levels encoding cardiac β 3 -adrenoceptors.In addition, G iα2 mRNA expressions were found to be increased in the cardiac tissue of diabetic rats as well.The effect of BRL 37344 on cardiac contractility was normalized upon treatment of diabetic rats with insulin.These data demonstrate an increased effect of β 3 -adrenoceptor stimulation on hemodynamic function of the heart in accordance with an increased mRNA levels encoding cardiac β 3 -adrenoceptors in 8-week diabetic rats.
Diabetes-induced endothelial damage leads to vascular dysfunction. The current study investigated the effects of short-term (4-week) streptozotocin (STZ)-induced diabetes on responses mediated by endothelium-derived contracting factors (EDCFs) as well as possible contributions of Rho-kinase and AMP-activated kinase (AMPK) signaling pathways. The effects of STZ-diabetes on vascular function were examined in isolated thoracic aorta preparations of 30-week-old rats (n = 27). The diabetes-associated changes in vascular function were studied with calcium ionophore A23187, acetylcholine, Rho-kinase inhibitor Y27632 ((R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride), and AMPK activator AICAR (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside). The phosphorylation of acetyl-CoA carboxylase, AMPK, and phospholamban and the protein levels of sarcoplasmic/endoplasmic Ca2+-ATPase 2 (SERCA2) and Rho-associated protein kinase (ROCKII) were measured in aortic preparations. Although the acetylcholine-mediated relaxation responses were preserved in 4-week STZ-induced diabetes, the increased activation of the Rho-kinase pathway was demonstrated via twofold enhancement in A23187-mediated contractile responses and significantly augmented protein levels of ROCKII. The AICAR-activated AMPK-mediated relaxation response was also augmented ∼4-fold in diabetic rats, without any alteration in phospholamban phosphorylation; further, this relaxation response suppressed A23187-mediated contraction in both groups. Diabetic rats showed an increase in AICAR-induced AMPK-mediated vasorelaxation and a 2.5-fold elevation of phosphorylated AMPK levels. These results indicate a possible compensation between hyperglycemia-induced endothelium-dependent hypercontractility and AMPK-mediated vasorelaxation in diabetes.
Vascular tonus is controlled by endothelium-derived relaxing factor (EDRF), endothelium-derived hyperpolarizing factor (EDHF) and endothelium-derived contracting factor (EDCF) under physiological circumstances. In pathological conditions, impairment of endothelium-derived relaxation can be caused by both decrease in EDRF release and increase in EDCF release. The increase in EDCF is observed with diseases such as hypertension and diabetes. The contribution of Rho-kinase and activated protein kinase (AMPK), which have opposite effects, to the increased EDCF responses was investigated. Rho-kinases are the effectors of Rho which is one of the small guanosine triphosphate-binding proteins. They increase cytosolic Ca+2 concentration and cause vascular smooth muscle to contract, keeping myosin light chain (MLC) in phosphorylated state by affecting myosin phosphatase target subunit which dephosphorylates the MLC. The activities of Rho-kinases increase with the increase of EDCF function. AMPK is the energy sensor of the cell. It provides a vasculoprotective effect by causing endothelium-dependent and endothelium-independent relaxation in smooth muscle. In contrast to Rho-kinase pathway activity, AMPK pathway activity decreases with diseases in which the EDCF function increases. In cases such as diabetes and hypertension that endothelial function impairs toward vasocontraction, it is considered that evaluating Rho-kinase and AMPK pathways which mediate contraction and relaxation in vascular smooth muscle respectively, would provide clues on choosing therapeutic target for pathologies in which endothelial dysfunction is observed.
