CHARACTERIZATION OF ANGIOTENSIN-II RECEPTOR SUBTYPES IN RAT-HEART

Angiotensin II exerts positive inotropic and chronotropic effects on the mammalian heart by binding to specific membrane receptors. Recently, two subtypes of angiotensin II receptors (AT1 and AT2) have been distinguished by using the nonpeptide antagonists losartan (previously known as DuP 753) and PD123177. To evaluate the tissue distribution and subtypes of angiotensin II receptors in rat heart, we performed a I-125-[Sar1,Ile8]angiotensin II in situ binding assay on tissue sections obtained from adult Sprague-Dawley rats (10 and 14 weeks old). Binding specificity was verified by competition with unlabeled [Sar1]angiotensin II. Distribution of AT1 and AT2 receptors was determined by competition with losartan and PD123177, respectively, and the density of the receptors was quantified by emulsion autoradiography. Angiotensin II receptors were widely distributed throughout the heart, with each receptor subtype accounting for approximately 50% of the specific binding. Binding density was comparable in the atria, right and left ventricles, intraventricular septum, and sinoatrial node, whereas it was significantly greater in the atrioventricular node. The AT1 receptor appears to interact with guanidine nucleotide regulatory proteins, because GTP-gamma-S causes dissociation of the radioligand from this receptor. In contrast, the AT2 receptor does not appear to directly interact with guanine nucleotide regulatory proteins, inasmuch as radioligand dissociation from this receptor subtype is not affected by GTP-gamma-S. Because angiotensin II has been reported to have growth-potentiating effects in several tissues, we examined angiotensin II receptors in fetal (embryonic days 16 and 19) and neonatal (1-, 2-, 3-, and 10-day-old) rats. A twofold increase in the density of both receptor subtypes was found immediately after birth, reaching a maximum on day 2 and decreasing toward prenatal values thereafter. Thus, in rat heart, AT1 and AT2 receptors are equally distributed over the myocardium. The density of these angiotensin II receptors is developmentally regulated

DISTRIBUTION OF ANGIOTENSIN-II RECEPTOR SUBTYPES IN RAT AND HUMAN KIDNEY

Angiotensin II initiates a variety of physiological effects in the kidney by binding to high-affinity receptors on plasma membranes. Recently, two subtypes of angiotensin II receptors have been distinguished on the basis of differences in signal transduction mechanisms, binding affinity to agonists and antagonists, and inhibition of binding by dithiothreitol. To evaluate the density and distribution of these receptor subtypes in the kidney, we performed an in situ autoradiographic study on frozen tissue sections obtained from rat and human kidneys. Sections were incubated with I-125-[Sar1,Ile8]angiotensin II and binding specificity was verified by competition with unlabeled [Sar1]angiotensin II. Angiotensin II receptor subtypes were characterized by competition with the nonpeptide receptor antagonists, DuP 753 (type 1) and PD123177 (type 2). Both rat and human kidney exhibited a high concentration of angiotensin II receptors in glomeruli and in the longitudinal bands traversing the outer portion of the medulla, corresponding to the medullary vascular bundles. Binding affinity (K(d) = 0.6 +/- 0.4 nM), determined in rat kidney, was similar to that reported previously in isolated glomeruli and membrane vesicles prepared from renal tubules. Angiotensin II binding was almost completely inhibited by DuP 753, whereas PD123177 had little effect. Thus the predominant angiotensin II receptor subtype in both rat and human kidney is type 1. The distribution of angiotensin II receptors correlates well with the intrarenal sites at which the peptide has its major physiological effects

EXPRESSION OF AT2-RECEPTORS IN THE DEVELOPING RAT FETUS

Angiotensin II is known primarily for its effects on blood pressure and electrolyte homeostasis, but recent studies suggest that angiotensin II may play a role in the regulation of cellular growth. This study was undertaken to identify the angiotensin II receptor subtypes expressed during fetal and neonatal development and to characterize their cellular localization. Using an in situ receptor binding assay on sagittal frozen sections of fetal and neonatal rats, bound I-125-[Sar1, Ile8]-angiotensin II was visualized by film and emulsion autoradiography. Bound radioligand was detected by E11 (embryonic day 11) and maximal binding occurred by E19-21. Radioligand binding remained unaltered 30 min after birth, whereas a noticeable and stable decrease was observed 12 h postparturition. The highly abundant angiotensin II receptors were shown to be AT2 by the marked reduction in radioligand binding achieved with PD123177 (10(-7) M), a specific AT2 receptor antagonist, whereas DuP 753 (10(-5) M), an AT1 receptor antagonist, had little effect. Emulsion autoradiography showed radioligand binding in the undifferentiated mesenchyme of the submucosal layers of the intestine and stomach, connective tissue and choroid surrounding the retina, subdermal mesenchyme adjacent to developing cartilage, diaphragm, and tongue. Residual AT2 receptors were found on the dorsal subdermal region of the tongue 72 h after birth. AT1 receptors were detected in the placenta at E13 and in the aorta, kidney, lung, liver, and adrenal gland at E19-21, consistent with an adult distribution. The transient expression of AT2 receptors in the mesenchyme of the fetus suggests a role of angiotensin II in fetal development

TISSUE-SPECIFIC REGULATION OF INSULIN-RECEPTOR MESSENGER-RNA LEVELS IN RATS WITH STZ-INDUCED DIABETES-MELLITUS

In rats with STZ-induced diabetes mellitus, a reduction in insulin secretion is associated with increased insulin binding in the liver, muscle, fat, and kidney, but not in the brain. To test the hypothesis that tissue-specific modulation of insulin receptors (IRs) in STZ-induced diabetes occurs at the level of mRNA, IR mRNA levels were measured in the liver, kidney, and brain of Sprague-Dawley rats 15 days after intravenous administration of STZ (60 mg/kg body weight) and compared with those of control rats. Diabetic rats were either left untreated or given differing insulin regimens that were designed to achieve varying degrees of metabolic control. IR mRNA levels were measured by slot blot hybridization with a P-32-labeled rIR probe and standardized by 28S ribosomal RNA determination. Hepatic IR mRNA levels were increased significantly in both untreated diabetic rats and in those that received low-dose (2 U/day) insulin therapy. In contrast, hepatic IR mRNA levels did not differ significantly from controls in those that received moderate doses of insulin (3-8 U/day) and were significantly less than controls in those that received the highest doses (6-10 U/day). Renal IR mRNA levels also were increased significantly in the untreated diabetic rats but not in those that received low- or moderate-dose insulin therapy, and were significantly less than controls in those that received the highest doses. A highly significant negative correlation was observed between the level of hepatic (r = -0.84, P < 0.001) and renal (r = -0.64, P < 0.001) IR mRNA, and the plasma concentration of insulin obtained at the time of death. No significant difference was observed in brain IR mRNA levels between untreated diabetic and control rats. Thus, in rats with insulin deficiency, modulation of insulin binding in the liver and kidney can be attributed, at least in part, to a change in steady-state IR mRNA levels

THE RENIN-ANGIOTENSIN SYSTEM IN STREPTOZOTOCIN-INDUCED DIABETES-MELLITUS IN THE RAT

It has been hypothesized that the renin-angiotensin system plays a pathophysiologic role in the renal hemodynamic abnormalities that occur in diabetes mellitus and thereby contributes to the development of diabetic nephropathy. In this study, the tissue-specific regulation of renin and angiotensinogen mRNA levels and the abundance of glomerular angiotensin II receptors were examined in male Sprague-Dawley rats (160 to 240 g) made diabetic with streptozotocin. One subgroup of diabetic rats remained untreated, whereas a second diabetic subgroup received twice-daily doses of insulin to ameliorate hyperglycemia. Animals were euthanized 2 wk after the induction of diabetes. Mean plasma glucose levels at the time of euthanasia were significantly elevated in the untreated diabetic animals when compared with controls or insulin-treated diabetic rats. Weight gain was similar in control and insulin-treated diabetic rats, whereas the untreated diabetic rats gained significantly less. Plasma renin concentration did not diff er between control, diabetic, and insulin-treated diabetic groups. In the kidney, no significant differences were found in either angiotensinogen or renin mRNA levels in diabetic animals, whereas glomerular angiotensin II receptors were significantly less abundant in untreated rats as compared with control or insulin-treated diabetic subgroups. Angiotensinogen mRNA levels were significantly lower in the livers and adrenals of diabetic rats in comparison to those in controls and insulin-treated diabetic rats, whereas angiotensinogen mRNA levels in the brain remained unaltered. Although it was demonstrated that angiotensinogen mRNA levels are regulated in a tissue-specific manner, no evidence was found for the activation of the systemic or renal renin-angiotensin system in diabetic animals and, in fact, it was found that the glomerular angiotensin II receptor number was decreased

Breast Cancer: Comparative Effectiveness of Positron Emission Mammography and MR Imaging in Presurgical Planning for the Ipsilateral Breast1

Overall, 61 (16%) of 388 participants had an appropriate change in surgical management based on MR findings—more than the 41 (11%) participants with an appropriate change based on positron emission mammography (PEM) findings (P = .003) and fewer than the 71 (18%) participants with an appropriate change based on combined PEM and MR findings (P = .004 for comparison with MR imaging alone); 25 (6.4%) women had excessive excisions on the basis of MR findings compared with 19 (4.9%) women who had them on the basis of PEM findings (P = .26) and 32 (8.2%) women who had them after undergoing combined PEM and MR imaging (P = .023 for comparison with MR imaging alone)