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Biomedical subjects

L A Sechi

Publications and source records attributed to L A Sechi.

At least 109 records · Page 6Linked to original sources
PubMed1993

Characterization of intergenic spacers in two rrn operons of Enterococcus hirae ATCC 9790.

Two DNA restriction enzyme fragments coding for the 3' termini of 16S rRNA, the 5' termini of 23S rRNA, and the intergenic spaces between them in Enterococcus hirae ATCC 9790 were cloned and sequenced. The intergenic space of one of these genes contains a tRNA(Ala) sequence, whereas the other does not. Nevertheless, the intergenic spaces contain several regions that exhibit high levels of sequence homology and are capable of forming structures with similar base pairs. An analysis of Southern blots of chromosomal DNA cut with one and two restriction enzymes indicated that E. hirae has a total of six rrn operons.

Base Sequence↗
PubMed1993

Autoradiographic characterization of angiotensin II receptor subtypes in rat intestine.

Angiotensin II is known to regulate motility and ion and water absorption in the intestine. These effects are presumed to be mediated by angiotensin II (ANG II) receptors that are present in both mucosal and muscular layers throughout the intestine. To evaluate tissue density and distribution of ANG II receptor subtypes (AT1 and AT2), we performed an in situ autoradiographic study on jejunum, ileum, and colon of Sprague-Dawley rats. Tissue sections (10 microns) were incubated with 500 pM 125I-[Sar1,Ile8]ANG II, fixed with paraformaldehyde vapors, and coated with photographic emulsion. Binding specificity was verified by competition with unlabeled [Sar1]ANG II (10 microM). AT1 and AT2 receptor distribution was characterized by competition with the nonpeptide antagonists losartan (10 microM) and PD123177 (10 microM), respectively, and the density of receptors was quantified by counting the silver grains overlying the different layers of intestinal wall. Specific binding was moderately abundant in the mucosa and the muscularis of both jejunum and ileum, whereas no binding was present in the submucosa and the serosa. Losartan inhibited 86% of radioligand binding to the mucosa in both jejunum and ileum, whereas PD123177 inhibited only 10%. The combination of the two compounds inhibited 96% of specific binding. In the colon, binding was significantly more abundant in the muscularis than in the mucosa. In this segment, losartan inhibited 90% and PD123177 16% of specific binding to muscularis. The combination of these compounds reduced binding by 97%. Thus the predominant ANG II receptor in all intestinal segments is AT1, but a small population of AT2 receptors also seems to be present.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1993

Acute effects of furosemide on blood pressure in functionally anephric, volume-expanded rats.

The hypotensive effect of loop diuretics is primarily mediated by a decrease in extracellular fluid volume that follows the intense diuresis. In the present study we investigated whether furosemide (1.25 mg/kg i.v.) can acutely lower blood pressure independently of its diuretic action. The experiments were performed in four groups of male Wistar rats: (a) rats in which furosemide was administered after bilateral ligation of renal vessels and saline (0.9% NaCl at a rate of 0.25 ml/min to a final volume of 1% of body weight) infusion; (b) rats in which furosemide was injected after bilateral ligation of ureters and saline infusion; (c) rats pretreated with indomethacin (3 mg/kg i.p. for 4 days) in which furosemide was injected after bilateral ligation of ureters and saline infusion; (d) sham-operated rats with intact kidneys. All the groups were compared with appropriate time controls. After furosemide injection, heart rate and blood pressure were serially recorded for 30 min by plethysmography. Hematocrit, plasma 6-keto-prostaglandin F1 alpha levels and plasma renin activity were measured at baseline and 20 min after furosemide injection. No change in blood pressure followed furosemide administration in rats with ligation of the renal vessels. Conversely, furosemide induced a rapid and significant fall in blood pressure associated with a significant increase in heart rate in rats with ligation of the ureters and rats with intact kidneys. Indomethacin pretreatment prevented the furosemide-induced decrease in blood pressure in rats with ligation of the ureters. Hematocrit and plasma 6-keto-prostaglandin F1 alpha levels were not affected by furosemide in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Urodilatin binds to and activates renal receptors for atrial natriuretic peptide.

Urodilatin is a recently described member of the atrial natriuretic peptide family, thought possibly to be synthesized in the kidney. To determine if urodilatin binding sites are present in rat and human kidney, we evaluated the effect of urodilatin on iodine-125-labeled atrial natriuretic peptide (ANP) (100 pM) binding to tissue sections using an in situ autoradiographic technique. 125I-ANP binding occurred primarily in glomeruli and medullary structures of both rat and human kidney. Increasing concentrations of urodilatin yielded a monophasic displacement of 125I-ANP binding with an IC50 of 4.2 nM, a value nearly identical to that achieved with unlabeled ANP (7.2 nM). In additional experiments, rat glomeruli and inner medullary collecting duct cells were isolated and incubated in vitro with either ANP or urodilatin (10(-11) to 10(-6) M) and cyclic guanosine-3',5'-monophosphate accumulation measured by radioimmunoassay. Dose-response curves for the two peptides were superimposable in each tissue; at 10(-6) M, ANP generated 613 +/- 41 and urodilatin 603 +/- 55 fmol cyclic guanosine monophosphate per 10 minutes per milligram protein in inner medullary collecting duct cells (p = NS). Thus, urodilatin is as effective as ANP in displacing 125I-ANP binding to both rat and human renal tissue and in generating cyclic guanosine monophosphate in renal target cells in the rat, suggesting that its physiological effects may occur through the same receptors and signaling pathways that mediate the actions of ANP.

Animals↗
PubMed1993

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 differ 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensinogen↗
PubMed1993

[Angiotensin II receptors in the heart conduction tissue].

Angiotensin II exerts a positive chronotropic effect on mammalian heart. This effect can be mediated either by activation of the sympathetic nervous system or binding to specific receptors located in cardiac conduction tissue. Recently, two angiotensin II receptor subtypes have been identified in rat tissues. In the present study, we have investigated tissue distribution of angiotensin II receptor subtypes in conduction tissue obtained from rat hearts, employing an in situ autoradiographic technique. Receptor subtypes were identified by use of the peptide antagonists losartan (AT1) and PD123,177 (AT2). Angiotensin II binding was homogeneously distributed in right and left ventricle, and interventricular septum, with each subtype accounting for approximately 50% of the specific binding. Receptor density in the conduction tissue, identified by acetylcholinesterase histochemistry, was quantitated by counting the silver grains on tissue sections which, following incubation, were dipped in photographic emulsion and developed. In both sinoatrial and atrioventricular node AT1 and AT2 receptors were homogeneously distributed. Receptor density in sinoatrial node was comparable to myocardium, whereas it was significantly higher (p < 0.02) in atrioventricular node. In conclusion, both AT1 and AT2 receptors are homogeneously distributed in cardiac conduction tissue. Binding density is higher in the atrioventricular node than in the other structures examined in our study, suggesting a possible role of angiotensin II in the atrioventricular conduction.

Angiotensin II↗
PubMed1993

[Angiotensin receptors in the rat myocardium during pre- and postnatal development].

Angiotensin II exerts positive inotropic and chronotropic effects on mammalian heart by binding to specific membrane receptors. Recently, 2 subtypes of angiotensin II receptors (AT1 and AT2) have been distinguished using the nonpeptide antagonists losartan and PD123177. Because angiotensin II has been reported to have growth potentiating effects in several tissues, we examined angiotensin II receptors in fetal (embryonic day 16 and 19), neonatal (1, 2, 3 and 10 days), and adult (10 and 16 weeks) rats. We performed an 125I-[Sar1,Ile8]-angiotensin II in situ binding assay on tissue sections obtained from Sprague-Dawley rats. 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 receptors quantitated 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 right and left ventricles, and interventricular septum. Throughout cardiac development a significant increase (p < 0.005) in the density of both receptor subtypes was found immediately after birth, reaching a maximum on day 2, and decreasing toward prenatal values thereafter. No variation in the proportion of the 2 receptor subtypes was observed during development. Thus, in rat heart, AT1 and AT2 receptors are equally distributed over the myocardium. The density of these angiotensin II receptors is developmentally regulated, suggesting a possible role of the cardiac renin-angiotensin system in heart growth and in the adaptation of the heart to postnatal circulatory conditions.

Analysis of Variance↗
PubMed1993

[The role of G-regulatory proteins in the intracellular mechanism of cardiac angiotensin-II receptors].

High-affinity angiotensin II receptors have been identified in cardiac tissue of many animal species. In the heart, angiotensin II exerts positive inotropic and chronotropic effects, constricts coronary vessels, and stimulates cell growth. In vascular smooth muscle and adrenal cortex angiotensin II interacts with guanidine nucleotide regulatory proteins because GTP-gamma-S causes dissociation of the radioligand from its receptor. To investigate whether angiotensin II interacts with guanidine nucleotide regulatory proteins also in cardiac tissue, we studied the effects of GTP-gamma-S on [Sar1, Ile8]-angiotensin II binding to angiotensin II receptor subtypes (AT1 and AT2) in hearts obtained from 16- to 20-week-old Sprague-Dawley rats. We employed an in situ technique performed on frozen tissue sections. Competition experiments performed with the nonpeptide inhibitors losartan and PD123177 allowed identification of both AT1 and AT2 angiotensin II receptors in rat heart. These receptors were present in comparable amounts. In a different set of experiments the effects of GTP-gamma-S (100 microM) on radioligand displacement from AT1 and AT2 receptors were studied. GTP-gamma-S caused a progressive dissociation of the radioligand from the AT1 receptor indicating that this receptor interacts with guanidine nucleotide regulatory proteins. In contrast, the AT2 receptor does not appear to directly interact with guanidine nucleotide regulatory proteins. In summary, the study shows that both angiotensin II receptor subtypes are present in rat heart and that guanidine nucleotide regulatory proteins are implicated in the signal transduction mechanism of the cardiac AT1 receptor.

Angiotensin II↗
PubMed1992

Insulin hypersecretion: a distinctive feature between essential and secondary hypertension.

Several studies have demonstrated that patients with hypertension have greater plasma insulin levels than normotensive subjects. The aim of the present study was to clarify if hyperinsulinemia in hypertension is a consequence of either increased pancreatic secretion or decreased hepatic clearance, and to determine whether abnormalities of glucose metabolism are equally present in essential and secondary hypertension. In an observational cross-sectional study, fasting blood glucose, plasma insulin, and plasma C-peptide levels were measured in five patient groups: 34 lean normotensive, 19 overweight normotensive, 25 lean essential hypertensive, 27 overweight essential hypertensive, and 20 secondary hypertensive subjects. The blood glucose/plasma insulin and plasma insulin/plasma C-peptide ratios were calculated as indexes of insulin sensitivity and hepatic insulin clearance, respectively. Subjects with essential hypertension and, to a greater extent, those who were overweight, exhibited significantly higher fasting insulin and C-peptide levels and significantly lower glucose/insulin ratios as compared with lean normotensive subjects. In contrast, no differences were observed between secondary hypertensive and control subjects. Mean blood pressure was significantly and independently correlated to body mass index, plasma insulin and plasma C-peptide levels, and the glucose/insulin ratio. In lean essential hypertensive and secondary hypertensive subjects, the insulin/C-peptide ratios were comparable to controls, indicating normal hepatic insulin clearance. In both overweight groups, a trend to increased insulin/C-peptide ratios was observed. This study shows that in essential hypertensive subjects, hyperinsulinemia is caused by insulin hypersecretion, whereas in overweight subjects, both increased insulin secretion and decreased hepatic insulin clearance might be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

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 125I-[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 (Kd = 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.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1992

Abnormalities of erythrocyte sodium transport systems in Bartter's syndrome.

The basic tubular alteration present in Bartter's syndrome is still a subject of controversy. The possibility that a generalized defect in the transmembrane ion transport underlies the disease has been extensively investigated. Previous evaluations of cellular sodium metabolism in Bartter patients showed extremely variable findings. We have examined in the red blood cells of two patients with Bartter's syndrome the intracellular Na+ and K+ concentrations, the activity of the ouabain-sensitive Na+/K+ pump, furosemide-sensitive Na+/K+ cotransport, Na+/Li+ countertransport and the rate constant of Na+ and K+ passive permeability. We have compared these values with those of healthy subjects and patients with chronic hypokalemia produced by conditions other than Bartter's syndrome. Ouabain-sensitive Na+/K+ pump activity was decreased in both patients, whereas Na+/Li+ countertransport was activated. One of the patients also exhibited markedly decreased intraerythrocyte K+ concentration and decreased furosemide-sensitive Na+/K+ cotransport. The other had increased Na+/K+ cotransport activity and Na+ passive permeability. Intracellular Na+ and passive permeability to K+ were normal in both subjects. Neither oral potassium supplementation (100 mEq/day) nor indomethacin treatment (150 mg/day) could correct these abnormalities. Our results are partially consistent with previous observations and indicate the existence of heterogenous abnormalities of erythrocyte sodium transport systems in patients with Bartter's syndrome which are not a consequence of chronic hypokalemia.

Adult↗
PubMed1992

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 125I-[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.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1992

Tissue-specific regulation of insulin receptor mRNA 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 32P-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.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

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 125I-[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.

Angiotensin II↗
PubMed1991

Serum insulin, insulin sensitivity, and erythrocyte sodium metabolism in normotensive and essential hypertensive subjects with and without overweight.

Increased insulin circulating levels and perturbations of intracellular sodium metabolism have been reported in essential hypertensive patients, leading to postulate their involvement in the pathophysiology of the disease. In-vitro studies have shown that insulin modulates the activity of some transmembrane sodium transporters. The aim of this investigation was to assess in subjects with essential hypertension and/or overweight, the levels of fasting serum insulin, the activity of sodium transporters and their possible relationships. In 18 lean normotensive, 12 overweight normotensive, 18 untreated lean essential hypertensive, and 16 untreated overweight essential hypertensive subjects, we measured the fasting levels of blood glucose and serum insulin, and calculated the glucose/insulin ratio as an index of sensitivity to insulin. In addition, in the red blood cells of these subjects, we evaluated the maximal rate of ouabain-sensitive Na/K pump, furosemide-sensitive outward Na/K cotransport, Nai/Lio countertransport, and the constant rate of passive permeability to Na. When compared to lean normotensive, overweight normotensive, lean hypertensive, and overweight hypertensive subjects exhibited significantly higher fasting insulin levels, with lower glucose/insulin ratio. No significant difference was found in the activity of Na/K pump, Na/K cotransport, and passive permeability to Na. The Nai/Lio exchange was significantly increased in both hypertensive groups. Mean blood pressure correlated positively and independently with body mass index and fasting insulinemia, and inversely with the glucose/insulin ratio. No relationships were found between blood pressure, fasting insulin levels or glucose/insulin ratio and the activity of sodium transport systems. We conclude that hyperinsulinemia and insulin resistance are associated with essential hypertension independently of overweight. These data lend support to the hypothesis that insulin is involved, concurrently with other factors, in the pathogenesis of essential hypertension in both lean and obese subjects.

Biological Transport↗