Angiotensin receptors in bovine umbilical artery and their inhibition by nonsteroidal anti-inflammatory drugs

1 The contractile effect of angiotensin II on bovine isolated umbilical arteries was compared to [125I]-angiotensin II binding by a subcellular fraction of that tissue. The ED50 of angiotensin was 3.1 +/- 2.8 x 10(-8) M, while the apparent dissociation constant was 4.9 +/- 1.6 x 10(-9) M. 2 Indomethacin, meclofenamate, and eicosatetraynoic acid inhibited angiotensin-induced contraction of the isolated artery and binding to a particulate fraction at comparable doses. Phenylbutazone inhibited [125I]-angiotensin binding more potently than the response. Inhibition by the first three agents was noncompetitive, whereas phenylbutazone inhibited competitively. 3 Inhibition of angiotensin activity by the nonsteroidal anti-inflammatory agents was not specific. These agents also inhibited 5-hydroxytryptamine-induced contraction, but not the contraction induced by KCl. 4 The data suggest that the angiotensin binding sites studied include receptors that mediate contraction of the isolated umbilical artery. Our data also indicate that indomethacin, meclofenamate, eicosatetraynoic acid and phenylbutazone are capable of direct inhibitory effects on receptors, as well as their well-known synthetase actions. The net effect of these activities will determine the change these agents cause in tissue responses to hormones.

Renal preservation resistance: evidence against myogenic vasoactive factors

Vasoconstriction is believed to be a dominant cause of high perfusion resistance during kidney preservation at low temperatures. An experiment was performed to study the effects of hypothermia on vasoactivity. Measurements were made on an apparatus that permitted perfusion resistance to be compared simultaneously in two isolated kidneys at different temperatures. With perfusion temperature serving as the variable, the vascular responses to several vasoactive agents were measured. Hypothermia diminished or altered the vascular responses to the agents. For example, no vasoconstriction was observed with Angiotensin II, dopamine, acetylcholine, or BaCl2 and no vasodilation was observed with papaverine or bradykinin in the hypothermic kidney. A significantly altered response was observed with norepinephrine. The responses were reversible upon return to normothermia. From these data, we conclude that myogenic vasoconstriction plays a questionable role in producing the elevated perfusion resistance observed in some hypothermic kidneys.

Attenuation of I- 125 radiation by chloroform and other dense solvents, and its relevance to radioimmunoassays: concise communication

The counting efficiency of iodine- 125 in well-type scintillation counters is reduced when the labeled compound is dissolved or suspended in chlorinated hydrocarbons or potassium iodide solution. The reduction is probably caused by absorption of the weak gamma and x-rays of I- 125 by the halogen atoms in the solvent or solute molecules. This phenomenon may introduce artifacts into procedures involving radioiodinated compounds and organic solvents and KI, but it could also be useful in differentiating bound from free labeled ligands by their differential solubility (and attenuation) in dense solvents. The reduction in counting efficiency can be overcome by evaporation of the solvent, or by the use of emitters with higher energy radiation.

Indomethacin blocks acute audiologic effects of furosemide in Meniere's disease

The acute audiologic effects of glycerin and furosemide were measured with and without indomethacin pretreatment in two patients. The positive effects of glycerin were not blocked by indomethacin. The positive effect of furosemide on discrimination score was blocked by indomethacin. The concomitant rise in plasma renin level after furosemide was also blocked by indomethacin. A role for prostaglandins in inner ear fluid dynamics is suggested by this study. It appears that glycerin and furosemide affect inner ear fluid dynamics by different mechanisms.

The effect of pregnancy on the angiotensin II pressor response in the rabbit

The pressor response to angiotensin II was measured in unanesthetized, chronically catheterized pregnant and nonpregnant rabbits. Angiotensin II was infused intravenously for 10 minutes at a dose of 50 and 124 ng/kg/min. No difference in control mean arterial blood pressure was observed between pregnant and nonpregnant rabbits. The pressure change in response to angiotensin II was significantly greater in nonpregnant rabbits than in pregnant rabbits (P less than 0.002). Plasma samples were analyzed for angiotensin II concentration by radioimmunoassay. The results showed that there was no difference in plasma angiotensin II concentration between pregnant and nonpregnant rabbits following angiotensin II infusions. In a separate series we observed the effect of 5 mg of phenoxybenzamine on the pressor response to angiotensin II. After phenoxybenzamine treatment the control mean arterial blood pressure was significantly greater in nonpregnant rabbits than in pregnant rabbits, but the change in pressure in response to angiotensin II in nonpregnant rabbits was not significantly different from that of pregnant rabbits. These results show (1) that pregnant rabbits have a decreased sensitivity to angiotensin II, (2) that this decreased sensitivity is not due to differences in plasma concentration of angiotensin II, and (3) that this differential sensitivity to angiotensin II can be prevented by alpha-receptor blockade.

Plasma renin concentration and phenobarbital levels in patients with epilepsy

Plasma renin activity, renin concentration, and renin substrate were measured in patients on long-term anticonvulsant medication. An inverse correlation was observed between phenobarbital levels and renin activity or concentration. There was a positive correlation between phenobarbital and renin substrate. Since elevation of renin substrate should have resulted in increased renin activity, it is possible that phenobarbital exerts 2 effects on the renin system: induction of renin substrate synthesis and suppression of renin release.

Low plasma renin concentration in patients with Meniere's disease (preliminary report)

Endolymphatic hydrops is the histopathologic hallmark of Meniere's disease. The cause of excess inner ear fluid is unknown, but the possibility of a systemic abnormality of fluid-solute regulation has been considered. One indicator of systemic fluid and electrolyte balance is the enzyme renin. Plasma renin levels were measured in patients with a clinical diagnosis of Meniere's disease and compared to a group of patients who did not have Meniere's disease. The mean plasma renin concentration of patients with Meniere's disease was statistically lower than that of the other subjects. The study's results are consistent with a systemic abnormality in fluid and solute regulation in some patients with M eniere's disease, leading to abnormal expansion of the extracellular fluid volume, and possibly contributing to endolympathic hydrops.

Angiotensin and bradykinin interactions with phospholipids

Reversible interactions were demonstrated between some phospholipids and some polypeptides related to angiotensin and bradykinin. The extent of the interaction was dependent on the structures of the lipid and peptide. The naturally occurring compounds that interacted most avidly were cardiolipin and (des-Asp1)-angiotensins. The apparent dissociation constant of this complex in chloroform was 10(-5) M. The complex contained more than one cardiolipin molecule/molecule of peptide. Kinins interacted most strongly with lecithin. The phospholipids altered the chromatographic behavior of radioiodinated derivatives of the polypeptides, and solubilized radioactive and unlabeled polypeptides in chloroform. In aqueous media, cardiolipin suspensions preferentially bound (des-Asp1)-angiotensin II, and inhibited its binding by antibody. The interactions were sensitive to pH and cations in the aqueous phase, and were reversed by some reagents added to the organic phase. These interactions have direct implications for binding reactions of peptides in vitro, and may bear upon the actions of the hormones in vivo.

Gestational changes in pulmonary converting enzyme activity in the fetal rabbit

Changes in angiotensin-converting enzyme were measured in the lungs of fetal rabbits isolated and perfused in situ at varying ages from 22 days gestation to 7 days of age under controlled conditions of flow, pH, and temperature. Enzyme activity was assessed by infusing bradykinin or angiotensin I in Krebs-Henseleit solution and measuring residual peptide in the effluent by radioimmunoassay. The levels of substrate studied were below those required for enzyme saturation. Lungs of 22 day gestation fetuses removed only one-third of either peptide. The activity at term and in neonatal life resulted in more than 80% peptide removal. The time of the greatest rise in the percent substrate cleared occurs earlier than the time of the greatest increase in lung and body weight. The lower percentage of substrate cleared in early gestation appears to result in part from a limited surface area for enzyme activity in the primitive fetal pulmonary microvascular bed, since morphological studies with fluorescein-tagged anticonverting enzyme antibody demonstrated the presence of enzyme in the lung as early as 17 days of gestation. Electron micrographs of the pulmonary endothelial cell surface reveal that the degree of surface infolding and hence surface area increases with gestation. The higher percentage of substrate cleared in later gestation closely parallels the structural and ultrastructural development of the vascular bed. The presence of converting enzyme in the placenta by the second third of gestation and the large size of the placenta suggest that this organ may be a major locus of converting enzyme activity in the fetus.

Aspects of bradykinin radioimmunoassay

125I-derivatives of Tyr1-kallidin, Tyr5-bradykinin, and Tyr8-bradykinin were prepared. A technique for purification of the monoiodinated derivative is described. Bradykinin antisera were tested for their ability to bind the mono-iodinated analogues. Each antiserum had a characteristic preference for one of the three labeled peptides. The sensitivity of each antiserum was greatest when it was used with the label bound most avidly by that antiserum. The specificity of an antiserum was not changed by varying the labeled analogue. Some common enzyme inhibitors had significant effects on the antigen-antibody reactions. Lecithin interfered with the reaction between antiserum and Tyr1-kallidin. The data suggest that antisera for bradykinin radioimmunoassay be tested with several radioactive iodobradykinins to maximize their usefulness. In addition, enzyme inhibitors used to stabilize levels of kinins in biological fluids should be tested for their effects on the assay. Biologic samples rich in lipid may give spurious radioimmunoassay results unless they are freed of those phospholipids that can bind labeled and unlabeled peptides.

Peptide-binding macromolecules in the blood of seriously ill or mentally retarded patients

This report describes macromolecules that bind (des-aspartic acid1)-angiotensin II, the des aspartic acid1 derivative of angiotensin I, and several biologically active and inactive analogues of these polypeptides. The macromolecules were found in the plasma of approximately 2 per cent of ambulatory adults and hospitalized children and 32 per cent of the patients at two institutions for the mentally retarded. The binding properties of these macromolecules were studied by incubating with peptides labeled with 125iodine, and separating bound from free labeled peptide using small gel filtration columns. The peptide-binding macromolecules from several patients were compared. They showed very similar specificity for a group of arginyl peptides of the des-aspartyl1-angiotensin sequence. The plasma binders differed from one another in their optimum pH and their mobility in electrophoretic fields. Those with more acid pH optima displayed more rapid electrophoretic mobility. The binders fell into two classes based on apparent molecular weight, approximately 140,000 and 250,000. Those with the higher apparent molecular weight contained a large proportion of binder that could be precipitated with antiserum to human IgA. Kinetic measurements showed that the plasma binders were somewhat heterogeneous with respect to affinity for (des-asp1)-angiotensin, with apparent association constants ranging from 10(7) to 10(8) M-1. Binding activity was labile to heat, and to treatment with pepsin or trypsin. It was inhibited by calcium, protamine, streptomycin, and some other cationic compounds. The plasma peptide binder differed in specificity and molecular weight from soluble angiotensin-binding molecules extracted from tissues, and from properties expected of a receptor for angiotensin. These macromolecules may be useful reagents for measuring (des-asp1)-angiotensins. Their presence in plasma samples may interfere with angiotensin assays in some circumstances.

Angiotensin III: (DES-Aspartic Acid-1)-Angiotensin II. Evidence and speculation for its role as an important agonist in the renin - angiotensin system

Evidence is reviewed that three and possibly four peptides formed from renin substrate have biological activity that merits their recognition as agonists. The decepeptide angiotensin I affects sites in the central nervous system and adrenal medulla. The octapeptide angiotensin II affects vascular and cardiac sites that mediate acute pressor responses, and also causes direct feedback inhibition of renin release. The heptapeptide (des-asp-1)-angiotensin II ("angiotensin III") stimulates aldosterone release.. It may exert its effects intracellularly at the adrenal glomerulosa and other sites. The fourth candidate is the (des-asp-1)-angiotensin I nonapeptide, but nothing is known of its activity or circulating levels. This formulation of the angiotensin reaction sequence and the effects of its individual congeners suggests several experiments. It also permits simple explanations for previously confusing data, such as the inability of immunization and anti-angiotensin II to prevent aldosterone responses, and the paradoxical preservation of adrenal responsiveness in Bartter's syndrome.

Inotropic agents in hypoxic cat myocardium: depression and potentiation

The effects of several inotropic agents were investigated in papillary muscle preparations from normal cats and cats that had undergone previous total extrinsic cardiac denervation. The papillary muscles were bathed in a modified Krebs-Ringer's solution which was equilibrated with 95% O 2 -5% CO 2 for the control drug studies or 5% O 2 -5% CO 2 -90% N 2 for the hypoxia studies. This degree of hypoxia produced a 32 ± 3% decrease in tension in papillary muscles from normal cats and a 14 ± 4% decrease in catecholamine-depleted papillary muscles. During hypoxia there was depression of the maximum response to ouabain and norepinephrine with otherwise unchanged dose-response curves. Deterioration of the hypoxic muscles occurred after exposure to norepinephrine concentrations of 5 x 10 -7 M and greater. The dose-response curve for angiotensin II was unchanged by hypoxia. However, during hypoxia, the dose-response curves for two heptapeptide analogues of angiotensin II, 1-des-5-Valand 1-des-5-Ile-angiotensin II, were augmented. The inotropic effects of these analogues under control and hypoxic conditions were the same in the normal and catecholamine-depleted muscles. The potentiation by hypoxia of the inotropic effects of the angiotensin II analogues is unique among the agents studied.