Cholesteryl hemisuccinate alters membrane fluidity, angiotensin receptors, and responses in adrenal glomerulosa cells

We examined the effects of cholesteryl hemisuccinate on membrane fluidity and angiotensin II (AII) actions in bovine adrenal glomerulosa cells. Incubating cells with cholesteryl hemisuccinate decreased membrane fluidity and markedly inhibited AII binding. The effect on binding was characterized by a decrease in AII receptor number. The effects of AII on phosphatidyl inositol turnover and calcium fluxes, proposed intermediaries of AII actions on aldosterone secretion, were less impaired than AII binding by cholesteryl hemisccinate. AII stimulation of aldosterone secretion was preserved despite the decrease in AII binding after cholesteryl hemisuccinate treatment. These results indicate that AII binding can be dissociated from its effects on aldosteronogenesis by a reagent that alters membrane fluidity.     

Role of angiotensin II-mediated AMPK inactivation on obesity-related salt-sensitive hypertension

Salt-sensitive hypertension is a characteristic of the metabolic syndrome. Given the links to cardiovascular events, the mechanisms underlying sodium metabolism may represent an important therapeutic target for this disorder. Angiotensin II (AII) is a key peptide underlying sodium retention. However, 5'AMP-activated protein kinase (AMPK) has also been reported to participate in the regulation of ion transport. In this study we examined the relationship between AII and AMPK on the development of hypertension in two salt-sensitive mouse models. In the first model, the mice were maintained on a high-fat diet (HFD) for 12 weeks, in order to develop features similar to the metabolic syndrome, including salt-sensitive hypertension. HFD-induced obese mice showed elevated systolic blood pressure and lower sodium excretion in response to salt loading, along with an increase in AII contents and inactivation of AMPK in the kidney, which were significantly improved by the treatment of an angiotensin II antagonist, losartan, for 2 weeks. To clarify the effects of AII, a second group of mice was infused with AII via an osmotic pump, which led to higher systolic blood pressure, and decreases in urinary sodium excretion and the expression of AMPK, in a manner similar to those observed in the HFD mice. However, treatment with an AMPK activator, metformin, improved the changes induced by the AII, suggesting that AII induced sodium retention works by acting on AMPK activity. Finally, we evaluated the changes in salt-sensitivity by performing 2-week salt loading experiments with or without metformin. AII infusion elevated blood pressure by salt loading but metformin prevented it. These findings indicate that AII suppresses AMPK activity in the kidney, leading to sodium retention and enhanced salt-sensitivity, and that AMPK activation may represent a new therapeutic target for obesity-related salt-sensitive hypertension.     

Angiotensin II receptors and inhibitory actions in Leydig cells

Rat Leydig cells possess functional high-affinity receptors for angiotensin II (AII). AII inhibits adenylate cyclase activity in Leydig cell membranes and reduces basal and human chorionic gonadotropin (hCG)-stimulated cAMP pools and testosterone production in intact cells. Treatment of cells with an inhibitory dose of forskolin (10(-9) M) and a submaximal dose of AII caused additive inhibition of hCG-stimulated events. The inhibitory action of AII was largely prevented by pertussis toxin prior to the addition of AII alone or in the presence of hCG. This study and our recent report on inhibitory action of low doses of forskolin, 10(-12)-10(-9) M (Khanum, A., and Dufau, M.L. (1986) J. Biol. Chem. 261, 11456-11459) are indicative of a pertussis toxin-sensitive subunit of adenylate cyclase available for acute regulation of Leydig cell function. 8-bromo-cAMP bypasses the inhibitory effect of forskolin as well as AII. We have, therefore, demonstrated functional AII high-affinity receptor and an acute inhibitory effect of AII on hCG action in Leydig cells. Our results have provided evidence for a pertussis toxin-sensitive guanine nucleotide inhibitory protein as mediator of the effect of AII. These findings further emphasized the importance of the cAMP pathway in the Leydig cells, and studies also suggest that tubular and locally produced AII could negatively modulate luteinizing hormone stimulation of Leydig cells.     

Stimulation and inhibition of resting muscle thermogenesis by vasoconstrictors in perfused rat hind limb

Angiotensin (AII) and serotonin (5-HT) are both vasoconstrictors of the constant-flow perfused rat hind limb that have opposite effects on thermogenesis, possibly the result of differing effects on vascular flow distribution between nutritive and non-nutritive pathways. In the present study interaction between the two opposing agents was examined with the expectation that the combined presence would show additive effects on pressure and mutually neutralizing effects on thermogenesis. Thus doses of AII and 5-HT that gave similar, but opposite, quantitative effects on thermogenesis were infused alone, in combination one after the other, or in combination with the order reversed, and the effects on perfusion pressure (PP) and thermogenesis (oxygen uptake, VO2) were compared. AII (3 nM) alone increased PP by 15+/-1 mmHg (1 mmHg = 133.3 Pa) and VO2 by 3.1-/+0.2 micromol.h(-1).g(-1), whereas 5-HT (1 microM) alone increased PP by 75+/-6 mmHg and inhibited VO2 by 3.9+/-0.2 micromol.h(-1).g(-1). When added in combination, the outcome depended on the order of addition. Following AII, infusion of 5-HT further increased PP by 160+/-11 mmHg and decreased VO2 by 6.3+/-0.2 micromol.h(-1)g(-1). Following 5-HT, infusion of AII further increased PP by 28+/-4 mmHg and increased VO2 by only 1.8+/-0.3 micromol.h(-1).g(-1). The prior presence of 5-HT (1 microM) shifted the AII dose-response curves for VO2 and pressure to the right and left, respectively. The prior infusion of AII increased the dose-dependent response to 5-HT in terms of both the inhibition of VO2 and the increase in PP. At low doses of 5-HT (10(-8)-10(-7) M), but not alpha-methyl serotonin (alphaMT), there was a marked vasodilatation-associated inhibition of AII-mediated increase in VO2. Overall the data show that the combined effect of AII and 5-HT differed from the simple addition of each separately. Since the order of addition appears to be critical in terms of thermogenic outcome, it is concluded that each vasoconstrictor exerts a specific hemodynamic action to affect access of the other to vascular receptor sites. These findings are consistent with the previously reported effects of these vasoconstrictors on substrate and insulin access to muscle of the perfused rat hind limb.     

Are polyamines involved in the contractile effects of angiotensin II in the rat aorta? (Polyamines and angiotensin II in rat aorta).

Angiotensin II (AII) is a central factor involved in the pathophysiology of arterial hypertension and atherosclerosis. On the other hand, polyamines represent a family of organic cations with low molecular weight, playing intracellular regulatory roles essential for the cellular growth and differentiation. The cellular contents, the synthesis and the transport of polyamines are increased following the actions of AII, as well as of other cellular growth factors. Our results show that the administration of polyamines as pre-treatment modulates the contractile effects of extracellular AII (80 nM). This modulation is concentration-dependent and dual: the lower concentrations amplify and the higher concentrations reduce the effects of AII in the isolated rat aorta rings without endothelium. Moreover, DL-alpha-Difluoromethylomithine (DFMO), a specific inhibitor of ornithine decarboxylase, does not significantly modify the contractile effects of AII. Thus, these data suggest that polyamines generated through this metabolic pathway are not involved in the contractile effects of AII in rat aortic vascular smooth muscle.     

An intracerebral, physiological role for angiotensin: effects of central blockade.

Although exogenous angiotensin II (AII) exerts a multitude of effects on the central nervous system, there is little evidence supporting a physiological role for the endogenously produced peptide. Some investigators have tested the hypothesis that AII is physiologically active in the brain with intracerebral infusions of blockers of the renin-angiotensin system. If blocker infusions produce effects that are opposite to exogenous AII infusions, it is evidence supporting a physiological role for endogenously generated angiotensin. Previous work has demonstrated that intraventricular infusion of AII elicits thirst and stimulates antidiuretic hormone and ACTH release. Intracerebral administration of AII also suppresses aldosterone secretion. Experiments that employed the blockers saralasin, a competitive inhibitor of AII, and SQ 20881, a converting enzyme blocker, are presented; results suggest that endogenous AII is involved in the control of thirst and peripheral hormone levels. Infusion of the blockers in the ventricular system led to changes in peripheral hormone concentrations opposite to that observed following infusions of AII.     

Evidences for the action mechanism of angiotensin II and its analogs on Plasmodium sporozoite membranes

Malaria is an infectious disease responsible for approximately one million deaths annually. Oligopeptides such as angiotensin II (AII) and its analogs are known to have antimalarial effects against Plasmodium gallinaceum and Plasmodium falciparum. However, their mechanism of action is still not fully understood at the molecular level. In the work reported here, we investigated this issue by comparing the antimalarial activity of AII with that of (i) its diastereomer formed by only d ‐amino acids; (ii) its isomer with reversed sequence; and (iii) its analogs restricted by lactam bridges, the so‐called VC5 peptides. Data from fluorescence spectroscopy indicated that the antiplasmodial activities of both all‐D‐AII and all‐D‐VC5 were as high as those of the related peptides AII and VC5, respectively. In contrast, retro‐AII had no significant effect against P. gallinaceum. Conformational analysis by circular dichroism suggested that AII and its active analogs usually adopted a β‐turn conformation in different solutions. In the presence of membrane‐mimetic micelles, AII had also a β‐turn conformation, while retro‐AII was random. Molecular dynamics simulations demonstrated that the AII chains were slightly more bent than retro‐AII at the surface of a model membrane. At the hydrophobic membrane interior, however, the retro‐AII chain was severely coiled and rigid. AII was much more flexible and able to experience both straight and coiled conformations. We took it as an indication of the stronger ability of AII to interact with membrane headgroups and promote pore formation. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

High degree of conversion of angiotensin I to angiotensin II in the mesenteric circulation of the isolated perfused terminal ileum of the cat.

Conversion of AI to AII has been studied in the mesenteric circulation of the isolated perfused cat terminal ileum. Infusion of AI through the mesenteric circulation induced a significantly potentiated response when the venous return was superfused over the rat colon and the rabbit aortic strip. Addition of converting-enzyme inhibitor, SQ 20881 to the perfusion medium competitively prevented the potentiation of AI on the assay organs without altering its direct effects. The percent conversion of AI to AII was found to be 68 in the mesenteric circulation. In contrast, infusion of AII through the mesenteric circulation has lost about 40% of its biological activity as measured on the same assay organs. SQ 20881 abolished the inactivation of AII in the mesenteric circulation. It is concluded that the mesenteric circulation of the isolated perfused cat terminal ileum is one of the major conversion areas of AI to AII. SQ 20881 prevented the conversion of AI to AII as well as abolishing the inhibition of AII passing through the mesenteric circulation.     

Regulation of glucose transport by angiotensin II and glucose in cultured vascular smooth muscle cells

Glucose transport in response to angiotensin II (AII) was assessed in cultured vascular smooth muscle (VSM) cells by measuring the uptake of [³H]-2-deoxyglucose, a radiolabeled non-metabolizable glucose analog. Significant stimulation occurred by 2 hr of exposure with the maximum effect being observed between 6 and 8 hr. AII effects were concentration dependent with a threshold response being detected at 0.1 nM. AII-stimulated transport was blocked by saralasin, an AII receptor antagonist, indicating that AII binding to a specific receptor is required for AII to elicit the transport response. AII-stimulated transport was also blocked when cells were incubated with cycloheximide for 6 hr, suggesting that protein synthesis is required for the long-term effects of AII on glucose transport. A specific protein synthesized in response to AII stimulation was the GLUT 1 glucose transporter as assessed by western blot analysis. Inhibition of protein kinase C (PKC) by bisindolylmaleimide and staurosporine did not affect VSM responsiveness to AII, suggesting that AII is capable of stimulating glucose transport through a PKC-independent mechanism; however, VSM responsiveness to AII did appear to be dependent upon the presence of extracellular calcium. The importance of calmodulin in mediating the response of VSM cells to AII was indicated by the inhibition of AII-stimulated glucose transport when VSM cells were incubated in the presence of the calmodulin inhibitors, calmidazolium and W7. Finally, glucose uptake increased with decreasing levels of glucose in the incubation medium. This was accompanied by a corresponding decrease in the relative effectiveness of AII in stimulating glucose uptake. J. Cell. Physiol. 177:94–102, 1998. © 1998 Wiley-Liss, Inc.     

Angiotensin stimulation of adrenal fasciculata cells

In this paper we provide evidence to show that the pathways by which adrenocorticotropic hormone (ACTH) and angiotensin II (AII) stimulate steroidogenesis in bovine fasciculata cells are only partially independent. Both hormones have the same intrinsic activity but a 500-fold higher dose of AII is required to achieve 50% stimulation of steroidogenesis. Whereas ACTH acts by way of cAMP, AII appears to operate through protein kinase C. The phorbol ester, 12-O-tetradecanoylphorbol-13 acetate (TPA), and the calcium ionophore, A23187, each stimulate steroidogenesis and, when added together, act synergistically. To test the relationship between the ACTH and AII pathways, we added the two hormones simultaneously and measured steroid production. When the hormones were present at submaximal concentrations, their effects were additive. At maximal doses, steroid production was 40% above that elicited by either hormone alone. In contrast to the action of AII in the glomerulosa cell where it inhibits ACTH-stimulated cAMP formation, AII causes no inhibition in the fasciculata. Cycloheximide inhibits steroidogenesis stimulated by AII or a mixture of TPA and A23187. Scatchard analysis of the binding of 125I-AII to particulates from adrenal cortical fasciculata indicates the presence of a single class of binding sites (Kd = 0.6 X 10(-8) M). Binding is not inhibited by ACTH. Biotin-containing AII analogs that bind specifically to the particulates have been evaluated as potential tools for avidin-biotin affinity chromatography of the receptor. One of these, [N epsilon-6-(biotinylamido)hexyllys1, Val5] AII, is a promising candidate for receptor isolation.     

Two possible actions for circulating angiotensin II in the control of vasopressin release

The supraoptic-hypophyseal tract is a primary system for the synthesis and release of vasopressin. Angiotensin II (AII) has been shown to release vasopressin when injected into the cerebral ventricles (IVT). However, intravenous (IV) AII injections have not produced consistent results. The present studies were conducted to examine the effects of AII delivered by either route on the unit activity of supraoptic nucleus (SON) magnocellular neurons. Rats were prepared with intracranial cannulas to insure delivery of drugs to the left lateral ventricle and with polyethylene catheters in the left jugular vein, femoral vein, and femoral artery for systemic injections and arterial pressure recordings. A ventral approach permitted recording from the SON without violating the ventricular-SON partition. Magnocellular neurons were electrophysiologically identified. In the majority of identified cells, IVT AII increased activity. In others pressor doses of AII IV inhibited firing while blood pressure was elevated. After sino-aortic denervation, AII IV excited SON neurons. Based on latency, and the fact that lesioning the anteroventral third ventricle blocked the action of AII IVT, the results indicate that AII IVT acts on a periventricular site to influence SON magnocellular neurons. Furthermore, systemic AII may have two effects on SON neurons: a central excitatory action, and an inhibition due to a baroreceptor reflex.     

Angiotensin II-norepinephrine relationship in the central nervous system

The effects of angiotensin II (AII) and bilateral nephrectomy on [3H] norepinephrine (NE) uptake in hypothalamus and medulla oblongata were studied in male rats. The endogenous NE content in hypothalamus increased 4, 24 and 48 h after nephrectomy with a simultaneous decreasing of plasma renin activity. Intraventricularly infused [3H] NE uptake increased in hypothalamus and medulla oblongata of nephrectomized animals in cytoplasmatic compartment as in granular stores, while it decreased in hypothalamus of AII-infused animals. [3H] NE metabolites radioactivity decreased in nephrectomized animals if they are compared with AII-infused ones. These changes were independent of systolic arterial pressure that was not modified in none of the groups. The study of the ratio granular/cytoplasmatic [3H] NE and metabolites radioactivity shows that AII probably acts on cellular membrane uptake of NE. The modification of metabolites/NE ratio in both stores would be due to AII action on MAO activity. The effects of AII and nephrectomy on [3H] NE uptake can explain the inverse relationship between circulating AII levels and NE content in the central nervous system (CNS).     

Central administration of angiotensin II receptor antagonists and arterial pressure regulation: a note of caution.

The blunting of arterial pressure increases to a variety of pressor agents or the lowering of arterial pressure in some models of hypertension following intracerebroventricular administration of an angiotensin II (AII) antagonist, has been interpreted as prima facie evidence for the involvement of the central AII system in these situations. Central administration of vasopressin or carbachol (a cholinergic agonist) produces pressor effects which have been reported to be due to an increase in the activity of the sympathetic nervous system. We now report that central administration of AII antagonists [either (Sar-1, Ile-8) AII or (Sar-1, Ala-8) AII] in rats prevents the majority (greater than 70%) of the pressor effects of intraventricular vasopressin or carbachol. These results can be interpreted in two ways. The first is that all of these pressor agents use a central angiotensinergic mechanism(s) to increase sympathetic nervous system activity. An alternative hypothesis is that centrally administered AII antagonists non-specifically inhibit sympathetic nervous system function.     

Phosphorylation of adrenal histone H3 is affected by angiotensin, ACTH, dibutyryl cAMP, and atrial natriuretic peptide

Angiotensin (AII) and atrial natriuretic peptide (ANP) exert opposite effects on phosphorylation of a 17.6 kDa nuclear protein from bovine adrenal glomerulosa cells. The protein was separated by sodium dodecyl sulfate electrophoresis and blotted onto polyvinylidene difluoride, and the N-terminal sequence was obtained. This sequence corresponded to histone H3. Another polyacrylamide gel electrophoresis system was used to confirm that AII stimulated the phosphorylation of histone H3. ACTH[1-24] stimulated phosphorylation of the same protein. Dibutyryl cAMP stimulated phosphorylation of a 17.6-kDa protein, and two gel electrophoresis systems confirmed that the protein affected was histone H3. In situ peptide mapping using papain, of either purified standard histone H3 or of the adrenal 17.6-kDa protein, produced the same major fragment as observed by silver staining. Therefore, the 17.6-kDa protein that is affected by AII, ANP, ACTH, and dibutyryl cAMP is histone H3. This finding suggests that in addition to their mutually antagonistic effects on acute steroidogenesis, AII and ANP may exert opposite effects on adrenal cell functions involving the nucleus.     

Angiotensin II and norepinephrine antagonize the secretory effect of VIP in rat ileum and colon

Vasoactive intestinal polypeptide (VIP) induces intestinal secretion of water and electrolytes in experimental animals and man. We assessed the ability of angiotensin II (AII) and norepinephrine (NE) to block the secretion evoked by VIP, in vivo. Ileal and colonic segments in rats were perfused in situ for two hours with a physiological buffer containing [14C]-PEG-4000 as a volume marker. Saline (0.9% NaCl) was infused intravenously during the first hour and VIP or a combination of VIP plus AII or NE was infused during the second hour. All (0.7 ng/kg/min) alone enhanced water absorption significantly (p less than 0.01) in the ileum and an appreciable, although not a statistically significant, effect was observed in the colon. AII antagonized the secretory effects of VIP in the ileum as well as in the colon. Norepinephrine (5 micrograms/kg/min) also reversed the effect of VIP on the small intestine and colon. Although the mechanism by which AII antagonizes the secretory effects of VIP has not been identified, it is probable that AII promotes absorption, at least in part secondary to release of mucosal NE.     

Angiotensin II receptors and mechanisms of action in adrenal glomerulosa cells

The plasma-membrane receptors, coupling mechanisms, and effector enzymes that mediate target-cell activation by angiotensin II (AII) have been characterized in rat and bovine adrenal glomerulosa cells. The AII holoreceptor is a glycoprotein of Mr approximately 125,000 under non-denaturing conditions. Photoaffinity labeling of AII receptors with azido-AII derivatives has shown size heterogeneity among the AII binding sites between species and target tissues, with Mr values of 55,000 to 79,000. Such variations in molecular size probably reflect differences in carbohydrate content of the individual receptor sites. The adrenal AII receptor, like that in other tissues, is coupled to the inhibitory guanine nucleotide inhibitory protein (Ni). However, studies with pertussis toxin have shown that stimulation of aldosterone production by AII is not mediated by Ni but by a pertussis-insensitive nucleotide regulatory protein of unidentified nature. Although Ni is not involved in the stimulatory action of AII on steroidogenesis, it does mediate the inhibitory effects of high concentrations of AII upon aldosterone production. The actions of AII on adrenal cortical function are thus regulated by at least two guanine nucleotide regulatory proteins that are selectively activated by increasing AII concentrations. The principal effector enzyme in AII action is phospholipase C, which is rapidly stimulated in rat and bovine glomerulosa after AII receptor activation. AII-induced breakdown of phosphatidylinositol bisphosphate (PIP2) and phosphatidylinositol phosphate (PIP) leads to formation of inositol 1,4,5-trisphosphate (IP3) and inositol 1,4-bisphosphate (IP2). These are metabolized predominantly to inositol-4-monophosphate, which serves as a marker of polyphosphoinositide breakdown, whereas inositol-1-phosphate is largely derived from phosphatidylinositol hydrolysis. The AII-stimulated glomerulosa cell also produces inositol 1,3,4-trisphosphate, a biologically inactive IP3 isomer formed from Ins-1,4,5-trisphosphate via inositol tetrakisphosphate (IP4) during ligand activation in several calcium-dependent target cells. The Ins-1,4,5-P3 formed during AII action binds with high affinity to specific intracellular receptors that have been characterized in the bovine adrenal gland and other AII target tissues, and may represent the sites through which IP3 causes calcium mobilization during the initiation of cellular responses.     

In vivo actions of angiotensin II on glomerular function

Investigations in which a variety of experimental approaches were used, i.e., micropuncture techniques, analysis of intrarenal hormonal receptor, and electron microscopic analysis of renal morphology, have substantiated a major role for angiotensin II (AII) within the kidney in the regulation of vascular resistances, glomerular function, and even tubular reabsorption. It is also clear that AII exerts a significant influence on glomerular hemodynamics in a variety of altered physiological and pathophysiological states. Recent studies suggest a rather complex interaction between AII and hormonal and adrenergic effects at the glomerular level. AII may also play an important functional role in the pathogenesis of certain forms of acute renal failure. The specific mechanism whereby AII decreases the glomerular ultrafiltration coefficient, however, remains to be fully elucidated. Although in vitro and in vivo studies have suggested that the glomerular effects of AII may be associated with contraction of glomerular mesangial cells, recent in vivo quantitative evaluation has suggested that a uniform vasoconstriction of glomerular capillaries with proportional reductions in glomerular surface area is probably not the sole mechanism for the AII-induced reductions in glomerular ultrafiltration coefficient.     

Inhibition by angiotensin II of some vasopressin effects on renal function in sheep.

The effects of intravenous infusions of arginine vasopressin (AVP) alone and with angiotensin II (AII) on renal function were studied in conscious Merino ewes. AVP at 11.5 pmol.min-1 caused an increase in water and electrolyte output which was associated with a rise in glomerular filtration rate (GFR), solute clearance, solute-free water reabsorption and tubular sodium reabsorption. Addition of AII of 100 ng.min-1 generally reversed all of these effects. The filtration fraction, which rose during AVP infusion, increased further when AII was added due to a greater fall in renal plasma flow than in GFR. The diuretic and electrolyte-excreting effects of infused AVP appeared to be brought about by an increase in GFR. It is suggested that this inappropriate effect of AVP, which is secreted in response to water deprivation, could be countered by the simultaneous production of AII.     

Identification of macrophage receptors for angiotensin: a potential role in antigen uptake for T lymphocyte responses?

To determine if macrophages express receptors for peptide antigens, guinea pig peritoneal exudate cells (PEC) were examined for their uptake of the octapeptide angiotensin II (AII). PEC were incubated with [3H]AII, with or without nonradioactive AII as a cold inhibitor, for varying lengths of time before harvesting to determine the cell-associated [3H]AII counts per minute. The PEC-associated [3H]AII increased from 90 to 120 min of incubation, then plateaued on additional incubation to 3.5 hr. Inclusion of nonradiolabeled AII into the culture decreased the cell-associated [3H]AII by 80 to 90% at all time points. The uptake of [3H]AII was temperature-sensitive, with maximum cell-associated [3H]-AII occurring at 37 degrees C and reduced uptake occurring at 4 degrees C. The association of [3H]AII with PEC was specific and saturable, and the inhibitory dose for reducing the cell-associated [3H]AII by 50% with nonradiolabeled AII was around 6 X 10(-6) M. Various AII analogs were also employed as inhibitors to determine the fine specificity of [3H]AII binding, and only those analogs with nonaromatic amino acid substitutions for the carboxyl terminal Phe8 showed reduced inhibitory activity, indicating that Phe8 is important for binding. Scatchard analysis of binding indicated that two classes of receptors interacted with AII: a low number of receptors with Ka approximately equal to 3.5 X 10(8) M-1, and a large number of relatively low affinity of binding showing a Ka approximately equal to 5 X 10(5) M-1. The cellular binding activity was associated with isolated PEC plasma membranes, and after density gradient fractionation of solubilized membranes, AII binding activity was primarily associated with molecules of m.w. of around 50,000. PEC were separated into macrophages and lymphocytes by adherence, and all of the [3H]AII binding activity was associated with the macrophage-enriched cells. These results show that macrophages express specific receptors for AII and related peptides that are responsible for most of the uptake of AII by macrophages. We discuss the relevance of this receptor for the immunologically important uptake of AII by macrophages, and a potential physiologic role in angiotensin-converting enzyme production.     

Identical mesenteric,femoral and renal vascular responses to angiotensins II and III in the dog

The effects of angiotensin II (AII) and its 1-des Asp analog (AIII) given intra-arterially (0.3–30 ng/kg) were compared in the mesenteric, femoral, and renal vascular beds in anesthetized dogs in which flow was measured with an electromagnetic flowmeter. As has been shown previously, AII and AIII produced similar changes in renal blood flow. In view of the reduced pressor activity of AIII it was surprising to find strikingly similar responses to AII and AIII in the mesenteric and femoral vascular beds. We conclude that the difference in pressor activity of these agents is attributable to something other than differences in their peripheral vascular receptor, and perhaps may be due to differences in their central actions.