Stimulation of spontaneous and dopamine-inhibited prolactin release from anterior pituitary reaggregate cell cultures by angiotensin peptides

In superfused anterior pituitary reaggregate cell cultures angiotensin II (AII) stimulated both spontaneous and dopamine-inhibited prolactin (PRL) release from subnanomolar concentrations. Angiotensin I (AI) and angiotensin III (AIII) also stimulated PRL release. The magnitude and rate of response to AI was equal to or only slightly lower than that to AII. However, the angiotensin converting enzyme (ACE) inhibitors captopril and teprotide (1 microM) completely abolished the PRL response to 0.1 nM AI and strongly reduced that to 1 nM AI. The intrinsic activity of AIII was lower than that of AII but could be enhanced by adding 2 microM of the aminopeptidase inhibitor amastatin to the superfusion medium. After withdrawal of AIII, PRL secretion rate rapidly returned to baseline levels, whereas after withdrawal of AI or AII, secretion fell to a level remaining significantly higher than basal release. The present findings indicate that stimulation of PRL release by AI is weak unless it is converted into AII by ACE and that aminopeptidase may be important in determining the magnitude and termination of the PRL response. Furthermore, the active peptides induce a different pattern of response.     

Postnatal development of renin-angiotensin system in rats

The changes occurring in several components of the rat renin-angiotensin system (RAS) were studied for the brief postnatal period, between the fourth and tenth week of life. The parameters were: plasma renin activity (PRA), plasma renin concentration (PRC), plasma renin substrate (PRS) and the plasma angiotensin II concentration (AII). A gradual decrease in PRA with age was noticed. Between the fourth and the eighth weeks of life, this was attributed to a corresponding decline in both PRC and PRS. However, between the eighth and tenth weeks, no changes in PRA could be detected, but PRC and PRS increased, perhaps as a consequence of the changes in renal function and the AII increase observed. In this second period, simultaneously with the RAS changes described, there was reduced sodium chloride excretion as the glomerular filtration rate (GFR) stabilized. The data presented suggest that this postnatal period is critical, in rats, for the maturation of the RAS component control mechanisms; they appear to be closely related to the development of the renal function.     

Alteration of the angiotensin cascade by schistosome ova

In schistosomiasis mansoni, the parasite ova lodge in the microvasculature of organs and induce granulomas. It is assumed that factors derived from the ova activate circulating mediators that help initiate the inflammation. Components of the angiotensin system are in plasma and may have a role in inflammation. Therefore, whether ova could alter plasma angiotensin metabolism was determined. Incubation of 1 ml of plasma with up to 1,000 ova increased plasma AII (angiotensin II) concentration as measured by radioimmunoassay. HPLC analysis of [125I]AI (angiotensin I) metabolism in plasma suggested that ova can increase the conversion of AI to AII. Ova did not alter plasma angiotensin-converting enzyme activity. The ova themselves did not contain or release components of the angiotensin system during culture. It is concluded that interaction of ova with plasma can affect the angiotensin cascade.     

Effects of angiotensin I-converting enzyme inhibitor, SQ 14225, in nomal men.

Effects of an orally active angiotensin I-converting enzyme inhibitor, SQ 14225, on the actions of angiotensin I (AI) infused intravenously for 120 to 390 min were studied in 5 normal men. When 20 ng/kg/min of AI infusion was started immediately after a single oral administration of 100 mg of SQ 14225, a significant rise in blood pressure (BP) was observed for the first 15 min, but BP began to fall from 17 min and returned to the pretreatment level at 45 min. This BP level continued at least to 120 min and in one subject to 180 min. In this subject BP began to rise again from 185 min and reached the level of 15 min at 390 min. Plasma AI level increased gradually from 45 min. At 15 min plasma renin activity (PRA) decreased and plasma aldosterone (PA) increased, but then PRA began to increase and PA began to decrease. At 120 min the values of PRA and PA were similar to the pretreatment values. In one subject plasma AI and PRA began to decrease and PA began to increase after 120 or 180 min. On the other hand, in the 5 men sole AI infusion caused a continued BP rise, PRA decrease and PA increase, and sole SQ 14225 administration caused increases in plasma AI and PRA and a decrease in PA but no BP change. From these results it was concluded that complete blockade and partial inhibition of AI conversion by 100 mg of oral SQ 14225 lasted for about 2.5 and 6.5 hr, respectively and that BP rise, PRA suppression and aldosterone stimulation after AI infusion were entirely due to the actions of angiotensin II converted from AI.     

Action of a human plasma fraction on tetradecapeptide,angiotensin I and angiotensin II

A protein fraction designated PF70 was isolated from human plasma and partially purified on Sephadex G-100. PF70 proteins, molecular weight 37, 000 to 41, 500, formed angiotensin I (AI) and angiotensin II (AII) from ¹⁴C-tetradecapeptide renin substrate (TDP) at 37 C. Hydrolysis was maximal at pH 6.9 but there was no change in the relative quantity of AI and AII formed at different pH values. Data indicate that AI was formed first and at a faster rate than AII, but typical converting enzyme activity was not detected. Radiolabeled AII was converted to Des-Asp¹-angiotensin II (angiotensin III); [³H]AI was degraded to a single tritiated product, possibly the nonapeptide. These aspartyl hydrolase reactions were apparently inhibited by TDP and were not involved in AI or AII generation from TDP. It is concluded that these enzymic activities represent two or more enzymes that are associated with the renin-angiotensin system.     

Cyclical changes in the renin-angiotensin-aldosterone system during the menstrual cycle of the baboon (Papio hamadryas)

Abstract: This study characterizes the renin-angiotensin-aldosterone system during the normal menstrual cycle in the baboon. Ten animals received a daily dose of an ACE inhibitor or placebo in a randomized blind cross-over design. Data were obtained during the mid-follicular and early luteal phases of normal non-pregnant menstrual cycles. All examinations and blood collections were performed with ketamine sedation: 7–kg by im injection. Blood pressure was recorded by sphygmomanometer. Serum ACE activity was measured by spectrophotometry. Aldosterone (ALDO), angiotensin I (AI), and angiotensin II (AII) were measured by radioimmunoassay. Plasma renin activity (PRA) was measured by AI generation. The renin-angiotensin-aldosterone system was found to be activated in the follicular phase and suppressed during the luteal phase of the normal non-pregnant menstrual cycle in the baboon.     

Stimulation of splenic prostaglandin release by angiotensin and specific inhibition by cysteine8-AII

The angiotensin induced release of prostaglandin E (PGE) like material from the isolated perfused rabbit spleen was studied. The PG releasing potency of angiotensin I (AI) was found to be 2–4 % that of angiotensin II (AII). The PG release by AI was shown not to be due to the conversion of AI to AII, but rather to the direct effect of AI. Both AI and AII induced PG release were found to be inhibited by cysteine⁸-AII. The PG release by epinephrine was not blocked by the angiotensin antagonist. Indomethacin (an inhibitor of PG biosynthesis) blocked the PG release induced by angiotensin or epinephrine.     

Effects of continuous angiotensin I-converting enzyme blockade on blood pressure, sympathetic activity and renin-angiotensin system in stroke-prone spontaneously hypertensive rats

The purpose of this study was to examine the effects of continuous angiotensin converting enzyme (ACE) blockade in stroke-prone spontaneously hypertensive rats (sp-SHR) on the renin-angiotensin system and on sympathetic activity. The pressor response to angiotensin II (AII) and norepinephrine (NE) were also examined after chronic blockade of ACE and compared to that of saline-treated controls. Captopril treatment had no effect on body weight. Serum ACE was significantly reduced on day 1; an effect that persisted through day 6 and day 10. Plasma renin activity (PRA) was elevated significantly on day 1 and remained at this high level throughout the 10 day observation period. Plasma NE was not altered by the chronic ACE blockade except on day 1, where there was a slight elevation of plasma NE in both groups. Pressor responses to AII and NE were not changed after chronic captopril treatment. It is observed that chronic inhibition of the renin-angiotensin system with captopril in sp-SHR resulted in a reduction of blood pressure, reduced serum ACE activity and elevated PRA. The constant plasma NE levels suggest that chronic inhibition of the renin-angiotensin system does not affect sympathetic activity. This study also indicates that long term inhibition of ACE does not alter pressor responses to either AII or NE.     

Effects of an angiotensin II antagonist; [sarcosine 1, isoleucine 8] angiotensin II, on blood pressure, plasma renin activity and plasma aldosterone concentration in hypertensive and normotensive subjects taking oral contraceptives.

To examine the involvement of renin-angiotensin-aldosterone system in the etiology of oral contraceptive induced hypertension, normal women (Group I), normotensive (Group II) and hypertensive (Group III) women taking Ovulen (R) were infused with a competitive angiotensin II (AII) antagonist, [1-sarcosine, 8-isoleucine] angiotensin II. The angiotensin II antagonist was infused at a rate of 600 ng/kg/min for 30 min 1.5 hrs after intravenous injection of 40 mg of furosemide. Blood pressure was monitored and pre-infusion and post-infusion plasma renin activity (PRA) and plasma aldosterone concentration (PAC) were determined. Pre-infusion PRA and PAC showed no significant differences among these three groups. In response to the AII antagonist infusion blood pressure rose in Groups I and II, but blood pressure responses in Group III were variable. Four out of the total 6 subjects had pressor responses and only one subject had a significant blood pressure reduction. In both Groups I and II, PRA decreased and PAC rose after infusion of the antagonist. In Group III, PRA decreased to a lesser degree and PAC showed no consistent change. These data suggest that the renin-angiotensin-aldosterone system in hypertensive women or oral contraceptives is different from that of the normotensive users. However, the pathophysiology of oral contraceptive induced hypertension is not homogenous and angiotensinogenic hypertension is uncommon.     

Conversion of angiotensin I to angiotensin II by cathepsin A isoenzymes of porcine kidney

We have reported the existence of a carboxypeptidase in a human renal extract that converts Angiotensin I (AI) to Angiotensin II (AII) in two steps with des-leu-AI (dl-AI) being formed as an intermediate. Since this carboxypeptidase had properties similar to cathepsin A, the ability of cathepsin A to metabolize AI was studied. Cathepsin A was purified from hog kidney with enzyme activity being monitored using both benzyloxycarbonyl-glutamyl-tyrosine (ZGT) and AI as substrates. The procedure separated the expected large and small molecular weight forms of cathepsin A as well as two additional isoenzymes. All of the isoenzymes had carboxypeptidase activity with ZGT, AI, and dl-AI. No detectable cleavage of AII was observed. Cathepsin A,S (small) activity with ZGT or AI as substrate was inhibited to a similar extent by diisopropylfluorophosphate, mersalyl acid, and a decapeptide renin inhibitor. It is concluded that the renal angiotensin carboxypeptidase activity is catalyzed by cathepsin A. By its ability to convert AI to AII, cathepsin A may be a component of the intrarenal renin-angiotensin system.     

The action of angiotensin on the isolated perfused cat heart

The effects of angiotensin I (AI) and angiotensin (AII) on myocardial contractility, heart rate and coronary perfusion were observed in the isolated perfused cat heart. AII (10^?11 mol) and AI (10^?10 mol) both caused slowly developing sustained increases in systolic pressure of approximately 55%. There were inconsistent small increases in heart rate. Coronary perfusion was initially diminished, but later increased to above control values during the positive inotropic effect. The actions of both AI and AII were blocked by 1 sar 8 ile AII (10^?9 mol). The converting enzyme inhibitors SQ 20881 (10^?8 mol) and SQ 14225 (10^?8 mol) blocked the effect of AI. The actions of AII or AI were not blocked by α or β adrenergic blockade or by prior treatment with reserpine.     

Characterization of metalloelastase-like activity from the plasma of a patient with Tangier disease.

An enzymatic activity with releases p-nitroaniline from 3-carboxypropionyl-trialanine p-nitroanilide (Suc[Ala]3NA) was characterized in blood plasma of patients with Tangier disease. This activity results from the sequential action of a metalloendopeptidase (MP) and an aminopeptidase (AP). These proteases were purified 134- (MP) and 82-fold (AP) from low density and very low density lipoproteins (LDL and VLDL) depleted Tangier plasma by DEAE-Trisacryl chromatography and gel filtration. MP and AP could be separated by polyacrylamide gel electrophoresis. MP shares some analogy with neutral endopeptidase (membrane metalloendopeptidase, EC 3.4.24.11) and is able to degrade human plasma fibronectin (mainly to fragments of 185, 168 and 128 kDa) as evidenced on Western blots. It cannot hydrolyse 3H-labelled insoluble elastin and apolipoprotein AII, but did cleave a dinitrophenyl-octapeptide as well as apolipoprotein AI to 25-kDa and 24-kDa fragments formed sequentially. It may therefore be partially responsible for the in vivo degradation of apoAI observed in Tangier disease.     

In vitro transformation of apoA-I-containing lipoprotein subpopulations: role of lecithin:cholesterol acyltransferase and apoB-containing lipoproteins

Two populations of apoA-I-containing lipoproteins are found in plasma: particles with apoA-II [Lp(AI w AII)] and particles without apoA-II [Lp(AI w/o AII)]. Both are heterogeneous in size. However, their size subpopulation distributions differ considerably between healthy subjects and patients with coronary artery diseases. The metabolic basis for such alterations was studied by determining the role of lecithin:cholesterol acyltransferase (LCAT) and apoB-containing lipoproteins (LpB) in the size subpopulation distributions of Lp(AI w AII) and Lp(AI w/o AII). ApoB-free and LCAT-free plasmas, prepared by affinity chromatography, and whole plasma were incubated at 4 degrees C and 37 degrees C for 24 hr. After incubation, Lp(AI w AII) and Lp(AI w/o AII) were isolated by anti-A-II and anti-A-I immunosorbents. Their size subpopulation distributions were studied by nondenaturing gradient polyacrylamide gel electrophoresis. At 4 degrees C most Lp(AI w AII) particles were in the range of 7.0-9.2 nm Stokes diameter. Incubation of plasma at 37 degrees C resulted in an overall enlargement of particles up to 11.2 nm and larger. These particles were enriched with cholesteryl ester and triglyceride and depleted of phospholipids and free cholesterol. Removal of LpB or LCAT from plasma prior to incubation greatly reduced their enlargement. At 4 degrees C, Lp(AI w/o AII) contained mostly particles of 8.5 and 10.1 nm. Incubation at 37 degrees C abolished both subpopulations with the formation of a new subpopulation of 9.2 nm. This transformation was identical in apoB-free plasma but was not seen in LCAT-free plasma. Our study shows that transformation of Lp(AI w AII) requires both LCAT and LpB. However, LpB is not necessary for the transformation of Lp(AI w/o AII) in vitro. The relevance of these in vitro studies to in vivo lipoprotein metabolism was demonstrated in a subject with hepatic triglyceride lipase deficiency.     

Local generation of angiotensin II as a mechanism of aldosterone secretion in rat adrenal capsules.

Angiotensin-converting enzyme (ACE) is found in the adrenal gland, but the role of adrenal ACE in the formation of angiotensin II (AII) and subsequent stimulation of aldosterone is unclear. We examined the effect of adrenal ACE activity on aldosterone secretion by superfusing rat adrenal capsules with angiotensin I (AI) in the presence and absence of the ACE inhibitor, lisinopril. Angiotensin I (10 microM) stimulated aldosterone secretion from 914 +/- 41 to 1465 +/- 118 pg/min/capsule (P less than 0.05). Simultaneous superfusion of AI plus lisinopril (100 microM) inhibited the stimulation of aldosterone by 73% (P less than 0.05). Perfusion of the capsules with angiotensin II (1 microM) stimulated aldosterone from 893 +/- 180 to 1466 +/- 181 pg/min/capsule (P less than 0.01). In contrast, simultaneous superfusion of AII plus lisinopril (100 microM) did not inhibit the AII stimulation of aldosterone. The failure of lisinopril to inhibit AII stimulation of aldosterone argues against a toxic or nonspecific action of lisinopril. The inhibition of AI stimulation of aldosterone release by lisinopril is mostly due to lisinopril inhibition of ACE and resulting decreased conversion of AI to AII. These results demonstrate that adrenal ACE may generate AII from AI in the adrenal gland, and this locally produce AII stimulates aldosterone.     

Reversible hypertension caused by calcium overloading in a patient with postoperative hypoparathyroidism

A 37-year-old woman with postoperative hypoparathyroidism had hypertension, and elevated plasma renin activity (PRA) and subsequent hyperaldosteronism during a two-month hypercalcemic period caused by vitamin D and excessive calcium supplements. The hypertension with elevated PRA, however, was resistant to the angiotensin II (AII) analog [Sar1, Ile8] ALL. PRA further increased and plasma aldosterone decreased in response to the [Sar1, Ile8] ALL. When the patient became normocalcemic, normotensive and normoreninemic, calcium gluconate (5 mg calcium/kg/h) was infused for one hour. The calcium infusion reproduced hypercalcemic hypertension mediated by an increase in total peripheral resistance. These observations suggest that the hypertension observed while taking vitamin D and excessive calcium supplements may be caused by a direct effect of calcium on peripheral blood vessels and the renin-angiotensin system may play a negligible role.     

Interaction between high-density lipoprotein subpopulations in apo B-free and abetalipoproteinemic plasma.

Two populations of high-density lipoprotein (HDL) particles exist in human plasma. Both contain apolipoprotein (apo) A-I, but only one contains apo A-II: Lp(AI w AII) and Lp(AI w/o AII). To study the extent of interaction between these particles, apo B-free plasma prepared by the selective removal of apo B-containing lipoproteins (LpB) from the plasma of three normolipidemic (NL) subjects and whole plasma from two patients with abetalipoproteinemia (ABL) were incubated at 37 degrees C for 24 h. Apo B-free plasma samples were used to avoid lipid-exchange between HDL and LpB. Lp(AI w AII) and Lp(AI w/o AII) were isolated from each apo B-free plasma sample before and after incubation and their protein and lipid contents quantified. Before incubation, ABL plasma had reduced levels of Lp(AI w AII) and Lp(AI w/o AII), (40% and 70% of normals, respectively). Compared to the HDL of apo B-free NL plasma, ABL HDL had higher relative contents of free cholesterol, phospholipid and total lipid, and contained more particles with apparent hydrated Stokes diameter in the 9.2-17.0 nm region. These differences were particularly pronounced in particles without apo A-II. Despite their differences, the total cholesterol contents of Lp(AI w AII) increased, while that of Lp(AI w/o AII) decreased in all five plasma samples and the amount of apo A-I in Lp(AI w AII) increased by 6-8 mg/dl in four during the incubation. These compositional changes were accompanied by a relative reduction of particles in the 7.0-8.2 nm Stokes diameter size region and an increase of particles in the 9.2-11.2 nm region. These data are consistent with intravascular modulation between HDL particles with and without apo A-II. The observed increase in apo A-II-associated cholesterol and apo A-I, could involve either the transfer of cholesterol and apo A-I from particles without apo A-II to those with A-II, or the transfer of apo A-II from Lp(AI w AII) to Lp(AI w/o AII). The exact mechanism and direction of the transfer remain to be determined.     

Immunoaffinity fractionation of high-density lipoprotein subclasses 2 and 3 using anti-apolipoprotein A-I and A-II immunosorbent gels

High-density lipoprotein (HDL) subclasses 2 and 3 prepared by density gradient ultracentrifugation have been further fractionated by immunoaffinity chromatography using antibody affinity gels targetting the major HDL apolipoproteins, A-I and A-II. Fractions containing A-I without A-II (AI w/o AII) and A-I with A-II (AI w AII) were isolated from both density ranges. Whereas there were similar concentrations of the major subfraction (HDL3(AI w AII] in both males and females, the remaining subfractions were present in higher concentrations in females as compared to males, in the order HDL3 (AI w/o AII) less than HDL2(AI w AII) less than HDL2(AI w/o AII). The difference was most marked for HDL2 (AI w/o AII), where plasma concentrations in females were almost 3-fold greater than in males. Compositional analyses indicated that the plasma concentrations of the fractions, rather than their compositions, were the major determinants of male-female differences in HDL levels. In contrast, fractions defined by similar apolipoprotein criteria and isolated from different density subclasses (i.e., HDL2(AI w/o AII) vs. HDL3(AI w/o AII) and HDL2(AI w AII) vs. HDL3(AI w AII] showed major compositional differences. This is suggestive of distinct lipoprotein particles.     

Isolated liver granulomas of murine Schistosoma mansoni contain components of the angiotensin system

Angiotensin I (AI) and angiotensin II/III (AII/III) were detected by radioimmunoassay in homogenates of isolated liver granulomas from mice infected for 8 wk with Schistosoma mansoni. Angiotensin I converting enzyme (ACE) activity, which could be completely inhibited by captopril, a specific ACE inhibitor, was also present as determined by radioassay. Spontaneous angiotensin I-generating activity was detected in homogenates that received supplemental angiotensinogen (protein renin substrate). This activity was partly inhibited by pepstatin, an acid protease inhibitor, indicating the presence of angiotensinogenase(s). Trypsinization of homogenates resulted in some AI generation, which suggests that homogenates had AI precursor. Treatment of infected mice with MK421, another specific ACE inhibitor, decreased granuloma ACE activity and AII content and size. AII, and to a lesser extent AIII, inhibited mouse peritoneal macrophage migration in an in vitro assay. These data support the contention that components of the angiotensin system are in the granuloma and may serve a function in regulation of the inflammation.     

Comparison of the biological effects of two angiotensin II analogues in hypertensive patients with sodium depletion

The effects on blood pressure (BP), plasma aldosterone concentration (PAC) and plasma renin activity (PRA) of two angiotensin II analogues (AII A), i.e., 1-sarcosine, 8-isoleucine angiotensin II (Sar¹, I1e⁸-AII) and 1-sarcosine, 8-alanine angiotensin II (Sar¹, Ala⁸-AII), were investigated in patients with hypertension with various etiologies on sodium depletion. The changes of BP, PAC and PRA on infusion of Sar¹, Ile⁸-AII and Sar¹, Ala⁸-AII were very similar. With both compounds, there were significant inverse correlations between the pre-infusion PRA and the changes in BP and PAC, and a significant positive correlation between the pre-infusion PRA and change in PRA. The slopes of the regression lines for the correlations of changes in BP, PAC and PRA, plotted as functions of the pre-infusion PRA for Sar¹, Ile⁸-AII and Sar¹, Ala⁸-AII were not statistically different. In clinical investigations, the two compounds seemed equally useful for detecting renin-dependency in hypertension.     

Intensity dependence of auditory evoked potentials in behaving cats

The intensity dependence of auditory evoked potentials (AEPs) recorded epidurally over the primary (AI) and secondary (AII) areas of the auditory cortex was studied in behaving cats during wakefulness, sleep and anesthesia. Four kHz tones of 50, 60, 70, and 80 dB SPL, presented in random order every 2 ± 0.2 s by a bone conductor, elicited clear changes of the AEP amplitudes with increasing stimulus intensity, but individual components displayed different responses curves. AEP components from the AI region showed saturation of their amplitude with stimulus intensity (P13, P34) or no amplitude increase (N19), while amplitude and intensity were linearly related in the AII area. The intensity dependence of the first positive component (P12/P13) was consistently stronger for the AEP recorded from the AI than from the AII area, while later components exhibited no difference between AI and AII. During slow wave sleep, the intensity dependence of this first positive component increased in the two areas, while that of later components decreased. Pentobarbital anesthesia abolished almost all later components and depressed the intensity dependence of the first positive component both in the AI and AII area. These results indicate that (1) clear intensity dependence of AEP exists in the cat auditory cortex and (2) this intensity dependence, especially that of the first positive AEP component, shares functional similarities to the human augmenting/reducing phenomenon in the auditory modality concerning regional differences and sleep-waking cycle.