The renin-angiotensin system (first of two parts)

An improved method for determination of active and total renin concentration in human plasma using an excess of sheep substrate

A method for measurement of renin concentration (PRC) in human plasma has been developed and validated experimentally and theoretically. Like most of the previous methods, the present method is based on a radioimmunoassay of angiotensin I generated during incubation of plasma with an excess of renin substrate. In the present study we used, as the substrate, sheep angiotensinogen partially purified from anephric sheep plasma by ammonium sulfate fractionation and pepstatin-aminohexyl-agarose chromatography. The advantage of using sheep substrate is that it has an exceptionally high affinity for human renin. The partially purified substrate, which contained no detectable renin activity, improved the sensitivity, allowing quantification of renin in low-renin plasma. Possible interfering influences of plasma proteins on the radioimmunoassay were eliminated by the introduction of a simple deproteinization step. For determination of total renin concentration (TRC), inactive renin was activated by exposing plasma to low pH or trypsin. Normal values of PRC and TRC after careful selection of assay conditions were 2.9 +/- 0.4 and 33.9 +/- 6.1 ng angiotensin I X ml-1 X h-1, respectively. As an illustrative example of usefulness of the assay, PRC determination of a patient with a ectopic renin-secreting tumor is presented.

Mechanisms of elevated blood pressure in human essential hypertension

This review of the mechanisms of elevation of blood pressure in human essential hypertension first focuses on individual mechanisms and their interrelations. The authors then try to identify those forms of essential hypertension in which the major determinants are known. When the most significant processes associated with elevated blood pressure in individual patients are understood, a rational approach to therapy can be undertaken even though the ultimate cause of the disorder is not understood.

Haemodynamic and humoral responses to chronic ketanserin treatment in essential hypertension

Ketanserin (120 mg/day) or placebo was given orally to 14 patients with mild to moderate essential hypertension according to a double blind crossover protocol, each treatment period lasting six weeks. Resting intra-arterial pressure in the recumbent position was reduced from 150/84 to 141/77 mm Hg; the hypotensive effect persisted throughout an uninterrupted graded exercise test to the point of exhaustion. The haemodynamic effects were similar at rest and during exercise. Overall, systemic vascular resistance decreased by 14%, heart rate fell by 5%, but stroke volume and cardiac output increased. Mean pulmonary arterial pressure and capillary wedge pressure were not significantly affected, but pulmonary vascular resistance decreased by 15%. The pressor response to methoxamine was significantly reduced by ketanserin. Both plasma noradrenaline and adrenaline concentrations increased, plasma renin activity and angiotensin II concentration decreased, and plasma aldosterone concentration was unchanged. The data indicate that ketanserin induces arteriolar dilatation, possibly related to an alpha-1-antagonistic action and to a reduced circulating angiotensin II concentration. The haemodynamic response is complex, and an increase in cardiac output limits the hypotensive effect. There is no firm evidence of an effect on venous tone as cardiac filling pressures do not change.

Synthesis of peptides related to the prosegment of mouse submaxillary gland renin precursor: an approach to renin inhibitors

The complete sequence of the structural gene coding for mouse submaxillary gland renin was recently reported and the amino acid sequence of preprorenin was deduced. This sequence includes a 45-amino acid peptide that corresponds to the prosegment of the renin precursor. To investigate whether peptides related to the renin prosegment are able to inhibit renin activity, we have synthesized four peptides having the following structures: Arg-Ile-Pro-OMe, butyloxycarbonyl(Boc)-Leu-Lys-Lys-Met-Pro-OMe, Boc-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe, and Boc-Glu-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe (corresponding to amino acids 12-14, 15-19, 12-19, and 11-19, respectively, of the renin prosegment). All four peptides were found to inhibit the activity of pure mouse submaxillary renin on a porcine synthetic tetra-decapeptide in vitro, and the most potent inhibitors exhibited IC50 values in the micromolar range. Enzymatic kinetic studies carried out using peptide 15-19 showed an uncompetitive or a mixed type of inhibition with a Ki value of 2.3 X 10(-6) M at 37 degrees C in 0.5 M citrate/phosphate buffer (pH 6.0).

Cloning and sequence analysis of cDNA for human renin precursor

The primary structure of human renin precursor has been deduced from its cDNA sequence. A library of cDNA clones was constructed from human kidney poly(A)+ RNA by applying the vector/primer method of Okayama and Berg. The library was screened for human renin sequences by hybridization with the previously cloned mouse renin cDNA. Of the 240,000 colonies screened, 35 colonies that were positive for hybridization were isolated. Two recombinant plasmids containing long inserts of about 1,300 and 1,600 base pairs were selected for sequence analysis. The amino acid sequence predicted from the cDNA sequence shows that the human renin precursor consists of 406 amino acids with a pre and a pro segment carrying 20 and 46 amino acids, respectively. A high degree of sequence homology was found upon comparison of the mouse and human renins. Close similarities were also observed in the primary structures of renin and aspartyl proteinases that have known three-dimensional structures, suggesting a similar tertiary structure for renin.

On the mechanism of serotonin-induced dipsogenesis in the rat

Subcutaneous administration of l-5-hydroxytryptophan (5-HTP), the precursor of serotonin, to female rats induces copious drinking accompanied by activation of the renin-angiotensin system. Neither a reduction in blood pressure nor body temperature accompanied administration of 5-HTP. The objective of the present study was to determine whether serotonin-induced dipsogenesis, like that of 5-HTP, is mediated via the renin-angiotensin system. Serotonin (2 mg/kg, SC)-induced drinking was inhibited by the dopaminergic antagonist, haloperidol (150 micrograms/kg, IP), which also inhibits angiotensin II-induced drinking. Both captopril (35 mg/kg, IP), an angiotensin converting enzyme inhibitor, and propranolol (6 mg/kg, IP), a beta-adrenergic antagonist, blocked serotonin-induced dipsogenesis. The alpha 2-adrenergic agonist, clonidine (6.25 micrograms/kg, SC), which suppresses renin release from the kidney, attenuated serotonin-induced water intake. The dipsogenic responses to submaximal concentrations of both serotonin (1 mg/kg, SC) and isoproterenol (8 micrograms/kg, SC) were additive rather than interactive suggesting that similar pathways mediate both responses. The serotonergic receptor antagonist, methysergide (3 mg/kg, IP), inhibited serotonin-induced drinking but had no effect on isoproterenol (25 micrograms/kg, SC)-induced dipsogenesis. However, neither serotonin (2 mg/kg, SC) nor isoproterenol (25 micrograms/kg, SC)-induced drinking was inhibited by cinanserin (25 micrograms/kg, IP). These data indicate that serotonin induces drinking in rats via the renin-angiotensin system. However, the results of the studies using methysergide suggest that serotonin appears to act at a point prior to activation of beta-adrenoceptors in the pathway leading to release of renin from the kidneys.

Vasodilator therapy of severe congestive heart failure: the special importance of angiotensin-converting enzyme inhibition with captopril

Successful ambulatory afterload reduction therapy of severe chronic congestive heart failure (CHF) required the extensive evaluation of hemodynamic effects of vasodilator agents, precise characterization of differential cardiocirculatory actions, and objective confirmation of extended salutary improvements of the heart failure state. This article describes results of a series of investigations with the angiotensin-converting enzyme (ACE) inhibitor captopril (CPT) in several patients with severe CHF. CPT causes predominant peripheral venodilation, resulting in marked decline in elevated left ventricular preload and modest augmentation of the depressed cardiac output. These hemodymanic effects of oral CPT are similar to the effects of nitroprusside and prazosin on increased ventricular preload, but the latter vasodilators cause greater rise in low cardiac pump output. Importantly, the beneficial cardiocirculatory action of oral CPT provided prolonged cardiac benefits with symptomatic improvements confirmed by objective enhancement in left ventricular function documented by cardiac catheterization, echocardiography, nuclear scintigraphy, and treadmill exercise. Thus, ACE inhibition with oral CPT successfully provides marked long-term augmentation of cardiac performance and clinical status in refractory CHF.

Comparative analysis of the hemodynamic actions of captopril and sodium nitroprusside in severe chronic congestive heart failure

The hemodynamic actions of the systemic vasodilators parenteral sodium nitroprusside (NP) and oral captopril (CPT) were compared in 11 patients with severe chronic congestive heart failure (CHF). While two agents produced similar reductions in mean blood pressure (NP, 90 to 70 mm Hg vs CPT, 88 to 74 mm Hg, p greater than 0.05) and left ventricular (LV) filling pressure (NP, 27 to 14 mm Hg vs CPT, 24 to 15 mm Hg, p greater than 0.05), they produce disparate effects on LV pump performance. NP raised cardiac index 35% (2.0 to 2.7 L/min/m2, p less than 0.005), whereas CPT increased this index 16% (1.9 to 2.2 L/min/m2, p less than 0.001). Concomitantly, the 31% elevation of stroke index produced by NP (26 to 34 ml/beat/m2, p less than 0.001) was greater (p less than 0.05) than the 15% rise produced by CPT (26 to 30 ml/beat/m2, p less than 0.001). Simultaneously, stroke work index showed similarly greater augmentation, and total systemic vascular resistance declined more with NP. These findings suggest that oral CPT is a predominant ventricular preload-lowering agent primarily likely to improve dyspnea related to severe pulmonary congestion in patients with advanced chronic CHF.

Complementary combined captopril and terbutaline therapy in severe chronic congestive heart failure

The hemodynamic effects of captopril (CPT) alone and in combination with the beta-adrenergic receptor agonist terbutaline (TBT) were evaluated in 10 patients with severe chronic congestive heart failure (CHF). The heart rate remained unchanged, while CPT lowered mean systemic blood pressure from 86 to 64 mm Hg (p less than 0.001) and decreased left ventricular filling pressure markedly from 27 to 19 mm Hg (p less than 0.001). The addition of TBT produced no further change in these variables (p greater than 0.05). Simultaneously, CPT augmented cardiac index (CI) from 2.1 to 2.9 L/min/m2 (p less than 0.001) and stroke index (SI) from 27 to 37 ml/beat/m2 (p less than 0.001). Concomitant CPT-TBT further raised CI to 3.2 L/min/m2 and SI to 40 ml/beat/m2 (both less than 0.001). Further, the CPT-effected decline in total systemic vascular resistance from 1577 to 841 dynes . sec . cm-5 (p less than 0.001) was not reduced additionally by CPT-TBT combination (p greater than 0.05). These results indicate than both CPT and TBT markedly augment cardiac function in CHF. Moreover, the salutary effects of the systemic vasodilator appear additive to the beneficial actions of the beta-adrenergic receptor agonist, thereby providing substantial augmentation of the function of the failing heart.

The purification and characterization of multiple forms of mouse submaxillary gland renin

Five forms of renin, A0, A, C, D and E, from mouse submaxillary gland were purified by a two-step procedure including chromatography on the immunoaffinity column and CM-cellulose column. Four renin fractions, A0, A, C and E were purified to homogeneity by the criteria of polyacrylamide gel electrophoresis, analytical isoelectric focusing and Ouchterlony double immunodiffusion. All these forms of renin have molecular weights of 40 000 as determined by gel filtration on Sephadex G-100 column. No high molecular weight renin could be demonstrated. Individual renin fractions showed similar angiotensin I formation activity, 52-158 ng angiotensin I/ng protein per h. No other protease activity could be detected with hemoglobin or casein as substrate. These purified proteins showed a discrete pattern of migration under polyacrylamide gel electrophoresis. Under denaturing condition in SDS-gel electrophoresis, all but fraction D showed a protein band with a molecular weight of 30 000. Fraction D showed a major component with molecular weight of 33 000. The isoelectric points of these renin forms varied from 5.46 to 5.76. They all reacted with antibody raised against renin A and showed similar pressor response activity with 20 ng quantities of the purified proteins. The closely related characteristics of these five forms of renin were further demonstrated by their similarity in peptide mapping patterns after limited digestion with Staphylococcus aureus V8 protease. The data suggest that these proteins are homologous proteins.

Long-term hemodynamic and clinical efficacy of captopril therapy in ambulatory management of severe chronic congestive heart failure

The 6-month extended vasodilator efficacy of the oral angiotensin converting enzyme (ACE) inhibitor, captopril (CPT), was evaluated by sequential cardiac catheterization, nuclear scintigraphy, echocardiography, treadmill exercise, and symptomatology in nine patients with severe chronic left ventricular (LV) failure (CHF). CPT lowered LV filling pressure (from 23 to 14 mm Hg acutely (p less than 0.001) and to 14 mm Hg (p less than 0.01) with continuous 6-month therapy; concomitantly CPT raised cardiac index from 2.03 to 2.46 L/min/m2 initially (p less than 0.02) and to 2.33 L/min/m2 (p less than 0.02) at 6 months. Simultaneously CPT raised LV ejection fraction from 0.21 to 0.25 acutely (p less than 0.01) and to 0.30 (p less than 0.001) and to 60 mm (p less than 0.001) at 6 months. These beneficial actions of CPT on LV pump function raised treadmill exercise duration (from 339 to 426 seconds initially (p less than 0.05) and to 499 seconds (p less than 0.05) at 6 months, while considerably reducing CHF symptomatology (p less than 0.001). Thus ACE inhibition by CPT provides markedly beneficial sustained hemodynamic and clinical improvement in advanced LV failure without fluid accumulation or late vasodilator drug tolerance.

Hormonal control of angiotensinogen production

The renin-angiotensin-aldosterone system appears to be under neural and hormonal control. Plasma angiotensinogen concentration is elevated in Cushing's disease, during pregnancy and in women taking oral contraceptives. An in vitro liver slice system was used to study the hormonal control of angiotensinogen synthesis and release in the rat. Dexamethasone administration in vivo resulted in increase in the in vitro rate of release of angiotensinogen by liver slices into the incubation media. This increase was inhibited by actinomycin D, an inhibitor of protein synthesis and vincristine which blocks secretion. Similarly, ethinyl estradiol treatment resulted in a 50% increase in angiotensinogen production. Hyperthyroid state was achieved by injecting rats with L-thyroxine daily for seven days. Hepatic production rate of angiotensinogen rose 21/2-fold above control and was accompanied by increases in plasma angiotensinogen concentration and plasma renin activity. In contrast, plasma angiotensinogen concentration and plasma renin activity were reduced in thyroidectomized rats. The rate of angiotensinogen production by liver slices of these rats decreased by five-fold below that of intact animals. These changes were largely corrected when thyroidectomized rats were treated with replacement doses of L-thyroxine. We conclude that hepatic angiotensinogen biosynthesis is under hormonal control. Glucocorticoid, estrogen and thyroid hormones all stimulate angiotensinogen production. These results may in part explain the pathogenesis of hypertension associated with certain disease states.

Renin synthesis by canine aortic smooth muscle cells in culture

Angiotensin-I generating activity has been detected in homogenates of arterial tissue but it remains unclear whether this enzymatic activity results from the presence of renin itself or from the action of other proteases such as cathepsin D. In an assay system employing anephric dog plasma as substrate and buffered to pH 7.4, we detected angiotensin-I generating activity in homogenates of canine aortic smooth muscle cells. This enzymatic activity was in large part inhibitable by renin-specific antisera raised to pure canine renal renin. Immunofluorescent study of cultured arterial smooth muscle cells was also performed using renin specific antiserum. Granular cytoplasmic immunofluorescence was detected when specific antirenin serum was used but not when preimmune serum was employed. The addition of pure canine renin to the renin antiserum during staining suppressed the granular immunofluorescence confirming the specificity of staining. Finally, biosynthetic radiolabelling studies were performed. Immunoprecipitation of newly synthesized proteins with antirenin serum and staphylococcal protein A followed by gel electrophoresis and autoradiography demonstrated the synthesis of an immunoreactive protein with the molecular weight of renin. Pretreatment of the antirenin serum with pure canine renin resulted in the disappearance of this immunoreactive protein band. Thus these studies provide multiple lines of evidence to indicate the in situ synthesis of renin by vascular smooth muscle cells.

Aldosterone in sustained essential hypertension

Plasma aldosterone (PA), plasma renin activity (PRA), extracellular fluid volume (EFV) and hepatic blood flow were measured in forty-four patients with sustained essential hypertension and compared with forty-two normotensive controls of same age and sex. All patient had inulin clearances within the normal range and balanced sodium intake and urinary output. In hypertensives, PA, PRA, EFV and hepatic blood flow were within normal ranges; the log-ratio PA:PRA was significantly elevated (P less than 0.001). In normotensives, a negative relationship was observed between PA and EFV (r=-0.55; P less than 0.001) while a positive relationship was observed between PA and PRA (=+0.70; P less than 0.001). In hypertensives, the two relationships were disrupted or less significant: for a given value of EFV, PA was more elevated in hypertensives than in normotensives; for a given value of PRA, PA was more evaluated in hypertensives than in normotensives. The results could not be explained on the basis of a disturbance in hepatic blood flow and/or in the metabolic clearance rate of aldosterone. The study provided evidence that, in patients with sustained essential hypertension and equilibrated sodium balance, there is an excess of plasma aldosterone relative to the levels of extracellular fluid volume and plasma renin activity. The excess of probably related to an abnormality in the adrenal secretion.

Abundant androgen regulated mRNAs in mouse submandibular gland: cell-free translation of renin precursor mRNA

Submandibular glands of male mice contain at least four abundant mRNAs that occur at low concentrations in glands of females. The male-specific mRNAs code for polypeptides of 48,000, 43,000, 29,000, and 27,000 MW. Androgenic regulation of these mRNAs is illustrated by their apparent absence in glands of castrate males and by their accumulation in glands of females treated with testosterone. Selective hybrid-arrested translation experiments also indicate reduced levels of these male-specific sequences in female gland cytoplasm. The 48,000 MW male-specific polypeptide is reduced in translation products directed by gland mRNA from C57BL10/J mice (variants deficient in salivary renin), suggesting the corresponding mRNA codes for a renin precursor. The identity of this polypeptide is confirmed by immune selection with renin-specific antibody.

Role of the renal nerves in the pathogenesis of one-kidney renal hypertension in the rat

Increased sympathetic nervous system activity has been demonstrated in established one-kidney one clip hypertension in the rat. To determine the importance of the renal nerves in this model of hypertension, renal denervation or sham operation was carried out 2 weeks after clipping. Systolic blood pressure (BP) after clipping the renal artery in 27 uninephrectomized male Charles River rats increased significantly from 125 +/- 3 mm Hg to a stable level of 185 +/-7 mm Hg by 2 weeks, in association with a positive sodium balance. Renal denervation in 13 animals resulted in a significant decrease in BP to 137 +/- 7 mm Hg, while no change in BP was seen after sham operation in 14 animals. There was no difference in mean daily water intake, mean daily sodium intake, mean daily urine volume, or mean fractional urinary sodium excretion between sham-operation and renal-denervated animals during the 2 weeks after operation. Plasma renin activity (PRA) and creatinine clearance were not significantly different at sacrifice 2 weeks after operation. Six of the renal-denervated rats were followed for 11 weeks after surgery. The BP rose again to hypertensive levels (187 +/- 8 mm Hg) by 5 weeks after renal denervation. Repeat renal denervation resulted in a significant decrease to 142 +/- 8 mm Hg. Renal denervation in eight rats with established one-kidney Grollman hypertension (185 +/- 8 mm Hg) also resulted ina significant decrease in systolic BP (143 +/- 8 mm Hg). The data demonstrate the importance of intact renal nerves in the maintenance of hypertension in the one-kidney renal hypertensive rat. The depressor effect of renal denervation is not mediated by alterations in sodium intake or excretion, water intake or excretion, creatinine clearance or PRA.

Peripheral conversion of L-5-hydroxytryptophan to serotonin induces drinking in rats

Female rats administered serotonin (0.25 to 4.0 mg/kg, s.c.) showed a dose-dependent increase in water intake. The dipsogenic response was nearly maximal when 2 mg/lg was administered s.c. and plateaued by 2 hr after treatment. l-5-Hydroxytryptophan (5-HTP), the precursor of serotonin, is also a potent dipsogen which induces drinking by way of the renin-angiotensin system. The possibility that the dipsogenic activity of 5-HTP is dependent on decarboxylation to serotonin was the objective of these studies. Either benserazide (30 mg/kg. s.c.), a central and peripheral decarboxylase inhibitor, or carbidopa (6.5 mg/kg, s.c.), a peripheral decarboxylase inhibitor, was administered 15 min prior to the dipsogen. Both decarboxylase inhibitors attenuated the dipsogenic response to 5-HTP (25 mg/kg, s.c.) but not to serotonin (2 mg/kg, s.c.). The peripheral serotonergic receptor antagonist, methysergide (3 mg/kg, i.p.), blocked the dipsogenic responses to both 5-HTP (25 mg/kg, s.c.) and serotonin (2 mg/kg, s.c.). There was no interaction between 5-HTP (18 mg/kg, s.c.) and serotonin (1 mg/kg, s.c.) when administered simultaneously with respect to their dipsogenic effects. Thus, the drinking response accompanying administration of 5-HTP occurs following peripheral conversion to serotonin which, in turn, activates peripheral serotonergic receptors. The mechanisms(s) by which activation of peripheral serotonergic receptors increases water intake is not known, but appears to involve release of renin from the kidney.

Effects of serotonin and L-5-hydroxytryptophan on plasma renin activity in rats

The effects of dipsogenic doses of l-5-hydroxytryptophan (5-HTP) and serotonin on plasma renin activity (PRA), blood pressure, and body temperature were determined in unanesthetized female rats. Both serotonin (2 mg/kg, s.c.) and 5-HTP (25 mg/kg, s.c.) induced six-fold increases in PRA measured 1 hr after drug administration. The central and peripheral decarboxylase inhibitor, benserazide (30 mg/kg, s.c.), as well as the peripheral decarboxylase inhibitor, carbidopa (6.5 mg/kg s.c.), prevented the increase in PRA associated with administration of 5-HTP. This suggests that 5-HTP must be converted to serotonin peripherally to increase PRA. At the doses used, serotonin decreased mean blood pressure and colonic temperature of unanesthetized rats while 5-HTP was without effect. The increase in PRA induced by 5-HTP does not appear, therefore, to be a response to either hypotension or a decrease in colonic temperature. Since 5-HTP must be converted to serotonin to initiate both a drinking response and an increase in PRA, the results suggest that the decrease in blood pressure and colonic temperature following administration of serotonin may not be important in induction of the drinking response and the increase in PRA. The mechanism by which activation of the renin-angiotensin system occurs following peripheral administration of either 5-HTP or serotonin remains for further study.

Renin producing Wilms' tumor

A 4-yr-old boy with Wilms' tumor, hypertension, and hyperreninemia is presented. Three times as much renin was extracted from tumor tissue as from adjacent renal parenchyma, suggesting that the tumor itself was the primary source of the renin and cause of the hypertension. Other reported cases of hypertension and increased renin production with Wilms' tumor are reviewed. Hypertension is a very frequent finding in patients presenting with Wilms' tumor. The possibility that many of these neoplasms may be found to hypersecrete renin if properly investigated is discussed.

Efficacy of oral angiotensin-converting enzyme inhibition with captopril therapy in severe chronic normotensive congestive heart failure

To evaluate the therapeutic efficacy of oral angiotensin-converting inhibition (ACE) with captopril in chronic normotensive congestive heart failure (CHF), acute and cardiocirculatory actions were determined by cardiac catheterization and forearm plethysmography, and ambulatory effects were assessed by echocardiography, nuclear angiography, treadmill exercise, and clinical symptomatology in 10 severe CHF patients. Captopril (90 mg) produced marked (peak 1 hour) and sustained (5 hours) left ventricular filling pressure (23 to 15 mm Hg), systemic vascular resistance decreases, and cardiac index increase (1.99 to 2.41 L/min/m2), while mean blood pressure declined mildly (87 to 80 mm Hg) without heart rate change. Both forearm venous tone and vascular resistance decreased considerably. After 1 week of ambulatory therapy (90 mg three times daily), nuclear angiographic ejection and echocardiogram shortening fractions increased, and exercise duration (341 to 453 sec) and New York Heart Association functional class (3.6 to 2.2) improved. Thus ACE-induced vasodilation by oral captopril improved cardiac performance and clinical status in refractory CHF.

Aetiology and control of cardiovascular reactions during trans-sphenoidal resection of pituitary microadenomas

Two groups of 12 patients were studied to determine the causes of hypertension during trans-sphenoidal resection of pituitary microadenomas. Two concentrations of lidocaine, 0.5 and 1.0 per cent with epinephrine 1/200,000, were used to infiltrate the nose and upper gingiva. Heart rate, electrocardiogram lead II and systolic and diastolic arterial blood pressures were monitored. Three stages were observed for changes in above parameters: nasal infiltration, nasal dissection and sellar exploration. Highly significant reductions in arterial blood pressure and pulse rate responses to infiltration and nasal dissection were achieved by increasing the lidocaine concentration used for infiltration from 0.5 to 1.0 per cent (p < 0.05). Our findings implicate reflex from nasal stimulation as the main cause of the adverse cardiovascular effects. Only minimal changes accompanied the progress of the intrasellar dissection in both groups.

Renin-angiotensin-aldosterone system

There is increased activity of the renin, angiotensin, aldosterone (RAA) system in infancy and childhood. An inverse relationship between plasma renin, aldosterone and age has been demonstrated. In childhood hypertension due to renovascular disease or pyelonephritic scarring peripheral plasma renin is increased. Renal vein renin measurements in children with renal hypertension have proved valuable in predicting surgical curability of the underlying lesion. The upper limit of normal for the renal venous renin ratio in normotensive children without renal disease is 1.5. Pharmacological blockade of the RAA system has a place in diagnosis and treatment of hypertensive children. The plasma renin aldosterone profile is diagnostically useful in the investigation of salt-wasting disease and can easily distinguish between aldosterone biosynthetic defects and pseudohypoaldosteronism.

The occurrence of hyperaldosteronism in infants with congestive heart failure

Serum aldosterone and plasma renin were measured in 20 normal infants and 15 infants with congestive cardiac failure. Serum aldosterone was significantly increased (151 +/- 38 ng/dl mean +/- standard error of the mean) in patients before treatment when compared with aldosterone in normal infants (29 +/- 7 ng/dl). Increasing serum aldosterone was related to increasing plasma renin. The response to furosemide appeared to be inversely related to serum aldosterone concentrations. In four infants, administration of an aldosterone antagonist (spironolactone) resulted in improved diuresis and decreased serum aldosterone. Hyperaldosteronism is an important factor contributing to fluid and sodium retention in infants with heart failure.

The effect of SAR1ALA8 AII on ovine uterine and umbilical blood flow

The effects of Sar1Ala8 AII (Saralasin), an angiotensin II (AII) receptor blocker, were examined in the late gestation ewe and fetus. Maternal administration of Saralasin resulted in a reduction in both mean maternal systemic arterial pressure and uterine blood flow. There were no changes in the measured fetal indices during maternal drug administration. Infusion of Saralasin to the fetus caused variable reductions in mean fetal arterial blood pressure and umbilical flow. There were no changes in maternal parameters measured. Therefore, in pregnant sheep in the third trimester, a component of normal uterine blood flow is maintained by endogenous AII, primarily through maintenance of adequate perfusion pressure.

The role of renin in the control of the circulation and in hypertensive disease

Renin is a hormone secreted by the juxtaglomerular cells of the kidney; it interacts with a plasma protein substrate to produce a decapeptide prohormone angiotensin I. Converting hormone located on vascular endothelium converts the decapeptide to an octapeptide, angiotensin II, which effects vasoconstriction, the secretion of aldosterone by the adrenal cortex, and retention of sodium by the kidney. The biosynthesis and control of renin secretion are not well understood, and the question as to whether renin is synthesized and stored in a larger precursor form is as yet unresolved. Whether or not higher molecular weight or inactive forms of renin in plasma have a role in controlling renin activity or whether they simply represent a degradative pathway for renin is as yet uncertain. The availability of several inhibitors of the renin-angiotensin system has served to define the role of renin both in normal cardiovascular homeostasis and in renovascular hypertension. It appears that renin plays an important role in maintaining blood pressure in the salt- or volume-depleted state and that it is responsible for the initial phases of renovascular hypertension in any model of this disease process. Renin's part in chronic renovascular hypertension depends on whether or not sodium is permitted to accumulate. If sodium intake is restricted or if sodium excretion is unimpaired (such as in two-kidney renovascular hypertension models), renin continues to play a significant role during the chronic phase.

A review of the consequences of fluid and electrolyte shifts in weightlessness

This review describes the renal-endocrine mechanisms related to the early losses of fluid-electrolytes from the body during weightlessness as well as their contribution to longer term adaptation of fluid-electrolyte balance. The hypotheses presented were generated by a systematic analysis of body fluid and renal dynamics observed under conditions of actual and simulated spaceflight. These have increased our understanding of the effects of acute headward fluid shifts on renal excretion, the factors promoting excess sodium excretion and the regulation of extracellular fluid composition.

Hyperreninemia and hyperaldosteronism in sickle cell anemia

Fourteen patients with sickle cell anemia, ages 6 to 20 years, were studied while ingesting high- and low-sodium diets. Although none of the patients had excessive urinary loss of sodium, the majority had elevated plasma renin activities and aldosterone secretion rates. The PRA was higher in patients over 10 years of age; ASR in patients receiving the high-sodium diet increased with age. Patients with sickle cell anemia appeared to compensate for urinary sodium loss between crises. The mechanism of this loss could be a defect in the function of either the distal tubule or the loop of Henle.

Rapid paper chromatographic separation of [14C] angiotensen II from some metabolites: application to organ distribution

A rapid, inexpensive method for the separation of 5-1-isoleucyl[14C] angiotensin II (A-II) from its various metabolites has been devised. A-II was extracted from tissues with absolute methanol (recovery 96%) and paper chromatographed in a butanol-acetic acid-water (18:2:5) medium for two ascents at 60 degrees C. The resulting RF for A-II of 0.45 was then compared with the RF values of three A-II metabolites produced by enzymatic degradation of the 14C-A-II and [14C]isoleucine. Trypsin degradation produced the [14C]hexapeptide metabolite, chymotryptic degradation produced the [14C]tetrapeptide metabolite and carboxypeptidase A degradation produced the [14C]heptapeptide. Increases in temperature produced a continuous increase in RF values for all the substances examined but the resolution decreased above 60 degrees C. Similarly, increases in the temperature caused the appearance of secondary peaks with some but not all peptides. The tryptic digest (hexapeptide) and the chymotryptic digest (tetrapeptide) are apparently acid- and heat-stable under the experimental conditions. All of the peptides examined failed to produce secondary peaks when heated at neutral pH. The method was used to study the tissue distribution of 14C-A-II after intravenous injection.

Preoperative and postoperative use of clonidine with neurolept anaesthesia

The abrupt cessation of clonidine therapy can induce a withdrawal syndrome. This may also appear immediately after anaesthesia if clonidine medication is discontinued during the operation day. We studied (1) whether the withdrawal syndrome occurs postoperatively as often as otherwise when clonidine therapy is discontinued, and (2) the action of this clonidine withdrawal on the circulation as compared to patients who received clonidine without interruption during the operation day. During the recovery period in 2 out of 10 patients in whom clonidine medication was discontinued, a hypertensive crisis occurred, which was relieved by clonidine readministration. Clonidine given with premedication eliminated high rises in blood pressure during anaesthesia. During the recovery period, the regular intramuscular administration of the same dose of clonidine as the patients had used orally decreased blood pressure to almost normotensive levels. The slightly increased urinary catecholamine excretion and plasma renin activity in these patients might, however, indicate that the circulatory homeostasis was disturbed in some degree. The results suggest that it is important to give clonidine continuously, even during the operation day. The dose may be the same as, or preferably somewhat smaller than that which the patients have previously received orally.

The quantitation of carbamino adduct formation of angiotensin II and bradykinin

The two equilibrium constants that define the extent of carbamino adduct formation with amines for all values of pH and PCO2 are determined for the alpha-amino groups of the peptide hormones angiotensin II(AII) and bradykinin (BK) by nuclear magnetic resonance techniques. From these constants the variation of carbamino adduct formation has been calculated over the pH range 6.60--8.00 with variable PCO2, and the results are superimposed upon standard pH-bicarbonate diagrams. PCO2, and the results are superimposed upon standard pH-bicarbonate diagrams. The mole fraction, Z, of carbamino adduct form of AII or BK shows a maximum variation in going from metabolic alkalosis, Z congruent to 0.30, to metabolic acidosis, Z congruent to 0.02, with Z near 0.2 for normal acid-base conditions. Adduct formation to hormone may alter the biological effect of the hormone (a) by limiting proteolysis, particularly at the amino-terminal, (b) by altering hormone binding affinity to specific receptors, or (c) by converting the hormone to an antagonist which binds to receptor but does not activate subsequent metabolic events. The requirements for any of these mechanisms to operate are examined in terms of simple equilibrium considerations, and experimental evidence of inhibition of an aminopeptidase model system is presented. These results are consistent with the hypothesis that regulation of some physiological processes through formation of carbamino adduct of peptide hormones is possible.