Assessment of the role of the renin-angiotensin system in cardiac contractility utilizing the renin inhibitor remikiren

1. The role of the renin-angiotensin system in the regulation of myocardial contractility is still debated. In order to investigate whether renin inhibition affects myocardial contractility and whether this action depends on intracardiac rather than circulating angiotensin II, the regional myocardial effects of systemic (i.v.) and intracoronary (i.c.) infusions of the renin inhibitor remikiren, were compared and related to the effects on systemic haemodynamics and circulating angiotensin II in open-chest anaesthetized pigs (25-30 kg). The specificity of the remikiren-induced effects was tested (1) by studying its i.c. effects after administration of the AT1-receptor antagonist L-158,809 and (2) by measuring its effects on contractile force of porcine isolated cardiac trabeculae. 2. Consecutive 10 min i.v. infusions of remikiren were given at 2, 5, 10 and 20 mg min-1. Mean arterial pressure (MAP), cardiac output (CO), heart rate (HR), systemic vascular resistance (SVR), myocardial oxygen consumption (MVO2) and left ventricular (LV) dP/dtmax were not affected by remikiren at 2 and 5 mg min-1, and were lowered at higher doses. At the highest dose, MAP decreased by 48%, CO by 13%, HR by 14%, SVR by 40%, MVO2 by 28% and LV dp/dtmax by 52% (mean values; P < 0.05 for difference from baseline, n = 5). The decrease in MVO2 was accompanied by a decrease in myocardial work (MAP x CO), but the larger decline in work (55% vs. 28%; P < 0.05) implies a reduced myocardial efficiency ((MAP x CO)/MVO2). 3. Consecutive 10 min i.c. infusions of remikiren were given at 0.2, 0.5, 1, 2, 5 and 10 mg min-1. MAP, CO, MVO2 and LV dP/dtmax were not affected by remikiren at 0.2, 0.5 and 1 mg min-1, and were reduced at higher doses. At the highest dose, MAP decreased by 31%, CO by 26%, MVO2 by 46% and LV dP/dtmax by 43% (mean values; P < 0.05 for difference from baseline, n = 6). HR and SVR did not change at any dose. 4. Thirty minutes after a 10 min i.v. infusion of the AT1 receptor antagonist, L-158,809 at 1 mg min-1, consecutive 10 min i.c. infusions (n = 5) of remikiren at 2, 5 and 10 mg min-1 no longer affected CO and MVO2, and decreased LV dP/dtmax by maximally 27% (P < 0.05) and MAP by 14% (P < 0.05), which was less than without AT1-receptor blockade (P < 0.05). HR and SVR remained unaffected. 5. Plasma renin activity and angiotensin I and II were reduced to levels at or below the detection limit at doses of remikiren that were not high enough to affect systemic haemodynamics or regional myocardial function, both after i.v. and i.c. infusion. 6. Remikiren (10(-10) to 10(-4) M) did not affect contractile force of porcine isolated cardiac trabeculae precontracted with noradrenaline. In trabeculae that were not precontracted no decrease in baseline contractility was observed with remikiren in concentrations up to 10(-5) M, whereas at 10(-4) M baseline contractility decreased by 19% (P < 0.05). 7. Results show that with remikiren i.v., at the doses we used, blood pressure was lowered primarily by vasodilation and with remikiren i.c. by cardiac depression. The blood levels of remikiren required for its vasodilator action are lower than the levels affecting cardiac contractile function. A decrease in circulating angiotensin II does not appear to be the sole explanation for these haemodynamic responses. Data support the contention that myocardial contractility is increased by renin-dependent angiotensin II formation in the heart.

Demonstration of renin mRNA, angiotensinogen mRNA, and angiotensin converting enzyme mRNA expression in the human eye: evidence for an intraocular renin-angiotensin system

AIMS/BACKGROUND

All components necessary for the formation of angiotensin II, the biologically active product of the renin-angiotensin system (RAS), have been demonstrated in ocular tissue or vitreous and subretinal fluid. The tissue concentrations of renin were too high to be explained by admixture of blood. This raises the possibility of an intraocular RAS, independent of the RAS in the circulation.

METHODS

In the present study, gene expression of RAS components in different parts of enucleated human eyes was investigated as evidence for tissue specific production.

RESULTS

By using pooled tissue samples renin mRNA could be detected with the RNAse protection assay in retinal pigment epithelium (RPE) choroid, but not in neural retina or sclera. With reverse transcription polymerase chain reaction (RT-PCR), renin mRNA was detected in individual samples of RPE choroid and neural retina, and not anterior uveal tract or sclera. Angiotensinogen and angiotensin converting enzyme (ACE) gene expression could be demonstrated by RT-PCR in individual RPE choroid and neural retina samples and marginally in sclera samples.

CONCLUSIONS

These results support the concept of intraocular synthesis of angiotensin II, independent of renin, angiotensin, and ACE in the circulation. Since gene expression was highest in ocular parts, which are highly vascularised, local angiotensin II may be involved in blood supply and/or pathological vascular processes such as neovascularisation in diabetic retinopathy.

Angiotensin-converting enzyme in the human heart. Effect of the deletion/insertion polymorphism

BACKGROUND

An insertion (I)/deletion (D) polymorphism of the angiotensin-converting enzyme (ACE) gene has been associated with differences in the plasma levels of ACE as well as with myocardial infarction, cardiomyopathy, left ventricular hypertrophy, and coronary artery disease.

METHODS AND RESULTS

We determined the cardiac ACE activity and the ACE genotype in 71 subjects who died of noncardiac disorders. Cardiac ACE activity was significantly higher (P < .01) in subjects with the ACE DD genotype (12.7 +/- 1.9 mU/g wet wt) compared with subjects with the ID (8.7 +/- 0.8 mU/g) and the II (9.1 +/- 1.0 mU/g) genotypes. This difference was independent of sex, age, and the time required for tissue collection.

CONCLUSIONS

Cardiac ACE activity is highest in subjects with the DD genotype. Elevated cardiac ACE activity in these subjects may result in increased cardiac angiotensin II levels, and this may be a mechanism underlying the reported association between the ACE deletion polymorphism and the increased risk for several cardiovascular disorders.

Effect of regional and systemic changes in vasomotor tone on finger pressure amplification

Pulse wave amplification, which leads to increased peripheral systolic pressure, is observed during vasoconstriction after head-up tilt and during exercise. This may influence finger pressure measurements with the Finapres. To distinguish between changes in regional vascular tone and changes in systemic hemodynamics as a cause of pulse wave amplification, we measured finger pressure, intra-arterial brachial artery pressure, heart rate, and left ventricular ejection time during high-dose intravenous and low-dose intra-arterial infusions of phenylephrine and sodium nitroprusside in eight subjects. Forearm blood flow was measured by means of venous occlusion plethysmography. Intravenous phenylephrine at the highest dose caused an increase in mean brachial artery pressure of 24 +/- 3 mm Hg, a decrease in heart rate of 10 +/- 11 beats per minute, and an increase in ejection time of 23 +/- 9 milliseconds (all P < .01), whereas pulse wave amplification was reduced. Finapres underestimated the rise in systolic brachial artery pressure of 41 +/- 9 mm Hg by 11 +/- 12 mm Hg (P < .01). Forearm blood flow did not change. Intravenous nitroprusside caused a decrease in mean brachial artery pressure of 23 +/- 9 mm Hg, an increase in heart rate of 18 +/- 11 beats per minute, and a decrease in ejection time of 36 +/- 31 milliseconds (all P < .01), whereas pulse wave amplification increased. Finapres underestimated the fall in systolic brachial artery pressure of 30 +/- 13 mm Hg by 9 +/- 10 mm Hg (P < .05). Forearm blood flow did not change. During regional infusion of phenylephrine and nitroprusside forearm flow halved and doubled, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitivity and specificity of a new ELISA method for determination of chromogranin A in the diagnosis of pheochromocytoma and neuroblastoma

We have evaluated a new commercially available ELISA kit for determination of plasma chromogranin A with respect to its usefulness in the diagnosis of neuroendocrine tumors, mainly pheochromocytoma. Serum and differently anticoagulated plasmas gave different chromogranin A concentrations. Control values (n = 21) were 18.9 +/- 5.8 units/l. Chromogranin A values > 30.4 units/l (mean + 2 S.D.) were considered elevated. In 22 patients suspected of (but found not to have) pheochromocytoma and in 24 patients with renovascular hypertension, 18% were found to have elevated chromogranin A concentrations. In renovascular hypertension chromogranin A correlated positively with serum creatinine; chromogranin A was strongly elevated especially in chronic renal failure. In 45 patients with pheochromocytoma, 13 (29%) had chromogranin A concentrations within the normal range, as had 3 out of 11 patients with neuroblastoma (27%). In 13 pheochromocytoma patients with elevated chromogranin A, measurements were repeated after surgical removal of the tumor; values then all fell within the normal range. We conclude that measurement of chromogranin A adds little to already existing methods for the diagnosis of pheochromocytoma.

Conversion and degradation of [125I] labelled angiotensin I in isolated perfused porcine coronary and carotid arteries

OBJECTIVE

The aims were (1) to quantitate angiotensin I to II conversion on the endothelial surface and at deeper sites in isolated arteries, (2) to assess whether the angiotensin II that is formed at deeper sites is released into the vascular lumen, and (3) to examine whether enzymes other than angiotensin converting enzyme (ACE) are involved in vascular angiotensin I to II conversion.

METHODS

Metabolism of [125I]-angiotensin I was studied in isolated perfused porcine coronary and carotid arteries after luminal administration of the labelled peptide (in the perfusion fluid) and after adventitial administration (in the organ bath). Measurements were made both in the presence and in the absence of captopril.

RESULTS

[125I]-angiotensin II was a major metabolite and its formation was virtually completely blocked by captopril, after both luminal and adventitial administration of [125I]-angiotensin I. In coronary arteries (n = 8), the [125I]-angiotensin I to II conversion rate after adventitial administration was about half that after luminal administration. In coronary arteries (n = 6) the conversion rate after adventitial administration was 10-20 times lower than after luminal administration. Degradation of [125I]-angiotensin I into peptides other than [125I]-angiotensin II was also observed, with both luminal and adventitial administration. No [125I]-angiotensin I or II was released into the organ bath after luminal administration of [125I]-angiotensin I, and very little [125I]-angiotensin I and II entered the lumen after adventitial administration of [125I]-angiotensin I.

CONCLUSIONS

(1) Vascular angiotensin I to II conversion is not limited to the endothelial surface. (2) ACE is the most important, if not the only, enzyme responsible for vascular angiotensin I to II conversion. (3) If angiotensin I and II are formed in the adventitia or media, little of these peptides will enter the vascular lumen.

Plasma semicarbazide-sensitive amine oxidase activity is elevated in diabetes mellitus and correlates with glycosylated haemoglobin

1. Semicarbazide-sensitive amine oxidase is a common name for a group of heterogeneous amine oxidases which are present in various mammalian tissues, especially in vascular smooth muscle cells, cartilage and adipose tissue, but also in plasma. 2. Plasma semicarbazide-sensitive amine oxidase activity was elevated in a group of 104 patients with insulin-dependent diabetes mellitus compared with normal control subjects (555 +/- 172 versus 352 +/- 102 m-units/l, P < 0.0005). 3. Plasma semicarbazide-sensitive amine oxidase activity was higher in subgroups with either retinopathy or nephropathy or both [583 +/- 116 (n = 34), 581 +/- 229 (n = 10) and 646 +/- 249 m-units/l (n = 19), respectively] than in the subgroup without overt complications [486 +/- 129 m-units/l (n = 41), P < 0.005]. 4. Plasma semicarbazide-sensitive amine oxidase activity was positively correlated with plasma glycosylated haemoglobin (r = 0.40; P < 0.0001) and with log urinary albumin excretion (r = 0.26; P < 0.025). 5. The possibility that semicarbazide-sensitive amine oxidase, by its conversion of endogenous amines like methylamine and aminoacetone into cytotoxic aldehydes, plays a role in the development of microvascular complications in diabetes mellitus, needs further investigation.

Effect of atrial natriuretic peptide on renal and vascular permeability in diabetes mellitus

Synthetic human atrial natriuretic peptide (ANP) (102-126) 0.01 microgram/kg per minute or vehicle was intravenously infused for 2 h in 10 patients with insulin-dependent diabetes mellitus and microalbuminuria (albumin excretion, 20 to 200 micrograms/min) and in 10 healthy subjects. In the diabetic group, the immunoglobulin G clearance was higher, but both size index and charge index as calculated from albumin and immunoglobulin clearances were equal compared with normal values. The fractional clearances of small dextrans (< 3.6 nm) were lower in diabetics, which was compatible with a depressed hydraulic permeability (Kf). During ANP infusion, the excretion of albumin and immunoglobulin G increased in the diabetic subjects (189 +/- 12 to 521 +/- 84 and 7.1 +/- 3.5 to 21 +/- 8.1 micrograms/min, respectively; both P < 0.05) only. In the diabetics, the clearance of dextrans > 54 A increased and our calculations indicated an increase in "shut-flow" (omega o). The transcapillary escape rate of albumin, which was elevated in the diabetics at baseline, increased in the diabetic group only. Thus, ANP uncovers altered size selectivity of the filtration barrier in a phase that is otherwise characterized by charge-selective changes only. Moreover, the increased susceptibility of the glomerular capillaries in diabetics to ANP seems to be part of a more generalized capillary abnormality, because ANP also increases the transcapillary escape of albumin.

Determination of semicarbazide-sensitive amine oxidase activity in human plasma by high-performance liquid chromatography with fluorimetric detection

We report here a simple and sensitive method for the measurement of semicarbazide-sensitive amine oxidase (SSAO) activity in human plasma. Benzaldehyde, generated during a 1-h incubation of plasma with benzylamine, is derivatized with the specific aldehyde reagent dimedone after prior deproteinization. Quantitation of the derivatization product is done by automated injection onto an isocratic high-performance liquid chromatographic system with fluorimetric detection. The assay shows good linearity and reproducibility (intra-assay C.V. 7%). Detection limit is 25 mU/l (= pmol/ml/min). In 51 healthy controls (age 49 +/- 13 yr, 20 males) the measured SSAO activity was 352 +/- 102 mU/l (mean +/- S.D.). A large number of samples (70-80) can easily be processed in one day by one technician.

Optimising glomerular filtration rate and effective renal plasma flow measurements using a simple pharmacokinetic model

We applied an open one compartment pharmacokinetic model for the determination of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) based on a rapid intravenous loading dose followed by a constant infusion of 125I-iothalamate and 131I-orthoiodohippurate in order to ensure constant plasma levels of the two clearance markers. The loading dose was based on the assumption that the volume of distribution of the two markers equals the extracellular volume (25% of the body weight). The infusion rate as calculated after the clearance of thalamate was estimated from body weight, age, sex and serum creatinine using Cockcrofts formula. The clearance of hippurate was assumed to be four times that of thalamate. We studied the reliability of this model in 212 patients with insulin dependent diabetes mellitus (IDDM; n = 74), nephrotic syndrome (NS; n = 18) and heart (HTX; n = 69) or kidney (KTX; n = 51) transplants. A steady state concentration was obtained in all patient groups, even when GFR was markedly depressed. In patients with diabetes, we observed more variance between plasma and urinary clearances of thalamate, which could be due to inaccuracies in urine sampling. In these patients, GFR should be measured using a method that is not dependent on urine collection. Also, the estimation of GFR by means of Cockcrofts equation seems to underestimate GFR in diabetic subjects.

Abnormal diurnal variation of blood pressure, cardiac output, and vascular resistance in cardiac transplant recipients

BACKGROUND

An attenuated or absent nocturnal decline in blood pressure has repeatedly been documented in cardiac transplant recipients. The present study was aimed at investigating the hemodynamic mechanism underlying this abnormality.

METHODS AND RESULTS

In 23 cardiac transplant recipients (11 to 36 months after transplantation) and in 23 control subjects matched for age and 24-hour mean arterial pressure, invasive 24-hour ambulatory blood pressure was measured by means of the Oxford technique. Beat-to-beat relative values of stroke volume were determined by means of a pulse-contour method, and relative changes of cardiac output (stroke volume x heart rate) and total peripheral vascular resistance (blood pressure/cardiac output) over the 24-hour period were calculated. The nocturnal decline in blood pressure was 20 +/- 8% (mean +/- SD) in control subjects but only 5 +/- 9% (P < .001) in cardiac transplant recipients. In control subjects, the nocturnal decline in blood pressure was associated with a nocturnal fall in cardiac output of 24 +/- 13%, whereas vascular resistance compared with daytime value did not change. The small nocturnal decline in blood pressure in cardiac transplant recipients was associated with an attenuated nocturnal fall in cardiac output of 14 +/- 12% (P < .05 versus control subjects). In addition, vascular resistance compared with daytime value was increased by 9 +/- 9% (P < .05) during the night. Both in cardiac transplant recipients and in control subjects, the nocturnal changes in blood pressure were correlated with the nocturnal changes in cardiac output but not with the nocturnal changes in total peripheral vascular resistance.

CONCLUSIONS

This study confirms the attenuated nocturnal fall in blood pressure in cardiac transplant recipients. Hemodynamically, this attenuated blood pressure decline is characterized by a reduced nocturnal fall in cardiac output, and it is associated with a nocturnal increase in vascular resistance.

Glomerular barrier function following conversion from cyclosporine to azathioprine in renal transplant recipients

The renal side effects are the major limitation of the use of cyclosporine in clinical transplantation. We studied the reversibility of changes in renal hemodynamics and glomerular barrier function in 17 patients with moderately impaired renal function at least 1 year after kidney transplantation. All patients were studied both during cyclosporine treatment and 3 months after conversion to azathioprine. During azathioprine treatment both glomerular filtration rate and effective renal plasma flow increased significantly (from 44.3 +/- 4.2 mL/min to 63.5 +/- 5.4 mL/min and from 192 +/- 12.8 mL/min to 260 +/- 14.6 mL/min, respectively). Despite the marked changes in renal hemodynamics, no significant changes were observed in the fractional clearances of uncharged dextrans. When calculating the characteristics of the filtration barrier, we observed a trend toward an increase in the ultrafiltration coefficient (Kt). This trend was abolished when an increase in net filtration pressure (delta P) was assumed to result from reduced prerenal vasoconstriction. We conclude that despite marked improvement of renal perfusion and glomerular filtration, conversion from cyclosporine to azathioprine did not significantly alter the permeability characteristics of the glomerular filtration barrier in renal transplant recipients with moderately reduced renal function. Improvement in renal function following conversion could result from an increase in either Kf or delta P. Since renal plasma flow was increased significantly, the observed improvement in glomerular filtration rate is likely to be, at least in part, due to an increase in glomerular capillary plasma flow.

Effects of DDAVP on renal hemodynamics and renin secretion in subjects with essential hypertension

Intravenous (i.v.) infusion of the selective vasopressin (V2) agonist 1-desamino-8-D-arginine vasopressin (DDAVP, Desmopressin) in humans causes a fall in blood pressure, an increase in heart rate, and a rise in plasma renin and noradrenaline. The present study was designed to demonstrate the vasodilatory properties of DDAVP in the renal circulation and to describe the effect of DDAVP on renin secretion. Seven male subjects (31-63 years) with hypertension, who showed no signs of renal parenchymal disease, received an i.v. infusion of DDAVP (400 ng/kg in 10 minutes). They were studied at the time they were undergoing renal vein renin sampling and renal angiography as part of the diagnostic work-up of their hypertension. 131I-Hippurate clearance was used to measure effective renal plasma flow (ERPF). True renal plasma flow was calculated as ERPF divided by the renal extraction ratio of 131I-hippurate. 125I-Thalamate clearance was used to measure glomerular filtration rate (GFR). Measurements were made before and 15-20 minutes after administration of DDAVP. Angiography was performed in the same session after the last blood samples had been collected. In all patients the renal arteries were normal and the extraction ratios of 131I-hippurate and 125I-thalamate (Ehip, Ethal) were not different for the left and right kidney, and in all seven patients a diagnosis of essential hypertension was made. After DDAVP systolic blood pressure decreased by 14.4 mmHg (2.0-26.8) (mean, 95% confidence interval, p < 0.05). Diastolic blood pressure decreased by 12.1 mmHg (2.9-21.7, p < 0.01). Heart rate increased by 17.5 bpm (11.7-23.2, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac renin and angiotensins. Uptake from plasma versus in situ synthesis

The existence of a cardiac renin-angiotensin system, independent of the circulating renin-angiotensin system, is still controversial. We compared the tissue levels of renin-angiotensin system components in the heart with the levels in blood plasma in healthy pigs and 30 hours after nephrectomy. Angiotensin I (Ang I)-generating activity of cardiac tissue was identified as renin by its inhibition with a specific active site-directed renin inhibitor. We took precautions to prevent the ex vivo generation and breakdown of cardiac angiotensins and made appropriate corrections for any losses of intact Ang I and II during extraction and assay. Tissue levels of renin (n = 11) and Ang I (n = 7) and II (n = 7) in the left and right atria were higher than in the corresponding ventricles (P < .05). Cardiac renin and Ang I levels (expressed per gram wet weight) were similar to the plasma levels, and Ang II in cardiac tissue was higher than in plasma (P < .05). The presence of these renin-angiotensin system components in cardiac tissue therefore cannot be accounted for by trapped plasma or simple diffusion from plasma into the interstitial fluid. Angiotensinogen levels (n = 11) in cardiac tissue were 10% to 25% of the levels in plasma, which is compatible with its diffusion from plasma into the interstitium. Like angiotensin-converting enzyme, renin was enriched in a purified cardiac membrane fraction prepared from left ventricular tissue, as compared with crude homogenate, and 12 +/- 3% (mean +/- SD, n = 6) of renin in crude homogenate was found in the cardiac membrane fraction and could be solubilized with 1% Triton X-100. Tissue levels of renin and Ang I and II in the atria and ventricles were directly correlated with plasma levels (P < .05), and in both tissue and plasma the levels were undetectably low after nephrectomy. We conclude that most if not all renin in cardiac tissue originates from the kidney. Results support the contentions that in the healthy heart, angiotensin production depends on plasma-derived renin and that plasma-derived angiotensinogen in the interstitial fluid is a potential source of cardiac angiotensins. Binding of renin to cardiac membranes may be part of a mechanism by which renin is taken up from plasma.

Diurnal variation of blood pressure in patients with catecholamine-producing tumors

To investigate the role of plasma catecholamines in diurnal blood pressure variation, invasive 24-h ambulatory blood pressure recordings (Oxford technique) were performed on 10 untreated patients; all had increased plasma concentrations of norepinephrine (mean 27.3; range 2.50 to 134.6 nmol/L) or epinephrine (mean 13.5; range 0.13 to 96.6 nmol/L) either attributable to a pheochromocytoma (n = 7) or a paraganglioma (n = 3). The nocturnal change in blood pressure was calculated as the percentage difference of blood pressure between night (midnight to 6 AM) and day (8 AM to 10 PM). The group average nocturnal change in blood pressure was 12.4%, ranging from a 32.0% decrease to a 2.8% increase, whereas the average nocturnal fall in heart rate was 18.6%, ranging from 2.2% to 33.4%. Although the nocturnal change in blood pressure was not significantly correlated with plasma values of norepinephrine (r = 0.60) or total catecholamines (r = 0.54), no nocturnal decrease in blood pressure occurred in the two patients with a plasma norepinephrine level of > 55 nmol/L. Recordings of three patients, all with a pheochromocytoma showed several paroxysms of blood pressure elevations, which lasted 18 to 47 min and had an amplitude of 32 to 94 mm Hg. In two cases these elevations had a true cyclic character. Our findings indicate that patients with a catecholamine-producing tumor may exhibit a normal diurnal blood pressure variation with a decrease in blood pressure during the night, suggesting that factors responsible for this diurnal variation remain operative in this condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin levels in the eye

PURPOSE

Ocular tissues contain renin and ocular fluids contain prorenin in amounts that are too high to be explained by admixture with blood or diffusion from blood. It was the purpose of the present study to obtain further evidence for the presence of a local renin-angiotensin system (RAS) in the eye.

METHODS

The authors measured the concentrations of angiotensins I and II (ANG I and II) in vitreous fluid and ocular tissues of anesthetized pigs and in human aqueous, vitreous, and subretinal fluid obtained during eye surgery.

RESULTS

In tissues obtained from normal porcine eyes (anterior uveal tract, neural retina, retinal pigment epithelium + choroid), ANG I and II were 5- to 100-fold higher than could be accounted for by contamination with blood. ANG I and II in ocular tissues are therefore unlikely to be derived from the circulation. In porcine vitreous fluid, ANG I and II were close to the limit of detection. In addition, during a 2-hour infusion of 125I-ANG I in the rabbit, 125I-ANG I in vitreous fluid reached a level only 1% of the level in arterial plasma. Thus, in the presence of an intact blood-retinal barrier, little or no ANG I or II enters the vitreous compartment. In human ocular fluids obtained from diseased eyes, ANG I and II levels were readily measurable and correlated linearly with the level of serum albumin, indicating that after partial breakdown of the BRB, diffusion of ANG I and II from the circulation into the eye may occur.

CONCLUSION

Results indicate that both ANG I and II are generated locally in ocular tissues with little leakage into ocular fluids. These findings, together with previously published data on renin and prorenin, show a high degree of compartmentalization of the RAS in the eye and are in agreement with similar findings in other tissues, where there is evidence for the existence of a local RAS.