M. Marin-Grez

The Intrarenal Renin-Angiotensin-System An Immunocytochemical Study on the Localization of Renin, Angiotensinogen, Converting Enzyme and the Angiotensins in the Kidney of Mouse and Rat*

SummaryThe localization of renin, converting enzyme (CE) and angiotensin II (ANG II) in the kidneys of rats and mice was investigated with immunocytochemical methods. According to the presence and specific intrarenal localization of these components of the renin-angiotensin-system (RAS) our results suggest that in addition to the well known systemic effects of the RAS, there are interactions of its components inside the kidney. These interactions may lead to the generation of an extra portion of ANG II in the renal blood stream with its target cells determined by the localization of CE at the luminal side of well defined endothelial areas. These intrarenal-intravasal reactions may or may not reinforce the action of “systemic” ANG II, generated prerenally. In addition, the existence of true intrarenal-interstitial interactions, with the different components and actions of this intrarenal RAS restricted entirely to the kidney is suggested by our results, particularly the demonstration of ANG II within epitheloid cells and the dissociation of systemic renin and ANG II from their local concentrations in renal hypertensive rats.ZusammenfassungDie intrarenale Verteilung von Renin, Converting enzyme (CE) und Angiotensin II (ANG II) wurde mit immunzytochemischen Methoden an Ratten und Mäusen untersucht. Die hier aufgezeigten spezifischen Verteilungsmuster dieser Komponenten des Renin-Angiotensin-Systems (RAS) legen die Annahme nahe, daß es neben den bekannten systemischen, durch ANG II vermittelten Effekten des RAS auch lokale Interaktionen von RAS-Bestandteilen innerhalb der Niere gibt. — Eine erste Folge dieser Interaktionen dürfte die intrarenale Generation einer zusätzlichen Portion von ANG II im Nierenblutstrom sein, deren Zielgebiet durch die spezifische Lokalisation von CE in bestimmten Endothelbereichen der Nierenstrombahn bestimmt wird. Solche intrarenal-intravasalen Reaktionen können für sich wirksam werden, aber auch den Effekt von „systemisch“, d.h. prärenal generiertem ANG II verstärken. — Unsere Ergebnisse sprechen weiter dafür, daß es neben diesen intrarenal-intravasalen auch echte intrarenal-interstitielle Interaktionen der RAS-Komponenten gibt, deren Wirkung sich über das im Interstitium der Nierenrinde generierte ANG II allein auf die Niere beschränkt. Für das Vorhandensein eines solchen lokal-intrarenalen RAS spricht vor allem der Nachweis von ANG II in den epitheloiden Zellen des JGA und die Dissoziation des systemischen — an der Plasmakonzentration abzulesenden — Renin und ANG II von deren lokal-intrarenalen Konzentrationen bei renal hypertensiven Ratten.

Immunoreactive renin and angiotensin II in the afferent glomerular arterioles of rats with hypertension due to unilateral renal artery constriction

SummaryThe immunoreactivity for renin and angiotensin II (ANG II) in the ischaemic and non-ischaemic kidney of rats with renovascular hypertension was compared with that of the kidneys of sham operated controls. In addition, the renin concentration of these kidneys and the plasma level of ANG II were determined in hypertensive and control animals. In parallel with the renin concentration of kidney cortex, the immunoreactivity, i.e. the JG-index for renin of the afferent arterioles from the ischaemic kidney was slighly increased, that from the nonischaemic kidney drastically decreased as compared to control kidneys. Similarly, the JG-index for ANG II was increased in the ischaemic and decreased in the non-ischaemic kidney although the plasma level of ANG II was elevated in the animals with renovascular hypertension. This difference in the immunocytochemically detectable ANG II and especially the decrease of ANG II in the non-ischaemic kidney in spite of elevated plasma ANG II levels is interpreted to result from similar differences in the local (extravascular) formation of ANG II by the intrarenal renin-angiotensin system.

SA446, a new orally active converting enzyme inhibitor: Antihypertensive action and comparison with captopril in stroke-prone spontaneously hypertensive rats

The converting enzyme inhibitors (CEI) SA446 and Captopril (CAP) were given orally at a dose of 50 mg/kg per day to adult stroke-prone spontaneously hypertensive rats (SHRSP) over a period of four weeks. Both CEI lowered arterial blood pressure (BP) to a similar extent. CAP was more inhibitory on the plasma renin-angiotensin system (RAS) than SA446. Both CEI lowered urinary aldosterone excretion but had little (SA446) or no (CAP) natriuretic effect. CAP reduced the pressor responses to intravenous (i.v.) angiotensin I (ANG I) more (52%) than SA446 (18%) and potentiated the depressor responses to i.v. bradykinin more (fortyfold) than SA446 (tenfold). In contrast, SA446 treatment reduced the pressor responses to intracerebroventricular (i.c.v.) ANG I by 21% and led to a rise in the hypothalamic renin concentration. Oral CAP treatment for four weeks did not produce these signs of a brain converting enzyme inhibition. It is concluded that SA446 is equally as antihypertensive as CAP in SHRSP. SA446 appears to penetrate more readily into the brain and to exert its action partly through inhibition of the brain RAS which is known to be stimulated in SHRSP.

Effects of sodium loading, desoxycorticosterone acetate, and corticosterone on urinary kallikrein excretion.

In male Sprague-Dawley rats, changes in kallikrein activity in urine were produced by high sodium intake (1% saline as drinking fluid for 14 days), and administration of desoxycorticosterone acetate (DOCA, 15 mg/kg s.c. for 5 days), and of corticosterone (2 x 0.2 or 2 x 20 mg/kg s.c. daily for 5 days). Salt loading caused a decrease in urinary kallikrein excretion (p less than 0.005), while DOCA produced an increase (p less than 0.001). While corticosterone, administered in the low dose, had no effect on urinary kallikrein excretion, the high dose, given for 5 days, diminished kallikrein excretion to about half the basal value (p less than 0.001). Simultaneously, the excretion of aldosterone decreased to about one third the amount measured in the corresponding control rats.

Relationship between the renal kallikrein activity and the urinary excretion of kallikrein in rats.

Adrenalectomy reduces, and sodium depletion increases, both the daily urinary excretion of kallikrein and the kallikrein activity in the renal cortex. These 2 variables were found to correlate significantly in normal, sodium depleted and adrenalectomized rats, thus supporting the view that kallikrein excretion reflects the activity of the enzyme in the kidney.

Kinins in cerebrospinal fluid: Reduced concentration in spontaneously hypertensive rats

Rat cerebrospinal fluid contains peptides which displace radiolabeled bradykinin from its specific antibodies. Two peptides which showed the same retention time as kallidin and bradykinin in a reverse phase high pressure liquid chromatography system were detected in cerebrospinal fluid of rats. The concentration of radioimmunologically detected kinins in the cerebrospinal fluid of spontaneously hypertensive rats of the Okamoto strain was lower than that of the Wistar Kyoto control rats.

Effect of Changes in Perfusion Pressure on Renal and Urinary Kallikrein in the Isolated Perfused Rat Kidney

Kallikrein activity in urine and in the renal cortex of the isolated rat kidney, perfused at constant pressure, decreased, while renal perfusate flow, glomerular filtration rate, excretion of sodium and of potassium and urine flow remained unchanged. Abrupt changes in perfusion pressure resulted in corresponding changes in renal perfusate flow, glomerular filtration rate, excretion of sodium and of potassium and urine flow. Urinary kallikrein increased little and transiently only, each time perfusion pressure was elevated. At the end of the experiments, a marked decrease in kallikrein activity in the renal tissue was found. From these results, it might be concluded that the excretion of kallikrein from the isolated perfused rat kidney resulted in a marked depletion of kallikrein stores in the kidney, probably due to an insufficient kallikrein synthesis.

Ureteral contractions induced by rat urine in vitro: Probable involvement of renal kallikrein

Rat urine, even at a 1∶10 final dilution in Tyrodes solution, stimulates contraction of the ureteral musculature in vitro. This effect can be ascribed to the presence of kallikrein or a kallikrein-like enzyme in urine. Isometric contractions of ureters were prevented by previous addition of aprotinin to the organ bath. Urine also lost its activity after inactivation of enzymes by heat or acid treatment.

Effect of dihydralazine on the renal kallikrein-kinin system of the rat.

Dihydralazine (0.1 mg/kg), injected intravenously into male Sprague-Dawley rats, caused a decrease in mean arterial blood pressure and an increase in renal plasma flow, while urine volume remained unchanged. Dihydralazine had no effect on kallikrein excretion in the urine and on kallikrein activity in the renal cortex. No correlation was found between renal kallikrein and either renal plasma flow or mean arterial blood pressure. The excretion of kinins in the urine rose markedly after the administration of dihydralazine; no correlation between urinary kinins and urinary or renal kallikrein was observed. Dihydralazine had no influence on the kininogen content of blood-free renal cortex. The enzymatic activity of kininase II in renal cortex was not impaired by dihydralazine. It is suggested that the increased formation of kinins within the kidney could be involved in the vasodilating and blood pressure lowering effect of dihydralazine.

Inhibition of the ureteral contractions induced by rat urine with kallikrein antibodies

Purified urinary kallikrein induces contractions of the rat ureter in vitro. Antibodies against kallikrein block the contractile response of the isolated ureter to rat urine.