Pharmacological evidence for the existence of a local renin-angiotensin system in porcine interlobar renal arteries

Losartan decreases glomerular filtration rate in isolated perfused porcine slaughterhouse kidneys

We investigated whether Losartan, an angiotensin II (Ang II) AT1 receptor antagonist, decreases renal vascular resistance (RVR) and increases glomerular filtration rate (GFR) in isolated perfused porcine slaughterhouse kidneys (11 control experiments and 11 Losartan experiments with 7.5mg Losartan in the preservation solution and 100(g/minute Losartan infused during perfusion). With perfusion, plasma renin activity (PRA) increased markedly from 3 +/- 1 to 90 +/- 17 ng Ang I/ml/h (control), and from 4 +/- 1 to 70 +/- 8 ng Ang I/ml/h (Losartan), plasma Ang II increased from 86 +/- 63 to 482 +/- 111 pg/ml (control), and from 73 +/- 42 to 410 +/- 91 pg/ml (Losartan). The GFR was decreased in Losartan experiments as compared with control experiments (5 +/- 1 versus 10 +/- 2 ml/min/100g kidney wt; p < 0.05). The RVR was the same in both groups (0.2 +/- 0.01 mm Hg/100g kidney wt/min/ml). Tubular sodium reabsorption was decreased in Losartan experiments as compared with control experiments (0.7 +/- 0.1 versus 1.4 +/- 0.3 mmol/min/100g kidney wt). Overall, Losartan accentuated pathophysiological signs of acute renal failure. Although other drugs have to be investigated, these results suggest that porcine slaughterhouse kidneys could be useful as a tool for research in areas such as transplantation and intensive-care medicine.

Role of kinins and angiotensin II in the vasodilating action of angiotensin converting enzyme inhibition in rat renal vessels

OBJECTIVE

To assess directly the vasodilating effects of angiotensin converting enzyme (ACE) inhibition in different renal vessels and to determine the role of kinins and angiotensin II (ANGII) therein.

METHODS

Lumen diameters of different vessels and glomerular blood flows were measured in cortical and juxtamedullary glomeruli by in-vivo microscopy in the split hydronephrotic kidney of anesthetized female Wistar rats.

RESULTS

Injection of the ACE inhibitor quinapril at a dose of 0.9 mg/kg intravenously, which blocks conversion of locally applied angiotensin I (1 mumol/l), increased glomerular blood flows by 39 +/- 6 and 18 +/- 4% in cortical and juxtamedullary glomeruli, respectively, due to vasodilatation in all renal vessels. The most pronounced vasodilatation was observed in interlobular arteries (19 +/- 2%) and in cortical afferent arterioles (16 +/- 3%). Pretreatment of the hydronephrotic kidney by local application of 40 nmol/l Hoe140, a bradykinin B2 receptor antagonist, or 3 mumol/l valsartan, an ANGII type 1 receptor antagonist, attenuated the vasodilatation in response to quinapril. ANGII receptor blockade affected only weakly, whereas bradykinin receptor blockade blunted markedly, the quinapril-induced vasodilatation, suggesting that kinins play an important role in our experimental model. Administration of valsartan, which abrogated the renal vasoconstriction induced by 10 nmol/l ANGII completely, caused vasodilation of magnitude similar to that caused by administration of quinapril. Yet, the vasodilatation induced by the combination of valsartan and quinapril was significantly larger than that induced by administration of quinapril alone in interlobular arteries, afferent arterioles, and cortical efferent arterioles.

CONCLUSIONS

Our results indicate that kinins and ANGII can contribute to the renal vasodilatation in response to ACE inhibitors, but ACE inhibitors appear to have only minor effects on ANGII levels in those renal vessels, which are the well-known sites of renin expression.

Angiotensin modulation of vascular tone and adrenergic neurotransmission in cat femoral arteries

1. AI and AII induced contractions in cat femoral arteries, which were inhibited by saralasin. 2. The response to AI was reduced by captopril and endothelium removal and by chymostatin in endothelium-denuded segments. 3. AII contractions were increased by indomethacin, L-NAME and endothelium removal. 4. AII and AI facilitated the adrenergic neurotransmission. This facilitation was inhibited by saralasin and/or captopril. 5. These data suggest: (1) AI is converted into AII in the endothelial and adventitial layer; (2) the contractions caused by AI and AII are mediated by AII receptors and are modulated by endothelial release of NO and PGI2; and (3) the existence of presynaptic AII receptors mediating the facilitation of neurotransmission caused by AI and AII.

Vasoconstrictive effects of angiotensin I and II in cat femoral arteries. Role of endothelium

1. AI and AII induced concentration-dependent contractions in cat femoral artery segments, the potency of AII being greater than that of AI. 2. The antagonist of AII receptors, saralasin (1 and 10 nM), inhibited the AI and AII responses. 3. Indomethacin (10 microM) and endothelium removal increased the responses to AII, whereas those induced by AI were barely affected. 4. The response induced by AI was reduced by captopril (200 microM). 5. These data suggest: (1) the contractions induced by AII are mediated by AII receptors and endothelial products derived from cyclooxygenase, (2) the response to AI is, in part, produced by its conversion into AII.

Studies of the renin-angiotensin system in the wall of rat femoral resistance vessels

The responses to angiotensinogen, angiotensinogen-(1-14) (tetradecapeptide, TDP), angiotensin I, and angiotensin II and the effect of the renin inhibitor, CH-66, the angiotensin-converting enzyme (ACE) inhibitor, perindopril, and the receptor antagonist, saralasin, were investigated in isolated femoral resistance arteries of the rat. The response to angiotensinogen in the presence of kallikrein was also investigated. Angiotensin I and TDP elicited a contraction which was not reduced by CH-66 but was inhibited by perindopril and saralasin. The response to angiotensinogen was small and not blocked by saralasin but the response to angiotensinogen that was mixed with renin for a few seconds was saralasin-sensitive and perindopril and CH-66 showed a tendency to block this response. The response to angiotensinogen was enhanced in the presence of kallikrein. These results suggest (1) the presence of a partial renin-angiotensin system (RAS) in this preparation, (2) that TDP is not converted via renin while both angiotensin I and TDP are converted through ACE in this preparation and (3) that the responses to angiotensinogen and TDP are different.