Different Effects of Various Vasodilators on Autoregulation of Renal Blood Flow in Anesthetized Dogs

Nobuyuki OGAWA and Hiroshi ONO

Department of Pharmacology and Toxicology, Hatano Research Institute, Food and Drug Safety Center, 729-5 Ochiai, Hadano, Kanagawa 257, Japan

Accepted March 24, 1986

Abstract-In order to examine whether the autoregulation of renal blood flow is equally influenced by all kinds of vasodilators, kidney perfusion experiments were performed in anesthetized dogs. The perfused kidney usually showed excellent autoregulation of blood flow over the perfusion pressure between 120 and 200 mmHg. Renal blood flow was increased by the renal arterial infusion of diltiazem (100 /cg/min), papaverine (10 mg/min) or nicorandil (300 ig/min) (at the basal perfusion pressure of 100 mmHg) and was maintained at an increased level while the infusion was continued. On the other hand, renal blood flow was increased only transiently by the infusion of nitroglycerin (50 ,ug/min), and the blood flow gradually decreased to the basal level in spite of the continuous infusion. Infusions of diltiazem and papaverine abolished the autoregulation of renal blood flow besides the vasodilator effect, but infusions of nitroglycerin and nicorandil have no effect on the autoregulation. Furthermore, sodium nitroprusside (30 /~g/min) and sodium nitrite (5 mg/min), which are assumed to produce vasodilation through cyclic GMP, also have no effect on the autoregulation of renal blood flow. In conclusion, all the vasodilators do not influence the renal blood flow autoregulation , and vasodilation caused by cyclic GMP is unconnected with the myogenic mechanism regulating the renal blood flow.

The autoregulation of renal blood flow is renal blood flow. In other words, some the maintenance of a stable blood flow level substances produce vasodilation without in spite of fluctuation in the renal perfusion affecting the myogenic response of the renal pressure. The presently accepted mechanism vascu lature. of the autoregulation is the myogenic The present study is to examine whether response of the vascular smooth muscle or not there exists a common mechanism adjusting the vascular tone to the change of among vasodilators which do not impair the perfusion pressure. This myogenic theory is autoregulation of renal blood flow. supported by the evidence that the auto regulation is effectively abolished by Materials and Methods vasodilators, such as papaverine, amino Twenty-seven mongrel dogs of either sex, phylline, verapamil and nifedipine (1-3). weighing 11-17 kg, fed on a pellet dog food Kiil et al. (4) reported that infusion of (CD-5, Clea Japan Co.) were anesthetized acetylcholine into the renal artery produced with a-chloralose (40 mg/kg) and urethane potent vasodilation on canine kidney, but (400 mg/kg) intravenously, preceded by failed to impair the autoregulation. We have sedation with morphine hydrochloride (2 mg/ obtained similar results with acetylcholine kg, s.c.). Pressure-controlled perfusion experi (N. Ogawa and H. Ono, unpublished results) ments were performed with the left kidney. and also with prostaglandin E2 and bradykinin Details of the procedure have been described (5). Thus, there are vasodilators devoid of previously (5). The left renal artery was potency to abolish the autoregulation of cannulated and perfused with blood con ducted from the carotid artery. An initial dose values of the control and during a drug of 500 U/kg of sodium heparin was given as treatment was done according to the paired anticoagulant. When necessary, smaller doses t-test, and those between groups was done of a-chloralose and urethane were supple according to Student's t-test (P<0.05). mented, and sodium heparin was supple mented constantly by 100 U/kg/hr. Perfusion Results pressure was controlled by the use of a Systemic blood pressure and renal blood Starling's pneumatic resistance. Perfusion flow: Table 1 shows the mean values for mean pressure and systemic blood pressure in the systemic blood pressure and renal blood flow femoral artery was measured with electric at the perfusion pressure of 100 mmHg, manometers (transducers: Statham P23Db before and during infusion of drugs. Renal and carrier amplifiers: San-ei 1206B). Renal blood flow was increased by the intra blood flow was measured by an electro arterial infusion of diltiazem (100 ttg/min), magnetic flowmeter (Narco RT-500). A test papaverine (10 mg/min), nicorandil (300 drug solution was infused into a rubber tube /-,g/min), sodium nitroprusside (30 fig/min) connected close to the shank of the renal and sodium nitrite (5 mg/min). The increase arterial cannula by the aid of an infusion of blood flow reached a maximum within pump (Harvard Apparatus 901). 3 min after the onset of the infusion and was Renal blood flow was allowed to stabilize sustained at an increased level during the for 30 min at the basal perfusion pressure of infusion. Mean systemic blood pressure was 100 mmHg; then perfusion pressure was significantly decreased by the infusion of changed stepwise between 60 and 200 each one of these drugs. The infusion of mmHg. After the control observation of the nitroglycerin (50 ,ag/min), however, produced blood flow responses to the stepwise changes only a transient vasodilation, and the initial of perfusion pressure between 60 and 200 vasodilation was nullified in spite of con mmHg, the infusion of a drug was started at tinuous infusion, though a decrease in the the basal perfusion pressure of 100 mmHg, systemic blood pressure was obvious and and pressure-flow relation was examined sustained. Then, the effect of nitroglycerin on again. the renal autoregulation was examined at the Following drugs were studied: diltiazem infusion rate of 50 iig/min. The infusion of hydrochloride (Tanabe), papaverine hydro 100 ,ug/min of diltiazem did not cause a chloride (Nakarai), nitroglycerin (NGA significant increase of blood flow below the 800128, 0.5 mg/ml aqueous solution, perfusion pressure of 80 mmHg. The infusion Nippon Kayaku), nicorandil (Chugai), of papaverine and nitro-compounds except sodium nitroprusside (Wako) and sodium nitroglycerin caused vasodilation at all nitrite (Wako). All drugs were dissolved in ranges of perfusion pressure. or diluted with saline. The dose of the drug is Autoregulation of renal blood flow: expressed as the weight of the base. Control observation usually confirmed The efficiency index of autoregulation excellent autoregulation of the renal blood (ARI) was calculated as follows (6): flow between 120 and 200 mmHg of the perfusion pressure and partial autoregulation between 100 and 120 mmHg. The blood flow changed pressure-dependently below where the renal blood flow changes to 100 mmHg. RBF2 from the initial value of RBF1 when Figure 1 illustrates the effects of diltiazem renal arterial (perfusion) pressure is altered (30 and 100 /tg/min) and papaverine (10 to PRA2 from the initial value of PRA,. mg/min) on autoregulation of renal blood Efficiency of the autoregulation was con flow. Autoregulation of renal blood flow was sidered as follows: ARI<0.3: excellently clearly abolished by diltiazem and papaverine. effective, ARI=0.3-0.7: partially effective, Simultaneous infusion of CaCI2 (30 mg/min) and ARI>0.7: virtually absent. restored the autoregulation impaired by 30 Statistical analysis of differences between zcg/min of diltiazem, but it was not effective Table 1. Mean systemic blood pressure and renal blood flow before and during the infusion of a drug at basal perfusion pressure of 100 mmHg

Fig. 1. Effects of (A) diltiazem (0Q: control, ~ -A: 30 ug/min, A----A: 100 ,ug/min, 17------V: simultaneous infusion of 30 mg/min of CaC12 and 30 pg/min of diltiazem, n=5) and (B) papaverine (0O: control, A---0: 10 mg/ min, n=5) on the pressure-flow curves in perfused dog kidney. Symbols and vertical bars represent means and S.E., respectively. *shows a significant difference from the corresponding value of the control (P<0.05). on restoring the autoregulation impaired by the vasodilators are shown in Table 2. The papaverine (not shown in the figure). Figures control ARI is in all experiments were less 2 and 3 illustrate the effects of nitroglycerin, than 0.5 between 100 and 120 mmHg and nicorandil, sodium nitroprusside and sodium less than 0.3 between 120 and 200 mmHg, nitrite on the autoregulation of renal blood indicating an effective autoregulation. ARI's flow. The infusion of nicorandil (300 /cg/ during infusion of nitroglycerin, nicorandil, min), sodium nitroprusside (30 /cg/min) or sodium nitroprusside and sodium nitrite sodium nitrite (5 mg/min) caused an increase were also less than 0.3 between 120 and in renal blood flow at all ranges of perfusion 200 mmHg, showing that the autoregulation pressure, but did not impair the auto was not influenced. On the other hand, the regulation, shifting the pressure-flow curve ARI's during infusion of diltiazem were upward. Nitroglycerin (50 /Lg/min) also increased at any perfusion pressure range. could not abolish the autoregulation in This effect was dose-related and ARI became addition to the lack of sustained vasodilation nearly 1.0 with the infusion of 100 /Lg/min as stated above, though the change in the of diltiazem, showing a complete abolition systemic blood pressure obviously showed of the autoregulation. ARI's during simul the effectiveness of the drug. Pressure-flow taneous infusion of CaCl2 (30 mg/min) curves before and during infusion of nitro with diltiazem (30 /ig/min) recovered to the glycerin overlapped each other. control value for 140-200 mmHg of perfusion ARI's before and during the infusion of pressure. ARI's were also increased by 10

Fig. 2. Effects of (A) nitroglycerin (Q Q: Fig. 3. Effects of (A) sodium nitroprusside control, z---0: 50 ,ug/min, n=4) and (B) (0-0: control, 0-- \: 30 yg/min, n=5) and nicorandil (0-0. control, 0- 300pg/min, (B) sodium nitrite (0-0: control, 0---:_;: n=4) on the pressure-flow curves in perfused dog 5 mg/min, n=4) on the pressure-flow curves on kidney. perfused dog kidney. Vasodilators and Autoregulation mg/min of papaverine infusion up to 0.7 acetylcholine) activated guanylate cyclase in 0.8, indicating that the autoregulation was vascular smooth muscle (17). considerably impaired. The nature of autoregulation of renal blood flow is generally accepted to be the Discussion myogenic response of the vascular smooth Analysis of pressure-flow curves and the muscle. The myogenic theory has been indexes of autoregulation (ARI) showed deduced from the fact that the autoregulation that autoregulation of renal blood flow was is abolished by the intra-arterial infusion of a impaired by diltiazem and papaverine; and it vasodilator papaverine (3). Ca antagonists was not impaired by nitroglycerin, nicorandil, such as verapamil and nifedipine also have sodium nitroprusside and sodium nitrite. been known to abolish renal autoregulation This lack of influence of the latter agents on through their effects on the vascular smooth the autoregulation can not be accounted for muscle (1). In the present experiment, by any insufficiency of the doses used another Ca antagonist, diltiazem, provided because, as shown Table 1, the increase of the similar result. Furthermore, this inhibitory renal blood flow at the perfusion pressure of effect of diltiazem was antagonized by 100 mmHg with the used doses of nicorandil, simultaneous infusion of excess calcium as sodium nitroprusside and sodium nitrite it was with verapamil and nifedipine (1). were comparable to or even greater than the Thus, the influx of calcium through the cell increase produced by papaverine or by membrane of renal vascular smooth muscle diltiazem. Thus, the different influence of is contributing to the renal vasculature in these agents on the autoregulation suggests adjusting its tone to the change of perfusion the presence of diversified mechanisms for pressure. renal blood flow regulation. The effect of papaverine was not an The Ca antagonist diltiazem, which blocks tagonized by simultaneous infusion of CaCl2 the Ca influx across various cell membranes, solution (2). The same result is obtained in has a potent vasodilator action (7-9). the experiment used aminophylline (2), Papaverine is a potent phosphodiesterase which is also known to be a potent phos inhibitor and induces the accumulation of phodiesterase inhibitor (18). It is generally cyclic AMP (10). On the other hand, nitro assumed that cyclic AMP plays an important glycerin and sodium nitroprusside raise cyclic role in the relaxation of vascular smooth GMP levels in bovine tracheal smooth muscle. Bhalla et al. (19) suggested that muscle (11 ), in guinea pig taenia coli (11 ) cyclic AMP might promote relaxation by and in rat ductus deferens (12). Furthermore, stimulating the removal of calcium from the nitro-compounds concentration-dependently cytoplasma. It is conceivable that increased relax bovine coronary arterial smooth muscle cyclic AMP can overcome the CaCl2 infusion (13) and rat aorta (14) in close association resulting in lowering the cellular calcium. with an increase of cellular cyclic GMP level. Furthermore, it was discussed that papaverine The vasodilation of nicorandil has also been and theophylline had no quantitative cor reported as cyclic GMP-related (15). It thus relation between cyclic AMP level and the appears that vasodilation mediated by degree of relaxation (20). It is also con cyclic GMP does not influence the auto sidered that these drugs may affect renal regulatory mechanism. This is also con blood flow autoregulation by means of sistent with the fact that acetylcholine did not mechanisms that do not depend on phos influence the autoregulation (reference 4 and phodiesterase inhibition. our unpublished observation), since The fact that all vasodilators do not abolish Furchgott and Zawadzki (16) have shown the autoregulation of renal blood flow may that acetylcholine-induced relaxation of arise from differences among the site and arterial strip was dependent on an intact mechanism of action of each vasodilator. endothelial cell layer, and other investigators For the time being, the authors cannot give have shown that the endothelium-derived any good explanation, but the following relaxant factor (obtained in relation to matters should be considered. The vascular

increased renal venous pressure on circulatory autoregulation of isolated dog kidneys. Circ. Res. 7, 643-648 (1959)

segment responsible for the renal autoregu Schmiedebergs Arch. Pharmacol. 285, 201-207 lation must be located proximally to the (1974) afferent arteriole (21-23). Some differences 2 Hashimoto, K., Ono, H. and O'Hara, N.: Blockade are known in the effect of vasodilators on of renal autoregulation by calcium antagonists. renal function. Thomas et al. (24) reported In Calcium-Antagonismus, Edited by Fleck that papaverine increased renal blood flow, enstein, A. and Roskamm, H., p. 221-229, but decreased glomerular filtration rate in Springer-Verlag, Berlin, Heidelberg and New York (1980) dogs. Treatment with Ca antagonists is reported to increase the glomerular filtration 3 Thurau, K. and Kramer, K.: Weitere Unter suchungen zur myogenen Natur der Auto rate and urine flow besides the renal blood regulation des Nierenkreislaufes. PflUgers Arch. flow in dogs and human patients (25, 26). Ges. Physiol. 269, 77-93 (1959) Bastron and Kaloyanides (27) reported that 4 Kid, F., Kjekshus, J. and Loyning, E.: Renal the infusion of sodium nitroprusside into the autoregulation during infusion of noradrenaline, renal artery of the isolated dog kidney angiotensin and acetylcholine. Acta Physiol, increased the renal blood flow and did not Scand. 76, 10-23 (1969) change the glomerular filtration rate in the 5 Ogawa, N. and Ono, H.: No role for prosta intact kidney. The nitro-compounds may not glandins and bradykinin in the autoregulation of have paralyzed the afferent arteriole, but may renal blood flow. Japan. J. Pharmacol. 39, act on a blood vessel other than the afferent 349-355 (1985) arteriole, though there is no evidence to 6 Semple, S.J.G. and DeWardener, H.E.: Effect of support this point. Furthermore, Ohmura et al. (28) showed that sodium nitroprusside counteracted the inhibitory effect of halthane on autoregulation of renal blood flow. It is 7 Sato. M., Nagao, T., Yamaguchi, I., Nakajima, H. also reported that acetylcholine increased and Kiyomoto, A.: Pharmacological studies on a renal blood flow without changing the new 1,5-benzothiazepine derivative (CRD-401). glomerular filtration rate (29). Therefore, Abe Arzneimittelforsch. 21, 1338-1343 (1971) and Okahara (30) suggest that Ca antagonists 8 Nagao, T., Sato, M., Nakajima, H. and Kiyomoto, dilate mainly the afferent arteriole and acetyl A.: Studies on a new 1,5-benzothiazepine choline dilates both afferent and efferent derivative (CRD-401). 11. Vasodilator actions. arterioles. Japan. J. Pharmacol. 22, 1-10 (1972) 9 lmai, S.: Effects of coronary vasodilators on the The present experiment has indicated that large conductance artery as compared with all kinds of vasodilators do not inhibit the those on the small resistive artery and arterioles. autoregulation of renal blood flow. In Japan. Circ. J. 40, 472 (1976) addition, it is suggested that vasodilators 10 Kukovetz, W.R. and Pdch, G.: Inhibition of which relax smooth muscle through cyclic cyclic-3',5'-nucleotide-phosphodiesterase as a GMP increase do not influence the auto possible mode of action of papaverine and regulation. similarly acting drugs. Naunyn Schmiedebergs Acknowledgements: We would like to express our Arch. Pharmakol. 267, 189-194 (1970) appreciation to Chugai Co., Ltd. for the supply of 11 Katsuki, S., Arnold, W.P. and Murad, F.: Effects nicorandil, to Nippon Kayaku Co., Ltd. for nitro of sodium nitroprusside, nitroglycerin and sodium azide on levels of cyclic nucleotides and glycerin and to Tanabe Co., Ltd. for diltiazem; and we thank Messrs. Hideo Katsumura, Syunji Yokota mechanical activity of various tissues. J. Cyclic, and Kazuichi Shukunobe for their technical assis Nucleotide. Res. 3, 239-247 (1977) tance. This work was supported by a Research 12 Schultz, K.D., Schultz, K. and Schultz, G.: Grant for Cardiovascular Diseases (57C-2) from the Sodium nitroprusside and other smooth muscle Ministry of Health and Welfare, Japan. relaxants increase cyclic GMP levels in rat ductus deferens. Nature 265, 750-751 (1977) 13 Kukovetz, W.R., Holzmann, S., Wurm, A. and References Pdch, G.: Evidence for cyclic GMP-mediated 1 Ono, H., Kokubun, H. and Hashimoto, K.: relaxant effects of nitro-compounds in coronary Abolition by calcium antagonists of the auto smooth muscle. Naunyn Schmiedebergs Arch. regulation of renal blood flow. Naunyn Pharmacol. 310, 129-138 (1979)

Influence of bradykinin and papaverine on renal and glomerular hemodynamics in dogs. Renal Physiol. 5, 197-205 (1982)

Imanishi, M., Okahara, T. and Yamamoto, K.: Effects of the calcium antagonist nicardipine on renal function and renin release in dogs. J. Cardiovasc. Pharmacol. 5, 254-259 (1983)

14 Lincoln, T.M. and Fisher-Simpson, V.: A com 22 Selkurt, E.E., Hall, P.W. and Spencer, M.P.: parison of the effects of forskolin and nitro Influence of graded arterial pressure decrements prusside on cyclic nucleotides and relaxation in on renal clearance of creatinine, p-aminohip the rat aorta. Eur. J. Pharmacol. 101, 17-27 purate and sodium. Am. J. Physiol. 159, 369 (1 983) 378 (1949) 15 Holzmann, S.: Cyclic GMP as possible mediator 23 Shipley, R.E. and Study, R.S.: Changes in renal of coronary arterial relaxation of nicorandil (SG brood flow, extraction of inulin, glomerular 75). J. Cardiovasc. Pharmacol. 5, 364-370 filtration rate, tissue pressure and urine flow (1983) with acute alterations of renal arterial blood 16 Furchgott, R.F. and Zawadzki, J.V.: The pressure. Am. J. Physiol. 167, 676-688 (1951) obligatory role of endothelial cells in the 24 Thomas, C.E., Bell, P.D. and Navar, L.G.: relaxation of arterial smooth muscle by acetyl choline. Nature 288, 373-376 (1980) 17 Ignarro, L.J., Burke, T.M., Wood, K.S., Wolin, M.S. and Kadowitz, P.J.: Association between 25 Abe, Y., Komori, T., Miura, K., Takada, T., cyclic GMP accumulation and acetylcholine elicited relaxation of bovine intrapulmonary artery. J. Pharmacol. Exp. Ther. 228, 682-690 (1983) 18 Wells, J.N. and Miller, J.R.: Inhibition of cyclic 26 Yokoyama, S. and Kaburagi, T.: Clinical effects nucleotide phosphodiesterase in muscle. of intravenous nifedipine on renal function. J. Trends Pharmacol. Sci. 4, 385-387 (1983) Cardiovasc. Pharmacol. 5, 67-71 (1983) 19 Bha!la, R.C., Webb, R.C., Singh, D. and Brock, T.: 27 Bastron, R.D. and Kaloyanides, G.J.: Effect of Role of cyclic AMP in rat aortic microsomal sodium nitroprusside on function in the isolated phosphorylation and calcium uptake. Am. J. and intact dog kidney. J. Pharmacol. Exp. Ther. Physiol. 234, H508-H514 (1978) 181, 244-249 (1972) 20 Kukovetz, W.P., Poch, G. and Holzmann, S.: 28 Ohmura, A., Wong, K.C., Pace, N.L. and Cyclic nucleotides and relaxation of vascular Johansen, R.K.: Effects of halothane and sodium smooth muscle. In Vasodilation, Edited by nitroprusside on renal function and auto Vanhoutte, P.M. and Leusen, I., p. 339-353, regulation. Br. J. Anaesth. 54, 103-108 (1982) Raven Press, New York (1981 ) 29 Thomas, C.E., Ott, C.E., Bell, P.D., Knox, F.G. 21 Forster, R.P. and Maes, J.P.: Effect of experi and Navar, L.G.: Glomerular filtration dynamics mental neurogenic hypertension on renal blood during renal vasodilation with acetylc"oline in flow and glomerular filtration rates in intact the dog. Am. J. Physiol. 244, F606-F611 (1983) denervated kidneys of unanesthetized rabbits 30 Abe, Y. and Okahara, T.: Control of renal blood with adrenal glands demedullated. Am. J. flow. Folia Pharmacol. Japon. 82, 1-10 (1983) Physiol. 150, 534-540 (1947) (Abs. in English)