Inhibitory Effects of Trifluoperazine and Chlorpromazine, Calmodulin Inhibitor, on Autoregulation of Renal Blood Flow Nobuyuki OGAWA, Syunji YOKOTA and Hiroshi ONO Departmentof Pharmacologyand Toxicology,Hatano ResearchInstitute, Food and DrugSafety Center,729-5, Ochiai,Hadano, Kanagawa257, Japan Accepted January 6, 1987 Abstract-An intra-arterial infusion of a calmodulin inhibitor trifluoperazine (3 mg/min) or chlorpromazine (5 mg/min) caused obvious inhibition of autoregu lation of renal blood flow in dogs. Simultaneous infusion of CaCl2 (30 mg/min) or Ca channel activator BAY K 8644 (5 fig/min) with these calmodulin inhibitors reduced renal blood flow, but could not block the inhibitory activity of calmodulin inhibitors on the autoregulation. The present experiment shows the contribution of the Ca-calmodulin system to the mechanism of autoregulation of renal blood flow. The renal blood flow is maintained infusion of a calmodulin inhibitor, tri remarkably constant by autoregulation over fluoperazine or chlorpromazine (7) in the a wide range of perfusion pressures. As for kidney of anesthetized dog. Furthermore, the the mechanism, presently it is accepted that effect of simultaneous infusion of CaCl2 or the principal process is the myogenic response BAY K 8644 with these calmodulin inhibitors of the vascular smooth muscle automatically was also examined. adjusting tone to the change of perfusion Ten mongrel dogs of either sex, weighing pressure. We have demonstrated a chain of 12-20 kg, were anesthetized with a evidence that autoregulation of renal blood chloralose (40 mg/kg) and urethane (400 flow is directly dependent on transmembrane mg/kg), intravenously, preceded by sedation influx of Ca21 through Ca channels; the with morphine hydrochloride (2 mg/kg, s.c.). abolition of autoregulation caused by The left renal artery was exposed retroperi verapamil, nifedipine and diltiazem was toneally, cannulated and perfused with blood antagonized by CaCl2 (1, 2) or BAY K 8644, conducted from the carotid artery by means a Ca channel activator (3, 4). Also we have of a Harvard peristaltic pump (Model 1215). reported that EDTA abolished renal auto An initial dose of 500 U/kg of sodium heparin regulation, and this effect of EDTA was was given as anticoagulant. Perfusion counteracted by simultaneous infusion of pressure was regulated by the use of CaCl2, but not by that of BAY K 8644 (4). Starling's pneumatic resistance through which Several investigators have shown that excess blood was conducted to the left the Ca-calmodulin system is involved in the jugular vein. A desired level of perfusion vascular smooth muscle activity (5, 6). pressure was obtained by changing the Therefore, the mechanism of renal blood flow pressure of the pneumatic resistance. autoregulation performed by the myogenic Perfusion pressure and systemic blood response, presumably activated by the Ca2+ pressure in the femoral artery were measured influx through Ca channels induced by the with an electric manometer (transducer: change of perfusion pressure may be de Statham P23Db and carrier amplifiers: San pendent on calmodulin. ei 1206B). Renal blood flow was measured The present experiment was designed to by an electromagnetic flowmeter (Narco RT test the above hypothesis. The pressure-flow 500). These parameters were recorded on an relation was examined before and during ink-writing oscillograph (San-ei 8S-53). Smaller doses of a-chloralose and urethane presented as means+S.E. were supplemented when necessary, and Control observations show a complete sodium heparin was supplemented con autoregulation which maintained renal blood stantly by 100 U/kg/hr. A drug solution was flow constant and an ARI value less than infused into a rubber tube connected close 0.1 in the range of 120-200 mmHg. Partial to the shank of the renal arterial cannula by autoregulation was also shown between 100 the aid of an infusion pump (Harvard Model and 120 mmHg (Figs. 1 and 2). 901). The intra-arterial infusion of trifluoperazine The experimental protocol consisted of 4 increased renal blood flow significantly at a periods. The first period was for the control, perfusion pressure above 120 mmHg and and the perfusion pressure was changed between 60 and 200 mmHg to examine the autoregulatory response to the renal vasculature. Then, in the second period, trifluoperazine (3 mg/min) or chlorpromazine (5 mg/min) was infused into the renal artery, and autoregulation was examined again. In the third period, simultaneous infusion of CaCI2 (30 mg/min) with tri fluoperazine or chlorpromazine was per formed, and the autoregulation was examined. In the forth period, BAY K 8644 (5 /cg/min) was infused with trifluoperazine or chlor promazine. The changing maneuver of the perfusion pressure was performed 10 min after the onset of each infusion. Doses of trifluoperazine and chlorpromazine were determined to cause adequate inhibition of the renal autoregulation by a preliminary search. BAY K 8644 was donated by Bayer AG. Trifluoperazine dihydrochloride and chlor promazine hydrochloride were purchased from Funakoshi and Wako, respectively. BAY K 8644 was dissolved in 99.5% ethanol to a concentration of 1 mg/ml. This stock solution was diluted to a desired concen tration with 0.9% saline. The dose of drugs is expressed as the weight of the base. The efficiency index of autoregulation (ARI) was calculated according to the Fig. 1. Effects of trifluoperazine-CaCl2 and -BAY K formula of Semple and DeWardener (8) : 8644 on the relationship of renal blood flow to renal perfusion pressure (upper panel) and the autoregula ARI (RBF2-RBF1)/RBF1 (P tory indexes of renal blood flow (lower panel) (n=5). RA2-PRA1)/PRA1 Symbols show means and vertical bars show S.E. where the renal blood flow changes RBF2 0-0: control pressure-flow, •-•-S: that dur from the initial value of RBF1 when renal ing infusion of 3 mg/min of trifluoperazine, A-••-A: that during simultaneous infusion of CaC12 (30 mg/ perfusion pressure is altered to PRA2from the min) with trifluoperazine, A-•••-A: that during initial value of PRA1. simultaneous infusion of BAY K 8644 (5 jig/min) Differences of means were analyzed with trifluoperazine. *shows a significant difference using the paired t-test and were considered from the corresponding value of the control (P< significant when P<0.05. Data will be 0.05). 8644 (5 ug/min) with trifluoperazine decreased renal blood flow and shifted the pressure-flow curve parallel to the right, but the autoregulation was still impaired. Con sequently, the blood flow rate was sig nificantly lower than the control rate at perfusion pressures below 120 mmHg (Fig. 1). The infusion of chlorpromazine (5 mg/ min) also caused a pressure-dependence of renal blood flow in all perfusion pressure ranges; i.e., chlorpromazine impaired the autoregulation (Fig. 2). ARI between 120 and 200 mmHg was higher than that of the control period (Fig. 2). Simultaneous infusion of CaCI2 (30 mg/min) or BAY K 8644 (5 fig/min) with chlorpromazine decreased renal blood flow to a level significantly lower than that of the control for perfusion pressures below 120 mmHg (Fig. 2). ARI during simultaneous infusion of CaCI2 or BAY K 8644 with chlorpromazine was even higher than during the infusion of chlor promazine alone (Fig. 2). Calmodulin has been considered to be an important regulator in the mechanism of vascular smooth muscle contraction (5, 6). Calmodulin inhibitor W-7 (5) produced relaxation of rabbit aortic strips with various agonist, and these agonist-induced con tractions were inhibited in a noncompetitive Fig. 2. Effects of chlorpromazine-CaCl2 and -BAY K fashion. W-7 also shifted the dose-response 8644 on the relationship of renal blood flow to renal curve for CaCI2 both rightward and down perfusion pressure (upper panel),and the autoregula ward (5, 6). This inhibitory effect of W-7 was tory indexes of renal blood flow (lower panel) (n=5). obviously different from those of Ca 0-0: control pressure-flow, •-•-6: that during antagonists such as verapamil and nifedipine infusion of 5 mg/min of chlorpromazine, A -A: (6). Thus, these observations suggested that during simultaneous infusion of CaC12 (30 that calmodulin contributed to a common mg/min) with chlorpromazine, A-•••-A: that during process in the course of smooth muscle simultaneous infusion of BAY K 8644 (5 pg/min) contraction. with chlorpromazine. *shows a significant differ Previously, one of the authors reported ence from the corresponding value of the control that verapamil and nifedipine inhibited renal (P<0.05). blood flow autoregulation, but these inhibitory effects were antagonized by caused a pressure-dependence of renal simultaneous infusion of CaCl2 with Ca blood flow and ARI higher than that of the antagonists in dog kidney (1). Furthermore, control period in all perfusion pressure ranges our recent study showed that the inhibitory (Fig. 1). Mean systemic blood pressure effects of verapamil and nifedipine in renal decreased significantly from 116±6 to 110±4 autoregulation were antagonized by simul mmHg (P<0.05) at 10 min after the start of taneous infusion of the Ca channel activator trifluoperazine infusion. Simultaneous BAY K 8644 (3, 4). Therefore, it is considered infusion of CaCl2 (30 mg/min) or BAY K that the mechanism establishing auto regulatory vascular response involves, at 2 Ogawa, N. and Ono, H.: Different effects of least partly, the process of Ca2+ entry through various vasodilators on autoregulation of renal Ca channels over changes of perfusion blood flow in anesthetized dogs. Japan. J. Pharmacol. 41, 299-306 (1986) pressure. 3 Ogawa, N. and Ono, H.: Different effects of The present study showed that calmodulin noradrenaline, angiotensin II and BAY K 8644 inhibitor, such as trifluoperazine and on the abolition of autoregulation of renal blood chlorpromazine, abolished renal blood flow flow by verapamil. Naunyn Schmiedebergs Arch. autoregulation. Kanamori et al.