Cyanoamidines. II. Synthesis and pharmacological activity of N-arylalkyl-N'-cyano-3-pyridinecarboxamidines

Relaxation of human placental arteries and veins by ATP-sensitive potassium channel openers

BACKGROUND

Adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) are important modulators of vascular tone. Preliminary data from our laboratory suggests that K(ATP) channels are expressed in the fetoplacental vasculature where addition of pinacidil, a specific K(ATP) opener, promotes relaxation. We aimed to assess the effects of KRN2391 and KRN4884 on the fetoplacental vasculature, which are putative K(ATP) channel openers.

MATERIALS AND METHODS

Functional activity of K(ATP) channels was assessed in chorionic plate arteries and veins using wire myography. Cromakalim-, KRN2391- and KRN4884-induced relaxations were assessed in the presence and absence of agonist-induced pretone. Cromakalim, an established K(ATP) channel opener, acted as control.

RESULTS

KRN2391 evoked significantly greater relaxation of chorionic plate arteries and veins than either KRN4884 or cromakalim. KRN2391-induced relaxation of precontracted arteries and veins was reduced in the presence of inhibitors of the nitric oxide pathway (L-NNA or LY83583). With KRN4884, there was no contribution of nitric oxide to the induced relaxation.

CONCLUSIONS

We conclude that K(ATP) channels play an important role in controlling placental vascular tone. KRN2391 induces relaxation of human placental blood vessels by activation of K(ATP) channels and via activation of nitric oxide-dependent pathways.

Antihypertensive properties of KRN4884, a novel long-lasting potassium channel opener

The antihypertensive action of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine ), a newly synthesized 3-pyridine derivative was examined in conscious spontaneously hypertensive rats (SHRs). A single administration of KRN4884 (0.5, 1.5 mg/kg, p.o.) produced a dose-dependent and long-lasting antihypertensive effect. The 7-day repeated administration of KRN4884 (0.5, 1.5 mg/kg, p.o.) did not diminish antihypertensive activity during the treatment period or induce rebound hypertension after the discontinuation of treatment. To examine the mechanism of the antihypertensive effect of KRN4884, we studied its vasorelaxing effects in rat isolated aortae precontracted with 25 mM KCl. Single application of KRN4884 showed a slower onset of inhibitory action than that of levcromakalim. KRN4884 was approximately 26-fold more potent than levcromakalim and 10-fold less potent than nilvadipine. KRN4884- and levcromakalim-induced vasorelaxation were antagonized by glibenclamide. Furthermore, we observed the recovery of the contraction inhibited by these drugs after repeated washing. The inhibitory effect of KRN4884 was restored only after four washes, whereas that of levcromakalim was completely restored after one wash. The nilvadipine-induced inhibitory effect was the most resistant to washing among these drugs. These results suggest that KRN4884 shows a long-lasting antihypertensive effect based on its potent potassium channel-opening action. The long-lasting action may be due to a slow association/dissociation with/from the binding sites on vascular smooth muscle.

Effects of KRN4884 (a novel K+ channel opener), levcromakalim, nilvadipine and propranolol on endothelin-1-induced heart disorders in anesthetized rats

The effects of KRN4884 (5-amino-N-[2-(2-chrolophenyl)ethyl]-N'-cyano-3-pyridinecarboxa midine), a novel K+ channel opener, on the electrocardiogram changes caused by the intracoronary administration of endothelin-1 (ET-1) were studied in anesthetized rats and compared with the effects of levcromakalim, a K+ channel opener; nilvadipine, a Ca2+ antagonist; and propranolol, a beta-adrenoceptor antagonist. KRN4884 (50 microg/kg, i.v.) and levcromakalim (300 microg/kg, i.v.) inhibited the ST segment elevation and the development of arrhythmias induced by ET-1 (5 microg, i.c.) and decreased the incidence of death. Nilvadipine (300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.) each prevented the ST segment elevation, but the suppressions of the occurrence of arrhythmias produced by nilvadipine and propranolol were less than that shown by KRN4884. KRN4884 (30 and 50 microg/kg, i.v.), levcromakalim (100 and 300 microg/kg, i.v.) and nilvadipine (100 and 300 microg/kg, i.v.) significantly decreased the mean blood pressure in a dose-dependent manner, but propranolol did not. The heart rate was decreased by nilvadipine (100 and 300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.), but was not affected by KRN4884 (30 and 50 microg/kg, i.v.) or levcromakalim (100 and 300 microg/kg, i.v.). These results suggest that pretreatments with KRN4884 and levcromakalim are more effective on ET-1-induced electrocardiogram changes than those with nilvadipine and propranolol.

Effect of KRN4884 on lipid metabolism in hyperlipidemic rats

1. KRN4884 is a novel pyridinecarboxamidine type potassium channel opener. 2. To determine whether KRN4884 affects lipid metabolism, we investigated its effects on serum lipid levels by using two types of hyperlipidemic rats: genetically hyperlipidemic obese Zucker rats and diet-induced hyperlipidemic rats fed a high fat diet. KRN4884 dose dependently decreased systolic blood pressure in Zucker rats. 3. Oral administration of KRN4884 (1-10 mg/(kg day) for 14 days dose dependently reduced serum triglyceride levels in Zucker rats. The reductions in serum triglyceride were associated with reductions in triglyceride in chylomicron and very low density lipoprotein. 4. KRN4884 produced no change in serum insulin and glucose levels in Zucker rats. 5. KRN4884 exhibited a similar triglyceride lowering effect in diet-induced hyperlipidemic rats. 6. These results suggest that KRN4884 has a beneficial effect on serum triglyceride levels as well as a hypotensive effect.

KRN4884, a novel K channel opener: antihypertensive effects in conscious renal hypertensive dogs

We examined the antihypertensive effects of KRN4884, 5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarbocamidine+ ++, in normotensive dogs, a high-renin model acute renal hypertensive dog (RHD), and a low-renin model chronic RHD in the conscious state, compared with levcromakalim and nilvadipine. KRN4884 decreased mean blood pressure (MBP) at a dose of 0.1 mg/kg p.o. in normotensive dogs and both RHDs. The decrease in MBP was greater in both RHDs than in normotensive dogs, and there were no significant differences between the two RHDs. A transient increase in heart rate (HR) accompanied the increase in MBP in all three types of dogs. In the chronic RHD, KRN4884 at doses of 0.05, 0.1, and 0.2 mg/kg produced a dose-dependent decrease in MBP. The antihypertensive effect of KRN4884 (0.1 mg/kg) was similar to those of levcromakalim (0.05 mg/kg) and nilvadipine (1.0 mg/kg) in magnitude and more prolonged than those of the compounds. The tachycardia induced by KRN4884 was similar to that induced by levcromakalim and was stronger than that induced by nilvadipine. In the 15-day repeated oral-administration study, KRN4884 (0.1 mg/kg) induced sustained hypotensive effects and transient increases in HR and plasma renin activity. No tolerance to the antihypertensive effect of KRN4884 was observed during a 15-day repeated dosing period. After withdrawal of KRN4884, no rebound phenomena in MBP and HR were observed. Neither the maximal concentration nor area under the curve (AUC) of KRN4884 in plasma were changed at days 1, 8, and 15. These data indicate that KRN4884 produces a strong and persistent antihypertensive response in both low-renin and high-renin models of RHD in a conscious state, which suggests that KRN4884 may be useful as an antihypertensive agent.

Effects of KRN4884, a novel pyridinecarboxamidine type KATP channel opener, on serum triglyceride levels in rats

1. The effects of KRN4884, a novel pyridinecarboxamidine type KATP channel opener, on serum triglyceride levels were investigated in Sprague-Dawley rats. 2. Oral administration of KRN4884 (3 mg kg-1) for 10 days caused a significant reduction in serum triglyceride levels, which was comparable to that of clofibrate (160 mg kg-1). Reduction in serum triglyceride levels by KRN4884 and clofibrate were accompanied by a reduction in triglyceride levels both in chylomicron and in very low density lipoprotein. KRN4884 treatment did not affect serum concentrations of total cholesterol and phospholipid, but did increase free fatty acid levels. Clofibrate reduced total cholesterol, phospholipid and free fatty acid levels. 3. Administration of clofibrate significantly decreased triglyceride secretion rate as measured by the Triton WR-1339 injection procedure, while KRN4884 did not. 4. Rats receiving KRN4884 exhibited an increase in lipoprotein lipase (LPL) activity both in adipose tissue and in skeletal muscle. There was an inverse correlation between serum triglyceride levels and tissue LPL activities. KRN4884 did not change hepatic triglyceride lipase (HTGL) activity. Clofibrate affected neither LPL nor HTGL activities. 5. It is concluded that administration of KRN4884 results in reduced serum triglyceride levels which may be due to the enhancement of LPL activity in peripheral tissues.