Effect of short-term administration of cromakalim on renal hemodynamics and eicosanoid excretion in essential hypertension

A major role for prostacyclin in nitric oxide-induced ocular vasorelaxation in the piglet

We studied the mechanisms of retinal and choroidal vasorelaxation elicited by nitric oxide (NO) using piglet eyes. The NO donors sodium nitroprusside (SNP) and diethylamine-NONOate caused comparable concentration-dependent relaxation that was partially (approximately 40%) attenuated by the guanylate cyclase inhibitors methylene blue and LY83583 and reduced to a lesser extent (approximately 25%) by the inhibitor of cGMP-dependent kinase, KT 5823. In contrast, NO-induced dilatation (by NO donors and endogenous NO after stimulation with bradykinin) was substantially (approximately 70%) diminished by the KCa channel blockers tetraethylammonium (TEA), charybdotoxin, and iberiotoxin; by the cyclooxygenase inhibitors indomethacin and ibuprofen; by the prostaglandin I (PGI2) synthase inhibitor trans-2-phenyl cyclopropylamine (TPC); and by the removal of endothelium; whereas relaxation of endothelium-denuded vasculature to SNP was unaltered by indomethacin, TPC, and charybdotoxin but was nearly nullified by methylene blue and the Kv channel blocker 4-aminopyridine. NO donors significantly increased PGI2 synthesis and the putative PGI2 receptor-coupled second messenger cAMP, from ocular vasculature (retinal microvessels and choroidal perfusate), and this increase in PGI2 formation was markedly reduced by TPC, tetraethylammonium, charybdotoxin, and/or the removal of endothelium, but it was only slightly reduced by methylene blue and LY83583. Also, SNP and KCa channel openers NS1619 and NS004 caused an increase in PGI2 synthesis in cultured endothelial cells, which was virtually abolished by KCa blockers. Finally, vasorelaxation to a cGMP analogue, 8-bromo cGMP, and protein kinase G stimulant beta-phenyl-1,N2-etheno-8-bromoguanosine 3':5'-cyclic monophosphate was mostly Kv dependent and, in contrast to NO, largely unrelated to PGI2 formation. In conclusion, data indicate that NO-induced ocular vasorelaxation is partly mediated by cGMP through its action on smooth muscle, and more importantly, by stimulating PGI2 formation of endothelial origin via a mechanism mostly independent of guanylate cyclase, which involves the opening of a KCa channel.

Effect of JTV-506, a novel vasodilator, on coronary blood flow in conscious dogs

Coronary vasodilator and hemodynamic profiles of JTV-506, a newly synthesized 2,2-bis-methoxymethyl benzopyran-derivative potassium channel opener, were evaluated in conscious dogs. JTV-506 (2.5-10 microg/kg, i.v.) elicited dose-dependent increases in coronary blood flow (CBF) and heart rate (HR) but only slight changes in mean blood pressure (MBP). Other vasodilators such as levcromakalim, nicorandil, diltiazem, and nitroglycerin, when administered intravenously, elicited increases in CBF and HR and a decrease in MBP. When dosed orally JTV-506 (0.01-0.1 mg/kg), levcromakalim (0.01-0.1 mg/kg), nicorandil (1-10 mg/kg), and nifedipine (3-30 mg/kg) also elicited increases in CBF and HR and a decrease in MBP. JTV-506 caused a marked increase in CBF with slight changes in HR and MBP. In contrast to JTV-506, however, the changes caused by levcromakalim, nicorandil, and nifedipine were accompanied by a marked increase in HR and a marked decrease in MBP. These results suggest that the action of JTV-506 on hemodynamics is different from that of other vasodilators, including reference potassium channel openers, and that the profile of cardiovascular action of JTV-506 may be useful in the treatment of angina pectoris.

Synthesis and selective coronary vasodilatory activity of 3,4-dihydro-2,2-bis(methoxymethyl)-2H-1-benzopyran-3-ol derivatives: novel potassium channel openers

A variety of compounds having a benzopyran such as levcromakalim generally exhibit potent antihypertensive activity. During extensive investigations aimed toward identifying K+ channel openers having selective coronary vasodilation without potent hypotensive and tachycardiac effects, we synthesized a series of 3,4-dihydro-2H-1-benzopyran-3-ol derivatives modified at positions 2, 4, and 6 in the benzopyran ring. Initially, compounds having two methoxymethyl groups at position 2 were found to show a selective effect on coronary blood flow (CoBF) relative to mean arterial pressure (MAP) in anesthetized dogs. To find more potent vasodilators, various benzopyran derivatives modified at position 4 were synthesized and structure-activity relationships were examined by evaluation of the extent and duration of the increase in CoBF in anesthetized dogs. As a result, compounds having a (1,6-dihydro-6-oxopyridazin-3-yl)amino group at position 4, in addition to the two methoxymethyl groups at position 2, were found to be more potent and to have an improved duration of action. Among these compounds, JTV-506, (-)-(3S,4R)-6-cyano-3,4-dihydro-4-[(1,6-dihydro-1-methyl-6-oxopyridaz in-3-yl)amino]-2,2-bis(methoxymethyl)-2H-1-benzopyran-3-ol, exhibited good selectivity for its effect. Administration of this compound (0.03 mg/kg, p.o.) elicited an increase of CoBF without a change of systemic blood pressure and heart rate (HR) in conscious dogs. Further evaluation was performed with respect to (i) the selectivity of its action on the coronary artery versus the aorta and (ii) its effects on MAP, HR, and electrocardiographic ST elevation. As a result, JTV-506 was selected as a potent and selective coronary vasodilator with various pharmacological features favoring clinical development.

Hyperfiltration and conservation of renal function in hypertensive nephrosclerosis patients

Renal glomerular hyperfiltration has been proposed as an important contributing factor to the progression of hypertensive nephrosclerosis in rats with reduced renal mass. However, no clinical studies have assessed the role of glomerular hyperfiltration in the pathogenesis of hypertensive nephrosclerosis in humans. In a prospective, randomized, long-term blood pressure control study with up to 3 years follow-up, we showed that good blood pressure control with a mean diastolic blood pressure < or = 95 mm Hg preceded by a 2- to 4-month period of diastolic blood pressure < or = 80 mm Hg improved renal function in hypertensive nephrosclerosis patients. Patients treated with minoxidil, an angiotensin-converting enzyme inhibitor (enalapril), or a calcium entry blocker (nifedipine) had improvement in renal function, as indicated by a positive slope of the reciprocal serum-creatine concentration versus time and an increment in glomerular filtration rate. These results suggested that improvement in renal function occurred with these major types of antihypertensive drug treatment. To assess the renal hemodynamics of minoxidil, enalapril, and nifedipine, eight patients with hypertensive nephrosclerosis were admitted to the General Clinical Research Center for renal clearance studies on each drug while ingesting a fixed-calorie, 12% protein, 40% fat, and 100 mEq Na/d diet. Mean blood pressure, effective renal plasma flow, and renal vascular resistance did not change during the three phases of treatment. However, minoxidil treatment increased the glomerular filtration rate by 48% versus enalapril and by 79% versus nifedipine. Since minoxidil treatment improves renal function while causing a relative hyperfiltration, glomerular hyperfiltration per se is an unlikely mechanism for the progression of hypertensive nephrosclerosis in humans.