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Endothelin (ET) has been implicated in the pathogenesis of several cardiovascular disorders because of its powerful vasoconstrictor and growth-promoting properties. The ET family consists of three isoforms, ET-1, ET-2 and ET-3. ET-1 appears to be the predominant member of the family generated by vascular endothelial cells. In view of the multiple cardiovascular actions of ET-1, there has been much interest in its contribution to the pathophysiology of hypertension and arteriosclerosis. We have been investigating the roles of ET(A) and ET(B) receptors in ET-1-related cardiovascular diseases using subtype-selective ET receptor antagonists and ET(B) receptor-deficient animals. Our studies have demonstrated that ET-1 overproduction and ET(A)-mediated ET-1 actions seem to play a crucial role in the development of several types of hypertensive and post-ischemic diseases. On the other hand, ET-1 biosynthesis and release are regulated at the transcriptional level, and various endogenous substances are known to stimulate ET-1 gene expression by DNA binding of transcription factors. We and others have recently demonstrated that nuclear factor-kappaB (NF-kappaB), a transcription factor with a pivotal role in inducing genes involved in immune, inflammatory and stress responses, is responsible for endothelial ET-1 production. In in vivo studies, agents that can inhibit the NF-kappaB activation improved the development of ET-1-related cardiovascular diseases. Thus, NF-kappaB inhibition may be a pertinent treatment for ET-1 related diseases.

The Fawn-Hooded Rat (FHR) spontaneously develops pulmonary hypertension (PH) at sea level, and an increased severity of this disease is observed upon exposure to mild hypoxia. A recent report suggested that lung hypoplasia with decreased alveolarization and altered vascular growth led by the decreased activity of endothelial nitric oxide synthase may contribute to the development of PH in the FHR. Exposure to mild hypoxia (P1O2 = 120 mmHg) leads to severe PH in FHR but not in Tester Moriyama rat, a strain that has a serotonin platelet storage-pool deficiency (PSPD) similar to that of the FHR. A serotonin PSPD does not appear to predispose FHR to PH. Endothelin-1 (ET-1) mRNA and peptide levels are increased in the hypertensive lungs of mildly hypoxic FHR. ET-1 may at least partly contribute to the development of PH in this strain.

We have previously reported that Sairei-to (TJ-114), a Japanese herbal medicine, prevented the production of endothelin-1 in anti-GBM nephritic rats, and that Alismatis Rhizoma (Takusha in Japanese), one of the twelve herbs composing TJ-114, might be responsible for the action. In order to further clarify the antinephritic components of TJ-114, we investigated the effects of Takusha extracts on various parameters, including endothelin-1 production of glomeruli in vitro and in vivo using anti-GBM nephritic rats. MeOH-100% MeOH and MeOH-50% MeOH fractions (31.3 microgram/ml or higher) strongly inhibited an increase in endothelin-1 concentration in culture medium when they were added to a culture of glomerular cells derived from nephritic rats. In addition, oral administration of the MeOH-100% MeOH fraction (30 mg/kg) ameliorated the proteinuria, increase in systolic blood pressure and changes in histopathological parameters in nephritic rats. Oral administration of the MeOH-100% MeOH fraction inhibited increase in endothelin-1 expression in the glomeruli of nephritic rats and in endothelin-1 production by a culture of glomerular cells derived from the nephritic rats. Alisols A and B, the main constituents of the MeOH-100% MeOH fraction, inhibited in vitro endothelin-1 production by glomerular cells derived from the nephritic rats. Oral administration of alisol B (30 mg/kg) prevented the endothelin-1 expression by glomeruli and the increase in endothelin-1 production by cultured nephritic glomerular cells. Oral administration of alisol B also ameliorated the proteinuria, the increase in systolic blood pressure and the changes in histopathological parameters in the nephritic rats. These results indicate that the antinephritic action of TJ-114, resulting from the inhibition of endothelin-1 production, may be attributed to the alisols in Takusha.

In order to clarify the antinephritic mechanisms of Sairei-to (TJ-114), its effects on the synthesis and expression of endothelin-1 were evaluated in rats with anti-glomerular basement membrane (GBM) nephritis. TJ-114 was administered orally once daily from the 20th day after anti-GBM serum injection and was continued throughout the experiment. TJ-114 prevented proteinuria and histopathological changes in the glomeruli of nephritic rats. TJ-114 inhibited elevation of the endothelin-1 concentration in the supernatant from cultured glomeruli of nephritic rats and the endothelin-1 positive area in the glomeruli. TJ-114 inhibited the elevation of systolic blood pressure and the number of proliferating cell nuclear antigen (PCNA)-positive cells per glomeruli. We also found that the constitutive Kampo medicine in TJ-114, Gorei-san (TJ-17), inhibited the synthesis and expression of endothelin-1. In addition, the constitutive herbs TJ-17, alismatis rhizoma (Japanese name "Takusha") and hoelen (Japanese name "Bukuryou") inhibited the synthesis and expression of endothelin-1. These results indicate that the antinephritic actions of TJ-114 may be due partially to the inhibition of endothelin-1 synthesis in the glomeruli.