入鹿山 容子

It has been reported that probucol is a lipid-lowering agent having a strong antioxidative effect and inhibitory action on vascular smooth muscle cell proliferation. In this work, we studied the effect of treatment with a 1% probucol diet on pulmonary hypertension induced by monocrotaline (MCT) in rats. Rats were fed a control or 1% probucol-supplemented diet for 7 days, then given a single subcutaneous injection of 60 mg/kg MCT or saline, and continuously fed the same diet for 20 days, respectively. MCT caused an increase in right ventricular systolic pressure (RVSP), an indicator of pulmonary hypertension, and central venous pressure (CVP) on day 20. In rats receiving a diet containing 1% probucol, RVSP was significantly lower than that in rats treated with control diet, and CVP remained essentially at the basal level. On day 20, MCT also caused an increase in the ratio of right ventricular (RV) to body weight (BW), compared to the control value, indicating the development of RV hypertrophy in MCT rats. RV hypertrophy was significantly inhibited in 1% probucol-treated rats. These findings suggest that chronic treatment with probucol effectively inhibits the progression of pulmonary hypertension in rats.

This study was designed to examine the immunomodulatory effects of dietary docosahexaenoic acid (DHA) in the absence of eicosapentaenoic acid (EPA). We investigated the effects of feeding dietary DHA ethyl ester (DHA-Et) (97% pure) at levels of 4.8 wt% of the total diet and of feeding EPA ethyl ester (EPA-Et) (99% pure) at 4.8 wt% on the inflammatory response in the challenge phase of the contact hypersensitivity reaction (CHR) in the ears of mice sensitized with 2,4-dinitro-1-fluorobenzene (DNFB). The effect of DHA-Et on T lymphocytes at the CHR site was examined using anti-CD4 antibodies. Furthermore, we examined the cytokines formed at the CHR site on the mRNA level. It was found that 24 h after the challenge, DHA-Et but not EPA-Et reduced the ear swelling. Infiltration of inflammatory cells, in particular, CD4-positive T lymphocytes, into the ears in the challenge phase of CHR was observed. DHA-Et reduced the infiltration of CD4-positive T lymphocytes into the ears. DHA-Et also decreased the expression of interferon-gamma, interleukin (IL)-6, IL-1beta, and IL-2 mRNA in ears. These observations suggest that DHA, but not EPA, may exert an antiinflammatory and immunosuppressive effect. The immunosuppressive effectiveness of fish oil may be attributed mainly to DHA.

In isolated superior mesenteric arteries, vasodilation induced by calcitonin gene-related peptide (CGRP) was significantly larger in 12-week-old spontaneously hypertensive rats (SHR) than Wistar-Kyoto rats (WKY). In WKY and 6-week-old SHR, most of the vasodilator response to CGRP was abolished by Nw-nitro-L-arginine and indomethacin. In contrast, the inhibitors caused no significant change in the response in 12-week-old SHR. Vasodilations induced by acetylcholine and isoproterenol were smaller in 12-week-old SHR than WKY, and that induced by sodium nitroprusside was comparable in both tissues. These results suggest that endothelium-independent vasodilator activity of CGRP is enhanced in hypertensive SHR, which overwhelms the decreased endothelium-dependent effects.

The actions of protein S (PS) on the scratch injury-induced proliferation of rat astrocytes (AC) were studied. PS (10-300 nM) markedly inhibited [3H]thymidine incorporation into injured AC. The effect of 100 nM PS was comparable with that of transforming growth factor-beta 1 (TGF-beta 1; 20 ng/ml). The incorporation of bromodeoxyuridine, which is usually detectable in AC along the border of the wound, was undetectable in the presence of 300 nM PS. The level of PS mRNA in the injured AC was slightly increased 15 h after the injury, although the level of its receptor, Tyro 3 mRNA was not changed significantly. The results of the present study suggest that PS plays an important role in tissue repair processes in the central nervous system (CNS) by suppressing the proliferation of AC as in the case of TGF-beta 1.

Although physiological processes related to vascular function differ greatly between resistance arteries and conduit arteries, it is not known whether the effects of endothelin-1 on these arteries differ in humans. In the present study, the conduit portion and the resistance portion of isolated human mesenteric arteries were suspended in a Krebs-Ringer solution. Norepinephrine and endothelin-1 produced concentration-dependent contractions in both portions. The EC50 value of norepinephrine in the resistance portion (3.7 x 10(-7) M, n = 8) did not differ from that in the conduit portion (3.4 x 10(-7) M, n = 7). However, the EC50 value of endothelin-1 in the resistance portion (3.0 x 10(-9) M, n = 8) was significantly lower than that in the conduit portion (1.1 x 10(-8) M, n = 7, P < 0.05). Although the maximum response to norepinephrine in the resistance portion (calculated as the percentage of 50 mM KCl-induced contraction) did not differ from that in the conduit portion, the maximum response to endothelin-1 in the resistance portion was significantly greater than that in the conduit portion. These results indicate that endothelin-1 induces more potent constriction in resistance portion than in conduit portion in isolated human mesenteric arteries.

Although physiological processes related to vascular function differ greatly between resistance arteries and conduit arteries, it is not known whether the effects of calcitonin gene-related peptide (CGRP), a vasodilator neuropeptide, on these arteries differ in humans. In the present study, the conduit portion and the resistance portion of isolated human mesenteric arteries were suspended in a Krebs-Ringer solution. CGRP produced vasorelaxations in both portions. The EC50 values were very low both in the resistance portion (2.4 x 10(-9) M, n = 7) and in the conduit portion (2.2 x 10(-9) M, n = 7). The maximum response to CGRP in the resistance portion was significantly greater than that in the conduit portion (94.6 +/- 4.0% vs. 64.1 +/- 2.6% relaxation of methoxamine-induced precontraction, both n = 7, p < 0.01). These data suggest that CGRP is one of the most potent endogenous vasodilators in both the resistance portion and the conduit portion of the human mesenteric arteries, and that CGRP induces more potent vasorelaxation in the resistance portion than in the conduit portion of these arteries.

The regulatory systems of endogenous endothelin-1 (ET-1) production from intact tissues and the effects of produced ET-1 on vascular tonus by a closed circuit perfusion system of rat mesenteric artery were investigated. It was demonstrated that ET-1 is released from intact mesenteric arterial beds from Wistar rats both under basal conditions and after stimulation with arginine-vasopressin (AVP) (10(-10)-10(-9) M). Furthermore, AVP (10(-10)-10(-9) M) markedly and dose-dependently induced the expression of prepro ET-1 mRNA in the mesenteric arterial beds. Increased release of ET-1 by AVP may contribute to maintaining vascular tonus. Concomitant addition of actinomycin D inhibited the increased expression of prepro ET-1 mRNA and reduced the amount of immunoreactive ET-1 found during the 6-hour perfusate from AVP (10(-10) M)-stimulated and -unstimulated tissues.

Endothelin-1 (ET-1) caused a dose-dependent vasoconstriction in rat aortic strips in vitro. The sensitivity to ET-1 was significantly higher in 12-week-old spontaneously hypertensive rats (SHR) than in age-matched Wistar-Kyoto (WKY) rats. In contrast, the sensitivity was not different between SHR and WKY rats at 6 weeks of age, which was close to that of 12-week-old SHR. Receptor binding study in microsomal preparations of the aortas with [125I]ET-1 showed that maximum binding value for ET-1 receptor in 12-week-old SHR was only 1.5-fold greater than that in WKY rats and that there was no significant difference in the Kd values. K(+)-depolarization induced vasoconstrictive responses that were also augmented in 12-week-old SHR. Resting membrane potential of the aorta was significantly depolarized in tissues from 12-week-old SHR compared with age-matched WKY rats. The resting membrane potentials were similar in the aorta from 6-week-old SHR and WKY rats, and were between those of 12-week-old SHR and WKY rats. When the aortic strips from 12-week-old WKY rats were partially depolarized in high K(+)-solution or in the presence of ouabain (0.1 mM), the vasoconstrictor effect of ET-1 became similar to that on the strips from SHR in a normal solution. These results suggest that, although age-dependent changes appear to be complicated, the lower resting membrane potential may account considerably for the larger sensitivity to ET-1 in the aorta from 12-week-old SHR than that from age-matched WKY rats.

Endothelin, a recently discovered endothelium-derived peptide, has been reported to produce potent vasoconstriction in various vessels of experimental animals. To study the involvement of endothelin in the regulation of vascular tonus in humans, isolated human mesenteric arteries were investigated by both pharmacological and immunohistochemical methods. The vasoconstrictor action of endothelin-1 was examined on ring segments of human mesenteric arteries. Endothelin-1 induced a slowly developing and sustained contraction, with an EC50 value (half-maximal effective concentration) of 2.9 x 10(-9) M, two orders of magnitude smaller than that of norepinephrine (EC50 of 3.9 x 10(-7) M), indicating that the vasoconstrictor action of endothelin-1 is about 100 times more potent than that of norepinephrine. The contractile effect of endothelin-1 was affected neither by adrenergic, cholinergic, histaminergic, nor serotonergic antagonists, nor by inhibitors of arachidonic acid metabolism. The vasoconstrictor response to endothelin-1 was effectively antagonized by nicardipine, a dihydropyridine Ca2+ channel blocker. Endothelin-1 profoundly augmented contractile response to Ca2+ in partially depolarized tissues. Immunohistochemical studies revealed for the first time that endothelin-like immunoreactivity was localized in endothelial cells of human mesenteric artery. The results of the present study indicate that endothelin-1 is one of the most potent vasoconstrictors in the human mesenteric artery and that it induces vasoconstriction via an ultimately accelerating Ca2+ influx through voltage-dependent Ca2+ channels. Since endothelin-1 can be located in human endothelial cells, it may play an important physiological or pathophysiological role.

To investigate the possible involvement of endothelin-1 (ET-1), an endothelium-derived potent vasoconstrictor peptide, in the pathophysiology of hypertension, plasma ET-1 levels in 15-week-old spontaneously hypertensive rats (SHR) and DOCA-salt hypertensive rats were measured with a sandwich-type enzyme immunoassay. The vasocontractile effect of ET-1 in aortic helical preparations was significantly more sensitive in DOCA-salt hypertensive rats than in control sham-operated rats, but plasma levels of ET-1 did not differ between them. Plasma ET-1 levels in genetically hypertensive rats (SHR and stroke-prone SHR) were significantly lower than those in age-matched normotensive Wistar-Kyoto (WKY) rats. The plasma concentrations of big ET-1, a precursor of ET-1, in both SHR and SHR-SP were significantly lower than those of WKY, suggesting that the production of ET-1 is decreased in rats of genetic hypertension. Although the vascular reactivity to ET-1 increased in both DOCA-salt hypertensive and genetically hypertensive rats, present findings of the plasma ET-1 levels suggest that the role of ET-1 in the vascular control system may be different in DOCA-salt hypertensive rats and genetically hypertensive rats.

Endothelin, an endothelium-derived vasoconstrictor peptide, and angiotensin II were intravenously injected into the femoral vein of normotensive Wistar-Kyoto (WKY) rats that had been anesthetized with urethane. Blood pressure and heart rate were recorded from a cannula inserted into the carotid artery. All experiments were carried out after treatment with adrenergic and cholinergic antagonists. Endothelin showed a potent, dose-dependent pressor action. The dose-response relations for the increase in blood pressure of rats receiving endothelin were comparable with those of rats receiving angiotensin II. However, endothelin showed far more long-lasting effects. Endothelin-induced responses consisted of three phases: a rapid and transient depressor phase and then two phases of pressor (transient and long-lasting) response. Nicardipine (0.1 mg/kg), a dihydropyridine Ca2+ channel blocker, markedly attenuated the slow phase of the pressor response but only slightly attenuated the rapid one. The pressor action of endothelin was not inhibited by continuous infusions of saralasin, which almost abolished the angiotensin II-induced pressor response. Endothelin-induced pressor response was also not attenuated by indomethacin, a prostaglandin synthesis inhibitor. These data provide evidence that endothelin produces a unique, potent, and long-lasting pressor response, which appears to be in part related to the activation of Ca2+ channels. In 12-week-old spontaneously hypertensive rats (SHR), the maximal pressor response to endothelin was slightly but significantly greater than that in age-matched WKY rats, but the dose dependency of the response was approximately consistent with that in WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

An endothelium-derived 21-residue vasoconstrictor peptide, endothelin, has been isolated, and shown to be one of the most potent vasoconstrictors known. Cloning and sequencing of preproendothelin complementary DNA shows that mature endothelin is generated through an unusual proteolytic processing, and regional homologies to a group of neurotoxins suggest that endothelin is an endogenous modulator of voltage-dependent ion channels. Expression of the endothelin gene is regulated by several vasoactive agents, indicating the existence of a novel cardiovascular control system.

The effect of capsaicin on the rat vas deferens was examined in relation to the role of endogenous calcitonin gene-related peptide (CGRP) in modifying the contractility of smooth muscles. Capsaicin attenuated the twitch response of the rat vas deferens induced by the transmural nerve stimulation (TNS) in vitro. The effect of capsaicin was transient and developed tachyphylaxis rapidly. Capsaicin inhibited the contraction induced by the direct electrical stimulation of the innervated tissues in the presence of tetrodotoxin but not of the surgically denervated tissues. CGRP-like immunoreactive nerves were demonstrated to be present in the rat vas deferens. Exogenously applied CGRP inhibited both the TNS-induced twitch response and the contraction induced by direct electrical stimulation. Both capsaicin and CGRP slightly hyperpolarized the resting membrane potential of smooth muscle cells but did not affect the amplitude of the excitatory junction potentials. The intensity of CGRP-like immunoreactivity was reduced markedly after the in vitro incubation of the tissue with capsaicin. No CGRP-like immunoreactive nerves were detected in the denervated tissues. Thus, capsaicin inhibited both the TNS-induced twitch response and the contraction induced by direct stimulation of the smooth muscles only when CGRP-like immunoreactive nerves were normally present. These results suggest that capsaicin releases endogenous CGRP and that the released CGRP inhibits the contraction of the rat vas deferens by acting directly on smooth muscle cells but not on the sympathetic nerves.