Synthesis and structure-activity study of protease inhibitors. V. Chemical modification of 6-amidino-2-naphthyl 4-guanidinobenzoate.

By developing 6-amidino-2-naphthyl 4-guanidinobenzoate (I, FUT-175) as a basic structure, its various derivatives were synthesized and their inhibitory activities on trypsin, plasmin, kallikrein, thrombin, C1r and C1s as well as on complement-mediated hemolysis were examined. The protective effect of these compounds on complement-mediated Forssman shock was also examined in guinea pigs. 6-Amidino-2-naphthyl 4-[(4,5-dihydro-1H-imidazol-2-yl)amino]-benzoate (41, FUT-187) was found to be a suitable compound for oral administration with anti-complement activity superior to that of compound I.

Acute effects of captopril on the baroreflex of normotensive and spontaneously hypertensive rats.

When captopril was injected intravenously in urethane anesthetized rats, a hypotensive effect accompanied by bradycardia was obtained, while an intravenous (i.v.) injection of prostaglandin I2 (PGI2), which induced hypotension of the same magnitude as the hypotensive effect obtained with captopril, caused a marked tachycardia. Simultaneously, sympathetic nerve activity recorded from abdominal sympathetic nerves was unchanged following injection of captopril, while it was significantly increased during hypotension induced by PGI2. The bradycardia, but not the hypotensive effects induced by captopril was abolished by i.v. pretreatment with atropine. Intracisternal injection of a small dose of captopril inhibited reflex tachycardia during hypotension induced by PGI2 and prolonged the hypotensive effect, while intravenous administration of this dose did not inhibit the reflex tachycardia induced by PGI2. In spontaneously hypertensive rats (SHR), the hypotensive effect of captopril was increased partly, however, the accompanying bradycardia was significantly reduced. These findings suggest that captopril inhibits the baroreflex and centrally activates the cardiac vagal nerve. Moreover in SHR, the effect of captopril on cardiac vagal activity was disturbed.

Centrally induced cardiovascular and sympathetic responses to hydrocortisone in rats.

Central effects of hydrocortisone were investigated by injecting it intracerebroventricularly (icv) while recording blood pressure and heart rate in awake rats. Dose-dependent increases in both blood pressure and heart rate occurred following injections of hydrocortisone. Pretreatment by icv injections of the angiotensin II antagonist, [Sar1-Ile8]angiotensin II, completely abolished vasopressor responses to subsequent injections of hydrocortisone. When rats were later anesthetized with urethan to allow recording of abdominal sympathetic nerve activity, hydrocortisone produced vasopressor responses accompanied by corresponding increases in sympathetic nerve firing, which were also abolished by central pretreatment with either [Sar1-Ile8]angiotensin II or angiotensin I converting-enzyme inhibitor, captopril. These results indicate that centrally administered hydrocortisone stimulates the brain renin-angiotensin system to produce vasopressor responses by increasing sympathetic nerve firing.

Cardiovascular and sympathetic nerve responses induced by intracerebroventricular injections of prostacyclin in rats.

Intracerebroventricular (ICV) injections of prostacyclin (PGI2) produced biphasic blood pressure responses consisting of an initial hypotensive phase followed by a sustained pressor phase in awake rats. Heart rate increased following such injections in either awake or anesthetized rats. PGI2, 1 microgram, produced biphasic responses and, 10 micrograms, purely vasodepressor responses in anesthetized rats, but abdominal sympathetic nerve firing recorded was consistently increased. Hypophysectomy did not affect the hypotensive phase of the responses. These results indicate that the initial hypotension can not be explained by centrally-induced changes in sympathetic nerve activity or vasopressin release, but may be due to peripheral effects of PGI2 leaking from the injection site.

Antihypertensive effect of nifedipine and its relationship to severity of hypertension.

The antihypertensive effect of nifedipine (Adalat), a Ca2+-antagonistic drug, was studied in patients with mild or severe hypertension. In both short- and long-term trials, nifedipine exerted a strong hypotensive effect, more pronounced in patients with severe than in cases with mild hypertension. The results of our short-term study showed a positive correlation between the maximum fall in blood pressure induced by nifedipine and pretreatment systolic blood pressure values or the total severity index score of hypertension. In our long-term trial, we also observed a positive correlation between maximum reduction of blood pressure--induced by nifedipine--and pretreatment values. However, no correlation between reduction of blood pressure and total severity index score of hypertension could be established. Our results indicate that nifedipine could be effective in the management of severe hypertension. The hypotensive action of nifedipine, at least partly due to its Ca2+ influx blocking action, suggests that etiologically hypertension may be connected with an abnormal calcium metabolism of the cardiovascular muscle cells.

Enhanced vascular reactivity to norepinephrine in salt-sensitive patients with hypertension.

Twenty patients with hypertension were studied under diets containing low and high salt to identify factors which might be involved in elevating blood pressure under sodium-loading. They were classified as "salt-sensitive" (SS) and "nonsalt-sensitive" (NSS) according to the presence or absence of greater than 10% increases in mean blood pressure when a low salt diet was replaced by a high salt diet. During high-sodium intake, the SS patients showed reduced urinary excretion of sodium and elevated plasma levels of aldosterone as compared with plasma renin activity. The SS patients also showed an enhanced pressor response to norepinephrine under both low-sodium and high-sodium diets. From these results, it is suggested that the sodium retention, which is probably related to nonsuppressed levels of PAC under sodium-loading, is one of the factors in elevating blood pressure in the SS patients. Moreover, the enhanced pressor response to norepinephrine seems to contribute, in part, to elevation of blood pressure in the SS patients under salt-loading.

Endogenous brain angiotensin II-mediated sympathetic nerve responses are not augmented in mature spontaneously hypertensive rats.

Conjugated estrogens injected into the lateral brain ventricle in awake rats elicited behavioral excitation and vasopressor responses. Magnitude of pressor responses was greater in spontaneously hypertensive rats (SHR) than in normotensive Kyoto Wistar rats (WKY). Pressor responses in SHR were abolished by central pretreatments of either captopril or angiotensin II analog. Under urethane anesthesia, conjugated estrogens still produced greater pressor responses in SHR, but accompanying increases in sympathetic nerve firings were the same in both WKY and SHR. These results suggest that while centrally-administered estrogens may activate the brain renin-angiotensin system to increase sympathetic nerve firing and thereby elevated blood pressure, SHR have larger pressor responses only because peripheral vascular reactivity has been increased.

Central vasopressor responses to conjugated estrogens in rats may be mediated via a renin-angiotensin system in the brain.

Central effects of sex steroids on cardiovascular regulation and on behavior were investigated by injecting conjugated estrogens i.c.v. in conscious or anesthetized rats. Conjugated estrogens (0.1-10 micrograms) produced dose-related increases in pressure and behavioral excitation in all rats and drinking in some rats. Marked increases ii pressure and excitation with tonic convulsions resulting in death were produced by similar injections of conjugated estrogens (100 micrograms). Pretreatment with angiotensin I converting enzyme inhibitor or angiotensin II analog abolished both vasopressor responses and behavioral excitation in conscious rats. When rats were later anesthetized with urethane to allow recording of sympathetic nerve activity, 10 and 100 micrograms of conjugated estrogens produced dose-related vasopressor responses accompanied by corresponding increases in peripheral sympathetic nerve activity. Again, converting enzyme inhibitor or angiotensin II analog abolished the increases in both blood pressure and sympathetic nerve activity. By contrast, when conjugated estrogens were injected i.v. up to 2 mg/kg, neither blood pressure nor sympathetic outflow was affected. Collectively, our results suggest that conjugated estrogens infused centrally activate a renin-angiotensin system in the brain, which results in sympathetic hyperactivity leading to blood pressure elevation.

The role of brain angiotensin II in the mechanism of the pressor responses to intracisternal injection of hypertonic NaCl in urethane anesthetized rats.

Intracisternal injections of hypertonic NaCl elicited the pressor responses in urethane anesthetized spontaneously hypertensive and normotensive Wistar rats. The intracisternal pretreatment of 1-Sar-8-Ile-angiotensin II, angiotensin II analog, could abolish the pressor responses to intracisternal injections of 5% NaCl in urethane anesthetized spontaneously hypertensive rats, while basal blood pressure was not affected by these pretreatment. Both intracisternal and intravenous administration of captopril, an angiotensin I converting enzyme inhibitor, did not alter the pressor effect of hypertonic NaCl in normotensive rats. Basal blood pressure was lowered by intravenous injection of captopril. The involvement of angiotensin II in the pressor mechanism of hypertonic NaCl was confirmed by the enhanced pressor responses to intracisternal injections of 5% NaCl in urethane anesthetized rats pretreated intracisternally with angiotensin II. These findings suggest that angiotensin II itself could play an important role in the pressor responses to intracisternal injections of hypertonic NaCl without involving a converting enzyme system.

Sympathetic and pressor hyperresponsiveness to intracisternal injections of hypertonic NaCl in DOCA hypertensive rats.

Blood pressure and sympathetic nerve activity were recorded before and after intracisternal injections of hypertonic NaCl solution in urethane anesthetized normotensive and deoxycorticosterone acetate (DOCA) hypertensive rats. Dose dependent pressor effects were recorded by intracisternal injections using normotensive Wistar rats. And the early phase of responses which were significantly depressed by blocking alpha-adrenergic receptors with phentolamine, accompanied by increased frequency of sympathetic nerve firing. Pressor responses and acceleration of the rate of sympathetic nerve firing produced by intracisternal injections of hypertonic NaCl were appreciably larger in DOCA hypertensives whose basal sympathetic nerve activity was elevated significantly than in normotensive rats. Pressor responses to intravenous injection of norepinephrine were also augmented, but responses to intracisternal injection were augmented more than those to norepinephrine injection. These findings suggest that sodium sensitive site which connects to pressor systems supposedly located around lower brain stem could be hypersensitive and eventually contribute to peripheral sympathetic hyperactivity in DOCA hypertension.