Hiroshi Shionoiri

Muscle sympathetic nerve activity in renovascular hypertension and primary aldosteronism.

Previous studies, including our own, have demonstrated that muscle sympathetic nerve activity (MSNA) is increased in patients with essential hypertension compared with normotensive subjects. However, the features of sympathetic nerve activity are still unknown in secondary hypertension. We examined MSNA in eight patients with renovascular hypertension and in 11 patients with primary aldosteronism. Twenty patients with essential hypertension and 20 normotensive subjects who were age-matched to the patients with renovascular hypertension and those with primary aldosteronism were also studied. The MSNA of a bundle of the tibial nerve was recorded by microneurography in supine subjects and expressed as both burst rate (bursts/min) and burst incidence (bursts/100 heart beats). Plasma renin activity and the plasma concentration of angiotensin II and aldosterone were also measured. MSNA was increased in the patients with renovascular hypertension compared with the patients with primary aldosteronism and those with essential hypertension and the normotensive subjects (p<0.01 for each). MSNA was decreased in the patients with primary aldosteronism compared with those with essential hypertension (p<0.01), and it was smaller than in the normotensive subjects (p<0.l). Furthermore, MSNA, plasma renin activity, and the plasma concentration of angiotensin II decreased significantly in five patients with renovascular hypertension 4–10 days after successful percutaneous renal angioplasty. Thus, the changes in MSNA seem to characterize the patbophysiology of renovascular hypertension and primary aldosteronism. Activation of the renin-angiotensin system may be involved in the increase in the central outflow of sympathetic nerve activity, thus exacerbating hypertension in patients with renovascular hypertension.

REDUCED BAROREFLEX CHANGES IN MUSCLE SYMPATHETIC NERVE ACTIVITY DURING BLOOD PRESSURE ELEVATION IN ESSENTIAL HYPERTENSION

To determine whether the baroreflex control of sympathetic nerve activity is altered in patients with essential hypertension, muscle sympathetic nerve activity (MSNA) was recorded microneurographically from the tibial nerves of 23 normotensive subjects and 23 patients with essential hypertension. When phenylephrine (2 micrograms/kg) was injected intravenously, although the pressor response of mean arterial blood pressure (MAP) was significantly enhanced in the hypertensives as compared with the normotensives, the reflex decrease in MSNA was significantly smaller in the hypertensives. Furthermore, the baroreflex slope for MSNA, used as an index of baroreflex sensitivity and calculated by relating the change in MSNA to the change in MAP, was significantly less in the hypertensives. Following the injection of nitroglycerin (2 micrograms/kg), there were no significant differences between the normotensives and hypertensives in the depressor response, the reflex increase in MSNA or the baroreflex slope for MSNA. These observations suggest that the baroreflex change in sympathetic nerve activity is reduced during phenylephrine-induced blood pressure elevation but not during nitroglycerin-induced hypotension in the hypertensives, and that the blunted response of sympathetic nerve activity occurring during hypertension in these hypertensive patients may underlie the maintenance of high blood pressure in essential hypertension.

Pharmacokinetic Drug Interactions with ACE Inhibitors

SummaryAngiotensin converting enzyme (ACE) inhibitors which have active moieties excreted mainly in urine require adjustment of either the dose or the interval between doses in patients with moderate to severe renal dysfunction or severe congestive heart failure. Those agents such as temocapril (CS 622) and fosinopril, excreted both in urine and bile, may not require such adjustment. Renal clearance of ACE inhibitors may be reduced and some accumulation may occur in elderly patients with mild renal dysfunction or congestive heart failure. The bioavailability of ACE inhibitors is reduced by concomitant food or antacids which may slow gastric emptying and raise gastric pH.Pharmacokinetic interactions with ACE inhibitors are unlikely in patients receiving thiazide or loop diuretics. When ACE inhibitors are given hyperkalaemia may occur in patients with renal insufficiency, those taking potassium supplements or potassium-sparing diuretics, and in diabetic patients with mild renal impairment. While no pharmacokinetic interaction precludes use of this combination, the pharmacokinetics of some ACE inhibitors are subject to greater variability when patients also receive β-blockers. Calcium antagonists and ACE inhibitors have additive antihypertensive effects and pharmacokinetic interactions between these agents are unlikely. One report exists of a significant effect of coadministered hydralazine on the pharmacokinetics and urinary excretion of lisinopril. Data on interactions between ACE inhibitors and digitalis are contradictory. There is no evidence that the concomitant use of ACE inhibitors and digoxin is associated with an increased risk of digitalis toxicity.ACE inhibitors are mainly excreted by glomerular filtration and renal tubular secretion. Possible interactions between ACE inhibitors and probenecid have been noted, with renal and total body clearance of ACE inhibitors being potentially reduced in the presence of probenecid. Probenecid pretreatment may enhance the pharmacodynamic response of ACE inhibitors.Few but contradictory data exist on the effects of H2-blockers on ACE inhibitor pharmacokinetics and little information is available on interactions between ACE inhibitors and hypo-glycaemic drugs. Some case reports link ACE inhibitors with the induction of lithium toxicity. Coadministration of lithium should be undertaken with caution, and frequent monitoring of lithium concentrations is recommended with all ACE inhibitors.Nonsteroidal anti-inflammatory drugs (NSAIDs) may attenuate the haemodynamic actions of ACE inhibitors. NSAIDs reduce renal excretion of ACE inhibitors, with a corresponding increase in circulating drug concentrations. There is little information available on the pharmacokinetic interaction with ACE inhibitors and cyclosporin, but caution should be employed when they are used together. Rifampicin (rifampin) may reduce the plasma ACE inhibitor concentrations and decrease the area under their plasma concentration-time curves, by enhancing the clearance of ACE inhibitors or altering their apparent volume of distribution.

Impaired baroreflex changes in muscle sympathetic nerve activity in adolescents who have a family history of essential hypertension

To evaluate the baroreflex changes and basal sympathetic vasomotor tone among three groups of adolescent normotensives or borderline hypertensives with and normotensives without a family history of hypertension, we continuously recorded muscle sympathetic nerve activity, arterial pressure and heart interval. Baroreflex slopes were calculated either by plotting the heart interval against the preceding peak systolic arterial pressure, or by relating the percentage changes in muscle sympathetic nerve activity to the mean changes in systolic arterial pressure produced by intravenous phenylephrine. The baroreflex slopes for the heart interval were significantly smaller in borderline hypertensive offspring (14 ± 2 ms/mmHg) than in control normotensives (23 ± 2 ms/mmHg) or normotensive offspring (19 ± 3 ms/mmHg), whereas those for muscle sympathetic nerve activity were significantly smaller both in normotensive offspring (-8.3 ± 1.0%/mmHg) and borderline hypertensive offspring (-7.9 ± 0.5%/mmHg) than in control normotensives (-16.3 ± 1.4%/mmHg). Baseline muscle sympathetic nerve activity was higher in borderline hypertensive offspring (20.1 ± 3.0 bursts/min) than in control normotensives (10.1 ± 1.2 bursts/min) or normotensive offspring (12.8 ± 1.4 bursts/min), and also the depressor responses to trimethaphan were significantly enhanced in borderline hypertensive offspring [-19.2 ± 2 versus 14 ± 1 (normotensive offspring) or 12 ± 2 (control normotensives)]. These results indicate that baroreflex inhibition of muscle sympathetic nerve activity was reduced in adolescents with a family history of hypertension even when they were normotensive. This reduced reflex sympatho-inhibition could lead to the development of hypertension by increasing sympathetic vasomotor tone.

Antihypertensive effects and pharmacokinetics of single and consecutive doses of cilazapril in hypertensive patients with normal and impaired renal function.

The antihypertensive effects and pharmacokinetic properties of cilazapril, a long-acting angiotensin-converting enzyme (ACE) inhibitor, were investigated in hypertensive patients with normal renal function (NRF; n = 5) and those with impaired renal function (IRF; n = 7). A 1.25-mg dose of cilazapril was administered orally once a day for 5 or 8 days. Measurement of blood pressure and sampling of blood specimens were done on the first and last days of treatment. Cilazapril induced significant falls in systolic and diastolic blood pressures as early as 1 h after administration. The antihypertensive effects were still present at 24 h postdose. Serum ACE activity was markedly suppressed over 24 h, with the enzyme inhibition greater in the IRF group. Plasma levels of the active diacid in the IRF group were higher than those in the NRF group, with significant differences in the peak levels and areas under the curve (AUC). A significant inverse correlation was found between the creatinine clearance and the AUC for the diacid. Cilazapril was well tolerated by all the patients, and no adverse reactions were observed. These results suggest that cilazapril has a long-lasting action and that it is a useful antihypertensive agent for controlling blood pressure in patients with either NRF or IRF.

Slow Hemodialysis Performed during the Day in Managing Renal Failure in Critically III Patients

Slow hemodialysis (HD) was performed for 10 h during the day in 11 critically ill patients with renal failure. The dialysis method was a modification of the pump-driven continuous venovenous HD. A nonsterile bicarbonate-containing hemodialysate was passed into the EVAL membrane dialyzer at a flow rate of 30 ml/min. No patient developed further hemodynamic instability during the treatment. The serum urea level was maintained below 20 mmol/l within 4 days of initiating the treatment. It allowed the patients to rest without interruption at night. This method was safely conducted by general nursing staff under the supervision of nephrologists on duty during the day. This schedule offers an approach to renal replacement therapy for hemodynamically unstable patients without any potential problem in the extracorporeal circulation at night.

Fosinopril: Clinical Pharmacokinetics and Clinical Potential

Fosinopril is a phosphorus-containing ester prodrug of an angiotensin-converting enzyme (ACE) inhibitor. It is hydrolysed mainly in the gastrointestinal mucosa and liver to the active diacid, fosinoprilat, which has unique pharmacological properties. The majority of the active moieties of other ACE inhibitors are excreted in the urine. This means that an adjustment in either the dosage and/or the administration interval is needed in patients with moderate to severe renal dysfunction, in order to reduce drug accumulation and the possibility of an excessive decrease in blood pressure or other adverse effects. On the other hand, fosinoprilat is excreted both in urine and bile (as with temocaprilat, zofenoprilat and spiraprilat), and thus an adjustment of dosage and/or administration interval may be unnecessary in patients with moderate to severe renal dysfunction, as impaired renal function influences little of the pharmacokinetics of fosinoprilat. Furthermore, the available evidence suggests that the pharmacokinetic variables of fosinoprilat in patients receiving haemodialysis were similar to those in patients with moderate to severe renal dysfunction. Dosage modifications or supplemental dose administration following dialysis may be unnecessary. The hypotensive effect of the combination of fosinopril and a diuretic is synergistic. Pharmacokinetic interactions with fosinopril are unlikely in patients receiving thiazide or loop diuretics. Fosinopril has beneficial effects for patients with hypertension and left ventricular hypertrophy because it produces an adequate reduction in blood pressure and reversal of left ventricular hypertrophy. There are a large number of studies of the pharmacokinetics of fosinopril. However studies of its pharmacokinetic drug interactions with other drugs are far fewer. Further investigations are needed in several clinical settings.

Presence of functional receptors for atrial natriuretic peptide in human pheochromocytoma

Pheochromocytoma, a catecholamine-secreting adrenomedullary tumor, has been shown to contain the functional receptor for human atrial natriuretic peptide(h-ANP). Release of catecholamines from tissue slices of pheochromocytoma was inhibited by h-ANP in a dose-dependent manner. Binding assays using 125I-ANP revealed a single class of high affinity binding sites for ANP. When covalently tagged with 125I-ANP and electrophoresed under non-reducing and reducing conditions, the receptor migrated as a 140-kDa band and a 70-kDa band, respectively, reflecting its disulfide-linked subunit structure. The presence of ANP receptor in pheochromocytoma was further demonstrated by immunohistochemistry; the tumor was positively stained with an antireceptor antiserum. The antiserum was also useful to establish the zona glomerulosa localization of ANP receptor in the normal human adrenal gland.

Glucose and lipid metabolism during long-term treatment with cilazapril in hypertensive patients with or without impaired glucose metabolism.

The effects of long-term cilazapril therapy on glucose tolerance and serum lipid profiles were investigated in 19 hypertensive patients: seven with normal glucose tolerance and 12 with glucose intolerance (including three patients with noninsulin-dependent diabetes). Cilazapril was administered once daily for a mean duration of 6.4 months. A 75-g oral glucose tolerance test was performed before and during long-term therapy with cilazapril. Cilazapril produced satisfactory control of blood pressure in both patient groups during long-term therapy. It was well tolerated by all patients. Neither fasting nor postglucose-load venous plasma glucose levels were altered in either group of patients, and no patients with normal glucose tolerance developed diabetes mellitus during the study. There were no significant changes in the insulinogenic index (ΔIRI/ΔBS at 30 min postglucoseload) in patients with normal or impaired glucose tolerance. No significant changes in fasting levels of serum cholesterol, HDL-cholesterol, LDL-cholesterol, and triglycerides were observed in either group. These results suggest that effective long-term cilazapril therapy does not compromise glucose or lipid metabolism in hypertensive patients. Cilazapril may have a clinical advantage in that it can be given to hypertensive patients without concern that it might alter their serum lipid concentrations or impair glucose tolerance.

Antihypertensive effects and pharmacokinetics of single and consecutive administration of doxazosin in patients with mild to moderate essential hypertension.

A single dose of doxazosin, a long-acting postsynaptic α1-adrenoceptor antagonist, was administered to seven patients with essential hypertension. Following administration of a single dose, all the patients except one who was forced to be discharged from the hospital for work, continuously received doxazosin once daily (o.d.) for evaluation of its consecutive dosing effect. The antihypertensive effect, pharmacokinetics, and effects on the plasma renin activity (PRA) of doxazosin were investigated. Following a 2-mg single dose of doxazosin, the systolic blood pressure (SBP) decreased significantly up to 12 h. whereas consecutive dosing produced a significant decrease in the SBP up to 24 h and a significant decrease in the mean blood pressure up to 24 h as compared with placebo. The pharmacokinetic parameters of doxazosin in both single- and consecutive-dose study were 18.9 and 25.8 ng/ml in Cmax, 11.1 and 12.9 h in half life (t1/2), and 182.0 and 273.0 ng h/ml in area under the curve (AUC)240, respectively. No significant changes were observed in PRA and plasma concentration of catecholamines. Neither were there any observable changes in endogenous creatinine clearance and in the urinary excretion rates of Na, K. and Cl. Doxazosin was well tolerated by all patients, and no untoward effects were observed. Doxazosin effectively reduces blood pressure and, because of its long t1/2 and minimal effects on PRA catecholamines. and electrolytes, seems to be a useful antihypertensive agent in patients with essential hypertension.