Enalapril in the treatment of hypertension with renal artery stenosis.

The converting enzyme inhibitor enalapril, in single daily doses of 10-40 mg, was given to 20 hypertensive patients with renal artery stenosis. The blood pressure fall six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II and to the concurrent fall in angiotensin II. Blood pressure fell further with continued treatment; the long term fall was not significantly related to pretreatment plasma renin or angiotensin II concentrations. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, fallen further. The rise in active renin during long term treatment was proportionally greater than the rise in angiotensin I; this probably reflects the fall in renin substrate that occurs with converting enzyme inhibition. Enalapril alone caused reduction in exchangeable sodium, with distinct increases in serum potassium, creatinine, and urea. Enalapril was well tolerated and controlled hypertension effectively long term; only two of the 20 patients required concomitant diuretic treatment.     

Pharmacological properties of the converting enzyme inhibitor, enalapril maleate (MK-421)

Enalapril maleate (MK-421), an ethyl ester, is an angiotensin-converting enzyme (ACE) inhibitor from a novel series of substituted N-carboxymethyldipeptides. The parent diacid (MK-422) N-[(S)-1-carboxy-3-phenylpropyl]-L-Ala-L-Pro of MK-421 inhibited hog plasma ACE with an I50 of 1.2 nM. Because deesterification occurs slowly or not at all in vitro, the in vitro I50 for enalapril was 1200 nM. However, both enalapril and MK-422 were potent inhibitors of ACE by the i.v. and oral routes in rats and dogs. In rats with experimental hypertension, enalapril was most potent in those models in which the renin-angiotensin system plays a dominant role (salt restriction, two-kidney Grollman) and in models rendered renin dependent by diuretics, although blood pressure reduction did occur in low or normal renin models such as spontaneously hypertensive rats, in which inhibition of ACE as measured by the blockade of angiotensin I pressor responses bore little temporal relationship to the later fall in blood pressure after enalapril.     

Systolic blood pressure responses to enalapril maleate (MK 421, an angiotensin converting enzyme inhibitor) and hydrochlorothiazide in conscious Dahl salt-sensitive and salt-resistant rats

Systolic blood pressure responses to enalapril maleate (MK 421, a new angiotensin converting enzyme inhibitor (CEI] and hydrochlorothiazide (HTZ) were studied in conscious Dahl salt-sensitive (DS) and salt-resistant (DR) rats maintained on a high salt (8.0% NaCl) and a normal salt (0.4% NaCl) diet. The DS rats were severely hypertensive after 3 weeks on the high salt diet whereas the systolic blood pressure (SBP) of the DR rats were normotensive. Oral treatment with enalapril (15-100 mg X kg-1 X day-1) and HTZ (60-400 mg X kg-1 X day-1) caused a significant reduction of SBP in the DS rats with the high salt diet (P less than 0.001); however, this was not observed until after 4 weeks of treatment when the dosage was 30 and 150 mg X kg-1 X day-1, respectively. Furthermore, enalapril therapy alone significantly reduced the SBP of all groups of rats regardless of diet or Dahl strain (P less than 0.001), but this was not observed until the end of the 7th week of therapy in DR rats on 8.0% NaCl and the end of the 3rd week of therapy for DR and DS rats on 0.4% NaCl. These results suggest that enalapril may lower SBP by mechanisms other than those related to an action as a CEI.     

Medical Grand Rounds: refractory hypertension and renal insufficiency in a patient with renal artery stenosis.

Renal artery stenosis has become increasingly common as a cause of refractory hypertension and renal insufficiency. There is a high prevalence of bilateral disease and the lesions tend to progress over time. Newer, less invasive, imaging modalities such as doppler ultrasound, magnetic resonance angiography, and spiral CT scanning are evolving technologies in the diagnosis of renal artery stenosis. Advances in surgical technique, particularly the development of extra-anatomical procedures such as spleno-renal and hepato-renal by pass, have significantly lowered surgical morbidity and mortality and provides revascularization options for patients with complex vascular disease that would previously not have been considered because of their high surgical risk. Improvements in angioplasty technique and the use of stents are broadening the types of lesions that can be successfully approached with these techniques and may be particularly helpful for patients with more severe cardiac or cerebrovascular disease. The benefits of revascularization may be even greater for preservation of renal function than for control of blood pressure in properly selected patients. It is difficult to predict which patients will benefit from surgical revascularization versus medical management of RAS. Knowledge of the progressive nature of RAS, the high prevalence of bilateral disease, and the clinical characteristics that correlate with progression (e.g., decreasing renal size) are helpful in guiding clinical decisions regarding intervention. Additional studies to determine the predictive value of non-invasive tests such as CRS, doppler ultrasound before and after administration of angiotensin converting enzyme inhibitors, and other tests, are needed to assist the clinician in identifying who will benefit most from revascularization both in terms of renal function and blood pressure control.     

Arterial hypertension and neurofibromatosis: renal artery stenosis and coarctation of abdominal aorta.

A 10-year-old girl had arterial hypertension, generalized neurofibromatosis, coarctation of the abdominal aorta and multiple stenoses at the origin of each renal artery. After resection of the stenotic areas and reimplantation of the renal arteries in the aorta, her arterial pressure decreased substantially. However, hypertension recurred and radiologic follow-up 4 1/2 years later showed distinct progression of the coarctation and renewed stenosis of all renal arteries at their origin. The stenotic areas showed eccentric intimal proliferation, frequently bulging into the lumen, with small nodular aggregates of smooth muscle cells and proliferation of fibrous tissue containing spindle-shaped nuclei in a palisading pattern. Hypertension associated with neurofibromatotic vascular disease has been described in 47 other patients in the literature. These patients have been young (mean age, 14 years) and predominantly male. In contrast to fibromuscular dysplasia, in which 95% of all stenoses are found in the distal two thirds of the renal arteries, in vascular neurofibromatosis more than 50% of the stenoses are found at the origin.     

Insulin sensitivity in patients with essential hypertension: no influence of the ACE inhibitor enalapril.

We studied the effect of an ACE inhibitor (Enalapril [ENA], 10 mg o.d.) and a calcium-channel blocker (Nitrendipine [NIT], 20 mg o.d.) on insulin sensitivity in a double-blind cross-over study. Insulin sensitivity was measured by a two-step hyperinsulinemic euglycemic clamp. Serum potassium concentrations were kept constant during the clamp procedure by means of a variable potassium infusion. Twenty patients with essential hypertension (age 35+/-12 years [mean+/-SD], BMI 31.9+/-5.0 kg m2, initial blood pressure 152+/-10/99+/-6 mmHg) were treated with ENA or NIT for 4 weeks, respectively, with a wash-out period of 3 weeks. No carry-over effects or period effects were observed. Both drugs induced a comparable decline in systolic and diastolic blood pressure (ENA - 15+/-9/ - 13+/-8 mmHg, NIT -16+/-8/- 12+/-6 mmHg). No significant change in body weight occurred with both treatments (ENA -0.4+/-2.0; NIT 0.6+/-1.1 kg). Neither drug had a significant impact on any parameter of insulin sensitivity measured (e.g. insulin sensitivity index SI: ENA 5.2+/-2.0 [basal 5.1+/-2.2], NIT 5.8+/-3.0 [basal SI 5.1+/-2.4) mi/min x m2/microU/ml). In conclusion, no significant differences between ENA and NIT on insulin sensitivity were observed. The reduction of blood pressure had no apparent effect on insulin sensitivity.     

Role of baroreflex in the pressor response of rats with hypertension developed by renal artery stenosis

We examined the interrelationships between the pressor response to the administration of norepinephrine and arginine vasopressin and baroreflex function in rats with hypertension of two days' duration induced by heminephrectomy and a clip placed on the right renal artery (2-day clipped rats). Mean arterial pressure was higher in the 2-day clipped rats than in heminephrectomized rats without clips (sham-operated rats). The pressor response in the 2-day clipped rats to both agents increased as compared to the sham-operated rats. This hyperresponsiveness was attenuated by administering an angiotensin II antagonist, [1-Sar, 8-Ile] angiotensin II. Baroreflex sensitivity was studied by measuring changes in arterial pressure and pulse interval in response to the injection of phenylephrine. Baroreflex sensitivity was not decreased but markedly increased in the 2-day clipped rats and unaffected by infusing the angiotensin II antagonist. These results provide evidence that 1) in the 2-day clipped rats there are exaggerated pressor responses to vasoconstrictors; 2) the hyperresponsiveness is not causally related to the change of baroreflex sensitivity; and 3) angiotensin II plays a significant role in the increased pressor responses; however, the baroreflex mechanism is not involved in attenuation of the hyperresponsiveness by the angiotensin II antagonist.     

Splint renal function after captopril in unilateral renal artery stenosis.

The renal extraction ratios of 131I-sodium iodohippurate (131I-Hippuran) and 125I-thalamate were greatly reduced on the affected side by 50 mg captopril in seven out of 14 patients with unilateral renal artery stenosis. With long term captopril 150 mg daily the uptake of 99mTc-diethylenetriaminepenta-acetic acid by the affected kidney, which was determined by scintillation camera renography, became almost zero in these seven patients, indicating severe reduction of the glomerular filtration rate. Function of the affected kidney returned on discontinuing treatment. The reduced extraction of sodium iodohippurate probably reflected a shortened plasma transit time through the kidney due to intrarenal vasodilatation. The reduced extraction of thalamate reflected a low filtration fraction, suggesting that the vasodilatation was, at least in part, at the level of the postglomerular arterioles. Captopril had little effect on the contralateral kidney and on the kidneys of 17 patients with essential hypertension, and serum creatinine concentrations showed minor changes. Radioisotope renography should be performed after beginning captopril treatment in patients with renal artery stenosis. This is also recommended for patients given captopril as a third line drug when renal artery stenosis has not been excluded. Hypertension is these patients is often severe and difficult to control. Renal artery disease is not rare in this difficult group and finding seriously impaired renal function on one side during captopril treatment may be diagnostic.     

Cilastatin (MK 0791) is a potent and specific inhibitor of the renal leukotriene D4-dipeptidase

The metabolism of leukotriene D4 to leukotriene E4 by a dipeptidase of kidney tissue is strongly inhibited by cilastatin (MK 0791) a known renal dehydropeptidase-I inhibitor. The comparison with similar enzyme activities from other tissues (liver, lung, serum, polymorphonuclear granulocytes) revealed a high specificity of cilastatin for the kidney enzyme which was found to be associated with the microsomal fraction. The lowest detectable inhibitory concentration of cilastatin within renal tissue was 8 X 10(-8)M.