Some thoughts on pathogenesis, therapy and prevention of hypertension

Pathogenesis of structural vascular changes in hypertension

The pathogenic role of angiotensin II (ANG II), dietary sodium chloride, sympathetic activation, obesity and aldosterone in the development of structural vascular changes (SVCs) in hypertension is considered from three perspectives (criteria): their utility in predicting hypertension and its complications (predictability); the effect of their inhibition or removal on the reversal of SVCs (reversibility); and their ability to induce SVCs in experimental animals (reproducibility). Only ANG II meets all three criteria. Importantly, ANG II increases preglomerular vascular resistance by inducing structural changes in renal cortical resistance arteries and arterioles. High salt intake, by dilating and thereby stiffening some arteries, may play a role in the development of systolic hypertension with aging, but does not produce structural changes in renal cortical resistance vessels. While high circulating levels of norepinephrine are associated with SVCs, the experimental evidence for the role of sympathetic nerve stimulation in the development of SVCs is inconclusive. Obesity is associated with hypertension, but is not known to be associated with SVCs. Salt-loading is required for aldosterone to produce SVCs, but vascular pathology in this experimental model differs from that in benign essential hypertension. The findings of this review indicate that SVCs in extra-renal sites by themselves do not lead to hypertension; structural changes in renal cortical arteries and arterioles that increase preglomerular vascular resistance are needed. Progressive trophic stimulation of preglomerular resistance vessels by itself may lead to hypertension. ANG II is prime candidate for such stimulus.

KT3-671, an angiotensin AT1 receptor antagonist, attenuates vascular but not cardiac responses to sympathetic nerve stimulation in pithed rats

Effects of KT3-671 on vascular and cardiac sympathetic neurotransmission were investigated in pithed rats. The pressor response to spinal stimulation (5 Hz) of the pithed rat without the adrenals was approximately 75% of that with the adrenals. Guanethidine (8 mg/kg, i.v.) decreased by about 76% the pressor response to sympathetic stimulation in the pithed rat with intact adrenals and the guanethidine-resistant response was almost completely abolished by bilateral adrenalectomy. Therefore, the following experiments were done using the pithed rat without the adrenals. KT3-671 (1-10 mg/kg, i.v.) as well as losartan (1-10 mg/kg, i.v.) inhibited dose-dependently the pressor response to sympathetic stimulation. KT3-671 was approximately four times more potent than losartan in inhibiting the pressor response. The two angiotensin II subtype 1 receptor antagonists (10 mg/kg, i.v.) did not affect the pressor response to exogenously administered norepinephrine. Neither KT3-671 nor losartan influenced the tachycardia induced by spinal stimulation and isoprenaline. Intravenous infusion of angiotensin II (100 ng/kg/min) did not affect both pressor and tachycardic responses to sympathetic stimulation. In conclusion, KT3-671 as well as losartan inhibits vascular but not cardiac sympathetic neurotransmission of the pithed rats, which may contribute to its overall antihypertensive efficacy.

ACE inhibition in chronic renal failure and in the treatment of diabetic nephropathy: focus on spirapril

The management of hypertension and nephropathy, in both diabetes and other forms of renal disease, is usually based on blood pressure reduction through an angiotensin-converting enzyme (ACE) inhibitor-based treatment regimen. With particular respect to the choice of ACE inhibitor drug, there are no definitive direct comparisons in the treatment of renal disease. In terms of blood pressure reduction, however, there is evidence that spirapril is at least as effective as the reference ACE inhibitor, enalapril. However, patients with diabetic nephropathy and/or chronic renal failure are at potential risk from drug accumulation if the preferred agent relies predominantly on glomerular filtration for its elimination. In this respect spirapril may have an advantage because it has been shown that there are no clinically relevant increases in the spirapril(at) concentrations (24 h post-dose) even in the setting of advanced renal failure (creatinine clearance <20 ml/min). Thus, there is no requirement to modify the dose and no concerns about drug accumulation or the potential for exaggerated therapeutic or adverse effects. In summary, an ACE inhibitor drug is seen as an integral component of the drug treatment regimen for patients with nephropathy. Where there is renal failure it may be prudent to administer a drug, such as spirapril, which also has alternative elimination mechanisms.

Efficacy and safety of spirapril in mild-to-moderate hypertension

Spirapril is a new angiotensin-converting enzyme (ACE) inhibitor. It is a prodrug with a resorption of about 50%. The active metabolite spiraprilat reaches maximal plasma concentration within 2-3 h after oral administration. Spirapril can be administered once daily because of its long duration of action caused by an elimination half-life of about 40 h. It undergoes renal and hepatic elimination. In contrast to other ACE inhibitors it has a narrow dose range; therefore, the recommended dose is 6 mg for most patients without the need for dose titration. Spirapril has no relevant drug interactions. In several studies, spirapril was given to patients with mild-to-moderate essential hypertension at doses of 1-24 mg/day. There was an identical blood pressure lowering effect at doses of 6-24 mg/day; doses of 1-3 mg/day were less effective. Twenty-four-hour blood pressure monitoring showed a trough:peak ratio up to 0.84. In studies comparing the effect of spirapril with enalapril, lisinopril, trandolapril or captopril, spirapril was at least as effective as the other substances. Besides treating uncomplicated mild-to-moderate essential hypertension, spirapril can be used in patients with diseases accompanying hypertension such as heart and renal diseases, diabetes mellitus, and lipid disturbances. Possible advantages of spirapril compared to other ACE inhibitors are the dual mechanism of elimination, the lack of need for dose titration and a low incidence of cough.

Antihypertensive activity and pharmacokinetics of KD3-671, a nonpeptide AT1-receptor antagonist, in renal hypertensive dogs

The antihypertensive activity and pharmacokinetics of KD3-671 (previously named KT3-671), a nonpeptide AT1-receptor antagonist, were investigated in renal hypertensive dogs with normal or high plasma renin activity (PRA). A single administration of KD3-671 at 3 and 10 mg/kg, p.o., to the hypertensive dogs with high PRA dose-dependently reduced mean blood pressure (MBP), which was not correlated with plasma KD3-671 concentration. Significant increases in PRA and plasma angiotensin (Ang) II occurred 2 h after KD3-671 dosing. Enalapril at 3 mg/kg, p.o., also reduced MBP. Neither KD3-671 nor enalapril affected heart rate. When given orally once a day for 29 days to the hypertensive dogs with normal PRA, KD3-671 at 3 and 10 mg/kg/day dose-dependently reduced MBP, which was smaller than that in the dogs with high PRA. This was the case for enalapril. The hypotension induced by the first dose of KD3-671 or enalapril was consistently observed after doses 8, 15, 22, and 29. After cessation of repeated dosing, no rebound phenomenon in MBP was observed. Pharmacokinetic parameters of KD3-671 were not influenced by repeated dosing. KD3-671 markedly increased both PRA and plasma Ang II concentration at 2 h after dosing. These results suggest that KD3-671 may be useful for the treatment of hypertension.

Red blood cell sodium-lithium countertransport and risk of future hypertension: the Olivetti Prospective Heart Study

An elevated red blood cell (RBC) sodium-lithium countertransport (Na-Li CT) is associated with high blood pressure (BP) in cross-sectional investigations; however, its value as a predictor of future hypertension, and thus of cardiovascular risk, has not been defined. The present study evaluated the association between Na-Li CT and risk of future hypertension in a sample of 106 untreated normotensive middle-aged men participating in the Olivetti Prospective Heart Study in southern Italy. BP, anthropometric and metabolic variables, and RBC Na-Li CT were measured at baseline in 1987 and at a follow-up visit in 1994 through 1995. Na-Li CT was stable over time (r=0.85) and was significantly associated to systolic BP in both visits. Of the 106 initially normotensive participants, 14 were found to be hypertensive at the 8-year follow-up examination. Eleven of these 14 hypertensives were in the highest tertile of systolic BP at baseline, and 9 of 11 also had an elevated baseline Na-Li CT. In multiple logistic regression analysis, baseline BP, Na-Li CT, and age were all significant predictors of the risk of future hypertension. Individuals with baseline systolic BP in the highest tertile had a 60% risk of developing hypertension if their Na-Li CT was also high, whereas their risk was only 5% if Na-Li CT was in the two lowest tertiles (P=0.003). RBC Na-Li CT was a valuable predictor of subsequent hypertension in middle-aged men with a high-normal BP level for their age.