Hypertensive vascular disease. The long term effect of rapid repeated reductions of arterial pressure with diazoxide

The patient with resistant hypertension. Cations, volume, and renal factors

Hypertension that is truly resistant to modern antihypertensive therapy is uncommon. In the majority of cases, apparent resistance is more likely associated with poor patient adherence, interacting drugs, drug interactions, and inappropriate drug dosages. Sodium and fluid volume play a major role in resistant hypertension. There is considerable evidence to support the role of dietary sodium restriction in successful nonpharmacological treatment of hypertension. Salt sensitivity in humans appears to represent at least one factor determining individual susceptibility to variable salt intakes. Sodium and water retention may lead to refractoriness to many antihypertensive agents, and there is evidence to suggest that extracellular fluid volume expansion also plays a role in many hypertensive patients. While retention of sodium and water is well established early in patients with renal parenchymal disease, hypertension associated with progression of renal parenchymal disease is complicated by other factors that include interactions between hemodynamic and humoral factors, functional changes in adrenergic responses, and structural vascular disease. The role of other cations such as potassium, calcium, and magnesium in resistant hypertension has yet to be established.

Effect of diazoxide-induced hypotension on cerebral blood flow in hypertensive rats

The effect on cerebral blood flow of acute diazoxide-induced hypotension was studied in rats with renal and spontaneous hypertension. Diazoxide (5 mg/kg, i.v. bolus), caused arterial pressure to fall rapidly to that of normotensive rats, i.e. c. 75 mmHg. There was a concomitant fall in cerebral blood flow of about 35% (P less than 0.01) in renal hypertensive rats and 25% (P less than 0.05) in spontaneously hypertensive rats; the greater fall in flow in the former corresponded to a greater drop in pressure. Flow remained at these reduced levels during a 2 h observation period. Histological examination revealed small areas of ischaemic damage in the brains of five of the twelve animals. In control hypertensive rats not given diazoxide, cerebral blood flow and blood pressure were stable during a 2 1/2 h period and there was no evidence of ischaemic damage to the brains. The diazoxide-induced reduction in cerebral blood flow was interpreted as being secondary to a blood pressure fall to below the lower limit of cerebral blood flow autoregulation. No evidence was found of direct effects on the cerebral circulation such as seen with ganglionic blockers, alpha-blockers and cerebral vasodilators.

Hypertensive emergencies: practical approach to treatment

In a hypertensive crisis, an antihyprtensive agent must be able to reduce blood pressure to safe levels rapidly and predictably. Parenteral therapy is usually necessary, and in general, agents that can be infused and titrated are preferable to those that cannot. This article tells which drugs to use in specific situations and gives explicit instructions for intravenous and oral administration.

Analysis of cerebrovascular action of diazoxide in conscious goats

The effects of diazoxide on cerebral blood flow were evaluated in unanesthetized goats under control conditions and after selective blockade of adrenergic or cholinergic receptors in cerebral vessels. Injections of diazoxide (1-27 mg) into the internal maxillary artery produced dose-dependent increases in cerebral blood flow, an increase of 90% occurring with the highest dose. Administration of phentolamine, propranolol, or atropine into the internal maxillary artery did not modify the cerebrovascular response to diazoxide. In reserpine-treated animals the cerebral effects of diazoxide were also unchanged. Intravenous injections of diazoxide (150-400 mg) produced sustained hypotension and tachycardia whereas cerebral blood flow was maintained within normal values or increased slightly. The normal cerebral vasoconstriction obtained with injections of norepinephrine directly into the internal maxillary artery was unaffected during the diazoxide induced-hypotension. These findings show that diazoxide exerts a powerful vasodilatory effect on cerebral vessels through mechanisms other than blockade of alpha-adrenergic receptors or inhibition of adrenergic activity. The results also indicate that activation of beta-adrenergic or atropine-sensitive vascular receptors in the cerebral response to diazoxide is negligible.

Dose-response relation of diazoxide in children with hypertension

Diazoxide was administered to sixteen pediatric patients (ages 10 months to 13 years) with secondary forms of hypertension. Admission BP was 178+/-8/130+/-5 mm Hg (mean +/- SEM). Diazoxide was administered rapidly intravenously in doses ranging from 2 to 7.5 mg/kg. A significant (P less than 0.001), linear log dose-response relation was obtained which showed that a 3 mg/kg dose of diazoxide lowered diastolic BP by an average of 30 mm Hg. In five patients reduction of idastolic BP by a single injection of diazoxide was no different than when the same total dose was given as two or three small injections repeated at fifteen to twenty minute intervals. It is concluded that 1) many hypertensive children respons significantly to doses of diazoxide smaller than the usually recommended 5 mg/kg; 2) diazoxide has a significant dose-response relation in hypertensive pediatric patients; and 3) the desired blood pressure response in hypertensive children can be titrated using repeated small injections of diazoxide.

Effect of diazoxide on left ventricular performance in hypertension

The effect of diazoxide on left ventricular performance during rest and isometric exercise (handgrip) was examined in 16 unselected hypertensive patients, 6 of whom had been pretreated with the beta-adrenergic blocking agent pindolol. Diazoxide regularly and promptly produced a fall in left ventricle systolic and end diastolic pressures, and an increase in heart rate and left ventricular dp/dtmax. Haemodynamic changes were maximal 2 minutes after injection of the drug and decreased little over the next 8 minutes. After beta-adrenergic blockade, diazoxide caused a more pronounced reduction in left ventricular systolic pressure and a less marked fall in end-diastolic pressure, whilst the diazoxide-induced rise in heart rate was partially and the increase of dp/dtmax was completly inhibited. The increase in systolic pressure during isometric exercise was not influenced by diazoxide, but the positive inotropic reaction was augmented. The findings appear to show that cardiac stimulation by diazoxide is due to a reflex mechanism transmitted by baroreceptors, and that improvement of cardiac performance is mainly due to a reduction of left ventricular after-load.

Variability in response to drugs

Variability in the response to drugs is due to three principal components-the disease, the responsiveness of tissues, and the concentration of the drug at its site of action (as reflected by its plasma concentration). The relative contributions of these components will differ not only for different drugs but also for different effects of the same drug. Rational drug therapy depends on knowledge of all three factors.

Action of diazoxide on skeletal muscle vascular resistance

Controversy exists as to whether arteriolar dilation after diazoxide (DZ) administration is due to a prolonged vascular effect that outlasts the presence of circulating levels of DZ or to equilibrium of arteriolar sites with circulating DZ. To resolve this question, the direct effects of DZ on the vascular resistance (VR) of the isolated blood-perfused (constant-flow) gracilis muscle were evaluated in 44 anesthetized dogs. Intra-arterial infusions of DZ resulted in falls in vascular resistance (-35.9±5.5 SEM %) which returned to control levels after the infusions, thus indicating that irreversible binding to arterioles or a prolonged arteriolar effect independent of plasma levels of the drug did not obtain. Decreases (- 16% to -35%) in VR could also be achieved by premixing DZ in the blood perfusion reservoir at concentrations between 40 and 100 mg/L (which may be achieved clinically); thus albumin binding does not abolish the activity of DZ. Decreases in VR by DZ were not related to stimulation of beta-adrenergic receptors, alteration in Na + or K + balance, or changes in venous levels of glucose, lactate, pO 2 , pCO 2 , or pH. When norepinephrine and angiotensin II were infused during diazoxide infusions their vasoconstrictor response was attenuated. Thus DZ has a direct effect in lowering VR which is independent of measurable changes in gracilis muscle metabolism. Moreover, the VR effect of DZ is not dependent on a prolonged arteriolar effect independent of plasma concentrations of the drug.

The value of aggressive therapy in the hypertensive patient with azotemia

By giving diazoxide intravenously and furosemide orally the diastolic blood pressure was kept under 110 mm Hg and the urinary output over 1 L/day for a 2-week period in 25 hypertensive patients with azotemia. During the first 2 weeks of treatment three patients died. Although the 40% decrease in mean arterial pressure in the remaining patients was associated with immediate improvement in the cardiovascular status, for example, clearing of congestive heart failure and papilledema, there was a 19% average increase in BUN and 17% average increase in serum creatinine values. Three months later, however, maintenance of the reduced arterial pressure was associated with average reductions of 24 mg/100 ml in BUN and of 2.8 mg/100 ml in serum creatinine below control values. Each of the patients who remained on therapy continued to do well. Twenty-six months later six additional patients had died. In the remaining 16 patients the average mean arterial pressure was 117 mm Hg; papilledema had cleared; the average concentration of BUN was 22 mg/100 ml; the average serum creatinine was 1.8 mg/100 ml.