Splanchnic blood flow in essential hypertension and in hypertensive patients with renal artery stenosis

Systemic diseases affecting the mesenteric circulation

The mesenteric circulation is acutely sensitive to processes that affect the entire body. Such systemic diseases and syndromes are reviewed with particular emphasis on the mechanisms by which they influence the mesenteric vasculature and blood flow.

Low-renin primary hypertension in a young patient treated with dexamethasone

We have studied a young untreated patient with low-renin hypertension. All the clinical tests were in normal range, except plasma renin activity, which was low. Also all traditional tests evaluating the adrenal function were normal. A test of supraphysiological ACTH stimulation revealed a partial enzymatic defect of adrenal 11-hydroxylase. The patient has been treated with dexamethasone (0.75 mg once daily), during 4 weeks. At the end of the treatment blood pressure reached normal values. The traditional adrenal function tests are not sufficient to exclude enzymatic abnormalities and their possible involvement in the pathogenesis of hypertension.

Borderline hypertension: relationship between age, hemodynamics and circulating catecholamines

The relationships between age, systemic and renal hemodynamics, circulating catecholamines (norepinephrine, epinephrine and dopamine) and intravascular volumes were studied in 38 normotensive subjects and in 77 patients with borderline essential hypertension. Borderline hypertensive patients had a higher cardiac index (p less than 0.02) and renal blood flow (p less than 0.05) than normotensive subjects if they were younger than 30 years of age, whereas in older patients no difference was observed. In contrast, total peripheral resistance was normal in young borderline hypertensive patients, but significantly increased (p less than 0.02) in patients older than age 40 years. Cardiac output (r = -0.28, p less than 0.01) and renal blood flow (r = -0.47, p less than 0.001) correlated inversely with age in the entire population and in both subgroups. Cardiac output also correlated closely with renal blood flow in all subjects (r = 0.45, p less than 0.001). Circulating norepinephrine levels increased with age (r = 0.25, p less than 0.05), whereas epinephrine concentration tended to decrease. Plasma and total blood volume correlated directly with cardiac output (r = 0.39, p less than 0.001) and inversely with peripheral resistance (r = -0.34, p less than 0.001). These data indicate that the hyperdynamic circulation (high cardiac output and renal blood flow) of borderline hypertension is found predominantly in patients younger than age 30 years. Older patients are characterized by an elevated total peripheral resistance and normal cardiac output. The age-dependent increase in circulating norepinephrine and decrease in epinephrine levels may participate in the shift of the hemodynamic profile from high-cardiac-output hypertension in the young to a high-arteriolar-resistance hypertension in the older patient.

The pharmacokinetics of trichlormethiazide in hypertensive patients with normal and compromised renal function

The pharmacokinetics of trichlormethiazide (TCZ) was studied in twelve patients after a single 4 mg dose. Seven patients had normal renal function with creatinine clearance greater than 90 ml/min. Five patients had compromised renal function with creatinine clearances averaging 48 +/- 29 ml/min. The TCZ plasma half life and area under the plasma concentration-time curve (AUC) were significantly greater in patients with impaired function, compared to patients with normal renal function. There were no significant differences between the two patient groups in terms of either rate of drug absorption or total urinary recovery of unchanged drug. Furthermore, there was no correlation between peak drug levels or AUC and renal excretion of water or electrolytes.

Distribution of cardiac output in different models of hypertension in the conscious rat

The distribution of cardiac output was determined by 15 micron radioactive microspheres in all the major organs of spontaneous, DOCA/NaCl and one kidney Goldblatt hypertensive rats and compared to normotensive Wistar rats. Although there were alterations in cardiac output distribution which were characteristic of each model of hypertension significant changes were common to all three were an increased distribution to skeletal muscle with decreases to the lungs, spleen and hepatosplanchnic tissues. The results suggest that alterations in peripheral resistance induced by hypertension are of unequal importance in the different vascular beds with certain vascular resistance changes occurring irrespective of the origin of the hypertension.

Renal haemodynamics before and after splanchnic block in patients with hypertension

In eighteen patients with hypertension of presumed renal origin the haemodynamics of the kidney were studied by arterial pressure recording, blood flow measurement and selective arteriography before and after a splanchnic block. The material was divided into kidneys with and kidneys without arterial stenosis. In these patients with hypertension a positive correlation was found between mean arterial pressure and renal vascular resistance both before and after the splanchnic block. In patients with renal arterial stenosis the change in relative renal vascular resistance was negatively correlated to the initial resistance, implying that in kidneys with a high initial vascular resistance the resistance decreased to a relatively greater extent than in kidneys with a low initial resistance. At high blood pressures ischaemic areas in the kidney were found. The volume of these areas is dependent upon sympathetic tone, such that a high sympathetic tone results in ischaemia of a larger volume of the kidney. This applies both to kidneys with and to those without arterial stenosis. The results of this investigation thus support the assumption that in the presence of hypertension a kidney is under the control of a sympathetic tone that may form a part of the pathogenetic process in hypertension.

Peripheral circulation in arterial hypertension

The underlying causes of hypertensive disease remain unclear. This article has attempted to highlight potential dysfunctions in arterial pressure regulation which could either initiate or sustain the hypertensive process. As has been suggested innumerable times hypertension must certainly be a multifactorial abnormality. The current state of knowledge about control of the peripheral circulation in high arterial pressure reinforces the view that interactions between neurogenic, myogenic, humoral, and structural factors are probably disrupted when hypertension appears.

Hemodynamic lesions in hypertension

Essential hypertension is increasingly recognized as a nonhomogenous disorder by various methods of study. The hemodynamic approach, coupled with clinical determination of the range and lability of blood pressure, has resulted in the description of several subgroups: labile hypertension with normal or elevated cardiac output, fixed or established hypertension with varying cardiac output and advanced hypertension with normal or low cardiac output. There is a tendency to postulate that these categories are stages of one disorder, but this remains to be proved. Still other patients have been described who may be further set off by exceptionally labile or hyperkinetic features. In some hypertensive patients, the peripheral resistance is normal; however, regardless of its numerical value, it is now considered to be increased if it fails to decrease normally in the presence of elevated cardiac output. Because an elevated cardiac output is the hemodynamic function that differentiates these groups, and renovascular hypertension as well, it is the focus of much current work. New interest in the central blood volume, the peripheral veins, and the portal veins and splanchnic circulation is focused on their connection with cardiac out-put. Newly appreciated, too, is the existence of parasympathetic inhibition in hypertension, which not only contributes to elevations of heart rate, cardiac output and possibly renin secretion, but also depresses baroreflex responses. Thus far, hemodynamic and endocrine mechanisms of hypertension have not been studied together, except possibly through the blood volume, which remains a highly controversial topic. In this paper, some recent work in the above areas is reviewed and emphasis is given to studies in man.