Shiro Nagano

Urinary dopamine excretion in normotensive subjects with or without family history of hypertension.

To define the role of the renal dopaminergic system in the pathogenesis of essential hypertension, urinary free dopamine excretion was examined in 23 normotensive subjects who had one or more first-degree relatives with essential hypertension, and also in 36 matched control subjects without any such family history. The group urinary dopamine excretion and urinary sodium excretion were not different. However, a significant urine dopamine-sodium relationship was apparent in the controls but not in the relatives due to relatively high dopamine output in those with lower sodium excretion. The two groups were similar as regards blood pressure (BP), plasma renin activity (PRA), prolactin and catecholamines. These findings demonstrate an alteration in the urine dopamine-sodium relationship in some normotensive subjects with genetic risk of hypertension.

Increased Urinary Dopamine Excretion in Young Patients with Essential Hypertension

The evidence that some older patients with essential hypertension have low urinary dopamine excretion has brought into question the levels of urinary dopamine and plasma dopa, the major source of urinary dopamine, in young patients with essential hypertension. Twenty-four-hour urine sodium, creatinine, dopamine and noradrenaline and plasma dopa were evaluated in 48 patients with essential hypertension aged 18 to 27 years and 25 normotensive subjects. In comparison with age-matched normotensive subjects, the hypertensive patients had higher urinary dopamine (1920 +/- 80 vs 1520 +/- 130 nmol/day, p < 0.01) and noradrenaline (216 +/- 11 vs 179 +/- 12 nmol/day, p < 0.05) excretion. There was a significant correlation between urinary dopamine and noradrenaline excretion. There was no difference in plasma dopa levels between normotensive and hypertensive subjects. These results suggest that the elevated conversion of dopa to dopamine in the kidney is leading to increased urinary dopamine excretion in young patients with essential hypertension.

Effect of L-dopa in Young Patients with Hypertension:

The effects of L-dopa on blood pressure, heart rate, plasma renin activity, norepinephrine, epinephrine and prolactin were studied in a randomized single-blind trial in 36 patients with essential hypertension. In response to L-dopa, 250 mg administered orally, the blood pressure decreased significantly as compared with the results of placebo treatment. The heart rate and plasma norepinephrine and epinephrine were unchanged. The plasma renin activity and prolactin decreased as a result of L-dopa administration. The administration of a peripheral DA2 dopamine receptor blocker, domperidone (20 mg, orally) prevented the L-dopa-induced reduction in plasma prolactin but failed to block the fall in blood pressure and plasma renin activity. These results suggest that the blood pressure-lowering effect of L-dopa may be mediated through multiple sites involving D1 dopamine receptors, the central nervous system, and the renin-angiotensin system.

Plasma prolactin, renin and catecholamines in young normotensive and borderline hypertensive subjects.

It has been reported that patients with essential hypertension have high plasma prolactin levels and suggested that reduced central dopaminergic activity may be a factor in the pathogenesis of essential hypertension. This study examines the influence of posture on plasma prolactin, plasma catecholamines, plasma renin activity, blood pressure and heart rate in 24 patients with borderline hypertension (age 19 +/- 1 years) and 20 normotensive subjects matched for age and body mass index. Supine plasma prolactin levels were similar in both groups [borderline hypertension, 11.3 +/- 0.7 ng/ml; normotensive, 10.7 +/- 0.8 ng/ml (mean +/- s.e.m.)] and no increase in plasma prolactin was observed after 10 min standing in both groups. Normotensive and borderline hypertensive subjects had similar values for supine and upright plasma renin activity and plasma norepinephrine. There were no significant correlations between supine plasma prolactin and supine blood pressure, supine plasma renin activity or plasma norepinephrine when data from both normotensive and borderline hypertensive subjects were combined. These results may provide indirect evidence against the occurrence of reduced central dopaminergic activity in borderline hypertension.

EFFECT OF A CALCIUM ENTRY BLOCKER ON BLOOD PRESSURE, PLASMA RENIN ACTIVITY, ALDOSTERONE AND CATECHOLAMINES IN NORMOTENSIVE SUBJECTS

The effects of the calcium entry blocker nifedipine on blood pressure, heart rate, plasma renin activity, aldosterone, noradrenaline and adrenaline were studied in 23 normotensive subjects in the supine and upright positions. Nifedipine, 10 mg administered sublingually, lowered mean blood pressure and increased heart rate, plasma noradrenaline and renin activity without increasing plasma aldosterone in the supine position. The increase in plasma aldosterone in response to upright posture was inhibited by nifedipine, whereas the rise in plasma noradrenaline was augmented. These results suggest that intracellular calcium is important as a regulator of aldosterone secretion as well as of vascular tone in normotensive subjects.

Effect of Captopril on Plasma Prolactin in Patients with Essential Hypertension

The effects of the angiotensin-converting enzyme inhibitor captopril on blood pressure, heart rate, plasma prolactin, and renin activity were examined in a single-blind, placebo-controlled trial on 30 patients with essential hypertension (15 given drug, 15 placebo). Captopril, 25 mg administered orally, reduced the blood pressure and increased the plasma renin activity. Captopril decreased mean plasma prolactin from 17.5±1.4 ng/mL to 9.1±1.0 ng/mL (p<0.001). Significant correlation was found between captopril-induced change from control values of plasma prolactin (Δplasma prolactin) vs Δplasma renin activity (r = -0.688, p<0.001). These results suggest that acute administration of captopril was accompanied by a reduction in plasma prolactin and that this reduction may be of clinical significance during therapy of hypertension.

Comment Effect of Xylitol on Individual Free Fatty Acids in the Plasma

In 1956, during the course of a study on pentosuria in guinea pig, a metabolic conversion of L-xylulose to D-xylulose via xylitol was discovered by Touster and his coworkers [1–3], and named the Glucuronic Acid Pathway which is metabolically connected with the Pentose Phosphate Pathway by phosphorylation. Evidence has accumulated concerning the metabolism of xylitol since that time in both basic and clinical fields. Lang [4] and his group [5] in Mainz administered xylitol preparation to diabetic patients and observed that xylitol is utilized well in the body and exerts little influence on the blood glucose level. Plasma free fatty acids (FFA) were found to be reduced by administration of xylitol [6, 7]. The present communication concerns with the further studies on the effect of xylitol on plasma fatty acids in hyperlipemic and diabetic patients.

Increased sympathetic nerve activity at home in young subjects with hypertension.

Plasma and urine norepinephrine, epinephrine, plasma renin activity and aldosterone were measured in 11 young men (mean age, 21 years) with a high blood pressure in the clinic who maintained a high home blood pressure and 12 men with an elevated clinic blood pressure who had a normal home blood pressure. Plasma samples were drawn following 30 min rest in the clinic, and 24-hour urine samples were collected at home. The two groups of hypertensives could not be distinguished on the basis of clinic blood pressure, plasma norepinephrine, epinephrine, renin activity or aldosterone. Patients with a high home blood pressure were characterized by a high urinary norepinephrine excretion. These results suggest that the patients whose blood pressure remained elevated at home had an increased sympathetic nerve activity at home.

Blood Pressure Response to a Calcium Entry Blocker in Normotensive Subjects With or Without a Family History of Hypertension

The possibility that a familial background of hypertension might influence the blood pressure response to a calcium entry blocker was evaluated in 15 normotensive relatives of patients with essential hypertension and 18 normoten sive subjects with no family history of hypertension. Under control conditions, blood pressure, heart rate, plasma noradrenaline, adrenaline, and renin activ ity did not differ between the two groups. Nifedipine, at a dose of 10 mg admin istered sublingually, lowered the blood pressure and increased the heart rate, plasma noradrenaline, and renin activity. The normotensive relatives of patients with essential hypertension did not differ in their responses from the normoten sive subjects with no family history of hypertension, with the exception of plasma noradrenaline thirty minutes after nifedipine. These results provide evi dence to suggest that there is no functional abnormality with increased depen dency of vascular smooth muscle tone on calcium influx in the prehypertensive state.

Comment The Substitution of Dietary Carbohydrate with Xylitol and its Effect on the Plasma Lipids

There is increasing evidence that various kinds of carbohydrate have a lipogenic effect. The present study was carried out to investigate the effect of xylitol on the plasma lipid and compare the effect with those of sucrose, and starch.