Urinary normetadrenaline excretion in essential hypertension

249

CLINICA CHIMICA ACTA

URINARY

NORMETADRENALINE

EXCRETION

IN ESSENTIAL

HYPERTENSION

A. W. STOTT*

AND R. ROBINSON

Group Pathological Laboratory, (Received

November

Wavwick (Great Britain)

zznd, 1966)

SUMMARY

Under identical conditions of posture and rest, patients with essential hypertension excrete in the urine significantly more normetadrenaline than normotensive patients. Our results suggest that these hypertensive patients secrete excessive amounts of noradrenaline and that this substance comes mainly from sympathetic nerve endings.

Noradrenaline is normally present in the peripheral blood in concentrations of about I pug/l(ref. I). It is an exceedingly potent hypertensive substance. There is much clinical evidence to suggest that patients with essential hypertension secrete abnormally large amounts of noradrenaline2~s and that this substance sustains their hypertension. Experimental evidence to support this suggestion, however, is still lacking. The practical difficulties of obtaining such evidence are formidable and for two main reasons. First, an increase of only 25% in the rate of secretion will account for the raised blood pressure of essential hypertension patients4, which is less than that evoked by many normal physiological stimuli, such as changes in posture; and secondly, noradrenaline is rapidly and effectively metabolised and the metabolites excreted. Recently, methods have become available for measuring these metabolites. Using one of these methods, we have studied the excretion of the noradrenaline metabolite normetadrenaline by normotensive and hypertensive patients. Our results support the suggestion that patients with essential hypertension secrete excessive amounts of noradrenaline. MATERIAL AND METHODS

The main outlines of noradrenaline metabolism are well known and are sum* Present address:

Pathology

Dept., George Eliot Hospital,

Nuneaton,

Warwicks.

Clin. Chim. Acta, 16 (1967) qg--252

STOTT, ROBINSON

250

marised, together with those of adrenaline in Fig. I. The metabolites, together with small amounts of unchanged catecholamines are excreted in the urine. The most abundant, and the easiest metabolite of noradrenaline to measure is HMMA (4-hydroxy-3-methoxy-mandelic acid). Unfortunately, this compound is also derived from adrenaline (see Fig. I). Its excretion thus reflects the combined secretions of adrenaline and noradrenaline. I Noradrenaline

-___

-+- Normetadrenaline

--

------i 11

I Adrenaline _____

+ Metadrenaline

----

II ~.

j. HMMA .~

I

Fig. I. The metabolism of adrenaline and noradrenaline. Reaction I is catalysed catechol-O-methyl transferase; Reaction II is catalysed by amine oxidase.

by the enzyme

As we were interested chiefly in obtaining some measure of noradrenaline secretion, we have measured instead normetadrenaline, the g-O-methyl derivative of noradrenaline. The method of Stott and Robinson6 was used. This technique measures the total normetadrenaline excreted (i.e. both free and combined). It also measures the excretion of the analogous adrenaline metabolite metadrenaline and these results we have also recorded. The technique has an inherent error of up to f 10% for the measurement of no~etadrenaline and up to + 15% for the measurement of metadrenaline. The subjects of the experiments were 25 normotensive adult patients and zo adult patients with essential hypertension. They were all hospital in-patients. The procedure was explained to them before the tests were begun to reduce the effect of emotion on catecholamine secretion. They first emptied their bladders completely and the urine was discarded. They then drank a glass of water to ensure a good flow of urine. For the next hour they rested sitting upright in a chair. After exactly 60 min they emptied their bladders completely and the specimens were saved for analysis. To eliminate the effects of diurnal rhythm, the tests were all performed between 9.30 a.m. and II a.m. RESULTS

Table I shows the excretion of normetadrenaline and metadrenaline by the normotensive and hypertensive groups of patients. Statistical analysis of the results (Student’s t-test) showed that the hypertensive patients excreted significantly more normetadrenaline than the normotensive patients (P< 0.01). Student’s t-test could TABLE

I

EXCRETIONOF ~ETADR~NALlNE

AND

NORMETADRENALINE

BY

NORMOTENSIVF.

PATIENTS

No. of patients

Normotensives Hypertensives Significance -

AND

HYPERTENSIVE

..-_____.~-

25 20

of differences

C&t. Chdm. Acta

16 (1967) 249-252

Normetadrena1in.e excretion (pg/milz) _ mean S‘L3.

Metadrenaline excretion (pgtmin) mean

S,D.

0.18 0.02 0.08 0.285 P < 0.01

0.18 0.24

0.02

0.12

0.05

O.l __

-

NORMETADRENALINE

EXCRETION

IN HYPERTENSION

2s

not be applied to the data on metadrenaline excretion because the F value was significantly high. A Fisher-Behrens test showed that the excretion of metadrenaline of the two groups of patients was not significantly different. It could not therefore be established that hypertensive patients secrete more adrenaline than normotensive patients. DISCUSSION

We have compared the excretion of normetadrenaline by normotensive and hypertensive patients under conditions which reduced the effects of posture, exercise, diurnal rhythm and, as far as possible, normal psychological stimuli, such as fear and apprehension, on noradrenaline secretion. We believe it was essential to do so as all these factors are known significantly to increase noradrenaline secretiona. Other workers in the past have not taken these precautions. Their results are conflicting. Von Euler et aL7, for example, measured the 24-h urinary excretion of noradrenaline by 500 patients with essential hypertension and found that only 16.4% of their patients excreted increased amounts of noradrenaline. Griffiths and Collinson* measured the 24-h output of total catecholamines (adrenaline plus noradrenaline). They found no difference between the output of the hypertensive and normotensive individuals. In contrast, Weil-Malherbe and Bones found that hypertensive patients secreted significantly more noradrenaline than normal subjects. More recently, the problem has been studied by measuring the 24-h excretion of the catecholamine metabolite HMMA. Again, there have been conflicting reports. Von StudnitzlO found that hypertensive patients excreted significantly more HMMA than normal subjects, but Crout et al.” and Georges and Whitby’* found no difference between the outputs of normotensive and hypertensive subjects. Our outstanding finding was that the hypertensive patients excreted significantly more normetadrenaline than normotensives when they were studied under comparable conditions. This suggests that the hypertensives secreted more noradrenaline than the normotensive group. However, other explanations could be advanced. It is possible, for example, that hypertensive patients are deficient in amine oxidase, the enzyme which converts normetadrenaline to HMMA or that hypertensives have abnormally high plasma clearances of normetadrenaline. However, as far as we are aware, there is no experimental evidence to support either of these hypotheses. Noradrenaline is secreted mainly by sympathetic nerve endings, but another important and significant source is the adrenal medulla. About 2074 of the catecholamine in the gland is noradrenaline; the other 80% is adrenaline. Since the hypertensive patients did no excrete excessive amounts of the adrenaline metabolite metadrenaline, there is no evidence that their adrenal medullary activity is high. Our results then, suggest that not only do hypertensive patients secrete excessive amounts of noradrenaline, but that this comes mainly from the sympathetic nerves and not from the adrenal medulla. No conclusions can be drawn from our work about the aetiology of essential hypertension, but our results are in accord with the view that in this condition the raised blood pressure is sustained by an excessive secretion of noradrenaline from sympathetic nerve endings. Clin. Chim. Acta,

16 (1967)

24g-a.~~

STOTT, ROBINSON

2.52 ACKNOWLEDGEMENTS

We wish to thank the Research Sub-Committee of the Birmingham Regional Hospital Board for a grant which enabled us to carry out these investigations. We gratefully acknowledge the co-operation and encouragement given to us by Drs. S. R. F. Whittaker and A. P. Prior. We are indebted to Mr. J. Ractliffe and Mr. G. R. Braithwaite of the Mathematics Department of the Lanchester College of Technology, Coventry, for carrying out the statistical analysis of our results. REFERENCES I 2 3 4 5 6 7

8 9

IO II 12

A. H. H. B. A. U. U.

T. DE VALI< AND H. L. PRICE, J. Clin. Invest., 35 (1956) 837. A. SCHROEDER, in Hypertensive Diseases, H. Kempton, London, (1953). A. SCHROEDER, in Mechanisms of Hypertension, Charles C. Thomas, Springfield, Ill., 1957. FOLKOW, in The Pathogenesis of Essential Hyfertension, Pergammon Press, London, 1962. W. STOTT AND R. ROBINSON, J. Clin. Pathol., 19 (1966) 487. S. VON EULER, in Noradrenaline, Charles C. Thomas, Springfield, Ill., 1956. S. VON EULER, S. HELLNER AND A. PURKHOLD, &and. J. Clin. Lab. Invest., 6 (1954) 54. W. J. GRIFFITHS AND S. COLLINSON, J. C&z. Pathol., IO (1957) 120. H. WEIL-MALHERBE AND A. D. BONE, J. Clin. Pathol., IO (1957) 138. W. VON STUDNITZ, Scan& J. Cl&. Lab. Invest., 12 (1960) Suppl. 48, p. 36. J. R. CROUT, J. J. PISANO AND A. SJOERDSMA, Am. Heart J., 61 (1961) 375. R. J. GEORGES AND L. G. WHITBY, J. C&z. Pathol., 17 (1964) 64.

Clin. Chim.

Acta,

16 (1967) 249-252