Biphasic effects of smoking on human serum dopamine-β-hydroxylase activity

Toxicology Letters, 60 (1992) 325-328 0 1992 Elsevier Science Publishers B.V. All rights reserved

TOXLET

325 0378-4274192/S

05.00

02709

Biphasic effects of smoking on human serum dopamine-p-hydroxylase activity

Teruo Nagaya”, Akemi Takahashib, and Michie Yokoyamab “Department

of Public Health,

Gifu University

Izumi Yoshidab

School of Medicine

and hGifU-shi Central

Public Health

Center, Gifti, (Japan) (Received (Accepted

9 October 1991) 16 December 1991)

Key words: Smoking

habits;

Nicotine;

Dopamine-P-hydroxylase;

Sympathetic

nerve activity;

Blood pres-

sure

SUMMARY To investigate droxylase

(DBH)

the chronic activity

effects

of smoking

was determined

on sympathetic

in 119 male non-smokers

nerve activity,

serum

dopamine-P-hy-

and 183 age-matched

male smokers.

The smokers were classified into 3 groups: 51 light smokers (l-19 cigarettes/day), 76 moderate smokers (20 cigarettes/day), and 56 heavy smokers (more than 20 cigarettes/day). The light smokers had the highest mean DBH activity,

and the heavy

smokers

had the lowest mean

DBH activity

in the 4 groups.

These

results suggest that light smoking stimulates the sympathetic nervous system, but that heavy smoking depresses the system. These biphasic changes in DBH activity are similar to the pharmacological effects of nicotine

on the peripheral

sympathetic

nervous

system.

INTRODUCTION

Cigarette smoke contains many chemical compounds. Among these, nicotine is thought to have the most effects on the human nervous system. Nicotine stimulates the sympathetic nervous system and adrenal medulla, and increases plasma catecholamine concentrations [ 11. Smoking also increases plasma catecholamine concentrations and induces transient hypertension in humans [l]. However, the chronic effects of smoking on the human sympathetic nervous system are obscure. Lower blood pressure in smokers than in non-smokers [2-51 may indicate suppression of the Correspondence to: Teruo Nagaya, Department 40 Tsukasa-machi, Gifu-shi 500, Japan.

of Public

Health,

Gifu University

School

of Medicine,

326

sympathetic nervous system by smoking. Dopamine-/?-hydroxylase (DBH), an enzyme converting dopamine to norepinephrine, is one of the catecholamine-synthesizing enzymes. Since DBH is secreted into the blood with catecholamines from sympathetic nerve terminals, and is much more stable in blood than catecholamines, serum DBH activity is a possible index of chronic sympathetic nerve activity [6]. In this study, serum DBH activity was determined in young male non-smokers and smokers to investigate the chronic effects of smoking on the sympathetic nervous system. SUBJECTS

AND METHODS

The subjects were 302 males who had visited the Gifu-shi Central Public Health Center for a health check for 30-year-olds from August 1989 to May 1990. All subjects were 30 years old and apparently healthy. The subjects were composed of I 19 non-smokers and 183 smokers. The smokers were classified into 3 groups according to the number of cigarettes smoked per day: 5 1 light smokers (1-l 9 cigarettes/day), 76 moderate smokers (20 cigarettes/day), and 56 heavy smokers (> 20 cigarettes/day). The data on the smoking habits of the subjects were taken from medical records in the Public Health Center. Venous blood was taken from each subject at 9910 a.m. before breakfast. The serum of the subjects was used for their ‘health check’, and the residual serum was stored at -20°C until DBH analysis by the method of Nagatsu and Udenfriend [7]. DBH activity was expressed in international units @mol/min)/l serum. One-way analysis of variance and Scheffe’s method were used to compare mean values for the 4 groups (non-smokers and 3 groups of smokers). Finally, the linear correlation coefficient test was used. All the tests were two-sided and statistical significance was fixed at P
Serum DBH activity in relation to smoking habits are summarized in Table I (means f SD) and P-values by Scheffe’s method for the 4 groups are presented in Table II. The mean DBH activities for the non-smokers and the total smokers were 22.9 and 22.2 IUil respectively (Table I). The difference was not significant. In subgroups of the smokers, the mean activities for the light, moderate and heavy smokers were 25.9, 22.1 and 18.8 IU/l, respectively. F- and P-values by one-way analysis of variance for the non-smokers and the 3 groups of smokers were 3.393 and 0.018 respectively (Table I). The Scheffe method revealed that light smokers had a significantly higher DBH activity than heavy smokers, but the differences in DBH activity between the two groups, except for the combination (light smokers vs. heavy smokers), were not significant (Table II). DBH activity was significantly negatively correlated with the number of cigarettes

321

TABLE SERUM

I DOPAMINE-p-HYDROXYLASE

30-YEAR-OLD Smoking

MALES

(MEAN

(DBH)

ACTIVITY

BY SMOKING

HABITS

habits

n

No. of cigarettes

DBH activity

per day

(IUIl serum)

Non-smokers

119

0

Smokers

183

21.7-t

22.2k11.6

51

11.6& 3.6

25.9+ 13.3

Moderate smokers Heavy smokers

76 56

20.0+ 33.2-t

22.1+_11.1

Total

302

0.0 7.9

18.8k 9.3 22.5*11.7

13.1z!z13.0

F

3.393

P

0.018 by one-way

302

22.9&l 1.9 9.6

Light smokers

F- and P-values

IN

i- SD)

analysis

of variance

for the 4 groups

(the non-smokers

and the 3 smoker

groups).

smoked subjects

per day in the 183 smokers (Y = -0.110, P = 0.056).

(I’ = -0.192,

P = 0.009)

but not in all the 302

DISCUSSION

The light smokers had the highest DBH activity, whereas the heavy smokers had the lowest DBH activity in the 4 groups (the non-smokers and the 3 groups of smokers). The difference in DBH activity between the two groups was significant. Therefore, the DBH activity was significantly negatively correlated with the number of cigarettes smoked per day in the smokers, but not in all the subjects including nonsmokers. These results suggest biphasic changes in DBH activity induced by smoking. Light smoking may stimulate the peripheral sympathetic nervous system, whereas heavy smoking may depress the system. These biphasic effects are similar to the pharmacological effects of nicotine on the peripheral nervous system. Small doses of TABLE

II

P-VALUES ANALYSIS

BETWEEN TWO GROUPS ASSESSED BY SCHEFFL’S OF VARIANCE FOR THE FOUR GROUPS

Groups

METHOD

AFTER

Non-

Light

Moderate

smokers

smokers

smokers

Non-smokers Light smokers

_ 0.500

0.500 _

0.978 0.367

0.198 0.021

Moderate smokers Heavy smokers

0.978 0.198

0.367 0.02 1

0.452

0.452 _

ONE-WAY

Heavy smokers

328

nicotine stimulate the peripheral symphathetic nervous system, but large doses depress the system [8]. The effects of smoking on DBH activity are possibly derived from the biological effects of nicotine in tobacco smoke. A previous study reported lower DBH activities in smokers than in non-smokers, but did not disclose the biphasic pattern found in the present study [9]. The previous report did not mention age distribution according to smoking habits in the subjects. Since serum DBH activity was influenced by age [lo, 111, the age of the subjects might have confounded the results in the previous study. In epidemiological studies, smokers had a lower blood pressure than non-smokers [2-51, and an inverse dose-response relationship between blood pressure and smoking was found in some studies [4,5]. These results suggest chronic depression of the sympathetic nervous system produced by smoking, and are consistent with our results in the heavy smokers, but not with those in the light smokers. The biphasic doseresponse relationship between blood pressure and smoking has not been found in human population studies. It is well known that blood pressure is influenced by many other factors (age, sex, body composition, exercise, personality, diet, drinking habits etc.). Since higher DBH activity in light smokers than in non-smokers is statistically insignificant in this study, such slight effects may be veiled by the effects of these other factors on blood pressure in human population studies. REFERENCES I Oates, J.A. and Wood, A.J.J. (1988) Pharmacologic tion. N. Engl. J. Med. 319, 1318-1330. 2 Green, findings. 3 Green,

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