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Dopamine-β-hydroxylase activity in serum following acute myocardial infarction: An evaluation of this parameter for routine use as an index of sympathetic activity
61
Clinica Chimica Acta, 69 (1976) 61-66 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
CCA 7691
DOPAMINE-P-HYDROXYLASE ACTIVITY IN SERUM FOLLOWING ACUTE MYOCARDIAL INFARCTION: AN EVALUATION OF THIS PARAMETER FOR ROUTINE USE AS AN INDEX OF SYMPATHETIC ACTIVITY
TORE GUTTEBERG, OLAV BORUD and JOHAN H. STRGMME * Division of Clinical Chemistry, Tromsq (Norway)
Institute of Medical Biology,
University of Troms$,
9000
(Received November 22,1975)
Summary Dopamine-fl-hydroxylase activity was measured in sera from 114 normal males and from 11 patients on the lst, 2nd, 3rd, 5th and 10th day following acute myocardial infarction. A significant elevation of dopamine-fl-hydroxylase levels (P < 0.001) was found during the first two days after infarction when compared with the lOth-day values. Only a few activities were above the reference range. Temporary elevations of glucose and glycerol levels were also found. Assay of serum dopamine-/3-hydroxylase may be a useful parameter of sympathetic activity in longitudinal studies in which each individual is used as his own reference.
Introduction Dopamine-/3-hydroxylase (DBH, EC 1.14.17.1) catalyses the final step in the synthesis of noradrenalin, i.e. the conversion of dopamine to noradrenalin. Noradrenalin and DBH are found together in granules in nervous tissue, especially sympathetic nerve endings and the adrenal medulla. These granules are released during sympathetic activity, and a fraction of the released DBH subsequently reaches the blood stream [l-3]. It seems likely that serum DBH arises in the main from the sympathetic nerves with only a minor fraction coming from the adrenal gland [ 1, 4-61. Serum DBH activity therefore, like the serum catecholamine level, appears to be an index of sympathetic activity. Planz et al. [7] have reported recently that in humans there is a linear relationship between graded work and serum DBH and a logarithmic relationship between graded work and serum catechol* To whom reprint requests should be addressed.
62
amines. Similarly, Naftchi et al. [ 81 have found a significant correlation between stages of induced hypertension, serum DBH and urinary excretion of noradrenalin in patients with quadriplegia. Finally, reports of high levels of DBH and catecholamines in serum from patients suffering from essential hypertension have led to suggestions that increased sympathetic activity is an important factor in the pathog~nesis of this disease [9,10]. The aim of the present work was to examine whether DBH activity in serum might be a
Patients The subjects studied were 3 women and 8 men with acute myocardial infarction. The diagnosis was confirmed by typical electroc~diographic changes, rises in serum creatine kinase activities (normal values <120 U/l) to a maximum on the second day (mean 1287 U/l, range 58-4200 U/l), and of serum aspartate aminotransferase activities (normal values 10-40 U/l) to a maximum on the third day (mean 227 U/l, range 93-663 U/l). All patients were admitted to the coronary care unit and monitored for a variable period from 3 days upwards. None of the patients died or required resuscitation during the lo-day observation period. Methods Blood samples were taken without anticoagulants on admission and at 8 a.m. on the other days. The samples were immediately placed on ice, and centrifuged within 30 min. The serum was stored at -20°C until analysed in series for each patient. DBH was assayed at 37°C essentialty as described by Nagatsu and Udenfriend [ 161 using tyramine as substrate. The final incubation mixture of 2.5 ml contained 0.1 ml serum. Aliquots were taken routinely from the incubation mixture at 10 and 20 min. The octopamine formed was oxidized to p-hydroxybenzaldehyde and measured in a Beckmann Model 25 spe~trophotometer at 330 nm. The linearity of the reaction was good for at least 30 min of incubation. The change of absorption between 10 and 20 min was used in the calculation of the catalytic activity, expressed in U (pm01 min-’ ), and the catalytic concentration was expressed in IJjl, Using a serum with an average activity of 55 U/l as test material, the relative standard deviation for precision within series was found to be 3.8%, and between series 7.8%. Glucose was assayed spectrophotometrically by the glucose oxidase method, using reagents from Boehringer, Mannheim, G.F.R. (Cat. No. 15756). The relative standard deviation for the precision between series of this method was 1.6%, and the reference range was 4.2-5.7 mmol/l. Glycerol was assayed in
63
by an enzymatic method, using reagents from Boehringer, Mannheim, G.F.R. (Cat. No. 15747). The reproducibility of this method was 6.7%, and the reference range was 0.02-0.68 mmol/l. The presence of possible serum DBH inhibitors in myocardial tissue was assayed as follows: freshly sampled dog myocardium kept at -8O”C, was cut into small pieces and homogenized at 0°C (Potter-Elvehjem homogenizer) in 10 volumes of 100 mmol/l Tris (pH 7.4) containing 0.25 mol/l sucrose. The homogenate was centrifuged at 10 000 X g for 10 min, and the supernatant tested for DBH inhibitors (for details see Table II). Results The reference range of DBH activities was determined by assaying sera from 114 nonhypertensive males aged 21-50 years. The blood was collected between 8.30 and 10.00 a.m. thus avoiding the 24-h rhythm [17]. The results showed a skewed distribution of the catalytic concentrations, ranging from 0 to 105 U/l, with the reference range covering 95% of the material of 7-85 U/l, mean 35 U/l (Fig. 1). Fig. 2 shows the results of DBH, glucose and glycerol in the sera of 11 patients following myocardial infarction. Table I gives the P-values obtained by paired comparison of the results from each day over the first five days with the respective results on the 10th day. DBH was significantly elevated on admission (1st day), and on the 2nd and 3rd day with averages of 149, 149 and 127%, respectively, of the lOth-day value. No significant difference was found between the 5th and 10th day (P > 0.05). Glucose was significantly elevated on the lst, 2nd, 3rd and 5th day, being 156, 140, 142 and 122%, respectively, of the lOth-day value. Glycerol was significant elevated (350%) on only the first day. There was also a markedly higher mean result (210%) on the second day compared to the lOthday value, but this was not statistically significant due to a high interindividual
20
G E i I= 10
:
50 Catalytic concentration
100 ( U/l)
Fig. 1. Distribution of DBH activities in serum from 114 males. aged 21-50 between 8.30 and 10.00 a.m., and serum assayed as described in Methods.
years. Blood was collected
q
BH
0
glucose
q
1
2
glycerol
5
3
Days after
10
infarction
Fig. 2. Mean ? S.E. of DBH, glucose, and glycerol in serum from 11 patients with acute myocardial infarction. The blood was collected on admission, and at 8 a.m. on the 2nd. 3rd, 5th and 10th day. The results are expressed as percent of the respective values on the 10th day. The mean lOth-day values for DBH, glucose and glycerol were 34.0 U/l. 5.90 mmol/l and 55 Lcmol/l. respectively.
variation as indicated by the large standard error of the mean (Fig. 2). Linear regression analysis failed to demonstrate any correlation between the levels of DBH and glucose, or between DBH and,glycerol on each day. Previously it has been shown that rat myocardium contains substances with the ability to inhibit DBH from bovine adrenal gland [ 181. To examine whether a similar inhibition could occur with the human serum enzyme, the effect of dog myocardium preparations on serum DBH was studied. Table II shows that inhibition of human serum DBH occurred only in the presence of very high concentrations of the myocardial supernatant.
TABLE
I
Statistical probability (P-values) for a null hypothesis obtained when comparing the levels of DBH, glucose and glycerol in serum during the first five days after myocardial infarction with those found on the 10th day. The Student’s f-test was applied to the results of Fig. 2. Day
DBH
Glucose
Glycerol _____~
O-1
CO.001
l-2
0.001~.005
2-3
0.0254.05
4-5
0.054.10
0.005-0.01
0.001---0.005
0.01+.02
0.05-0.10
10.001 0.01-0.02
0.64.7 0.20+.25
TABLE II THE INHIBITORY
EFFECT OF DOG MYOCARDIAL
SUPERNATANT
ON DBH OF HUMAN SERUM
Different volumes of the supernatant of homogenized dog myocardium were mixed with 0.5 ml serum. Water was added so that the final serum dilution was 1 : 10 in accordance with the assay of serum DBH (see Methods). The catalytic concentration of DBH in serum diluted with water and no supernatant has been taken as 100% (82 U/l). No DBH activity was detected in the myocardial supernatant itself. The results are expressed as mean t S.D. of 4 parallel determinations. S~~rnatant
: serum
DBH activity
(vfv>
(%)
0: 1 : 1: 1: 9 :
100 105 105 90 24
l(0) * 50 (1 mg) lO(5mgf 5 (10 mg) 1 (450 mg)
+ + f * +
12 2.3 5.7 23 8.0
-
~_I_
* Weight of myocardium added to 0.5 ml serum.
Discussion The levels of stress parameters such as glucose, glycerol and free fatty acids depend not only on catecholamines, but also on other regulatory factors. In contrast, DBH like noradren~in may be considered as a primary parameter of sympathetic activity [ 191. However, DBH differs from noradrenalin by having a much slower clearance rate in blood, the half-life of the former in sheep being estimated as about 3 h [20]. The level of the enzyme may therefore be expected to reflect better the general situation of the patient over a period of hours than would catecholamine levels, since the latter tend rather to reflect the situation at the instant of sampling. Moreover, catecholamines are highly unstable components in vitro and difficult to assay precisely. As has been convincingly demonstrated by several authors [ll-13,211, acute myocardial infection represents a well defined clinical condition regularly associated with increased sympathetic activity. In 11 patients we found a definite increase in the average DBH activity of serum on the 1st and 2nd day following acute myocardial infarction. However, only 1 of the 11 results obtained over the 1st and 2nd day was above the reference range used for DBH. In comparison, 9 of the 11 first-day levels of glucose and glycerol were above the reference range for these two parameters. Previously a 5- to lo-fold increase of catecholamine levels in plasma has been found following acute myocardial infarction [ll]. Accordingly DBH seems to be a far less sensitive parameter of sympathetic activity than both cate~hol~ines and the secondary parameters glycerol and glucose. This considered together with the large biological variation of DBH makes this serum enzyme unsuitable as a routinely used parameter of stress, Conclusions along these lines have also been made by previous authors [3,221. A puzzling feature of the present results is that while nerve endings seem to release a constant ratio of DBH and noradrenalin [ 191 and while the clearance rate of the former is much slower than that of the latter, DBH is still a lowsensitivity index of sympathetic activity. Two possible explanations of this
apparentdichotomy
come to mind. Firstly, DBI-I is a much larger molecule than nuradre~~~n and thus may well take longer to reach the bloodstream. Secondly, the blood of infarct patients may contain specific DBH inhibitors that are not inactivated by the N-ethylmaleimide present in the incubation mixture. It has previously been shown that rat heart preparations possess an inhibitory effect on partially purified bovine adrenal DBH [lS]_ However, the present results show that the human serum enzyme is very resistant to inhibition by the supernatant obtained from a homogenate of dog myocardium. lnhibition was noted only at extremely high concentrations of supernatant which presumably bear no relationship to the in vivo situation following myocardiai infarction. The data here presented show that statistically significant elevations of serum DBH levels were found on the 1st and 2nd day only when each result was compared with the corresponding 10th day value, At this latter date, the serum DBH activity of each patient had probably returned near to the individual baseline. Most likely a much lower intra- than inter-individual variation explains why significant increases were obtained in this ca$e only. It seems therefore that measurements of DBH may be useful in longitudinal studies in which each individual may be his own reference, However, the lack of sensitivity of this serum parameter and its large reference range appear to make it unsuitable as a routinely used index of sympathetic activity in clinical work.
We are grateful
to Mrs. ashild
Johansen
for skilled technical
assistance
References Life Sci 14, 1593 1 Geffen. L. (1974) 2 Axelrod, J. (1972) Pharmacol. Rev. 24,233 in Neurosycho3 Goldstein, M., Freedman, L.S., Ebstein, R.P.. Park, D.H. and Kashimoto, T. (1974) yharmaeology of Monoamines and Their Regulatory Enzymes (Usdin, E., ed.), PP. 105-119, Raven Press. New York R.M., Kvetnanaky, R., Ax&rod, J_ and Kopin, I,& (1971) Nature New Biol, 230,287 4 WeinshiXboum, 5 Roffman, M., Freedman, L.S. and Goldstein, M. (1973) Life Sci. 12,369 R.M. and Ax&ad, J. (1971) Science 173,931 6 Weinshilboum, H. (1975) Eur. J. Clln. Phar. 7 Planz, G., Wiethold. G., Appel, E., Bahmer, D., Palm, D. and Grobecker, macol, 8, 181 Circ. Res. 35,850 8 Naftchi, N.E., Wooten, G.F., Cowman. E.W. and Axeirod. J. (1974) CIi. Sci. 44, 617 9 G&fen, L.B., Rush, R.A., Louis, W.J_ and Doyle. A.E, (1973) Gunnelis, J.C., Robinson, R.R., Schanberg, S.M. and Kirsbner, N. 11974) Circ. Res. 10 Stone, R.A., SUPPI. 34/35,1-47 11 Videbaek, J.. Christensen. N.J. and Sterndorff, I3. (1972) Circulation 46, 846 12 Christensen, N.J. and Videbaek, J. (1974) J. Clin. Invest. 54, 278 P.E. and Oganov, R.G. (1972) Am. Heart J. 83, 182 13 Lukomsky, T.W. (1968) Lancet i, 710 14 Oliver, M.F., Kuriet~, V.A. and Greenwood, Br. Heart J. 36. 996 16 Carlstrom, S. and Gustafson, A. (1974) Clin. Chem. 18, 980 l.6 Nagatsu, T. and Udenfriend, S. (1972) Exporientia 30, 605 17 Qkada, T.. Fujita, T., Ohta. T., Kato, T.. Ikuta, K. and Nagatsu, T. (1974) Research, pp. 195-ZOO, Pergamon 18 Molinoff, P.B. and Orcutt. J.C. (1973) In Frontiers in Catecholsmine Press. Oxford R.M., Thee, N.B., Johns-n, D.G., Kopin, I.J. and Axelrod. J. (1971) Science 274,1349 19 Weinshilboum, Circ. Ras. 31, 444 20 Rush, R.A. and Geffen, L.B. (1972) Troyer. W.G., Thompson, H.K., Bogdonoff, M.D. and Wallace, A.G. (1968) Arch. Int. 21 Klein, R.F., Med. 122, 476 E. and Canlas, A. (1974) J. Clin. Pharmacol. 14, 354 22 Leon. AS., Thomas, P.E., Sernatinger.
Clinica Chimica Acta, 69 (1976) 61-66 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
CCA 7691
DOPAMINE-P-HYDROXYLASE ACTIVITY IN SERUM FOLLOWING ACUTE MYOCARDIAL INFARCTION: AN EVALUATION OF THIS PARAMETER FOR ROUTINE USE AS AN INDEX OF SYMPATHETIC ACTIVITY
TORE GUTTEBERG, OLAV BORUD and JOHAN H. STRGMME * Division of Clinical Chemistry, Tromsq (Norway)
Institute of Medical Biology,
University of Troms$,
9000
(Received November 22,1975)
Summary Dopamine-fl-hydroxylase activity was measured in sera from 114 normal males and from 11 patients on the lst, 2nd, 3rd, 5th and 10th day following acute myocardial infarction. A significant elevation of dopamine-fl-hydroxylase levels (P < 0.001) was found during the first two days after infarction when compared with the lOth-day values. Only a few activities were above the reference range. Temporary elevations of glucose and glycerol levels were also found. Assay of serum dopamine-/3-hydroxylase may be a useful parameter of sympathetic activity in longitudinal studies in which each individual is used as his own reference.
Introduction Dopamine-/3-hydroxylase (DBH, EC 1.14.17.1) catalyses the final step in the synthesis of noradrenalin, i.e. the conversion of dopamine to noradrenalin. Noradrenalin and DBH are found together in granules in nervous tissue, especially sympathetic nerve endings and the adrenal medulla. These granules are released during sympathetic activity, and a fraction of the released DBH subsequently reaches the blood stream [l-3]. It seems likely that serum DBH arises in the main from the sympathetic nerves with only a minor fraction coming from the adrenal gland [ 1, 4-61. Serum DBH activity therefore, like the serum catecholamine level, appears to be an index of sympathetic activity. Planz et al. [7] have reported recently that in humans there is a linear relationship between graded work and serum DBH and a logarithmic relationship between graded work and serum catechol* To whom reprint requests should be addressed.
62
amines. Similarly, Naftchi et al. [ 81 have found a significant correlation between stages of induced hypertension, serum DBH and urinary excretion of noradrenalin in patients with quadriplegia. Finally, reports of high levels of DBH and catecholamines in serum from patients suffering from essential hypertension have led to suggestions that increased sympathetic activity is an important factor in the pathog~nesis of this disease [9,10]. The aim of the present work was to examine whether DBH activity in serum might be a
Patients The subjects studied were 3 women and 8 men with acute myocardial infarction. The diagnosis was confirmed by typical electroc~diographic changes, rises in serum creatine kinase activities (normal values <120 U/l) to a maximum on the second day (mean 1287 U/l, range 58-4200 U/l), and of serum aspartate aminotransferase activities (normal values 10-40 U/l) to a maximum on the third day (mean 227 U/l, range 93-663 U/l). All patients were admitted to the coronary care unit and monitored for a variable period from 3 days upwards. None of the patients died or required resuscitation during the lo-day observation period. Methods Blood samples were taken without anticoagulants on admission and at 8 a.m. on the other days. The samples were immediately placed on ice, and centrifuged within 30 min. The serum was stored at -20°C until analysed in series for each patient. DBH was assayed at 37°C essentialty as described by Nagatsu and Udenfriend [ 161 using tyramine as substrate. The final incubation mixture of 2.5 ml contained 0.1 ml serum. Aliquots were taken routinely from the incubation mixture at 10 and 20 min. The octopamine formed was oxidized to p-hydroxybenzaldehyde and measured in a Beckmann Model 25 spe~trophotometer at 330 nm. The linearity of the reaction was good for at least 30 min of incubation. The change of absorption between 10 and 20 min was used in the calculation of the catalytic activity, expressed in U (pm01 min-’ ), and the catalytic concentration was expressed in IJjl, Using a serum with an average activity of 55 U/l as test material, the relative standard deviation for precision within series was found to be 3.8%, and between series 7.8%. Glucose was assayed spectrophotometrically by the glucose oxidase method, using reagents from Boehringer, Mannheim, G.F.R. (Cat. No. 15756). The relative standard deviation for the precision between series of this method was 1.6%, and the reference range was 4.2-5.7 mmol/l. Glycerol was assayed in
63
by an enzymatic method, using reagents from Boehringer, Mannheim, G.F.R. (Cat. No. 15747). The reproducibility of this method was 6.7%, and the reference range was 0.02-0.68 mmol/l. The presence of possible serum DBH inhibitors in myocardial tissue was assayed as follows: freshly sampled dog myocardium kept at -8O”C, was cut into small pieces and homogenized at 0°C (Potter-Elvehjem homogenizer) in 10 volumes of 100 mmol/l Tris (pH 7.4) containing 0.25 mol/l sucrose. The homogenate was centrifuged at 10 000 X g for 10 min, and the supernatant tested for DBH inhibitors (for details see Table II). Results The reference range of DBH activities was determined by assaying sera from 114 nonhypertensive males aged 21-50 years. The blood was collected between 8.30 and 10.00 a.m. thus avoiding the 24-h rhythm [17]. The results showed a skewed distribution of the catalytic concentrations, ranging from 0 to 105 U/l, with the reference range covering 95% of the material of 7-85 U/l, mean 35 U/l (Fig. 1). Fig. 2 shows the results of DBH, glucose and glycerol in the sera of 11 patients following myocardial infarction. Table I gives the P-values obtained by paired comparison of the results from each day over the first five days with the respective results on the 10th day. DBH was significantly elevated on admission (1st day), and on the 2nd and 3rd day with averages of 149, 149 and 127%, respectively, of the lOth-day value. No significant difference was found between the 5th and 10th day (P > 0.05). Glucose was significantly elevated on the lst, 2nd, 3rd and 5th day, being 156, 140, 142 and 122%, respectively, of the lOth-day value. Glycerol was significant elevated (350%) on only the first day. There was also a markedly higher mean result (210%) on the second day compared to the lOthday value, but this was not statistically significant due to a high interindividual
20
G E i I= 10
:
50 Catalytic concentration
100 ( U/l)
Fig. 1. Distribution of DBH activities in serum from 114 males. aged 21-50 between 8.30 and 10.00 a.m., and serum assayed as described in Methods.
years. Blood was collected
q
BH
0
glucose
q
1
2
glycerol
5
3
Days after
10
infarction
Fig. 2. Mean ? S.E. of DBH, glucose, and glycerol in serum from 11 patients with acute myocardial infarction. The blood was collected on admission, and at 8 a.m. on the 2nd. 3rd, 5th and 10th day. The results are expressed as percent of the respective values on the 10th day. The mean lOth-day values for DBH, glucose and glycerol were 34.0 U/l. 5.90 mmol/l and 55 Lcmol/l. respectively.
variation as indicated by the large standard error of the mean (Fig. 2). Linear regression analysis failed to demonstrate any correlation between the levels of DBH and glucose, or between DBH and,glycerol on each day. Previously it has been shown that rat myocardium contains substances with the ability to inhibit DBH from bovine adrenal gland [ 181. To examine whether a similar inhibition could occur with the human serum enzyme, the effect of dog myocardium preparations on serum DBH was studied. Table II shows that inhibition of human serum DBH occurred only in the presence of very high concentrations of the myocardial supernatant.
TABLE
I
Statistical probability (P-values) for a null hypothesis obtained when comparing the levels of DBH, glucose and glycerol in serum during the first five days after myocardial infarction with those found on the 10th day. The Student’s f-test was applied to the results of Fig. 2. Day
DBH
Glucose
Glycerol _____~
O-1
CO.001
l-2
0.001~.005
2-3
0.0254.05
4-5
0.054.10
0.005-0.01
0.001---0.005
0.01+.02
0.05-0.10
10.001 0.01-0.02
0.64.7 0.20+.25
TABLE II THE INHIBITORY
EFFECT OF DOG MYOCARDIAL
SUPERNATANT
ON DBH OF HUMAN SERUM
Different volumes of the supernatant of homogenized dog myocardium were mixed with 0.5 ml serum. Water was added so that the final serum dilution was 1 : 10 in accordance with the assay of serum DBH (see Methods). The catalytic concentration of DBH in serum diluted with water and no supernatant has been taken as 100% (82 U/l). No DBH activity was detected in the myocardial supernatant itself. The results are expressed as mean t S.D. of 4 parallel determinations. S~~rnatant
: serum
DBH activity
(vfv>
(%)
0: 1 : 1: 1: 9 :
100 105 105 90 24
l(0) * 50 (1 mg) lO(5mgf 5 (10 mg) 1 (450 mg)
+ + f * +
12 2.3 5.7 23 8.0
-
~_I_
* Weight of myocardium added to 0.5 ml serum.
Discussion The levels of stress parameters such as glucose, glycerol and free fatty acids depend not only on catecholamines, but also on other regulatory factors. In contrast, DBH like noradren~in may be considered as a primary parameter of sympathetic activity [ 191. However, DBH differs from noradrenalin by having a much slower clearance rate in blood, the half-life of the former in sheep being estimated as about 3 h [20]. The level of the enzyme may therefore be expected to reflect better the general situation of the patient over a period of hours than would catecholamine levels, since the latter tend rather to reflect the situation at the instant of sampling. Moreover, catecholamines are highly unstable components in vitro and difficult to assay precisely. As has been convincingly demonstrated by several authors [ll-13,211, acute myocardial infection represents a well defined clinical condition regularly associated with increased sympathetic activity. In 11 patients we found a definite increase in the average DBH activity of serum on the 1st and 2nd day following acute myocardial infarction. However, only 1 of the 11 results obtained over the 1st and 2nd day was above the reference range used for DBH. In comparison, 9 of the 11 first-day levels of glucose and glycerol were above the reference range for these two parameters. Previously a 5- to lo-fold increase of catecholamine levels in plasma has been found following acute myocardial infarction [ll]. Accordingly DBH seems to be a far less sensitive parameter of sympathetic activity than both cate~hol~ines and the secondary parameters glycerol and glucose. This considered together with the large biological variation of DBH makes this serum enzyme unsuitable as a routinely used parameter of stress, Conclusions along these lines have also been made by previous authors [3,221. A puzzling feature of the present results is that while nerve endings seem to release a constant ratio of DBH and noradrenalin [ 191 and while the clearance rate of the former is much slower than that of the latter, DBH is still a lowsensitivity index of sympathetic activity. Two possible explanations of this
apparentdichotomy
come to mind. Firstly, DBI-I is a much larger molecule than nuradre~~~n and thus may well take longer to reach the bloodstream. Secondly, the blood of infarct patients may contain specific DBH inhibitors that are not inactivated by the N-ethylmaleimide present in the incubation mixture. It has previously been shown that rat heart preparations possess an inhibitory effect on partially purified bovine adrenal DBH [lS]_ However, the present results show that the human serum enzyme is very resistant to inhibition by the supernatant obtained from a homogenate of dog myocardium. lnhibition was noted only at extremely high concentrations of supernatant which presumably bear no relationship to the in vivo situation following myocardiai infarction. The data here presented show that statistically significant elevations of serum DBH levels were found on the 1st and 2nd day only when each result was compared with the corresponding 10th day value, At this latter date, the serum DBH activity of each patient had probably returned near to the individual baseline. Most likely a much lower intra- than inter-individual variation explains why significant increases were obtained in this ca$e only. It seems therefore that measurements of DBH may be useful in longitudinal studies in which each individual may be his own reference, However, the lack of sensitivity of this serum parameter and its large reference range appear to make it unsuitable as a routinely used index of sympathetic activity in clinical work.
We are grateful
to Mrs. ashild
Johansen
for skilled technical
assistance
References Life Sci 14, 1593 1 Geffen. L. (1974) 2 Axelrod, J. (1972) Pharmacol. Rev. 24,233 in Neurosycho3 Goldstein, M., Freedman, L.S., Ebstein, R.P.. Park, D.H. and Kashimoto, T. (1974) yharmaeology of Monoamines and Their Regulatory Enzymes (Usdin, E., ed.), PP. 105-119, Raven Press. New York R.M., Kvetnanaky, R., Ax&rod, J_ and Kopin, I,& (1971) Nature New Biol, 230,287 4 WeinshiXboum, 5 Roffman, M., Freedman, L.S. and Goldstein, M. (1973) Life Sci. 12,369 R.M. and Ax&ad, J. (1971) Science 173,931 6 Weinshilboum, H. (1975) Eur. J. Clln. Phar. 7 Planz, G., Wiethold. G., Appel, E., Bahmer, D., Palm, D. and Grobecker, macol, 8, 181 Circ. Res. 35,850 8 Naftchi, N.E., Wooten, G.F., Cowman. E.W. and Axeirod. J. (1974) CIi. Sci. 44, 617 9 G&fen, L.B., Rush, R.A., Louis, W.J_ and Doyle. A.E, (1973) Gunnelis, J.C., Robinson, R.R., Schanberg, S.M. and Kirsbner, N. 11974) Circ. Res. 10 Stone, R.A., SUPPI. 34/35,1-47 11 Videbaek, J.. Christensen. N.J. and Sterndorff, I3. (1972) Circulation 46, 846 12 Christensen, N.J. and Videbaek, J. (1974) J. Clin. Invest. 54, 278 P.E. and Oganov, R.G. (1972) Am. Heart J. 83, 182 13 Lukomsky, T.W. (1968) Lancet i, 710 14 Oliver, M.F., Kuriet~, V.A. and Greenwood, Br. Heart J. 36. 996 16 Carlstrom, S. and Gustafson, A. (1974) Clin. Chem. 18, 980 l.6 Nagatsu, T. and Udenfriend, S. (1972) Exporientia 30, 605 17 Qkada, T.. Fujita, T., Ohta. T., Kato, T.. Ikuta, K. and Nagatsu, T. (1974) Research, pp. 195-ZOO, Pergamon 18 Molinoff, P.B. and Orcutt. J.C. (1973) In Frontiers in Catecholsmine Press. Oxford R.M., Thee, N.B., Johns-n, D.G., Kopin, I.J. and Axelrod. J. (1971) Science 274,1349 19 Weinshilboum, Circ. Ras. 31, 444 20 Rush, R.A. and Geffen, L.B. (1972) Troyer. W.G., Thompson, H.K., Bogdonoff, M.D. and Wallace, A.G. (1968) Arch. Int. 21 Klein, R.F., Med. 122, 476 E. and Canlas, A. (1974) J. Clin. Pharmacol. 14, 354 22 Leon. AS., Thomas, P.E., Sernatinger.