Life Sciences Vol . 21, pp . 1675-1678 Printed in the U .S .A .
Pargamon Press
HYPERURICEMIA IN THE RAT FOLLOWING HYPOTHALAMIC STIMULATION Takahiko Sumi and Yuri Umeda Division of Psychopharmacology, Psychiatric Research Institute of Tokyo 2-1-8, Kamikitazawa, Setagaya-Ku, Tokyo, Japan (Received in final form October 24, 1977)
SUMMARY Ventromedial hypothalamic electrical stimulation elicited a marked elevation of plasma uric acid with a rise in plasma allantoin in the rat . The magnitude of this hyperuricemia was greater than that of the hyperglycemia which was also produced by the ventromedial stimulation . On the other hand, lateral hypothalamic stimulation did not significantly affect the plasma levels of either of the purine metabolites . These results strongly indicate that the ventromedial hypothalamus is specifically very active in producing hyperuricemia in the rat . A number of psychosomatic studies have shown that the plasma levels of uric acid sometimes reflect psychological characteristics and degree of stresses of human body (1,2) . These findings seem to suggest an involvement of higher central nervous system in the development of a certain type of hyperuricemia . In the various brain areas, the ventromedial hypothalamic neucleus (VMH) and the lateral hypothalamic area (LH) have been reported to play prominent roles in the regulation of peripheral metabolic processes such as carbohydrate (3,4) and lipid (5) metabolism . From these views, we expected that the hypothalamus plays important roles in the development of hyperuricemia . However, we have not yet obtained any informations about the role of hypothalamus in producing hyperuricemia as well as in regulating peripheral purine metabolism . Then, we attempted to study the activity of the hypothalamus in alternating the plasma levels of major purine metabolites, i .e . uric acid and allantoin, in the rat by means of electrical stimulation of the hypothalamus . MATERIALS AND METHODS Wistar strain male rats weighing 250 to 3008 were used . The rats were given a conventional rat diet and water ad libitum . A bipolar stainless steel electrode was implanted in the VMH or the LH of the rat according to the De Groot atlas (6) . Three weeks after the surgery, the rat received chronic implantation of a polyethylene cannula into the abdominal aorta . The rat was under pentobarbital anesthesia during these surgeries . Three to five 1675
1676
Hypothalamus and Hyperuricamia
Vol . 21, No . 11, 1977
days after the cannulation, we kept the rat unanesthetized in a Ballman cage and then dilivered monophasic square wave electric current with an electric stimulator through the implanted elecThe stimulation parameters were 50 Hz, 5 msec duration and trode . current . The stimulus of 2 sec was applied during alterna0 .2 mA Electrode placement tive 30 sec intervals for a period of 15 min . was identified microscopically after experiments . . at interBlood samples (about 0 .12 ml each) were withdrawn Fifty syringe . a heparinized artery by vals from the cannulated mixed with 500 microliters of plasma from the sampled blood were min in a boiling water pl of 6 .5 mM acetic acid, heated for 2 the resultant deproteinized . From bath, and next centrifugated was used for supernatant, two 200 }xl samples were collected : one and another method (7) uricase-peroxidase by the uric acid assay reductase method (8) . was for allantoin assay by the glyoxylate subjected to glucose An additional 101 sample was collected and (9) . determination RESULTS Fig .lA shows the effects of electrical stimulation of the In response to VMH or the LH on the plasma levels of uric acid . the VhII-I stimulation, plasma uric acid rose strikingly and reached to 2 .8-fold of the initial level at the end of 15 min duration of the stimulation . The elevated uric acid immediately began to fall on cessation of the stimulation . The LH stimulation slightly elevated the uric acid and the magnitude of maximum elevation was only 1 .5-fold of the initial level . It can be concluded therefore that the VIII can produce a marked hyperuricemia which is not a nonspecific response to the stress of the brain stimulation . In the rat as well as in other most mammals, hepatic uricase converts a large part of uric acid into allantoin . Therefore, plasma allantoin should reflect such an elevation of plasma uric We confirmed this by simulacid induced by the VIrII-I stimulation . Followtaneous measurement of plasma allantoin levels (Fig .1B) . ing the VMH stimulation, plasma allantoin gradually increased, attained a peak of 1 .9-fold of the initial level at about 10 min after end of the stimulation and thereafter returned to the initial level very slowly . This slow and prolonged allantoin response can be explained by the action of hepatic uricase, although the decrease in the urinary excretion of plasma allantoin might contribute, at least partially, to the allantoin response . The minute elevation of plasma uric acid following the LH stimulation did not lead to noticeable changes of plasma allantoin . As has been reported by many authors (3,4), the stimulation of the VirII-1 elicites a hyperglycemia . Under our experimental conditions VMH stimulation, but not LH stimulation, produced a 1 .6 fold maximum elevation of plasma glucose level (Fig . 1C) . It is therefore obvious that hyperuricemia accompanies hyperglycemia during VMH stimulation . DISCUSSION This study presents strong evidences that the electrical stimulation of the ventromedial hypothalamus induces a rapid elevation of the plasma uric acid level, and a later rise in plasma allantoin, which presumably reflects the breakdown of uric acid by hepatic uricase . Although we can not give, at present, any experimental results to explain a neurological sequence leading
Vol . 21, No . 11, 1977
Hypothalamus and Hyperuricemia
1677
" VMH O LH contra
o
3
~ 20-
0
15
30
45 60 Minutes
0
15
30
45 60 Minutes
10
OJ
30
45 60 N~nutes
OJ
FIG . 1 Effects of electrical stimulation of the VMH or the LH on the plasma levels of uric acid (A), allantoin (B) and glucose (C) in the rat . Non-stimulated rats receiving an electrode-implantation in the VMH were served as control : significant differences were not observed between the VMH-implanted control rats and the LH-implanted control rats . Solid blocks show duration of the stimulation . Each point is Mean t SE . for five to six rats . to the induction of this hyperuricemia, the present study does suggest the possibility that the hypothalamus plays a prominent role in the development of neurogenic hyperuricemia in the human body as well as in the rat . Since renal excretion of uric acid is negligible in the rat (10), and could not have an effect on plasma uric acid levels in such a short period of the stimulation time, the rise in plasma uric acid could well reflect the increase in uric acid production . Therefore, the VMH-induced hyperuricemia would be likely to be the result of biochemical events leading to the production of uric acid . On the basis of this view, it is highly probable that VMH specifically regulates peripheral purine metabolism similarly to its regulatory action on hepatic carbohydrate metabolism (3) . However, there is no evidence as yet that an actual biochemical change is induced by brain stimulation . Then, other possible hypotheses are next proposed . One possible hypothesis is immediate and transient shifts of preformed uric acid from intracellular sites to extracellular fluid . It is also possible that the contraction of extracellular volume causes the increase in the plas-
1678
Hypothalamus and Hyperuricemia
Vol . 21, No . 11, 1977
ma uric acid concentration . This is made less likely, however, by the rapid fall in plasma uric acid after cessation of the stimulation, but not excluded as active uricase could account for the decline . Another plausible hypothesis is a shift of blood flow such that the hepatic blood flow is reduced, and uric acid which would otherwise be degraded by the uricase escapes the degradation . This hypothesis is also less acceptable because plasma allantoin did not decrease but increase even during the period of the electrical stimulation . Further biochemical as well as neurological studies are in progress in order to clarify the mechanism of this VMI-I-induced hyperuricemia . ACKNOWLEDGEMENT We thank to Dr . Takashi Shimazu (Division of Neurochemistry, Psychiatric Research Institute of Tokyo) for his useful advice for stereotaxic technique . REFERENCES 1 . G . M . Brooks and E . Mueller, J . Am . Med . Soc . 19 5 415-418 (1966) . 2 . R . H . Rahe, R . T . Rubin and R. J . Arthur, Psychosom . Med . 36 258-268 (1974) . 3 . T . Shimazu and S . Ogasawara, Am . J . Physiol . 221 1787-1793 (1975) . 4 . L . A . Frohman and L . L . Bernardis, Am . J . Physiol . 221 15961603 (1971) . 5 . A. Kumon, A . Takahashi, T . Hara and T . Shimazu, J . L Ei d Res . 17 551-558 (1976) . 6 . T. De Groot, J . Com . Neurol . 113 389-400 (1959) . . Kis i, K~Fakahashi and F . Kakimoto, 7 . T . Sumi, Y . Ume a, Clin . Chim . Acta 73 233-239 (1976) . 8. T. umi, Y . Ume a,Y . Kishi, F . Kakimoto and K . Yakahashi, Anal . Biochem .75 563-567 (1976) . 9. . G . ui sult, P . J . Brignac and M . Juneau, Anal . Chem . 40 1256-1263 (1968) . 10 . S . 0 . Byers, M. Friedman and M . N . Garfield, Am . J . Physiol . 150 677-681 (1947) .
Pargamon Press
HYPERURICEMIA IN THE RAT FOLLOWING HYPOTHALAMIC STIMULATION Takahiko Sumi and Yuri Umeda Division of Psychopharmacology, Psychiatric Research Institute of Tokyo 2-1-8, Kamikitazawa, Setagaya-Ku, Tokyo, Japan (Received in final form October 24, 1977)
SUMMARY Ventromedial hypothalamic electrical stimulation elicited a marked elevation of plasma uric acid with a rise in plasma allantoin in the rat . The magnitude of this hyperuricemia was greater than that of the hyperglycemia which was also produced by the ventromedial stimulation . On the other hand, lateral hypothalamic stimulation did not significantly affect the plasma levels of either of the purine metabolites . These results strongly indicate that the ventromedial hypothalamus is specifically very active in producing hyperuricemia in the rat . A number of psychosomatic studies have shown that the plasma levels of uric acid sometimes reflect psychological characteristics and degree of stresses of human body (1,2) . These findings seem to suggest an involvement of higher central nervous system in the development of a certain type of hyperuricemia . In the various brain areas, the ventromedial hypothalamic neucleus (VMH) and the lateral hypothalamic area (LH) have been reported to play prominent roles in the regulation of peripheral metabolic processes such as carbohydrate (3,4) and lipid (5) metabolism . From these views, we expected that the hypothalamus plays important roles in the development of hyperuricemia . However, we have not yet obtained any informations about the role of hypothalamus in producing hyperuricemia as well as in regulating peripheral purine metabolism . Then, we attempted to study the activity of the hypothalamus in alternating the plasma levels of major purine metabolites, i .e . uric acid and allantoin, in the rat by means of electrical stimulation of the hypothalamus . MATERIALS AND METHODS Wistar strain male rats weighing 250 to 3008 were used . The rats were given a conventional rat diet and water ad libitum . A bipolar stainless steel electrode was implanted in the VMH or the LH of the rat according to the De Groot atlas (6) . Three weeks after the surgery, the rat received chronic implantation of a polyethylene cannula into the abdominal aorta . The rat was under pentobarbital anesthesia during these surgeries . Three to five 1675
1676
Hypothalamus and Hyperuricamia
Vol . 21, No . 11, 1977
days after the cannulation, we kept the rat unanesthetized in a Ballman cage and then dilivered monophasic square wave electric current with an electric stimulator through the implanted elecThe stimulation parameters were 50 Hz, 5 msec duration and trode . current . The stimulus of 2 sec was applied during alterna0 .2 mA Electrode placement tive 30 sec intervals for a period of 15 min . was identified microscopically after experiments . . at interBlood samples (about 0 .12 ml each) were withdrawn Fifty syringe . a heparinized artery by vals from the cannulated mixed with 500 microliters of plasma from the sampled blood were min in a boiling water pl of 6 .5 mM acetic acid, heated for 2 the resultant deproteinized . From bath, and next centrifugated was used for supernatant, two 200 }xl samples were collected : one and another method (7) uricase-peroxidase by the uric acid assay reductase method (8) . was for allantoin assay by the glyoxylate subjected to glucose An additional 101 sample was collected and (9) . determination RESULTS Fig .lA shows the effects of electrical stimulation of the In response to VMH or the LH on the plasma levels of uric acid . the VhII-I stimulation, plasma uric acid rose strikingly and reached to 2 .8-fold of the initial level at the end of 15 min duration of the stimulation . The elevated uric acid immediately began to fall on cessation of the stimulation . The LH stimulation slightly elevated the uric acid and the magnitude of maximum elevation was only 1 .5-fold of the initial level . It can be concluded therefore that the VIII can produce a marked hyperuricemia which is not a nonspecific response to the stress of the brain stimulation . In the rat as well as in other most mammals, hepatic uricase converts a large part of uric acid into allantoin . Therefore, plasma allantoin should reflect such an elevation of plasma uric We confirmed this by simulacid induced by the VIrII-I stimulation . Followtaneous measurement of plasma allantoin levels (Fig .1B) . ing the VMH stimulation, plasma allantoin gradually increased, attained a peak of 1 .9-fold of the initial level at about 10 min after end of the stimulation and thereafter returned to the initial level very slowly . This slow and prolonged allantoin response can be explained by the action of hepatic uricase, although the decrease in the urinary excretion of plasma allantoin might contribute, at least partially, to the allantoin response . The minute elevation of plasma uric acid following the LH stimulation did not lead to noticeable changes of plasma allantoin . As has been reported by many authors (3,4), the stimulation of the VirII-1 elicites a hyperglycemia . Under our experimental conditions VMH stimulation, but not LH stimulation, produced a 1 .6 fold maximum elevation of plasma glucose level (Fig . 1C) . It is therefore obvious that hyperuricemia accompanies hyperglycemia during VMH stimulation . DISCUSSION This study presents strong evidences that the electrical stimulation of the ventromedial hypothalamus induces a rapid elevation of the plasma uric acid level, and a later rise in plasma allantoin, which presumably reflects the breakdown of uric acid by hepatic uricase . Although we can not give, at present, any experimental results to explain a neurological sequence leading
Vol . 21, No . 11, 1977
Hypothalamus and Hyperuricemia
1677
" VMH O LH contra
o
3
~ 20-
0
15
30
45 60 Minutes
0
15
30
45 60 Minutes
10
OJ
30
45 60 N~nutes
OJ
FIG . 1 Effects of electrical stimulation of the VMH or the LH on the plasma levels of uric acid (A), allantoin (B) and glucose (C) in the rat . Non-stimulated rats receiving an electrode-implantation in the VMH were served as control : significant differences were not observed between the VMH-implanted control rats and the LH-implanted control rats . Solid blocks show duration of the stimulation . Each point is Mean t SE . for five to six rats . to the induction of this hyperuricemia, the present study does suggest the possibility that the hypothalamus plays a prominent role in the development of neurogenic hyperuricemia in the human body as well as in the rat . Since renal excretion of uric acid is negligible in the rat (10), and could not have an effect on plasma uric acid levels in such a short period of the stimulation time, the rise in plasma uric acid could well reflect the increase in uric acid production . Therefore, the VMH-induced hyperuricemia would be likely to be the result of biochemical events leading to the production of uric acid . On the basis of this view, it is highly probable that VMH specifically regulates peripheral purine metabolism similarly to its regulatory action on hepatic carbohydrate metabolism (3) . However, there is no evidence as yet that an actual biochemical change is induced by brain stimulation . Then, other possible hypotheses are next proposed . One possible hypothesis is immediate and transient shifts of preformed uric acid from intracellular sites to extracellular fluid . It is also possible that the contraction of extracellular volume causes the increase in the plas-
1678
Hypothalamus and Hyperuricemia
Vol . 21, No . 11, 1977
ma uric acid concentration . This is made less likely, however, by the rapid fall in plasma uric acid after cessation of the stimulation, but not excluded as active uricase could account for the decline . Another plausible hypothesis is a shift of blood flow such that the hepatic blood flow is reduced, and uric acid which would otherwise be degraded by the uricase escapes the degradation . This hypothesis is also less acceptable because plasma allantoin did not decrease but increase even during the period of the electrical stimulation . Further biochemical as well as neurological studies are in progress in order to clarify the mechanism of this VMI-I-induced hyperuricemia . ACKNOWLEDGEMENT We thank to Dr . Takashi Shimazu (Division of Neurochemistry, Psychiatric Research Institute of Tokyo) for his useful advice for stereotaxic technique . REFERENCES 1 . G . M . Brooks and E . Mueller, J . Am . Med . Soc . 19 5 415-418 (1966) . 2 . R . H . Rahe, R . T . Rubin and R. J . Arthur, Psychosom . Med . 36 258-268 (1974) . 3 . T . Shimazu and S . Ogasawara, Am . J . Physiol . 221 1787-1793 (1975) . 4 . L . A . Frohman and L . L . Bernardis, Am . J . Physiol . 221 15961603 (1971) . 5 . A. Kumon, A . Takahashi, T . Hara and T . Shimazu, J . L Ei d Res . 17 551-558 (1976) . 6 . T. De Groot, J . Com . Neurol . 113 389-400 (1959) . . Kis i, K~Fakahashi and F . Kakimoto, 7 . T . Sumi, Y . Ume a, Clin . Chim . Acta 73 233-239 (1976) . 8. T. umi, Y . Ume a,Y . Kishi, F . Kakimoto and K . Yakahashi, Anal . Biochem .75 563-567 (1976) . 9. . G . ui sult, P . J . Brignac and M . Juneau, Anal . Chem . 40 1256-1263 (1968) . 10 . S . 0 . Byers, M. Friedman and M . N . Garfield, Am . J . Physiol . 150 677-681 (1947) .
