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Uptake of serotonin by human platelets and its relevance to CNS involvement in hypertension
Life Sciences, Vol . 25, pp . 195-200 Printed in the U.S .A .
Pergamon Press
UPTAKE OF SEROTONIN BY HUMAN PLATELETS AND ITS RELEVANCE TO CNS INVOLVEMENT IN HYPERTENSION Krishna P . Bhargava, Nirmal Raina, Nisha Miara, Rirpa Shanker and Satya Vrat Department of Pharmacology ~ Therapeutics Ring George's Medical College Lucknow - 226003 INDIA (Received in final form May 23, 1979) SUtß1ARY The central serotoaergic neurones seem to have important regulatory function on the cardiovascular egetem. Since human blood platelets and eerotonin (5-HT) containing neurones in the central nervous system have numerous similarities, the uptake of serotonia by human platelets was investigated in normal subjects and in patients of essential hypertension . The 5-HT content of platelets as well as 5-HT uptake by the platelets were significantly reduced in hyperteasive subjects as compared to control . It appears that a deficiency of eerotonin centrally may lead to disiahibition of the serotoaergic mechanisms leading to hypertension . Moreover, a decreased activity of serotoaergic neurones may co-exist with an overactivity of catecholaminergic neurones in essential hypertension, which is discussed. This is probably the first report of altered eerotonin mechanism in clinical hypertension . There is overwhelming evidence in favor of a central neurotransmitter role for eerotonin (5-hydroxytryptamine, 5-HT) (1) . The presence of serotoaergic neurone systems in the central nervous system (CNS) has been demonstrated by the hietochemical fluorescence technique (2) . The monoamine neurones are located in anatomical areas of the CNS concerned with cardiovascular control (3) . The serotoaergic and catecholaminergic neurones seem to subserve important regulatory functions on the spinal vasomotor neurones (4) . It is, therefore, possible that a defect in either (or both) of the central monoaminergic neurone systems may result in hypertension . Since it is not possible to study the central neurones is clinical hypertension by direct means one has to adopt indirect methods of study . The human blood platelets are readily accessible and possess amine storage vesicles, a cell membrane transport mechanism for eerotonin and other characteristics which are similar to the serotoaergic neurones (5,6) . The uptake of eerotonin by platelets has served as a model for the study of neuronal eerotonin in several neuro-psychiatric diseases (7,5,9) . Although hypertension ie a cardiovascular disease yet it may arise from a disorder in the central serotoaergic neurones concerned in vasomotor control . It was with this objective that the blood platelet model was employed is clinical cases of hypertension . This appears to be the first report of platelet aerotonia in human hypertension . 0024-3205/79/020195-05$02 .00/0 Copyright (c) 1979 Pergamon Press Ltd
196
Human Platelet Serotonin Uptake
Vol . 25, ~lo . 2,
1979
METHODS Selection of Patients and Controls : Patients with established hypertension were selected for the study. All the patients were male, age 35-55 years and their blood pressure was in the range 160/100 to 180/110 mm Hg . They were admitted to hospital at least one week prior to the test . All the hypertensive patients were subjected to detailed clinical and laboratory evaluation to exclude secondary hypertension . Age and sex-matched healthy control volunteers had blood pressure ranging from 120/70 to 140/80 mm Hg . Drugs and food items known to influence biogenic amines were forbidden to all subjects . Collection of blood and preparation of latelet rich plasma (PRP) : The method followed for preparation of platelet rich plasma (PRP was essentially that of Born and Gilson (10) . All glassware was ailiconized . Human blood was collected from the arm vein and immediately transferred into centrifuge tubes made of cellulose acetate . Each tube containing YO ml of blood mixed with 1 ml of sodium citrate (0 .129 M) was cooled to 0°C, and centrifuged at 200 g for 20 minutes at 0°C. The supernatant plasma which was rich in platelets (PRP) was sucked off . 0 .1 ml of PRP was mixed with 1 .9 ml of solution containing 1% (w/v) formaldehyde in 3% (w/v) sodium citrate and the platelets in this solution were counted in a haemocytometer chamber . Incubation of PRP with 5-HT : 1 ml of PRP was incubated at 37°C for 30 minutes with solution of 5-HT which was added in an amount of 0 .1 ml containing either 1 .5 ug or 3.0 ug 5-HT . After incubation the tubes were cooled to 0°C and centrifuged at 15,000 g for 20 minutes at 0°C. The supernatant plasma was decanted and the inner walls of the tubes above the platelets and sediment were wiped with filter paper to remove the adhering plasma . Extraction and recovery of 5-HT : The platelet pellet was dispersed in 1 ml of distilled water . The suspension was frozen and thawed three times to extract the 5-HT present in platelets . Bioassay of 5-HT : 5-HT in platelets was assayed on the uterus of rat The tissue pretreated with 250 ug/100 gm atilboeatrol daily for three days . was superfused at the rate of 1 drop/sec . at 25-26°C with de Jalon's solution . The unknown and standard solutions were applied by Superfusion at the rate of 1 drop/sec . for 30 seconds . The de Jalon superfusion was interrupted during addition of 5-HT solution and for 60 seconds subsequently . The interval between The sensitivity of the method was application of 5-HT solution was 10 minutes, of the order of 250 pg . The 5-HT values were expressed se ng/108 platelets ± SE and the. significance of the differences between levels in the controls and in hypertensive subjects were calculated using the Student's t test . RESULTS The 5-HT content of plateThe results of the study are given in Table I. This compares lets in control subjects was found to be 54 .2 ng/108 platelets . Decrease in favorably with the values obtained by other investigators (11,12) . 5-HT content of platelets of hypertensive subjects was found to be statistically significant (p ~ < 0.01), the mean value of 5-HT was 25 .1 ng/10 8 platelets in the disease . Besides the low basal Serotonin level in the hypertensive subjects, another significant observation was a low uptake of the amine by the platelets. In the control, the uptake of 5-AT by platelets after 30 minutes incubation with a concentration of 3 .0 ug 5-HT was 179 .82 and in the hypertensive subjects, under similar conditions the uptake was only 59 .7 ng/10 8 platelets .
Vol . 25, No . 2,
1979
Human Platelet Serotonin Uptake
197
The apparent lack of difference is the uptake of 5-HT between the normotensive and the hyperteasive platelets at 1 .5 yg concentration of 5-HT may be either due to the marked difference in the basal 5-HT content of the two plate lets or an altered uptake mechanism in the hyperteasive platelet . It will be apparent from the figures that in the normotenaive platelets where the basal 5-HT content was twice that of the hyperteasive, however, the uptake in both cases at this concentration (1 .5 ug) was almost the same . However, unless more data is available, this inconsistency in the uptake of 5-HT at the two different concentrations of 1 .5 and 3.0 ug cannot be fully reconciled . TABLE I BASAL SEROTONIN (5-HT) LEVEL AND UPTAKE BY PLATELETS FROM NORMOTENSIVE AND HYPERTENSIVE HUMAN SUBJECTS, VALUES ARE EXPRESSED IN ng/108 PLATELETS ± S .E .
Group
Platelet 5-HT content
-
Platelet 5-HT uptake following 30~ incubation in 1 ml PRP at 37°C Concentrations of 5-HT 1 .5 ug 3.0 Vg
Normotenaive (4)
54 .2 ± 16
44 .55 ± 17 .3
Hypertenaive
25 .1 ± 8 .9*
45 .5
±
179 .82 ± 28 .9
9 .3
59 .7
± 12 .18*
*Significantly different from control, p <0 .01 . DISCUSSION The uptake of aerotonin by platelets has frequently been employed as a model for the study of neuronal uptake of the amine (7,8,9) . There are numerous similarities between the blood platelets and the CNS serotonergic synaptosomes ; both share common biochemical properties se well as several morphological features (5,6) . A close parallelism seems to exist between the blood platelets and the neuron is relation to the disposition of aerotonin, however, this parallelism does not seem to hold good with other monoamines (7) . The platelet model could provide reliable information on the role of serotonergic neurones in yet unexplored diseases . The central nerwus system plays a vital role is the regulation of blood pressure . While the etiology of essential hypertension is not known, it ie realized that "stress" and CNS factors play important contributory part is the pathogenesis of the disease. From experimental studies, it is clear that the monoamiaergic neurones in the CNS exercise important controlling influence on the blood pressure . The aerotonergic neuron systems have been mapped out in the brain (3) and a descending pathway, the bulbo-spinal tract, terminating at the lateral column of the spinal cord seems to regulate the activity of the spinal autonomic neurones (4) . There is, however, no tmanimity regarding the role of central serotonergic neurones is blood pressure control . Exogenous admini~tration of aerotonin into the brain of the anaesthetized dogs and cats induces a decrease in the sympathetic outflow and a resultant fall in blood preesure (13,14,15,16,17) . However, in the anaesthetized rats iatraventricular administration of aerotonin resulted in hypertension (18) . Reduction of central aerotonin levels by pats-chlorophenylalanine (pCPA) in conscious rats resulted in a rise of blood pressure (19,20,21) . Aowever, similar reduction in the
198
Human Platelet Serotonin Uptake
Vol . 25, No . 2,
1979
central aerotonin by administration of p-CPA or 5,6-dihydroxytryptamine resulted in a fall in blood pressure in rabbits (22,23) . Increase in the central aerotonin level by intravenous administration of 5-hydroxytryptophan in spinal cats was reported to either decrease the sympathetic discharge (24) or increase the sympathetic discharge (25) . Thus, the role of central serotonergic neurones in blood pressure regulation is still debatable. Species variation may account for discrepancies in the studies on the effects of central aerotonin. If the results obtained from the platelet model in our study in hypertensive subjects can be applied to the serotonergic neurones, it is proposed that Our find there is a deficiency of central aerotonin in essential hypertension . ings would favor an inhibitory role of central serotonergic neurones on the human blood pressure . The deficiency of aerotonin centrally may lead to a disinhibition of the serotonergic mechanism resulting in hypertension . Recently we have shown increase in the 3-methoxy 4-hydroxyphenyl glycol (MHPG), a metabolite of catecholamines in the CSF of patients suffering from essential hypertension (26) . This may indicate an overactivity of the catecholaminergic neurones coexisting with a decreased activity of serotonergic neurones in essential hypertension. The aerotonin turnover in the platelet may not be a true index of neuronal aerotonin. It may be argued that the aerotonin in the neuronal system is governed by presynaptic receptors which are lacking in the platelet model. Fur thermore, the monoamine oxidase in the platelets ie of the B type whereas in the neurone it is of A type, for which the aerotonin is the true substrate. It would, therefore, be rewarding to obtain more direct proof of aerotonin turnover in the central neurones in hypertension . REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 . 15 . 16 . 17 . 18 . 19 . 20 . 21 . 22 . 23 . 24 .
T .N . CHASE and D.L . MURPHY, Ann : Rev. Pharmacol . 13 181-197 (1973) . R . FUXE, T . HOKFELT and U . UNGERSTEDT, Adv . Pharmâcol . Sci . _6A 235-251 (1968) . P .I . BORNER, Physiol. Rev . 51 312-367 (1971) . R .J . NEUMAYR, B .D . HARE and~.N .!FRANZ, Life Sci . _14 793-804 (1974) . J .M . SNEDDON, Prog . Neurobiol . 1 151-198 (1973) . M.K . PAASONEN, L . AHTEE and E . SOLATUNTURI, Prog . Brain Res. _34 269-279 (1971) . S .M . STAHL, Arch . Gen . Psychiatry _34 509-516 (1977) . D .J . BOULLIN and R.A . O'BRIEN, J . Physiol. 212 287-297 (1971) . J . TUOMISTO and E . TURIAINEN, Nature _262 596-598 (1976) . G .V .R . BORN and R .E . GILSON, J. Physiol. _146 472-491 (1959) . M.R . PAASONEN, J . Pharm. Pharmacol . _17 681-697 (1965) . R .M . HARDISTY and R.S . STACEY, J. Physiol . _130 711-720 (1955) . K .P . BHARGAVA and K .K . TANGRI, Brit . J. Pharm. _14 411-414 (1959) . K.H . GINZEL and S .R . KOTTEGODA, J. Physiol . 123 277-288 (1954) . N .TH . DASKALOPOULOS and H . SCfiMITT, 6th Int . Congress Pharm. Helsinki p . 634 (1975) . T . BAUM and A .T . SHROPSHIRE, Neuropharmacol . _14 227-233 (1975) . J .W . McCUBBIN, Y . KANERO and I .H . PAGE, Circulation Res . _8 849-858 (1960) . M.K . KRSTIC and D . DJURROVIC, Experientia _32 1187-1189 (1976) . A. ITO and S .M . SCHANBERG, J . Pharm . Exp . Ther . _181 65-75 (1972) . Y . YAMORI, W. DE JONG, H. YAMABE, W . LOVENBERG and A. SJOERDSMA, J. Pharm. Pharmacol . 24 690-695 (1972) . W. DE JONG, F.P . NIJRAMP and B. BOHUS, Arch . Int . Pharmacodyn . _213 272-284 (1975) . Clin . Exp. Pharm. Physiol. 1 219-229 (1974) . L .M .H . WING and J .P . CHALMERS, L .M .H . WING and J .P . CHALMERS, Circulation Res . _35 504-513 (1974) . B .D . HARE, R.J . NEUMAYR and D .M . FRANZ, Nature 239 336-337 (1972) .
Vol . 25, No . 2, 1979
Human Platelet Serotonin Uptake
199
25 . G . HAEUSLER, Progress in Brain Research W . De Jong, A,P, Provost and A,P, Shapiro (ede .) _47 95-109 (1977) . 26 . R .R . SARAN, R .C . AAUJA, N .N . GUPTA, M . HASAN, R .P . BHARGAVA, R . SHANKER and K . KISHOR, Science 200 317-318 (1978) .
Pergamon Press
UPTAKE OF SEROTONIN BY HUMAN PLATELETS AND ITS RELEVANCE TO CNS INVOLVEMENT IN HYPERTENSION Krishna P . Bhargava, Nirmal Raina, Nisha Miara, Rirpa Shanker and Satya Vrat Department of Pharmacology ~ Therapeutics Ring George's Medical College Lucknow - 226003 INDIA (Received in final form May 23, 1979) SUtß1ARY The central serotoaergic neurones seem to have important regulatory function on the cardiovascular egetem. Since human blood platelets and eerotonin (5-HT) containing neurones in the central nervous system have numerous similarities, the uptake of serotonia by human platelets was investigated in normal subjects and in patients of essential hypertension . The 5-HT content of platelets as well as 5-HT uptake by the platelets were significantly reduced in hyperteasive subjects as compared to control . It appears that a deficiency of eerotonin centrally may lead to disiahibition of the serotoaergic mechanisms leading to hypertension . Moreover, a decreased activity of serotoaergic neurones may co-exist with an overactivity of catecholaminergic neurones in essential hypertension, which is discussed. This is probably the first report of altered eerotonin mechanism in clinical hypertension . There is overwhelming evidence in favor of a central neurotransmitter role for eerotonin (5-hydroxytryptamine, 5-HT) (1) . The presence of serotoaergic neurone systems in the central nervous system (CNS) has been demonstrated by the hietochemical fluorescence technique (2) . The monoamine neurones are located in anatomical areas of the CNS concerned with cardiovascular control (3) . The serotoaergic and catecholaminergic neurones seem to subserve important regulatory functions on the spinal vasomotor neurones (4) . It is, therefore, possible that a defect in either (or both) of the central monoaminergic neurone systems may result in hypertension . Since it is not possible to study the central neurones is clinical hypertension by direct means one has to adopt indirect methods of study . The human blood platelets are readily accessible and possess amine storage vesicles, a cell membrane transport mechanism for eerotonin and other characteristics which are similar to the serotoaergic neurones (5,6) . The uptake of eerotonin by platelets has served as a model for the study of neuronal eerotonin in several neuro-psychiatric diseases (7,5,9) . Although hypertension ie a cardiovascular disease yet it may arise from a disorder in the central serotoaergic neurones concerned in vasomotor control . It was with this objective that the blood platelet model was employed is clinical cases of hypertension . This appears to be the first report of platelet aerotonia in human hypertension . 0024-3205/79/020195-05$02 .00/0 Copyright (c) 1979 Pergamon Press Ltd
196
Human Platelet Serotonin Uptake
Vol . 25, ~lo . 2,
1979
METHODS Selection of Patients and Controls : Patients with established hypertension were selected for the study. All the patients were male, age 35-55 years and their blood pressure was in the range 160/100 to 180/110 mm Hg . They were admitted to hospital at least one week prior to the test . All the hypertensive patients were subjected to detailed clinical and laboratory evaluation to exclude secondary hypertension . Age and sex-matched healthy control volunteers had blood pressure ranging from 120/70 to 140/80 mm Hg . Drugs and food items known to influence biogenic amines were forbidden to all subjects . Collection of blood and preparation of latelet rich plasma (PRP) : The method followed for preparation of platelet rich plasma (PRP was essentially that of Born and Gilson (10) . All glassware was ailiconized . Human blood was collected from the arm vein and immediately transferred into centrifuge tubes made of cellulose acetate . Each tube containing YO ml of blood mixed with 1 ml of sodium citrate (0 .129 M) was cooled to 0°C, and centrifuged at 200 g for 20 minutes at 0°C. The supernatant plasma which was rich in platelets (PRP) was sucked off . 0 .1 ml of PRP was mixed with 1 .9 ml of solution containing 1% (w/v) formaldehyde in 3% (w/v) sodium citrate and the platelets in this solution were counted in a haemocytometer chamber . Incubation of PRP with 5-HT : 1 ml of PRP was incubated at 37°C for 30 minutes with solution of 5-HT which was added in an amount of 0 .1 ml containing either 1 .5 ug or 3.0 ug 5-HT . After incubation the tubes were cooled to 0°C and centrifuged at 15,000 g for 20 minutes at 0°C. The supernatant plasma was decanted and the inner walls of the tubes above the platelets and sediment were wiped with filter paper to remove the adhering plasma . Extraction and recovery of 5-HT : The platelet pellet was dispersed in 1 ml of distilled water . The suspension was frozen and thawed three times to extract the 5-HT present in platelets . Bioassay of 5-HT : 5-HT in platelets was assayed on the uterus of rat The tissue pretreated with 250 ug/100 gm atilboeatrol daily for three days . was superfused at the rate of 1 drop/sec . at 25-26°C with de Jalon's solution . The unknown and standard solutions were applied by Superfusion at the rate of 1 drop/sec . for 30 seconds . The de Jalon superfusion was interrupted during addition of 5-HT solution and for 60 seconds subsequently . The interval between The sensitivity of the method was application of 5-HT solution was 10 minutes, of the order of 250 pg . The 5-HT values were expressed se ng/108 platelets ± SE and the. significance of the differences between levels in the controls and in hypertensive subjects were calculated using the Student's t test . RESULTS The 5-HT content of plateThe results of the study are given in Table I. This compares lets in control subjects was found to be 54 .2 ng/108 platelets . Decrease in favorably with the values obtained by other investigators (11,12) . 5-HT content of platelets of hypertensive subjects was found to be statistically significant (p ~ < 0.01), the mean value of 5-HT was 25 .1 ng/10 8 platelets in the disease . Besides the low basal Serotonin level in the hypertensive subjects, another significant observation was a low uptake of the amine by the platelets. In the control, the uptake of 5-AT by platelets after 30 minutes incubation with a concentration of 3 .0 ug 5-HT was 179 .82 and in the hypertensive subjects, under similar conditions the uptake was only 59 .7 ng/10 8 platelets .
Vol . 25, No . 2,
1979
Human Platelet Serotonin Uptake
197
The apparent lack of difference is the uptake of 5-HT between the normotensive and the hyperteasive platelets at 1 .5 yg concentration of 5-HT may be either due to the marked difference in the basal 5-HT content of the two plate lets or an altered uptake mechanism in the hyperteasive platelet . It will be apparent from the figures that in the normotenaive platelets where the basal 5-HT content was twice that of the hyperteasive, however, the uptake in both cases at this concentration (1 .5 ug) was almost the same . However, unless more data is available, this inconsistency in the uptake of 5-HT at the two different concentrations of 1 .5 and 3.0 ug cannot be fully reconciled . TABLE I BASAL SEROTONIN (5-HT) LEVEL AND UPTAKE BY PLATELETS FROM NORMOTENSIVE AND HYPERTENSIVE HUMAN SUBJECTS, VALUES ARE EXPRESSED IN ng/108 PLATELETS ± S .E .
Group
Platelet 5-HT content
-
Platelet 5-HT uptake following 30~ incubation in 1 ml PRP at 37°C Concentrations of 5-HT 1 .5 ug 3.0 Vg
Normotenaive (4)
54 .2 ± 16
44 .55 ± 17 .3
Hypertenaive
25 .1 ± 8 .9*
45 .5
±
179 .82 ± 28 .9
9 .3
59 .7
± 12 .18*
*Significantly different from control, p <0 .01 . DISCUSSION The uptake of aerotonin by platelets has frequently been employed as a model for the study of neuronal uptake of the amine (7,8,9) . There are numerous similarities between the blood platelets and the CNS serotonergic synaptosomes ; both share common biochemical properties se well as several morphological features (5,6) . A close parallelism seems to exist between the blood platelets and the neuron is relation to the disposition of aerotonin, however, this parallelism does not seem to hold good with other monoamines (7) . The platelet model could provide reliable information on the role of serotonergic neurones in yet unexplored diseases . The central nerwus system plays a vital role is the regulation of blood pressure . While the etiology of essential hypertension is not known, it ie realized that "stress" and CNS factors play important contributory part is the pathogenesis of the disease. From experimental studies, it is clear that the monoamiaergic neurones in the CNS exercise important controlling influence on the blood pressure . The aerotonergic neuron systems have been mapped out in the brain (3) and a descending pathway, the bulbo-spinal tract, terminating at the lateral column of the spinal cord seems to regulate the activity of the spinal autonomic neurones (4) . There is, however, no tmanimity regarding the role of central serotonergic neurones is blood pressure control . Exogenous admini~tration of aerotonin into the brain of the anaesthetized dogs and cats induces a decrease in the sympathetic outflow and a resultant fall in blood preesure (13,14,15,16,17) . However, in the anaesthetized rats iatraventricular administration of aerotonin resulted in hypertension (18) . Reduction of central aerotonin levels by pats-chlorophenylalanine (pCPA) in conscious rats resulted in a rise of blood pressure (19,20,21) . Aowever, similar reduction in the
198
Human Platelet Serotonin Uptake
Vol . 25, No . 2,
1979
central aerotonin by administration of p-CPA or 5,6-dihydroxytryptamine resulted in a fall in blood pressure in rabbits (22,23) . Increase in the central aerotonin level by intravenous administration of 5-hydroxytryptophan in spinal cats was reported to either decrease the sympathetic discharge (24) or increase the sympathetic discharge (25) . Thus, the role of central serotonergic neurones in blood pressure regulation is still debatable. Species variation may account for discrepancies in the studies on the effects of central aerotonin. If the results obtained from the platelet model in our study in hypertensive subjects can be applied to the serotonergic neurones, it is proposed that Our find there is a deficiency of central aerotonin in essential hypertension . ings would favor an inhibitory role of central serotonergic neurones on the human blood pressure . The deficiency of aerotonin centrally may lead to a disinhibition of the serotonergic mechanism resulting in hypertension . Recently we have shown increase in the 3-methoxy 4-hydroxyphenyl glycol (MHPG), a metabolite of catecholamines in the CSF of patients suffering from essential hypertension (26) . This may indicate an overactivity of the catecholaminergic neurones coexisting with a decreased activity of serotonergic neurones in essential hypertension. The aerotonin turnover in the platelet may not be a true index of neuronal aerotonin. It may be argued that the aerotonin in the neuronal system is governed by presynaptic receptors which are lacking in the platelet model. Fur thermore, the monoamine oxidase in the platelets ie of the B type whereas in the neurone it is of A type, for which the aerotonin is the true substrate. It would, therefore, be rewarding to obtain more direct proof of aerotonin turnover in the central neurones in hypertension . REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 . 15 . 16 . 17 . 18 . 19 . 20 . 21 . 22 . 23 . 24 .
T .N . CHASE and D.L . MURPHY, Ann : Rev. Pharmacol . 13 181-197 (1973) . R . FUXE, T . HOKFELT and U . UNGERSTEDT, Adv . Pharmâcol . Sci . _6A 235-251 (1968) . P .I . BORNER, Physiol. Rev . 51 312-367 (1971) . R .J . NEUMAYR, B .D . HARE and~.N .!FRANZ, Life Sci . _14 793-804 (1974) . J .M . SNEDDON, Prog . Neurobiol . 1 151-198 (1973) . M.K . PAASONEN, L . AHTEE and E . SOLATUNTURI, Prog . Brain Res. _34 269-279 (1971) . S .M . STAHL, Arch . Gen . Psychiatry _34 509-516 (1977) . D .J . BOULLIN and R.A . O'BRIEN, J . Physiol. 212 287-297 (1971) . J . TUOMISTO and E . TURIAINEN, Nature _262 596-598 (1976) . G .V .R . BORN and R .E . GILSON, J. Physiol. _146 472-491 (1959) . M.R . PAASONEN, J . Pharm. Pharmacol . _17 681-697 (1965) . R .M . HARDISTY and R.S . STACEY, J. Physiol . _130 711-720 (1955) . K .P . BHARGAVA and K .K . TANGRI, Brit . J. Pharm. _14 411-414 (1959) . K.H . GINZEL and S .R . KOTTEGODA, J. Physiol . 123 277-288 (1954) . N .TH . DASKALOPOULOS and H . SCfiMITT, 6th Int . Congress Pharm. Helsinki p . 634 (1975) . T . BAUM and A .T . SHROPSHIRE, Neuropharmacol . _14 227-233 (1975) . J .W . McCUBBIN, Y . KANERO and I .H . PAGE, Circulation Res . _8 849-858 (1960) . M.K . KRSTIC and D . DJURROVIC, Experientia _32 1187-1189 (1976) . A. ITO and S .M . SCHANBERG, J . Pharm . Exp . Ther . _181 65-75 (1972) . Y . YAMORI, W. DE JONG, H. YAMABE, W . LOVENBERG and A. SJOERDSMA, J. Pharm. Pharmacol . 24 690-695 (1972) . W. DE JONG, F.P . NIJRAMP and B. BOHUS, Arch . Int . Pharmacodyn . _213 272-284 (1975) . Clin . Exp. Pharm. Physiol. 1 219-229 (1974) . L .M .H . WING and J .P . CHALMERS, L .M .H . WING and J .P . CHALMERS, Circulation Res . _35 504-513 (1974) . B .D . HARE, R.J . NEUMAYR and D .M . FRANZ, Nature 239 336-337 (1972) .
Vol . 25, No . 2, 1979
Human Platelet Serotonin Uptake
199
25 . G . HAEUSLER, Progress in Brain Research W . De Jong, A,P, Provost and A,P, Shapiro (ede .) _47 95-109 (1977) . 26 . R .R . SARAN, R .C . AAUJA, N .N . GUPTA, M . HASAN, R .P . BHARGAVA, R . SHANKER and K . KISHOR, Science 200 317-318 (1978) .