- Email: [email protected]
Reduced serotonin uptake by spontaneously hypertensive rat platelets
Life Sciences, Vol. 29, pp. 2375-2379 Printed in the U.S.A.
Pergamon Press
REDUCED SEROTONIN UPTAKE BY SPONTANEOUSLY HYPERTENSIVE RAT PLATELETS R. Prina, E. Dolfini ~, T. Mennini ~, A. Palermo and A. Libretti Clinica Medica, Universit~ di Milano, Ospedale "Sacco" Via G.B. Grassi 74, 20157 MILAN ~Istituto di Ricerche Farmacologiche "Mario Negri" Via Eritrea 62, 20157 MILAN, Italy (Received in final form October 12, 1981) Summary Platelets of Spontaneous Hypertensive (SH) rats show a significant reduction in serotonin uptake, compared with that of rats with normal blood pressure. The difference was due to the Vmax, which was about 40% of normals, while the Km values were almost constant. The possible analogy between blood platelets and serotonergic nerve terminals in SH rats is considered in the evaluation of the results. The function of serotonin containing neurons in the central nervous system has been investigated by several authors in order to clarify this system's role in the regulation of arterial pressure (1-13). However, there is still no agreement whether these structures have an inhibitory or facilitatory role on preganglionic sympathetic neurons. Blood platelets seem to have numerous similarities with serotonergic nerve terminals, and have been widely used as useful, easily accessible model for the study of neuronal serotonergic function in several neuropsychiatric diseases (14-16) and recently in the study of clinical hypertension (17). In fact 5HT accumulates by blood plate]ets by active transport and is stored in vesicles, in close parallel with serotonergic nerve endings (18-23). In 1979 Bhargava et al. (17) reported altered serotonin uptake by platelets in clinical hypertension. They suggested that the lowered content and uptake of serotonin by blood platelets might indicate an analogous defect in central neurons. In our study we have investigated the uptake of serotonin in blood platelets and in synaptosomes of Wistar-Kyoto (WK) rats with normal blood pressure, and of Spontaneous Hypertensive (SH) rats with high pressure (180-2OO rmnHg). The aim of this study was to confirm a deficit in blood platelet serotonin uptake and to check the possible analogy between blood platelets and serotonergic nerve terminals in SH rats, taken as a model of a spontaneous hypertension (24-25). Materials and Methods Animals Male Spontaneous Hypertensive rats and Wistar-Kyoto rats from Charles River, all between 11-13 weeks old, housed in standard laboratory conditions, i.e. constant room temperature (21 + l°C) and relative humidity (60%) with free access to water and food, were used in our experiments. Animals were 0024-3205/81/232375-05502.00/0 Copyright (c) 1981 Pergamon Press Ltd.
2376
Reduced Serotonin Uptake by SHR Platelets
Vol. 29, No. 23, 1981
killed by inhalation of ethyl ether.
Blood was collected from the inferior cava vein in i0 ml disposable plastic syringes containing 1 ml 0.126 M trisodium citrate and transferred into centrifuge tubes. Each tube was centrifuged at 150 x g for 15 minutes. The supernatant plasma which was rich in platelets (PRP) was sucked off. Platelets were counted in a haemocytometer chamber.
14C-5HT creatinine sulphate (60 mCi/mmol) was purchased from the Radiochemical Centre, Amersham. Aliquots of 1.5 ml rat PRP were preincubated in a water bath at 37°C for 5 minutes. Then I00 microliters of PRP were added to 14C-5HT at various concentrations ranging between O.125 and 2 ~mol and incubated for 30 sec at 37°C. Incubation was stopped by adding 1 ml ice-cold 0.4% EDTA in 0.9% NaCI solution and chilling the tubes rapidly in melting ice. The samples were then centrifuged at i0,000 x g for 1 minute in an Eppendorf 5412 centrifuge and the platelet-free supernatant was discarded. The sedimented platelet 'pellet' was then disrupted by adding 0.2 ml 85% formic acid for at least one hour. Radioactivity was measured by liquid scintillation countin§ (Beckman LS 7500) in Aqua Luma. Uptake was expressed as pmol of 14C-5HT/IO° platelets/min. Zero Time samples were obtained by diluting samples with 1 ml ice-cold EDTA-saline solution before adding 0.I ml PRP, in order to exclude the active transport of serotonin, and subtracted from the respective uptake samples to give net uptake values (26).
Synaptosomes were obtained from whole brains and 14C-5HT uptake was determined as previously described (27). Briefly, 0.6 ml of synaptosome suspension in Krebs-Henseleit buffer, containing 0.5-1 mg proteins/ml, was incubated with various 14C-5HT concentrations ranging from 0.05 to 0.5 ~mol, at 37°C for 5 min. Incubation was stopped by adding 0.5 ml cold Krebs buffer, and samples were ragidly vacuum-filtered through Millipore filters, 0.6 ~ pore size. Passive diffusion was determined in parallel samples maintained at 4°C and subtracted from the respective uptake samples to give net uptake values. Calculations
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
and Statistics .
.
.
.
.
.
.
.
.
.
.
Kinetic parameters of 14C-5HT uptake (K m and Vmax) were calculated from net uptake values by the linear transformation method of Woolf (26). K m and Vma x for WK and SH rats were compared using Student's t test. Results Figure 1 shows the 14C-5HT uptake by platelets of WK and SH rats. Serotonin uptake by SH rat platelets was less than by control rat platelets. The difference was due to the Vmax , which was about 40% of normals, while the K m values were almost constant. The amounts of serotonin accumulated in zero time samples were not different in the two experimental models (unpublished results). When 14C-5HT uptake was studied in synaptosomes of WK or SH rats, no significant differences were found (K m 0.14 and O.122amol , Vma x 12.19 and 10.67 pmol 14C-5HT/mg of protein/minute for WK and SH rats, respectively). In order to verify the possibility that plasma of SH rats contained some inhibitory factors of 14C-5HT uptake, we incubated rat synaptosomes of another strain (Sprague Dawley CD/COBS) in plasma from WK and SH rats. 14C-5HT accumulated by s~naptosomes incubated with plasma from WK and SH rats was 0.163 and O.155 pmol i C-5HT/mg of protein/minute respectively, indicating that SH
Vol. 29, No. 23, 1981
Reduced Serotonin Uptake by SHR Platelets
2377
rat plasma had no inhibitory effect on serotonin uptake in synaptosomes. Krn
0.167,
Vmax
180-
o SH 0.7 +_0.2 °84.5"_17.6 • WK 0.8+-0.1 206.2-*36.3
0.0835
90
0.0167-
18,
0'5.
1'
1.5 '
2'
i
i
!
i
0.5
1
1.5
2
FIG. 1 Left: linear transformation of Woolf (/--S~/V plotted versus / S/) Right: Michaelis M~nten plot of data ~V versus / S/) V were expressed as pmoles 14C-5HT/IO ~ platelets/min; /--ST were ~uM 14C-5HT concentrations. Mean values + S.D. of Km and Vmax are reported p O.O1, Student's t test. Experiments were repeated twice, using 4 animals per group, with similar results. Discussion In the present study it has been shown that in platelets of SH rats there is a significant reduction in serotonin uptake. This may well indicate a specific defect of 5HT active transport, because the free diffusion of serotonin through the membrane was linear and similar for WK and SH rats. The Vma xvalues were significantly (p ( 0 . 0 1 ) different, but Km values, indicating the affinity of the carrier for 5HT, were almost constant; probably this indicates the presence of a non-competitive inhibition mechanism. Since blood platelets have numerous similarities with serotonergic nerve terminals and have been used as a model for the study of neuronal serotonergic functions (14-17), we studied serotonin uptake in synaptosomal preparations of SH rats in order to check for any possible analogous defect in nerve endings. Our experiments failed to show any such alteration, as Vmax and Km of 14C-5HT uptake were similar in synaptosomes of normotensive and hypertensive rats. This point calls for further studies, in order to rule out with greater certainty a possible analogy between blood platelets and synaptosomes in the study of hypertension. In our experiment synaptosomal preparations are derived from the whole brain and the possibility that limited alterations in specific brain areas directly involved in hypertension could be 'masked' because of their limited quantitative significance for whole brain serotonin uptake must be
2378
Reduced Serotonin Uptake by SHR Platelet
Vol. 29, No. 23, 1981
considered. Moreover our experiments were made only in ll-13-week-old this alteration in uptake might be age-dependent.
rats and
In order to investigate the presence of an inhibitory plasmatic factor in SH rat plasma a synaptosomal preparation of another strain was incubated in SH and WK rat plasma. The results of this study showed that SH rat plasma had no inhibitory influence on serotonin uptake in synaptosomes. For this reason we can conclude that the reduced serotonin uptake in platelets of SH rats is due only to the active transport and is probably not influenced by a plasmatic factor. Although not definitive, our results do suggest the existence of a 5HT-uptake defect present principally in blood platelets, which might be due to a 5HT storate-pool deficiency or to an alteration in the membrane. The first hypothesis has its basis in reports (28-31) of apparently genetically determined conditions of human thrombopathy characterized by a decrease in nucleotides and serotonin platelet pool, probably associated with a lack of the specific storage organelles; in these conditions accumulation of 5HT, not due to an impairment of the membrane carrier, could be reduced. The second hypothesis, i.e. the existence of a functional or structural alteration of the membrane carrier, could be related to altered cellular content and active transport of ions in hypertension (32-35). There is known to be a close relationship (36-37) between plasmatic Na+/K + and the accumulation of 5HT by blood platelets, as the carrier function depends on the sodium concentration gradient through the platelet membrane, maintained by a Na+/K + pump. References 1. 2. 3. 4. 5. 6. 7. 8. 9. iO. Ii. 12. 13. 14. 15. 16. 17. 18.
19.
R.J. NEUMAYR, B.D. HARE and D.N. FRANZ, Life Sci. 14 793-806 (1974). M.K. KRSTIC and D. DJURKOVIC, Experientia 32 1187-1189 (1976)• G. HAEUSLER, Prog. Brain Res. 47 95-109 (1977). H.G. BAUMGARTEN, L. LACHENMAYER and H.G. SCHLOSSBERG, Z. Zellforsch. mikrosk. Anat. 125 553-569 (1972). J. DALY, K. FUXE and G. JONSSON, Brain Res. 49 476-482 (1973). L.M.H. WING and J.P. CHALMERS, Clin. exp. Pharmacol. Physiol. ~, 219-229 (1974). L.M.H. WING and J.P. CHALMERS, Circ. Res. 35 504-513 (1973). K.P. BHARGAVA and K.K. TANGRI, Br. J. Pharma---col. 14 411-414 (1959~. B.D. HARE, R.J. NEUMAYR and D.N. FRANZ, Nature 239 336-337 (1972). N.Th. DASICALOPOULOS and H. SCHMITT, Abstracts 6th International Congress of Pharmacology, Helsinki, July 20-25, p.634 (1975). A. ITO and S.M. SCHANBERG, J. Pharmacol. exp. Ther. 189 392-404 (1974). Y. YAMORI, W.DE JONG, H. YAMABE, W. LOVENBERG and A. SJOERSDMA, J. Pharm. Pharmacol. 24 690-695 (1972). W. DE JONG, F.P. NIJKAMP and B. BOHUS, Arch. Int. Pharmacodyn. 213 272-284 (1975). S.M. STAHL, Arch. gen. Psychiat. 34 509-516 (1977). D.J. BOULLIN and R.A. O'BRIEN, J. Physiol. (London) 212 287-297 (1971). J. TUOMISTO and E. TUKIAINEN, Nature 262 596-598 (1976). K.P. BHARGAVA, N. RAINA, N. MISRA, K. SHANKER and S. VRAT, Life Sci. 25 195-200 (1979) J.L• GORDON, H.J. OLVERMAN and A.H. DRUMMOND, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.361-372. Raven Press, New York (1978). M. DA PRADA, J.G. RICHARDS and H.P. LOREZ, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.331353. Raven Press. New York (1978).
Vol. 29, No. 23, 1981
Reduced Serotonin Uptake by SHR Platelets
2379
20. G. DE GAETANO, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.373-384. Raven Press, New York (1978). 21. S.M. STAHL and H.Y. MELTZER, J. Pharmacol. exp. Ther. 205 118-132 (1977). 22. J.M. SNEDDON, Prog. Neurobiol. 1 151-198 (1973). 23. M.K. PAASONEN , L. AHTEE and E. SOLATUNTURI, Prog. Brain Res. 34 269279 (1971). 24. J.M. SAAVEDRA, H. GROBECKER and J. AXELROD, Circ. Res. 42 529-534 (1978). 25. K. MORI, Jap. Circ. Res. 37 609-618 (1973). 26. M. WIELOSZ, M. SALMONA, G. de GAETANO and S. GARATTINI, NaunynSchmiedeberg's Arch. Pharmacol. 296 59-65 (1976). 27. T. MENNINI, R. PATACCINI and R. SAMANIN, Br. J. Pharmacol. 64 75-82 (1978). 28. H. HOLMSEN and H.J. WEISS, Blood 39 197-209 (1972). 29. J.G. WHITE, Am. J. Pathol. 63 403-410 (1971). 30. R.M. HARDISTY, D.C. MILLS and K. KETSA-ARD, Br. J. Haematol. 23 679692 (1972). 31. H.J. WEISS, Ann. N.Y. Acad. Sci. 201 161-173 (1972). 32. S.M. FRIEDMAN, M. NAKASHIMA, R.A. MclNDOE and C.L. FRIEDMAN, Experientia 32 476-478 (1976). 33. C.J. LIMAS and J.N. COHN, Circ. Res. 40, suppl., 163-169 (1977). 34. A.W. JONES, Circ.Res. 33 563-572 (1973). 35. S.M. FRIEDMAN, Hypertension ! 572-582 (1979). 36. J.M. SNEDDON, Br. J. Pharmacol. 37 680-688 (1969). 37. J.M. SNEDDON, Br. J. Pharmacol. 43 834-844 (1971).
Pergamon Press
REDUCED SEROTONIN UPTAKE BY SPONTANEOUSLY HYPERTENSIVE RAT PLATELETS R. Prina, E. Dolfini ~, T. Mennini ~, A. Palermo and A. Libretti Clinica Medica, Universit~ di Milano, Ospedale "Sacco" Via G.B. Grassi 74, 20157 MILAN ~Istituto di Ricerche Farmacologiche "Mario Negri" Via Eritrea 62, 20157 MILAN, Italy (Received in final form October 12, 1981) Summary Platelets of Spontaneous Hypertensive (SH) rats show a significant reduction in serotonin uptake, compared with that of rats with normal blood pressure. The difference was due to the Vmax, which was about 40% of normals, while the Km values were almost constant. The possible analogy between blood platelets and serotonergic nerve terminals in SH rats is considered in the evaluation of the results. The function of serotonin containing neurons in the central nervous system has been investigated by several authors in order to clarify this system's role in the regulation of arterial pressure (1-13). However, there is still no agreement whether these structures have an inhibitory or facilitatory role on preganglionic sympathetic neurons. Blood platelets seem to have numerous similarities with serotonergic nerve terminals, and have been widely used as useful, easily accessible model for the study of neuronal serotonergic function in several neuropsychiatric diseases (14-16) and recently in the study of clinical hypertension (17). In fact 5HT accumulates by blood plate]ets by active transport and is stored in vesicles, in close parallel with serotonergic nerve endings (18-23). In 1979 Bhargava et al. (17) reported altered serotonin uptake by platelets in clinical hypertension. They suggested that the lowered content and uptake of serotonin by blood platelets might indicate an analogous defect in central neurons. In our study we have investigated the uptake of serotonin in blood platelets and in synaptosomes of Wistar-Kyoto (WK) rats with normal blood pressure, and of Spontaneous Hypertensive (SH) rats with high pressure (180-2OO rmnHg). The aim of this study was to confirm a deficit in blood platelet serotonin uptake and to check the possible analogy between blood platelets and serotonergic nerve terminals in SH rats, taken as a model of a spontaneous hypertension (24-25). Materials and Methods Animals Male Spontaneous Hypertensive rats and Wistar-Kyoto rats from Charles River, all between 11-13 weeks old, housed in standard laboratory conditions, i.e. constant room temperature (21 + l°C) and relative humidity (60%) with free access to water and food, were used in our experiments. Animals were 0024-3205/81/232375-05502.00/0 Copyright (c) 1981 Pergamon Press Ltd.
2376
Reduced Serotonin Uptake by SHR Platelets
Vol. 29, No. 23, 1981
killed by inhalation of ethyl ether.
Blood was collected from the inferior cava vein in i0 ml disposable plastic syringes containing 1 ml 0.126 M trisodium citrate and transferred into centrifuge tubes. Each tube was centrifuged at 150 x g for 15 minutes. The supernatant plasma which was rich in platelets (PRP) was sucked off. Platelets were counted in a haemocytometer chamber.
14C-5HT creatinine sulphate (60 mCi/mmol) was purchased from the Radiochemical Centre, Amersham. Aliquots of 1.5 ml rat PRP were preincubated in a water bath at 37°C for 5 minutes. Then I00 microliters of PRP were added to 14C-5HT at various concentrations ranging between O.125 and 2 ~mol and incubated for 30 sec at 37°C. Incubation was stopped by adding 1 ml ice-cold 0.4% EDTA in 0.9% NaCI solution and chilling the tubes rapidly in melting ice. The samples were then centrifuged at i0,000 x g for 1 minute in an Eppendorf 5412 centrifuge and the platelet-free supernatant was discarded. The sedimented platelet 'pellet' was then disrupted by adding 0.2 ml 85% formic acid for at least one hour. Radioactivity was measured by liquid scintillation countin§ (Beckman LS 7500) in Aqua Luma. Uptake was expressed as pmol of 14C-5HT/IO° platelets/min. Zero Time samples were obtained by diluting samples with 1 ml ice-cold EDTA-saline solution before adding 0.I ml PRP, in order to exclude the active transport of serotonin, and subtracted from the respective uptake samples to give net uptake values (26).
Synaptosomes were obtained from whole brains and 14C-5HT uptake was determined as previously described (27). Briefly, 0.6 ml of synaptosome suspension in Krebs-Henseleit buffer, containing 0.5-1 mg proteins/ml, was incubated with various 14C-5HT concentrations ranging from 0.05 to 0.5 ~mol, at 37°C for 5 min. Incubation was stopped by adding 0.5 ml cold Krebs buffer, and samples were ragidly vacuum-filtered through Millipore filters, 0.6 ~ pore size. Passive diffusion was determined in parallel samples maintained at 4°C and subtracted from the respective uptake samples to give net uptake values. Calculations
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
and Statistics .
.
.
.
.
.
.
.
.
.
.
Kinetic parameters of 14C-5HT uptake (K m and Vmax) were calculated from net uptake values by the linear transformation method of Woolf (26). K m and Vma x for WK and SH rats were compared using Student's t test. Results Figure 1 shows the 14C-5HT uptake by platelets of WK and SH rats. Serotonin uptake by SH rat platelets was less than by control rat platelets. The difference was due to the Vmax , which was about 40% of normals, while the K m values were almost constant. The amounts of serotonin accumulated in zero time samples were not different in the two experimental models (unpublished results). When 14C-5HT uptake was studied in synaptosomes of WK or SH rats, no significant differences were found (K m 0.14 and O.122amol , Vma x 12.19 and 10.67 pmol 14C-5HT/mg of protein/minute for WK and SH rats, respectively). In order to verify the possibility that plasma of SH rats contained some inhibitory factors of 14C-5HT uptake, we incubated rat synaptosomes of another strain (Sprague Dawley CD/COBS) in plasma from WK and SH rats. 14C-5HT accumulated by s~naptosomes incubated with plasma from WK and SH rats was 0.163 and O.155 pmol i C-5HT/mg of protein/minute respectively, indicating that SH
Vol. 29, No. 23, 1981
Reduced Serotonin Uptake by SHR Platelets
2377
rat plasma had no inhibitory effect on serotonin uptake in synaptosomes. Krn
0.167,
Vmax
180-
o SH 0.7 +_0.2 °84.5"_17.6 • WK 0.8+-0.1 206.2-*36.3
0.0835
90
0.0167-
18,
0'5.
1'
1.5 '
2'
i
i
!
i
0.5
1
1.5
2
FIG. 1 Left: linear transformation of Woolf (/--S~/V plotted versus / S/) Right: Michaelis M~nten plot of data ~V versus / S/) V were expressed as pmoles 14C-5HT/IO ~ platelets/min; /--ST were ~uM 14C-5HT concentrations. Mean values + S.D. of Km and Vmax are reported p O.O1, Student's t test. Experiments were repeated twice, using 4 animals per group, with similar results. Discussion In the present study it has been shown that in platelets of SH rats there is a significant reduction in serotonin uptake. This may well indicate a specific defect of 5HT active transport, because the free diffusion of serotonin through the membrane was linear and similar for WK and SH rats. The Vma xvalues were significantly (p ( 0 . 0 1 ) different, but Km values, indicating the affinity of the carrier for 5HT, were almost constant; probably this indicates the presence of a non-competitive inhibition mechanism. Since blood platelets have numerous similarities with serotonergic nerve terminals and have been used as a model for the study of neuronal serotonergic functions (14-17), we studied serotonin uptake in synaptosomal preparations of SH rats in order to check for any possible analogous defect in nerve endings. Our experiments failed to show any such alteration, as Vmax and Km of 14C-5HT uptake were similar in synaptosomes of normotensive and hypertensive rats. This point calls for further studies, in order to rule out with greater certainty a possible analogy between blood platelets and synaptosomes in the study of hypertension. In our experiment synaptosomal preparations are derived from the whole brain and the possibility that limited alterations in specific brain areas directly involved in hypertension could be 'masked' because of their limited quantitative significance for whole brain serotonin uptake must be
2378
Reduced Serotonin Uptake by SHR Platelet
Vol. 29, No. 23, 1981
considered. Moreover our experiments were made only in ll-13-week-old this alteration in uptake might be age-dependent.
rats and
In order to investigate the presence of an inhibitory plasmatic factor in SH rat plasma a synaptosomal preparation of another strain was incubated in SH and WK rat plasma. The results of this study showed that SH rat plasma had no inhibitory influence on serotonin uptake in synaptosomes. For this reason we can conclude that the reduced serotonin uptake in platelets of SH rats is due only to the active transport and is probably not influenced by a plasmatic factor. Although not definitive, our results do suggest the existence of a 5HT-uptake defect present principally in blood platelets, which might be due to a 5HT storate-pool deficiency or to an alteration in the membrane. The first hypothesis has its basis in reports (28-31) of apparently genetically determined conditions of human thrombopathy characterized by a decrease in nucleotides and serotonin platelet pool, probably associated with a lack of the specific storage organelles; in these conditions accumulation of 5HT, not due to an impairment of the membrane carrier, could be reduced. The second hypothesis, i.e. the existence of a functional or structural alteration of the membrane carrier, could be related to altered cellular content and active transport of ions in hypertension (32-35). There is known to be a close relationship (36-37) between plasmatic Na+/K + and the accumulation of 5HT by blood platelets, as the carrier function depends on the sodium concentration gradient through the platelet membrane, maintained by a Na+/K + pump. References 1. 2. 3. 4. 5. 6. 7. 8. 9. iO. Ii. 12. 13. 14. 15. 16. 17. 18.
19.
R.J. NEUMAYR, B.D. HARE and D.N. FRANZ, Life Sci. 14 793-806 (1974). M.K. KRSTIC and D. DJURKOVIC, Experientia 32 1187-1189 (1976)• G. HAEUSLER, Prog. Brain Res. 47 95-109 (1977). H.G. BAUMGARTEN, L. LACHENMAYER and H.G. SCHLOSSBERG, Z. Zellforsch. mikrosk. Anat. 125 553-569 (1972). J. DALY, K. FUXE and G. JONSSON, Brain Res. 49 476-482 (1973). L.M.H. WING and J.P. CHALMERS, Clin. exp. Pharmacol. Physiol. ~, 219-229 (1974). L.M.H. WING and J.P. CHALMERS, Circ. Res. 35 504-513 (1973). K.P. BHARGAVA and K.K. TANGRI, Br. J. Pharma---col. 14 411-414 (1959~. B.D. HARE, R.J. NEUMAYR and D.N. FRANZ, Nature 239 336-337 (1972). N.Th. DASICALOPOULOS and H. SCHMITT, Abstracts 6th International Congress of Pharmacology, Helsinki, July 20-25, p.634 (1975). A. ITO and S.M. SCHANBERG, J. Pharmacol. exp. Ther. 189 392-404 (1974). Y. YAMORI, W.DE JONG, H. YAMABE, W. LOVENBERG and A. SJOERSDMA, J. Pharm. Pharmacol. 24 690-695 (1972). W. DE JONG, F.P. NIJKAMP and B. BOHUS, Arch. Int. Pharmacodyn. 213 272-284 (1975). S.M. STAHL, Arch. gen. Psychiat. 34 509-516 (1977). D.J. BOULLIN and R.A. O'BRIEN, J. Physiol. (London) 212 287-297 (1971). J. TUOMISTO and E. TUKIAINEN, Nature 262 596-598 (1976). K.P. BHARGAVA, N. RAINA, N. MISRA, K. SHANKER and S. VRAT, Life Sci. 25 195-200 (1979) J.L• GORDON, H.J. OLVERMAN and A.H. DRUMMOND, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.361-372. Raven Press, New York (1978). M. DA PRADA, J.G. RICHARDS and H.P. LOREZ, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.331353. Raven Press. New York (1978).
Vol. 29, No. 23, 1981
Reduced Serotonin Uptake by SHR Platelets
2379
20. G. DE GAETANO, in Platelets: A Multidisciplinary Approach, eds. G. de Gaetano and S. Garattini, pp.373-384. Raven Press, New York (1978). 21. S.M. STAHL and H.Y. MELTZER, J. Pharmacol. exp. Ther. 205 118-132 (1977). 22. J.M. SNEDDON, Prog. Neurobiol. 1 151-198 (1973). 23. M.K. PAASONEN , L. AHTEE and E. SOLATUNTURI, Prog. Brain Res. 34 269279 (1971). 24. J.M. SAAVEDRA, H. GROBECKER and J. AXELROD, Circ. Res. 42 529-534 (1978). 25. K. MORI, Jap. Circ. Res. 37 609-618 (1973). 26. M. WIELOSZ, M. SALMONA, G. de GAETANO and S. GARATTINI, NaunynSchmiedeberg's Arch. Pharmacol. 296 59-65 (1976). 27. T. MENNINI, R. PATACCINI and R. SAMANIN, Br. J. Pharmacol. 64 75-82 (1978). 28. H. HOLMSEN and H.J. WEISS, Blood 39 197-209 (1972). 29. J.G. WHITE, Am. J. Pathol. 63 403-410 (1971). 30. R.M. HARDISTY, D.C. MILLS and K. KETSA-ARD, Br. J. Haematol. 23 679692 (1972). 31. H.J. WEISS, Ann. N.Y. Acad. Sci. 201 161-173 (1972). 32. S.M. FRIEDMAN, M. NAKASHIMA, R.A. MclNDOE and C.L. FRIEDMAN, Experientia 32 476-478 (1976). 33. C.J. LIMAS and J.N. COHN, Circ. Res. 40, suppl., 163-169 (1977). 34. A.W. JONES, Circ.Res. 33 563-572 (1973). 35. S.M. FRIEDMAN, Hypertension ! 572-582 (1979). 36. J.M. SNEDDON, Br. J. Pharmacol. 37 680-688 (1969). 37. J.M. SNEDDON, Br. J. Pharmacol. 43 834-844 (1971).