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Distribution and placental transfer of C14-serotonin in pregnant rats
14
Distribution and placental transfer of C ·serotonin in pregnant rats Z. KOREN, M.D. Y. PFEIFER, B.A. F. G. SULMAN, M.D., D.V.M. Jerusalem, Israel
I N P R E v I o u s studies, 3 we established that the serotonin content of the human placenta gradually increases in a normally developing pregnancy. In young placentas it amounts to an average of 6 /Jog per gram tissue and it rises to 15 /Jog per gram tissue in mature placentas obtained from normal term deliveries. At the same time, the enzymatic activity of placental monoamine oxidase vvhich destroys serotonin shovved a re~ verse proportion, being highest at the beginning of gestation and gradually dropping to the lowest level at term. Maternal serotonin is quite capable of diffusing across the placenta, but since the latter and the amniotic fluid contain a high level of monoamine oxidase, 3 • 6 ordinary amounts of serotonin are deaminated during passage to the fetus and thus made harmless. Because of the relatively large content of endogenous serotonin in many tissues, it is difficult to obtain reliable and precise information regarding the distribution and transfer of serotonin circulating during the different stages of pregnancy. Axelrod and Inscoe~ were the first to use radioactive serotonin for studies of uptake, binding, and distribution of serotonin in animal tissues.
Using this method, studies on pregnant rats were performed by us. This allowed us to study the passing of 5=hydroxytryptamine=3C 14-creatinine sulfate through rat placentas from both maternal and fetal sides, and the distribution between maternal and fetal tissues. Methods and material
Radioactive serotonin ( 5-hydroxytryptamine-3-C14-creatinine sulfate) was obtained from Amersham (Great Britain). Pregnant albino rats of the Hebrew University strain were kept on a stock diet. The experiments were performed on rats between the seventeenth and the nineteenth day of gestation. The abdomen was opened under light ether anesthesia and either 1 mi. of the serotonin C 14 -solution was injected into the lower abdominal aorta, or a dose of 0.1 mi. was injected into each amniotic sac, visible through the transparent myometrium. Intrafetal injections were effected by introducing a No. 25 gauge needle through the uterine wall into the peritoneum of each fetus. On the average, 9 fetuses were present (range 6 to 12) and the total radioactivity introduced per animal was 0.1 to 0.2 IJ.C C 14-serotonin. The rats were then dosed, sutured, and, at intervals ranging from 5 minutes to 24 hours, again anesthesized and bled through the abdominal aorta. Various tissues were then removed and measured for radioactivity (blood, heart, lungs, intestines, adrenals, kidneys, myometrium, fetal tissues) . The tissues were
From the Department of Obstetrics and Gynecology, Rothschild-H adassah University Hospital, and the Department of Applied Pharmacology, School of Pharmacy, Hebrew University. Generously aided by United States National Institute of Health Grant No. MH 06 999-01.
290
Placental transfer of C14·serotonin
Volume 9:, Number 2
quickly excised, weighed, rinsed with cold normal saline solution, and extracted thoroughly by homogenization in 46 per cent KOH. Up to 2 mg. of every organ was dissolved in boiling 46 per cent KOH, after cooling diluted to 10 mi., and 0.1 ml. from each of the solutions was applied to chromatographic paper at separate spots, the longitudinal distance between each spot being 4 em. A solution of 0.005 p,c radioactive serotonin was used as control and standard. The paper strips were scanned with a Packard radiochromatogram scanner Model 7200 connected to a Packard recording ratemeter Model 380. The settings were as follows: 0.5 em. per minute and window 5 mm. It was found that under these conditions the size a...'ld form of the spot only minimally affected the linearity of the determinations. Radioactivity was calculated by cutting out the area of the recorded peaks, weighing them, and comparing the weight with that of the standard. The final calculation took into account dilution and weight of the dissolved organs. Results
Tables I through III comprise representative data from 39 rats on the distribution of radioactivity recovered from several selected maternal tissues, as compared with that found in the pooled placentas and fetuses of the same animal. The illustrations represent typical samples. Intra-aortic injection of C 14 -serotonin into mother rats. There was a wide range in the ability of tissues to take up circulating sero-
291
Table I. Distribution of serotonin after intra-aortic injection into pregnant rats*
I Min5 I 10 I Min-
1
I utes I utes IHour Maternal tissue Blood Liver Spleen Small intestine Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta Fetal tissue Brain Intestine H eart-lungs Liver Kidneys Carcass Head Total fetus
11.0 8.3 9.0
11.0 7.0 8.0 10.0
17.0 5.0 7.0
17.0 58.0 12.0 6.0 4.0
9.0 28.0 13.0 9.0 6.0
52.0 10.0 36.0 2.0 8.0
t
t
t
3.0 3.0
t t t t t t
8.0 6.0 1.0
t
5.0 8.0
t t
18.0
t
I
6 24 Hours Hours
5.0 9.0 5.0 4.0
3.0 16.0 3.0
12.0 10.0 10.0 3.0
7.0 13.0 4.0 4.0
t
t
4.0
t
t
t
t t
t
t
t t t t t
2.0
t
2.0
t t
2.0
*Mean values of distribution of l mg. containing 0.1 p.c C"-serotonin within the bodies of five groups of 3 pregnant rats each. Serotonin is expressed as p.g/ Gm. of tissue after different time intervals as calculated from radioactivity. tMeasur·ement below the sensitivity o£ our se lup (equivalent to l p.g serotonin).
tonin (Table I and Fig. 1). After administration of C 14 -serotonin into the maternal aorta, the radioactivity trapped in the maternal tissues concentrated mainly in the large intestines, lungs, liver, and kidneys. The placenta trapped only low amounts of radioactivity within 5 minutes ; 10 minutes after injection
TRAAORTIC INJECTION AI er 5 tn>nu ts
Fig. l. Pwdiochromatogram of the effects of an intra-aortic injection of C 14 -serotonin. Highest radioactivity was found in maternal lung, liver, kidneys, and large intestine, and no evident radioactivity in fetal tissues.
292
Koren, Pfeifer, and Sulmon
May 15, 1966
Am.
J, Obst.
& Gynec.
these vanished quickly, and after 24 hours most of the radioactivity had disappeared. The recovery on the fetal side amounted to only a very small fraction in the brain, liver, and heart-lung preparation which appeared as late as after a lapse of 10 minutes and disappeared after one hour. In other organs, no significant radioactivity was found. Intra-amniotic injection of C 14-serotonin. The low penetrability through the maternalfetal barrier was also evident when C 14 serotonin was administered into the amniotic cavity (Table II and Fig. 2). Placental and fetal tissues became strongly labeled, whereas only a small proportion reached the maternal tissues, apart from the myometrium, which became strongly labeled with C 14-serotonin. Lung and kidneys were the first to store C 14 serotonin, later this was taken over by the adrenals, heart, and intestines. Although the fetal tissues were capable of assimilating most
of the C 14 -serotonin, an appreciable portion of the radioact1v1ty was stili detected in the amniotic fluid after 5 and 10 minutes. One hour after injection, the exact amount of this residual activity could not be determined because of the difficulty of quantitative collection of the amniotic fluid. The fetuses concentrated C 14-serotonin mainly in the intestines, heart, lungs, liver, and brain. Intraperitoneal injection of C 14-serotonin into rat fetuses. After injection of C 14 serotonin into the fetal peritoneum only a fraction crossed the placenta, similar quantities later being taken up by the myometrium (Table III and Fig. 3). However, in these cases, permeability was higher in the fetusmother direction than vice versa, i.P., the mother-fetus direction. There was a wide range in the ability of tissues to take up circulating C 14 -serotonin. After 5 to 60 minutes, maternal tissues had some concentra-
Tabie II. Distribution of serotonin after intra-amniotic injection*
Tahie III. Distribution of serotonin after fetal intraperitoneal injection* 5 .. I
15
Minutes Maternal tissue Blood T ' Liver
Spleen Small =~"---"-=-UJLC:HIUC:
Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta Fetal tissue Brain Intestine Heart-lungs Liver Kidneys Carcass Head Total fetus
t
1 6 1 24 Hour I Hours Hours
1.0
.L
.L
t t
t t
I
I
4.0
t
t t
t
MinI utes Mat ern a[ tissue Blood T ~--- --
r" u.u
Spleen Small
6.0
LIVer
t
3.0
: - ... ~~ ... ! - -
t
I
15
Minutes
7.0 6.0 2.6 1.6
Hour
'"
"t.U
24 Hours
t
t
·'I·
2.0
~
I
2.0 13.0 5.0 3.0
...tI t
Ull.CtllHH:;;;
5.0
5.0
3.0
t
9.0
t
t
2.0
7.0
t t t
t t t
t t t
44.0 31.0 5.0 66.0 23.0 22.0
t 4.0
26.0 47.0
16.0 5.0
t t 13.0 9.0
15.0 2.0 5.0 3.0 1.0 22.0
3.0
*Mean values of distribution of 1 mg. containing 0.1 J.LC C 14 ~serotonin within the bodies of four groups of 3 pregnant rats each. Serotonin is expressed as JLg/Gm. of tissue after different time intervals as calculated irom radioactivity. tMeasurement below the sensitivity of our setup lent to 1 pg serotonin).
Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta
2.0 21.0 3.0 3.0
(equiva~
F eta[ tissue Brain Intestine Heart-lungs Liver Kidneys Carcass Head Total fetus
3.0 10.0
t t t t
8.0 14.0
t 88.0 122.0 96.0
t 16.0
2. 7 24.0 4.5 13.0 3.0 2.0 23.0 17.0
t
69.0 39.0 33.0 28.0 27.0
t t
5.0 7.0
t
60.0 31.0 51.0 48.0 10.0
t t t
11.0 12.0
t
46.0 24.0 68.0 29.0
t
·*Mean values of distribution of mg. containing 0.1 C 1•~serotonin within the bodies of four groups of 3 pregnant rats each. Serotonin is expressed as p.g/Gm. of tissue after different time intervais as caicuia£ed irom radioactivity. J..LC
tMeasurement below the sensitivity of our SPtup ( equivalent !o 1 JJ.g serotonin).
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Fig. 3. Radiochromatogram of the eff ects of an intraperitoneal injecti on of C 1 •-serotonin . Very high concentrations of radioac tivity are found in fetal heart, lungs, liver, intestines, and carcass. In materna l tissues increased radio activity was found in ovary, myometrium , and placenta.
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INJECTIO N
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INTRAPERITONEAL
Fig. 2. Radiochromatogram of the effec ts of an intra-amniotic injection of CH-serotonin. In fetal tissues, the highest radioactivity was found in intestines and liver, heart-lungs, kidneys, and carcass. Highest radioac tivity was found in placental and maternal myometrium and smaller amounts in maternal kidneys and lungs.
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Koren, Pfeifer, and Sulman
tions of C 14 -serotonin in all organs, the bulk being in the myometrium and adrenals. After 24 hours, serotonin was metabolized and disappeared in a!! organs except the myometrium. Fetal tissues having the highest concentration of serotonin were the intestines, heart-lung, liver, and carcass. In the kidneys the concentration of radioactivity began after l 5 minutes and lasted for 24 hours. The brain showed practically no uptake of radioactive similated by the fetal intestines was as high as that of all other tissues together, because of the injections being given intraperitoneally. Comment
The fact that the uterine muscle is capable of accumulating a large amount of serotonin is of great importance. The instillation of serotonin into the lumen of the rat uterus leads to uterine hyperemia, edema, and to an increase in mitoses, similar to that produced by estrogen. 9 Snyder and associates' showed that the major portion of uterine CH-serotonin was found in the cell sap. This would suggest that serotonin is firmly bound to soluble cell constituents which may protect it from enzymatic destruction by the large amounts of monoamine oxidase which have been shown to be present in the uterus. 10 Serotonin has contractile effects on the uterus, thus the changes in the uterine binding of serotonin may influence uterine motility under varying physiological conditions. During estrus this sensitivity is very high, and a rat uterus may, after estrogen priming, react with maximum responses to serotonin concentrations as low as 10-s or 10- 9 • 1 Snyder and associates 8 observed that marked variations in the C 14 serotonin concentration in the uterus are related to estrus. During proestrus, estrus, and metestrus, the C 14 -serotonin concentration was significantly lower than during diestrus, when the weight of the uterus was lowest. In pregnancy the binding capacity of C 14-serotonin is proportionately higher, as shown by our results. In our pregnant rats, it was found that
~!a1 15, 1%ti Am. J. Ohst. & (;ynec.
the serotonin content of the placenta nses from the twelfth day of gestation. This finding confirms previous observations reported by Robson and Senior 7 on mice. VVe also observed that, concomitantly, the monoamine oxidase content of the rat placenta falls from the twelfth day of gestation. We have similarly shown in women that the serotonin content of the placenta gradually increases during pregnancy. 4 The enzymatic activity of placental monoamine oxidase (which destroys serotonin and protects the fetus against maternal serotonin and catecholamines) shows a reverse tendency. being highest at the beginning of gestation and gradually decreasing, it reaches the lowest level at term. These significant facts lead us to assume that the physiologic decrease of placental monoamine oxidase at the end of pregnancy. together with an increase in the binding capacity of serotonin in the uterine muscle and the high estrogen level. may trigger the release of serotonin from its uterine stores, thus initiating labor. These observations would then suggest that serotonin plays a part no less important than that of oxytocin in the initiation of parturition. Such an action would be local only. This may be derived from the fact that the serotonin level in the maternal circulation does not increase during pregnancy. This hypothesis is now supported by the fact that abortion or early delivery can be induced after local application of monoamine oxidase inhibitors into the amniotic sac of humans and animals at any stage of pregnancy."· :.a Summary
Direct piacentai transfer of C 1 "-serotonin administered to pregnant albino rats was found to be very !o,v, v;hether introduced by intra-aortic, intra-amniotic, or intrafetal injection. However, a high uptake was found in the myometrium. The possible effect of this high uptake and storage of serotonin in the pregnant myometrium as a trigger for abortion or normal labor is discussed.
Placental transfer of C 4 -serotonin
Volume 95 Number 2
295
REFERENCES I.
2. 3. 4. 5. Sa.
Abrahams, U. S., and Pickford, M.: Brit. J. Pharmacol. 11: 33, 1956. Axelrod, ]., and Inscoe, J. K.: J. Pharmacol. & Exper. Therap. i46: 276, 1964. Brzezinski, A., Koren, Z., Pfeifer, Y., and Sulman, F. G.: J. Obst. & Gynaec. Brit. Comm. 69: 661, 1962. Koren, Z., Pfeifer, Y., and Sulman, F. G.: AM. J. 0BST. & GYNEC. 93: 411, 1965. Koren, Z., Pfeifer, Y., and Sulman, F. G.: Fertil. & Steril. 16: 393, 1965. Koren, Z.: J. Obst. & Gynaec. Brit. Comm. "'7't)a
1"-•
.,.,~
IIJ,
1
nt::h..
.lJUJ.
6. Luschinsky, H. L., and Singher, H. 0.: Arch. Biochem. 19: 95, 1948. 7. Robson, J. M., and Senior, J. B.: Brit. J. Pharmacoi. 22: 380, 1964. 8. Snyder, S. H., Wurtman, R. J., Axelrod, J., and Chu, E. W.: J. Pharmacol. & Exper. Therap. 146: 276, 1964. 9. Spaziani, E.: Endocrinology 72: 180, 1963. 10. Wurtman, R. J., Axelrod, J., and Potter, L. T.: J. Pharmacol. & Exper. Therap. 143: 314, 1964. D
I..
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Jerusalem, Israel
Distribution and placental transfer of C ·serotonin in pregnant rats Z. KOREN, M.D. Y. PFEIFER, B.A. F. G. SULMAN, M.D., D.V.M. Jerusalem, Israel
I N P R E v I o u s studies, 3 we established that the serotonin content of the human placenta gradually increases in a normally developing pregnancy. In young placentas it amounts to an average of 6 /Jog per gram tissue and it rises to 15 /Jog per gram tissue in mature placentas obtained from normal term deliveries. At the same time, the enzymatic activity of placental monoamine oxidase vvhich destroys serotonin shovved a re~ verse proportion, being highest at the beginning of gestation and gradually dropping to the lowest level at term. Maternal serotonin is quite capable of diffusing across the placenta, but since the latter and the amniotic fluid contain a high level of monoamine oxidase, 3 • 6 ordinary amounts of serotonin are deaminated during passage to the fetus and thus made harmless. Because of the relatively large content of endogenous serotonin in many tissues, it is difficult to obtain reliable and precise information regarding the distribution and transfer of serotonin circulating during the different stages of pregnancy. Axelrod and Inscoe~ were the first to use radioactive serotonin for studies of uptake, binding, and distribution of serotonin in animal tissues.
Using this method, studies on pregnant rats were performed by us. This allowed us to study the passing of 5=hydroxytryptamine=3C 14-creatinine sulfate through rat placentas from both maternal and fetal sides, and the distribution between maternal and fetal tissues. Methods and material
Radioactive serotonin ( 5-hydroxytryptamine-3-C14-creatinine sulfate) was obtained from Amersham (Great Britain). Pregnant albino rats of the Hebrew University strain were kept on a stock diet. The experiments were performed on rats between the seventeenth and the nineteenth day of gestation. The abdomen was opened under light ether anesthesia and either 1 mi. of the serotonin C 14 -solution was injected into the lower abdominal aorta, or a dose of 0.1 mi. was injected into each amniotic sac, visible through the transparent myometrium. Intrafetal injections were effected by introducing a No. 25 gauge needle through the uterine wall into the peritoneum of each fetus. On the average, 9 fetuses were present (range 6 to 12) and the total radioactivity introduced per animal was 0.1 to 0.2 IJ.C C 14-serotonin. The rats were then dosed, sutured, and, at intervals ranging from 5 minutes to 24 hours, again anesthesized and bled through the abdominal aorta. Various tissues were then removed and measured for radioactivity (blood, heart, lungs, intestines, adrenals, kidneys, myometrium, fetal tissues) . The tissues were
From the Department of Obstetrics and Gynecology, Rothschild-H adassah University Hospital, and the Department of Applied Pharmacology, School of Pharmacy, Hebrew University. Generously aided by United States National Institute of Health Grant No. MH 06 999-01.
290
Placental transfer of C14·serotonin
Volume 9:, Number 2
quickly excised, weighed, rinsed with cold normal saline solution, and extracted thoroughly by homogenization in 46 per cent KOH. Up to 2 mg. of every organ was dissolved in boiling 46 per cent KOH, after cooling diluted to 10 mi., and 0.1 ml. from each of the solutions was applied to chromatographic paper at separate spots, the longitudinal distance between each spot being 4 em. A solution of 0.005 p,c radioactive serotonin was used as control and standard. The paper strips were scanned with a Packard radiochromatogram scanner Model 7200 connected to a Packard recording ratemeter Model 380. The settings were as follows: 0.5 em. per minute and window 5 mm. It was found that under these conditions the size a...'ld form of the spot only minimally affected the linearity of the determinations. Radioactivity was calculated by cutting out the area of the recorded peaks, weighing them, and comparing the weight with that of the standard. The final calculation took into account dilution and weight of the dissolved organs. Results
Tables I through III comprise representative data from 39 rats on the distribution of radioactivity recovered from several selected maternal tissues, as compared with that found in the pooled placentas and fetuses of the same animal. The illustrations represent typical samples. Intra-aortic injection of C 14 -serotonin into mother rats. There was a wide range in the ability of tissues to take up circulating sero-
291
Table I. Distribution of serotonin after intra-aortic injection into pregnant rats*
I Min5 I 10 I Min-
1
I utes I utes IHour Maternal tissue Blood Liver Spleen Small intestine Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta Fetal tissue Brain Intestine H eart-lungs Liver Kidneys Carcass Head Total fetus
11.0 8.3 9.0
11.0 7.0 8.0 10.0
17.0 5.0 7.0
17.0 58.0 12.0 6.0 4.0
9.0 28.0 13.0 9.0 6.0
52.0 10.0 36.0 2.0 8.0
t
t
t
3.0 3.0
t t t t t t
8.0 6.0 1.0
t
5.0 8.0
t t
18.0
t
I
6 24 Hours Hours
5.0 9.0 5.0 4.0
3.0 16.0 3.0
12.0 10.0 10.0 3.0
7.0 13.0 4.0 4.0
t
t
4.0
t
t
t
t t
t
t
t t t t t
2.0
t
2.0
t t
2.0
*Mean values of distribution of l mg. containing 0.1 p.c C"-serotonin within the bodies of five groups of 3 pregnant rats each. Serotonin is expressed as p.g/ Gm. of tissue after different time intervals as calculated from radioactivity. tMeasur·ement below the sensitivity o£ our se lup (equivalent to l p.g serotonin).
tonin (Table I and Fig. 1). After administration of C 14 -serotonin into the maternal aorta, the radioactivity trapped in the maternal tissues concentrated mainly in the large intestines, lungs, liver, and kidneys. The placenta trapped only low amounts of radioactivity within 5 minutes ; 10 minutes after injection
TRAAORTIC INJECTION AI er 5 tn>nu ts
Fig. l. Pwdiochromatogram of the effects of an intra-aortic injection of C 14 -serotonin. Highest radioactivity was found in maternal lung, liver, kidneys, and large intestine, and no evident radioactivity in fetal tissues.
292
Koren, Pfeifer, and Sulmon
May 15, 1966
Am.
J, Obst.
& Gynec.
these vanished quickly, and after 24 hours most of the radioactivity had disappeared. The recovery on the fetal side amounted to only a very small fraction in the brain, liver, and heart-lung preparation which appeared as late as after a lapse of 10 minutes and disappeared after one hour. In other organs, no significant radioactivity was found. Intra-amniotic injection of C 14-serotonin. The low penetrability through the maternalfetal barrier was also evident when C 14 serotonin was administered into the amniotic cavity (Table II and Fig. 2). Placental and fetal tissues became strongly labeled, whereas only a small proportion reached the maternal tissues, apart from the myometrium, which became strongly labeled with C 14-serotonin. Lung and kidneys were the first to store C 14 serotonin, later this was taken over by the adrenals, heart, and intestines. Although the fetal tissues were capable of assimilating most
of the C 14 -serotonin, an appreciable portion of the radioact1v1ty was stili detected in the amniotic fluid after 5 and 10 minutes. One hour after injection, the exact amount of this residual activity could not be determined because of the difficulty of quantitative collection of the amniotic fluid. The fetuses concentrated C 14-serotonin mainly in the intestines, heart, lungs, liver, and brain. Intraperitoneal injection of C 14-serotonin into rat fetuses. After injection of C 14 serotonin into the fetal peritoneum only a fraction crossed the placenta, similar quantities later being taken up by the myometrium (Table III and Fig. 3). However, in these cases, permeability was higher in the fetusmother direction than vice versa, i.P., the mother-fetus direction. There was a wide range in the ability of tissues to take up circulating C 14 -serotonin. After 5 to 60 minutes, maternal tissues had some concentra-
Tabie II. Distribution of serotonin after intra-amniotic injection*
Tahie III. Distribution of serotonin after fetal intraperitoneal injection* 5 .. I
15
Minutes Maternal tissue Blood T ' Liver
Spleen Small =~"---"-=-UJLC:HIUC:
Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta Fetal tissue Brain Intestine Heart-lungs Liver Kidneys Carcass Head Total fetus
t
1 6 1 24 Hour I Hours Hours
1.0
.L
.L
t t
t t
I
I
4.0
t
t t
t
MinI utes Mat ern a[ tissue Blood T ~--- --
r" u.u
Spleen Small
6.0
LIVer
t
3.0
: - ... ~~ ... ! - -
t
I
15
Minutes
7.0 6.0 2.6 1.6
Hour
'"
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24 Hours
t
t
·'I·
2.0
~
I
2.0 13.0 5.0 3.0
...tI t
Ull.CtllHH:;;;
5.0
5.0
3.0
t
9.0
t
t
2.0
7.0
t t t
t t t
t t t
44.0 31.0 5.0 66.0 23.0 22.0
t 4.0
26.0 47.0
16.0 5.0
t t 13.0 9.0
15.0 2.0 5.0 3.0 1.0 22.0
3.0
*Mean values of distribution of 1 mg. containing 0.1 J.LC C 14 ~serotonin within the bodies of four groups of 3 pregnant rats each. Serotonin is expressed as JLg/Gm. of tissue after different time intervals as calculated irom radioactivity. tMeasurement below the sensitivity of our setup lent to 1 pg serotonin).
Kidneys Adrenal Lungs Heart Muscle Brain Myometrium Placenta
2.0 21.0 3.0 3.0
(equiva~
F eta[ tissue Brain Intestine Heart-lungs Liver Kidneys Carcass Head Total fetus
3.0 10.0
t t t t
8.0 14.0
t 88.0 122.0 96.0
t 16.0
2. 7 24.0 4.5 13.0 3.0 2.0 23.0 17.0
t
69.0 39.0 33.0 28.0 27.0
t t
5.0 7.0
t
60.0 31.0 51.0 48.0 10.0
t t t
11.0 12.0
t
46.0 24.0 68.0 29.0
t
·*Mean values of distribution of mg. containing 0.1 C 1•~serotonin within the bodies of four groups of 3 pregnant rats each. Serotonin is expressed as p.g/Gm. of tissue after different time intervais as caicuia£ed irom radioactivity. J..LC
tMeasurement below the sensitivity of our SPtup ( equivalent !o 1 JJ.g serotonin).
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Fig. 3. Radiochromatogram of the eff ects of an intraperitoneal injecti on of C 1 •-serotonin . Very high concentrations of radioac tivity are found in fetal heart, lungs, liver, intestines, and carcass. In materna l tissues increased radio activity was found in ovary, myometrium , and placenta.
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INJECTIO N
(FOETUS)
INTRAPERITONEAL
Fig. 2. Radiochromatogram of the effec ts of an intra-amniotic injection of CH-serotonin. In fetal tissues, the highest radioactivity was found in intestines and liver, heart-lungs, kidneys, and carcass. Highest radioac tivity was found in placental and maternal myometrium and smaller amounts in maternal kidneys and lungs.
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tions of C 14 -serotonin in all organs, the bulk being in the myometrium and adrenals. After 24 hours, serotonin was metabolized and disappeared in a!! organs except the myometrium. Fetal tissues having the highest concentration of serotonin were the intestines, heart-lung, liver, and carcass. In the kidneys the concentration of radioactivity began after l 5 minutes and lasted for 24 hours. The brain showed practically no uptake of radioactive similated by the fetal intestines was as high as that of all other tissues together, because of the injections being given intraperitoneally. Comment
The fact that the uterine muscle is capable of accumulating a large amount of serotonin is of great importance. The instillation of serotonin into the lumen of the rat uterus leads to uterine hyperemia, edema, and to an increase in mitoses, similar to that produced by estrogen. 9 Snyder and associates' showed that the major portion of uterine CH-serotonin was found in the cell sap. This would suggest that serotonin is firmly bound to soluble cell constituents which may protect it from enzymatic destruction by the large amounts of monoamine oxidase which have been shown to be present in the uterus. 10 Serotonin has contractile effects on the uterus, thus the changes in the uterine binding of serotonin may influence uterine motility under varying physiological conditions. During estrus this sensitivity is very high, and a rat uterus may, after estrogen priming, react with maximum responses to serotonin concentrations as low as 10-s or 10- 9 • 1 Snyder and associates 8 observed that marked variations in the C 14 serotonin concentration in the uterus are related to estrus. During proestrus, estrus, and metestrus, the C 14 -serotonin concentration was significantly lower than during diestrus, when the weight of the uterus was lowest. In pregnancy the binding capacity of C 14-serotonin is proportionately higher, as shown by our results. In our pregnant rats, it was found that
~!a1 15, 1%ti Am. J. Ohst. & (;ynec.
the serotonin content of the placenta nses from the twelfth day of gestation. This finding confirms previous observations reported by Robson and Senior 7 on mice. VVe also observed that, concomitantly, the monoamine oxidase content of the rat placenta falls from the twelfth day of gestation. We have similarly shown in women that the serotonin content of the placenta gradually increases during pregnancy. 4 The enzymatic activity of placental monoamine oxidase (which destroys serotonin and protects the fetus against maternal serotonin and catecholamines) shows a reverse tendency. being highest at the beginning of gestation and gradually decreasing, it reaches the lowest level at term. These significant facts lead us to assume that the physiologic decrease of placental monoamine oxidase at the end of pregnancy. together with an increase in the binding capacity of serotonin in the uterine muscle and the high estrogen level. may trigger the release of serotonin from its uterine stores, thus initiating labor. These observations would then suggest that serotonin plays a part no less important than that of oxytocin in the initiation of parturition. Such an action would be local only. This may be derived from the fact that the serotonin level in the maternal circulation does not increase during pregnancy. This hypothesis is now supported by the fact that abortion or early delivery can be induced after local application of monoamine oxidase inhibitors into the amniotic sac of humans and animals at any stage of pregnancy."· :.a Summary
Direct piacentai transfer of C 1 "-serotonin administered to pregnant albino rats was found to be very !o,v, v;hether introduced by intra-aortic, intra-amniotic, or intrafetal injection. However, a high uptake was found in the myometrium. The possible effect of this high uptake and storage of serotonin in the pregnant myometrium as a trigger for abortion or normal labor is discussed.
Placental transfer of C 4 -serotonin
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2. 3. 4. 5. Sa.
Abrahams, U. S., and Pickford, M.: Brit. J. Pharmacol. 11: 33, 1956. Axelrod, ]., and Inscoe, J. K.: J. Pharmacol. & Exper. Therap. i46: 276, 1964. Brzezinski, A., Koren, Z., Pfeifer, Y., and Sulman, F. G.: J. Obst. & Gynaec. Brit. Comm. 69: 661, 1962. Koren, Z., Pfeifer, Y., and Sulman, F. G.: AM. J. 0BST. & GYNEC. 93: 411, 1965. Koren, Z., Pfeifer, Y., and Sulman, F. G.: Fertil. & Steril. 16: 393, 1965. Koren, Z.: J. Obst. & Gynaec. Brit. Comm. "'7't)a
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6. Luschinsky, H. L., and Singher, H. 0.: Arch. Biochem. 19: 95, 1948. 7. Robson, J. M., and Senior, J. B.: Brit. J. Pharmacoi. 22: 380, 1964. 8. Snyder, S. H., Wurtman, R. J., Axelrod, J., and Chu, E. W.: J. Pharmacol. & Exper. Therap. 146: 276, 1964. 9. Spaziani, E.: Endocrinology 72: 180, 1963. 10. Wurtman, R. J., Axelrod, J., and Potter, L. T.: J. Pharmacol. & Exper. Therap. 143: 314, 1964. D
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