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In utero defecation by the normal fetus: A radionuclide study in the rabbit
In Utero Defecation by the Normal Fetus: A Radionuclide Study in the Rabbit By Arbay
0. Ciftci, F. Cahit Tanyel,
Meral T. Ercan, ibrahim Karnak, Ankara, Turkey
l An experimental study was performed to investigate the excretion function of the liver, gastrointestinal motility, and in utero defecation by radionuclide techniques in 24 New Zealand white rabbit fetuses at 25 days’ gestation (fullterm, 31 to 32 days). 0.1 mL of technetium 99m (ggmTc)-HIDA (a derivative of iminodiacetic acid) containing 1 mCi of radioactivity was injected into the gluteus muscle of each fetus, which had been exposed through the uterus. After replacing the fetus and uterus into the abdomen, and beginning 1 hour after injection, a live fetus was killed each hour for 24 hours. Tissue samples from the lung, heart, stomach, kidney, bladder, liver, meconium in the proximal, mid, and distal bowel, and amniotic fluid were taken. The radioactivity of each sample was determined by a gamma counter and the percentage uptake per gram of tissue was calculated. The very low radioactivity levels detected in the stomach, kidneys, and bladder indicated the in vivo stability of ggmTc-HIDA. ggmTcHIDA is predominantly trapped by the liver via systemic circulation and is excreted into the gastrointestinal tract through which it passes into the amniotic fluid. Demonstrated passage of excreted ggmTc-HIDA through the fetal liver and into the gastrointestinal tract and amniotic fluid strongly suggests that fetal defecation is a physiological event. Copyright o 1996 by W.B. Saunders Company
INDEX WORDS: physiology.
In utero
defecation,
fetus,
ggmTc-HIDA,
fetal
CCORDING to current concepts, the human fetus does not defecate, and the passage of meconium into the amniotic fluid is an indicator of fetal distress.1,2 However, for 12% to 25% of deliveries complicated by meconium staining, no definitive cause is found.3 Additionally, meconium-stained amniotic fluid is observed at the time of delivery in 8% to 16% of pregnancies. 4 Of the infants born with meconium-stained fluid, only 2.1% have meconium aspiration syndr0me.j These findings, in addition to other reports, suggest that fetal defecation may be a physiological event.6-1’ We have developed the hypothesis that fetal defecation is a physiological event independent from fetal distress and associated with a clearance mechanism of the amniotic fluid. The hypothesis was partially proven by a previous study in which we have shown that goat fetuses defecate contrast medium into the amniotic cavity in the absence of fetal distress, with normal central venous blood gas values.13 The present study focuses on the same hypothesis and aims to investigate hepatic excretion function, intestinal mo-
A
JournalofPediafr,cSurgery,
Vol31,No
lO(OctoberJ.1996:pp
1409-1412
Nebil Btiyiikpamukqu,
and Akgiin
tility, and in utero defecation, methods in a rabbit model. MATERIALS
Hiqs6nmez
using radionuclide
AND METHODS
Twenty-four fetuses of five New Zealand white rabbits were used, on day 25 of gestation (full term, 31 to 32 days). Surgical procedures were performed as previously reported.14 The rabbits were anesthetized using ketamine (10 mg intravenously) and were placed on a heating blanket. Anesthesia was maintained by 2% halothane in oxygen via mask inhalation. The abdomen was shaved and prepared with povidone-iodine. Using aseptic technique, the uterus was lifted from the abdomen through a midline vertical incision without kinking of the uterine vessels. One fetus was selected, and its lower half was discriminated by palpation. A purse-string suture was passed through both the uterine wall and the amniotic membranes overlying the lower half of the fetus, as a whole layer. Hysterotomy was performed, and the lower extremities of the fetus were exposed through the purse string. Special attention was given to preventing amniotic fluid loss during hysterotomy and fetus extraction. 0.1 mL of technetium 99m (99mTc)-HIDA (a derivative of iminodiacetic acid) containing 1 mCi of radioactivity was injected into the right gluteus muscle of the fetus. The fetus was returned to the uterine cavity, followed by amniotic fluid replacement with approximately 2 mL of warmed saline, and the purse string suture was secured. This procedure was used for all fetuses. After replacing the uterus into the abdomen, and beginning 1 hour after injection, a live fetus was killed each hour for 24 hours. Amniotic fluid was emptied and retained for evaluation. The fetuses were autopsied, and tissue samples from the lung, heart, stomach, kidney, bladder, liver, and meconium in the proximal (duodenum and jejunum), mid (terminal ileum), and distal portions (descending colon) of the bowel were taken and weighed. The radioactivity of each sample was determined by counting against a standard prepared from 1:lOO dilution of the injected solution in a gamma counter (model LB 2111; Berthold, Bad Wildbald, Germany) in the energy range of 100 to 200 keV, to include the photopeak of 140 keV belonging to 99mTc. The percentage of uptake was calculated by dividing the count rate of each sample by the mean of five standard samples: Sample count rate % Uptake: Mean of standard count rate The percentage of uptake per gram of tissue (% uptake/g tissue) for each sample was calculated by dividing the % uptake computed
From the Departments of Pediatric Surgery and Nuclear Medicine, Institute of Child Health, Hacettepe University, Ankara, Turkey. Address reprint requests to F. Cahit Tanyel, MD, Professor in Pediatric Surgery Hacettepe University Medical Faculty, Hacettepe, WIOOAnkara, Turkey. Copyright o I996 by W B. Saunders Company 0022-3468/9613110-0019$03.00/O 1409
1410
CIFTCI
above by the weight of the tissue sample: % Uptake Tissue weight RESULTS
The mean weight of the 24 fetuses was 24.2 f 2.1 g (range, 23.1 to 26.2 g). All fetuses were found to be alive when they were exposed through the uterus. The percentage of injected dose per gram of tissue (% ID/g) in the heart, lung, stomach, kidney, and bladder is shown in Fig 1. % ID/g in the liver, bowel lumen (meconium), and amniotic fluid is shown in Fig 2. The radioactivity values detected in reference organs are at negligible levels compared with those of the liver, bowel lumen, and amniotic fluid. 99mTc-HIDA administered intramuscularly is absorbed by capillaries in the muscle and is trapped by the liver via the systemic circulation. At this phase, the peak values of radioactivity detected in the lung and the heart were below 0.3 % ID/g at 8 and 11 hours, respectively. The low radioactivity levels detected in the stomach, kidneys, and urinary bladder indicated the in vivo stability of 99mT~-HIDA and the absence of in vivo pertechnetate (ggmTc04-), because unlabeled pertechnetate would accumulate and be excreted by these organs. The high quantity of radioactivity detected in the liver proved it to be the target organ. The peak value was observed at the 13th hour. 9gmTc-HIDA is excreted from the liver into the small intestine. The peak values noted in the lumen of proximal, mid, and distal bowel were at 8, 12, and 14 hours, respectively. The distal bowel began to show radioactivity after the proximal bowel. The incline and decline phases of radioactivity in the bowel lumen clearly showed the transport of radioactive meconium. % injected 0.25
dose/g
ET AL
Amniotic fluid began to show radioactivity at the 8th hour and reached the peak value at the 20th hour. In other words, radioactivity in amniotic fluid was detected at the same time as the peak value of proximal bowel and reached the highest value 6 hours after the peak value of the distal bowel. DISCUSSION
The fetus can perform a variety of gastrointestinal functions. Swallowing has been observed at 16 weeks’ gestation, and bowel peristalsis has occurred as early as 8 weeks’ gestation.15 Intestinal motor activity of the gut moves the intraIumina1 contents from one specialized region of the gut to the next. Gastrointestinal functions of the fetus increase with gestational age. In general, the older the fetus, the greater the amount of meconium descending through the intestinal tract. Today there is no doubt that the intestinal content is transported by intestinal peristalsis during intrauterine life.lW-17 Amniotic fluid plays an important role in the gastrointestinal tract development18 and nutrition of the fetus.19 The amniotic fluid represents a dynamic fetal compartment, and its turnover rate is very high. The human fetus exchanges the amniotic fluid volume totally by urinating, swallowing, and respiratory tract secretions every 24 to 48 hours in the last trimester.13J5 This exchange, caused by fluid dynamics, forms the effective clearance mechanism of the amniotic fluid. The clearance mechanism is postulated to be suppressed in the presence of fetal distress conditions.20-25We have suggested that detection of meconium-stained amniotic fluid might not be related to meconium passage after fetal distress; rather, it might reflect impaired clearance of already stained amniotic fluid caused by intrauterine defecation.13
tissue
T
Time (hour) 0
I
2
3
. . . . ..Lung
4
5
6
7
./.‘#lI..,. I.‘ Heart
8
9 101112131415161718192021222324 -Kidney
-Bladder
--.-Stomach
Fig tected
1. Levels in reference
of radioactivity organs.
de-
IN UTERO
1411
DEFECATION
% injected
dose/g
tissue
ia T
Fig 2. Levels of radioactivity detected in fetal liver, intestine, and amniotic fluid.
0 -Proximal
1
2
3
4 bow.
5
6 -Mid
In the present study, we used a radiolabeled substance (99mTc-HIDA), which is predominantly excreted by the biliary tract,15 and followed its passage through the gastrointestinal tract and into the amniotic fluid. Although the intramuscular injection method has not been reported before, we have adopted this route for its ease and accessibility. 9gmTc-HIDA is absorbed by the capillaries and is carried to the liver by systemic circulation, reaching maximum uptake at 13 hours. We have clearly demonstrated, for the first time, the transport of radioactive meconium through the gastrointestinal tract and into the amniotic fluid by use of a radiopharmaceutical. Although no simultaneous blood gas measurements were obtained, the normal biliary, gastrointestinal, and urinary system functions, in addition to the well-being of the fetuses before death, make fetal distress conditions less likely in our experimental model. The reliability of the method was tested by the uptake of radioactivity measurements in the reference organs, including the stomach, kidney, and bladder. In all ggmT~radiopharmaceuticals, 1% to 2% 99mT~ as pertechnetate ion (ie, free Tc) can be present.26 After entering the systemic circulation, it localizes in the stomach and is also excreted by the urinary system. We obtained very low uptake values for these organs, indicating the in vivo stability of 99mTc-HIDA and the absence of free 99mT~. Otherwise, it would be impossible to prove the mode of entry of radioactive meconium to the amniotic fluid by intrauterine defecation, because amniotic fluid radioactivity might be attributable to excreted free 9gmT~from the urinary system. Therefore, passage of excreted 99mTc-HIDA through fetal liver and into the gastrointestinal tract and amniotic fluid (respectively) strongly supports the hypothesis that fetal defecation is a physiological event. For further confirmation, the
7
8
9 1011 bow.
222324
12131415161718192021
-....-Distal
bow
-Amniotic
fluid
-.--
Time (hour)
Liver
same experimental design is currently being used with a new group of fetuses, in which surgical closure of anus is being performed. In addition to the present study, there is other evidence in the literature relating to physiological intrauterine defecation. The presence of anal meconium has been interpreted as positive proof of intrauterine defecation. Fetal defecation was considered to be a routine physiological event through the second trimester, until anal sphincter innervation is completed.6 The concept of fetal defecation in early and midpregnancy is strengthened by the findings of high levels of both disaccharidases and intestinal alkaline phosphatase (both specific to the fetal gut) in amniotic fluid during pregnancy.‘J Fetal defecation could explain the many cases of Rh-negative (and thus unaffected) infants who have shown low but definite levels of bilirubin in amniotic fluid after amniocentesis in Rh-negative woman with antibodies.6 As much as 10% to 20% of total amniotic fluid protein comes from the fetal gut, which suggests that the mode of entry into the amniotic sac may by fetal defecation.9 The observation of numerous meconium pigment-laden macrophages in the membranes of a placenta without gross staining suggests the possibility of silent intrauterine defecation with subsequent clearance of meconium from the amniotic fluid by fetal swallowing and/or macrophage uptake.lOJl Defecation into the amniotic sac and subsequent meconiophagy were observed to be normal occurrences in guinea pigs that underwent experimentation.i2 Additionally, it has been suggested that the peritonitis encountered in gastrochisis might result from intrauterine defecation.27 In light of the evidence in the literature and our findings, we conclude that the fetus who swallows and urinates routinely may also defecate into the amniotic cavity within physiological conditions.
1412
CIFTCI
ET AL
REFERENCES 1. Alger LS, Kisner HJ, Nagey DA: The presence of meconiumlike substance in second-trimester amniotic fluid. Am J Obstet Gynecol150:380-3851984 2. Desmond MM, Moore J, Lindley JE, et al: Meconium staining of the amniotic fluid. A marker of fetal hypoxia. Obstet Gynecol9:91-103,1957 3. Fujikura T, Klionsky B: The significance of meconium staining. Am J Obstet Gynecol121:45-50,1975 4. Davis RO, Philips JB, Harris BA, et al: Fetal meconium aspiration syndrome occuring despite airway management considered appropriate. Am J Obstet Gynecol151:731-736,1985 5. Brown BL, Gleicher N: Intrauterine meconium aspiration. Obstet Gynecol57:26-291981 6. Abramoirich DR, Gray ES: Physiological fetal defecation in midpregnancy. Obstet Gynecol60:29-31,1982 7. Potier M, Melancon SB, Dallaire L: Developmental patterns of intestinal disaccharidases in human amniotic fluid. Am J Obstet ‘Gynecol131:73-79,1978 8. Mulivor RA, Mennuti MT, Harris H: Grigin of the alkaline phosphatases in amniotic fluid. Am J Obstet Gynecol 135:77-80, 1979 9. Morin PR, Potier M, Dallaire L, et al: Prenatal detection of intestinal obstruction: Deficient amniotic fluid disaccharidases in affected fetuses. Clin Genet 18:217-222,198O 10. Bourne GL: The human amnion and chorion. London, England, Lloyd-Luke, 1962, pp 143-165 11. Naeye RL: Functionally important disorders of the placenta, umblical cord, and fetal membranes. Hum Path01 18:680-691,1987 12. Becker RF, Windle WF, Barth EE, et al: Fetal swallowing, gastrointestinal activity and defecation in amnio. An experimental roentgenologic study in the guinea pig. Surg Gynecol Obstet 70:603-614,194O 13. Kizilcan F, Karnak I, Tanyel FC, et al: In utero defecation of the nondistressed fetus: A roentgen study in the goat. J Pediatr Surg 29:1487-1490,1994 14. Kizilcan F, Tanyel FC, Btiytikpamukcu N, et al: Fetal survival after in utero experiment in the rabbit. Lab Anim Sci 44:144-147,1994
15. Neu J: Functional development of the fetal gastrointestinal tract. Semin Perinatol13:224-235,1989 16. MC Lain CR: Amniography studies of the gastrointestinal motility of the human fetus. Am J Obstet Gynecol 86:1079-1087, 1963 17. Ostrea EM, Naqvi M: The influence of gestational age on the ability of the fetus to pass meconium in utero. Acta Obstet Gynecol Stand 611275277,1982 18. Karnak I, Tanyel FC, Unsal I, et al: Esophageal ligation: Effects on the development of fetal organic systems. Eur J Pediatr Surg (in press) 19. Wesson DE, Muraji T, Kent F, et al: The effect of intrauterine esophageal ligation on growth of fetal rabbits. J Pediatr Surg 19:389-399, 1984 20. Sherman DJ, Ross MG, Day L, et al: Fetal swallowing: Response to graded maternal hypoxemia. J Appl Physiol 71: 1856-1861,199l 21. Perks AM, Cassin S: The effects of arginine vasopressin and other factors on the production of lung liquid in fetal goats. Chest 81:63-65, 2982 (suppl) 22. Rurak DW: Plasma vasopressin levels during hypoxemia and the cardiovascular effects of exogenous vasopressin in foetal and adult sheep. J Physiol277:341-357,1978 23. Nishino T, Kohchi T, Honda Y, et al: Differences in the effects of hypercapnia and hypoxia on the swallowing reflex in cats. Br J Anesth 58:903-908,1986 24. Hooper SB, Dickson KA, Harding R: Lung liquid secretion, flow and volume in response to moderate asphyxia in fetal sheep. J Dev Physiol10:473-485,198s 25. Ross MG, Erin G, Leake RD, et al: Fetal lung liquid regulation by neuropeptides. Am J Obstet Gynecol 150:421-425, 1984 26. Saha GB: Uses of radiopharmaceuticals in nuclear medicine, in Saha GB (ed): Fundamentals of Nuclear Pharmacy, chap 12. New York, NY, Springer-Verlag, 1992, pp 227-304 27. Tanyel FC, Aktug T: Letter to the editor. J Pediatr Surg 30:1534,1995
0. Ciftci, F. Cahit Tanyel,
Meral T. Ercan, ibrahim Karnak, Ankara, Turkey
l An experimental study was performed to investigate the excretion function of the liver, gastrointestinal motility, and in utero defecation by radionuclide techniques in 24 New Zealand white rabbit fetuses at 25 days’ gestation (fullterm, 31 to 32 days). 0.1 mL of technetium 99m (ggmTc)-HIDA (a derivative of iminodiacetic acid) containing 1 mCi of radioactivity was injected into the gluteus muscle of each fetus, which had been exposed through the uterus. After replacing the fetus and uterus into the abdomen, and beginning 1 hour after injection, a live fetus was killed each hour for 24 hours. Tissue samples from the lung, heart, stomach, kidney, bladder, liver, meconium in the proximal, mid, and distal bowel, and amniotic fluid were taken. The radioactivity of each sample was determined by a gamma counter and the percentage uptake per gram of tissue was calculated. The very low radioactivity levels detected in the stomach, kidneys, and bladder indicated the in vivo stability of ggmTc-HIDA. ggmTcHIDA is predominantly trapped by the liver via systemic circulation and is excreted into the gastrointestinal tract through which it passes into the amniotic fluid. Demonstrated passage of excreted ggmTc-HIDA through the fetal liver and into the gastrointestinal tract and amniotic fluid strongly suggests that fetal defecation is a physiological event. Copyright o 1996 by W.B. Saunders Company
INDEX WORDS: physiology.
In utero
defecation,
fetus,
ggmTc-HIDA,
fetal
CCORDING to current concepts, the human fetus does not defecate, and the passage of meconium into the amniotic fluid is an indicator of fetal distress.1,2 However, for 12% to 25% of deliveries complicated by meconium staining, no definitive cause is found.3 Additionally, meconium-stained amniotic fluid is observed at the time of delivery in 8% to 16% of pregnancies. 4 Of the infants born with meconium-stained fluid, only 2.1% have meconium aspiration syndr0me.j These findings, in addition to other reports, suggest that fetal defecation may be a physiological event.6-1’ We have developed the hypothesis that fetal defecation is a physiological event independent from fetal distress and associated with a clearance mechanism of the amniotic fluid. The hypothesis was partially proven by a previous study in which we have shown that goat fetuses defecate contrast medium into the amniotic cavity in the absence of fetal distress, with normal central venous blood gas values.13 The present study focuses on the same hypothesis and aims to investigate hepatic excretion function, intestinal mo-
A
JournalofPediafr,cSurgery,
Vol31,No
lO(OctoberJ.1996:pp
1409-1412
Nebil Btiyiikpamukqu,
and Akgiin
tility, and in utero defecation, methods in a rabbit model. MATERIALS
Hiqs6nmez
using radionuclide
AND METHODS
Twenty-four fetuses of five New Zealand white rabbits were used, on day 25 of gestation (full term, 31 to 32 days). Surgical procedures were performed as previously reported.14 The rabbits were anesthetized using ketamine (10 mg intravenously) and were placed on a heating blanket. Anesthesia was maintained by 2% halothane in oxygen via mask inhalation. The abdomen was shaved and prepared with povidone-iodine. Using aseptic technique, the uterus was lifted from the abdomen through a midline vertical incision without kinking of the uterine vessels. One fetus was selected, and its lower half was discriminated by palpation. A purse-string suture was passed through both the uterine wall and the amniotic membranes overlying the lower half of the fetus, as a whole layer. Hysterotomy was performed, and the lower extremities of the fetus were exposed through the purse string. Special attention was given to preventing amniotic fluid loss during hysterotomy and fetus extraction. 0.1 mL of technetium 99m (99mTc)-HIDA (a derivative of iminodiacetic acid) containing 1 mCi of radioactivity was injected into the right gluteus muscle of the fetus. The fetus was returned to the uterine cavity, followed by amniotic fluid replacement with approximately 2 mL of warmed saline, and the purse string suture was secured. This procedure was used for all fetuses. After replacing the uterus into the abdomen, and beginning 1 hour after injection, a live fetus was killed each hour for 24 hours. Amniotic fluid was emptied and retained for evaluation. The fetuses were autopsied, and tissue samples from the lung, heart, stomach, kidney, bladder, liver, and meconium in the proximal (duodenum and jejunum), mid (terminal ileum), and distal portions (descending colon) of the bowel were taken and weighed. The radioactivity of each sample was determined by counting against a standard prepared from 1:lOO dilution of the injected solution in a gamma counter (model LB 2111; Berthold, Bad Wildbald, Germany) in the energy range of 100 to 200 keV, to include the photopeak of 140 keV belonging to 99mTc. The percentage of uptake was calculated by dividing the count rate of each sample by the mean of five standard samples: Sample count rate % Uptake: Mean of standard count rate The percentage of uptake per gram of tissue (% uptake/g tissue) for each sample was calculated by dividing the % uptake computed
From the Departments of Pediatric Surgery and Nuclear Medicine, Institute of Child Health, Hacettepe University, Ankara, Turkey. Address reprint requests to F. Cahit Tanyel, MD, Professor in Pediatric Surgery Hacettepe University Medical Faculty, Hacettepe, WIOOAnkara, Turkey. Copyright o I996 by W B. Saunders Company 0022-3468/9613110-0019$03.00/O 1409
1410
CIFTCI
above by the weight of the tissue sample: % Uptake Tissue weight RESULTS
The mean weight of the 24 fetuses was 24.2 f 2.1 g (range, 23.1 to 26.2 g). All fetuses were found to be alive when they were exposed through the uterus. The percentage of injected dose per gram of tissue (% ID/g) in the heart, lung, stomach, kidney, and bladder is shown in Fig 1. % ID/g in the liver, bowel lumen (meconium), and amniotic fluid is shown in Fig 2. The radioactivity values detected in reference organs are at negligible levels compared with those of the liver, bowel lumen, and amniotic fluid. 99mTc-HIDA administered intramuscularly is absorbed by capillaries in the muscle and is trapped by the liver via the systemic circulation. At this phase, the peak values of radioactivity detected in the lung and the heart were below 0.3 % ID/g at 8 and 11 hours, respectively. The low radioactivity levels detected in the stomach, kidneys, and urinary bladder indicated the in vivo stability of 99mT~-HIDA and the absence of in vivo pertechnetate (ggmTc04-), because unlabeled pertechnetate would accumulate and be excreted by these organs. The high quantity of radioactivity detected in the liver proved it to be the target organ. The peak value was observed at the 13th hour. 9gmTc-HIDA is excreted from the liver into the small intestine. The peak values noted in the lumen of proximal, mid, and distal bowel were at 8, 12, and 14 hours, respectively. The distal bowel began to show radioactivity after the proximal bowel. The incline and decline phases of radioactivity in the bowel lumen clearly showed the transport of radioactive meconium. % injected 0.25
dose/g
ET AL
Amniotic fluid began to show radioactivity at the 8th hour and reached the peak value at the 20th hour. In other words, radioactivity in amniotic fluid was detected at the same time as the peak value of proximal bowel and reached the highest value 6 hours after the peak value of the distal bowel. DISCUSSION
The fetus can perform a variety of gastrointestinal functions. Swallowing has been observed at 16 weeks’ gestation, and bowel peristalsis has occurred as early as 8 weeks’ gestation.15 Intestinal motor activity of the gut moves the intraIumina1 contents from one specialized region of the gut to the next. Gastrointestinal functions of the fetus increase with gestational age. In general, the older the fetus, the greater the amount of meconium descending through the intestinal tract. Today there is no doubt that the intestinal content is transported by intestinal peristalsis during intrauterine life.lW-17 Amniotic fluid plays an important role in the gastrointestinal tract development18 and nutrition of the fetus.19 The amniotic fluid represents a dynamic fetal compartment, and its turnover rate is very high. The human fetus exchanges the amniotic fluid volume totally by urinating, swallowing, and respiratory tract secretions every 24 to 48 hours in the last trimester.13J5 This exchange, caused by fluid dynamics, forms the effective clearance mechanism of the amniotic fluid. The clearance mechanism is postulated to be suppressed in the presence of fetal distress conditions.20-25We have suggested that detection of meconium-stained amniotic fluid might not be related to meconium passage after fetal distress; rather, it might reflect impaired clearance of already stained amniotic fluid caused by intrauterine defecation.13
tissue
T
Time (hour) 0
I
2
3
. . . . ..Lung
4
5
6
7
./.‘#lI..,. I.‘ Heart
8
9 101112131415161718192021222324 -Kidney
-Bladder
--.-Stomach
Fig tected
1. Levels in reference
of radioactivity organs.
de-
IN UTERO
1411
DEFECATION
% injected
dose/g
tissue
ia T
Fig 2. Levels of radioactivity detected in fetal liver, intestine, and amniotic fluid.
0 -Proximal
1
2
3
4 bow.
5
6 -Mid
In the present study, we used a radiolabeled substance (99mTc-HIDA), which is predominantly excreted by the biliary tract,15 and followed its passage through the gastrointestinal tract and into the amniotic fluid. Although the intramuscular injection method has not been reported before, we have adopted this route for its ease and accessibility. 9gmTc-HIDA is absorbed by the capillaries and is carried to the liver by systemic circulation, reaching maximum uptake at 13 hours. We have clearly demonstrated, for the first time, the transport of radioactive meconium through the gastrointestinal tract and into the amniotic fluid by use of a radiopharmaceutical. Although no simultaneous blood gas measurements were obtained, the normal biliary, gastrointestinal, and urinary system functions, in addition to the well-being of the fetuses before death, make fetal distress conditions less likely in our experimental model. The reliability of the method was tested by the uptake of radioactivity measurements in the reference organs, including the stomach, kidney, and bladder. In all ggmT~radiopharmaceuticals, 1% to 2% 99mT~ as pertechnetate ion (ie, free Tc) can be present.26 After entering the systemic circulation, it localizes in the stomach and is also excreted by the urinary system. We obtained very low uptake values for these organs, indicating the in vivo stability of 99mTc-HIDA and the absence of free 99mT~. Otherwise, it would be impossible to prove the mode of entry of radioactive meconium to the amniotic fluid by intrauterine defecation, because amniotic fluid radioactivity might be attributable to excreted free 9gmT~from the urinary system. Therefore, passage of excreted 99mTc-HIDA through fetal liver and into the gastrointestinal tract and amniotic fluid (respectively) strongly supports the hypothesis that fetal defecation is a physiological event. For further confirmation, the
7
8
9 1011 bow.
222324
12131415161718192021
-....-Distal
bow
-Amniotic
fluid
-.--
Time (hour)
Liver
same experimental design is currently being used with a new group of fetuses, in which surgical closure of anus is being performed. In addition to the present study, there is other evidence in the literature relating to physiological intrauterine defecation. The presence of anal meconium has been interpreted as positive proof of intrauterine defecation. Fetal defecation was considered to be a routine physiological event through the second trimester, until anal sphincter innervation is completed.6 The concept of fetal defecation in early and midpregnancy is strengthened by the findings of high levels of both disaccharidases and intestinal alkaline phosphatase (both specific to the fetal gut) in amniotic fluid during pregnancy.‘J Fetal defecation could explain the many cases of Rh-negative (and thus unaffected) infants who have shown low but definite levels of bilirubin in amniotic fluid after amniocentesis in Rh-negative woman with antibodies.6 As much as 10% to 20% of total amniotic fluid protein comes from the fetal gut, which suggests that the mode of entry into the amniotic sac may by fetal defecation.9 The observation of numerous meconium pigment-laden macrophages in the membranes of a placenta without gross staining suggests the possibility of silent intrauterine defecation with subsequent clearance of meconium from the amniotic fluid by fetal swallowing and/or macrophage uptake.lOJl Defecation into the amniotic sac and subsequent meconiophagy were observed to be normal occurrences in guinea pigs that underwent experimentation.i2 Additionally, it has been suggested that the peritonitis encountered in gastrochisis might result from intrauterine defecation.27 In light of the evidence in the literature and our findings, we conclude that the fetus who swallows and urinates routinely may also defecate into the amniotic cavity within physiological conditions.
1412
CIFTCI
ET AL
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