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Fetal to maternal transport of oxytocin across the dual perfused human placenta
Placenta (I989), Vol. IO
5’4
placental cotyledon was used to study its transfer to the fetal compartment at maternal concentrations similar to those in DKA. Results: Values are expressed as mean f s.e. clearance index = clearance relative to antipyrine clearance. [BOHB] b’M) I.0
2.5 5.0 7.5
Flux (pnol/min) 0.47 1.09 2.57 3.19
f f f f
0.07 0.16 0.43 0.44
Clearance (ml/min) 0.47 0.43 0.51 0.43
f f f f
0.07 0.06 0.09 0.06
Clearance index 39.14 36.65 40.97 36.44
Open circuit perfusions (n = 5) with increasing maternal [BOHB] resulted in a linear increase in the rate of transfer to the fetal side (FLUX); FLUX = 0.452 [B0HBl-_o.o18. Neither clearance nor clearance index changed with [BOHB]. In closed circuit perfusions (n = 3) with 5 mM BOHB, the fetal/maternal [BOHB] was not different from I (1.04 f 0.02, compared to I .68 f 0.04 for 50 mM leucine under similar conditions). Together these verify transfer by passive diffusion. In open circuit perfusions at 5 mM maternal [BOHB], the cotyledon extracted 5.33 f 0.69 pmol/min (I I .4 per cent) from the maternal side, retained 2.76 f 0.81 pmol/min (5.9 per cent) and transferred 2.57 f 0.43 pmol/min (5.5 per cent) to the fetal side [BOHB] > IO mM were toxic to the cotyledon. transfer of BOHB by the human placenta is by passive Conclusions: (I) Maternal-t-fetal diffusion. (2) [BOHB] double those seen in DKA are toxic to the perfused cotyledon. (3) The placenta may store and/or metabolize some BOHB.
FETAL TO MATERNAL TRANSPORT OF OXYTOCIN ACROSS THE DUAL PERFUSED HUMAN PLACENTA A. Malek, M. J. Meadows, F. C. Miller 8z D. Mattison (Department of Obstetrics and Gynaecology, University of Arkansas for Medical Sciences, Little Rock, AR, USA and Division of Human Risk Assessment, National Centre for Toxicological Research, Jefferson, AR, USA) Fetal hormone signals to the maternal organism may play a role in parturition. For example, the anencephalic human and sheep fetus typically have prolonged gestation. Although the putative fetal signal remains to be defined, oxytocin (OX) has been suggested to fulfil that role. Fetal umbilical artery OX concentrations (I 5-40 pg/ml) are higher than umbilical vein concentrations (4-12 pg/ml) and peripheral maternal concentrations are even lower (I-IO pg/ml). Circulating concentrations of OX are low, or absent, in the anencephalic fetus. In addition, injection of OX into umbilical vessels has been suggested to shorten the third stage of labour and enhance separation of retained placenta. These data suggest that fetal OX may play a role in parturition. If fetal OX is to play a role, one possible route may involve transport across the placenta into the maternal circulation. To explore this question, we have conducted a series of experiments in which OX was injected as a bolus or infused into the fetal circulation and measured in the maternal circulation of the dually perfused term human placenta. In the experiments reported here, [3H] OX and [I ‘C] inulin (IN) were simultaneously infused into the fetal artery (FA) for ~oomin. OX and IN concentrations were assessed in MV, FV, MA and FA by liquid scintillation counting. In two experiments little IN or OX was transferred into
.4bstrmts: European Placenta Group
5’5
the maternal circulation. In one experiment substantial amounts of both IN and OX were transferred into the maternal circulation. In the third experiment intermediate amounts of both were transferred into the maternal circulation. If MV (IN) is plotted against MV (OX) the data points form a straight line with intercept not significantly different from o and a slope of approximately I, (r = 0.96). These data suggest that OX transfer from fetal to maternal circulation is not different from IN transfer. If the fetal circulation is intact, little OX would reach rhe maternal circulation. However, in the presence of fetal to maternal leaks, substantial and undefined quantities of fetal OX may have access to the maternal circulation. These data suggest that a putative role for fetal OX in the initiation of labour must involve a route other than access to the maternal circulation across the placenta. In addition, given that OX is a hypotensive agent, clinical misadventure may result from umbilical OX injection to shorten the third stage of labour.
6E4-
5E4
-
0
IE4
2E4
3E4 F4C]
4E4
5E4
6E4
inulin cpm
ENERGY PRODUCTION BY THE DUALLY PERFUSED TERM HUMAN PLACENTA IN VITRO: [“‘PI NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY AT 2.0 AND 4.7 TESLA A. Malek, R. K. Miller, D. R. Mattison, R. Bryant, M. Panigel & L. Neth (Departments of Obstetrics and Gynaecology, and Biophysics, University of Rochester, Rochester, NY, USA, Department of Obstetrics and Gynaecology, University of Arkansas, and National Centre for Toxic Research, Little Rock, AR, USA) The placenta is responsible for fetal well being, which requires high energy production for active transport and protein synthesis. Previous investigations have suggested that placental ATP remains constant or decreases after initiation of perfusion. Those ATP levels were determined after freeze clamping which, unfortunately, requires termination of perfusion. In contrast, we have assessed placental energy generation by measuring ATP and inorganic phosphate (Pi) during in vitro perfusion with modified M199 tissue culture medium using [3rP] nuclear magnetic resonance (NMR) spectroscopy at 2.0 Tesla (T) and 4.7 T. At higher magnetic field strengths (4.7T) adjacent resonance lines are better separated and signal to noise ratios higher. Perfusion conditions included: (i) control, up to IO h; (ii) ischemia, produced by halting the perfusion pumps up to 4 h; and (iii) metabolic inhibition, produced by
5’4
placental cotyledon was used to study its transfer to the fetal compartment at maternal concentrations similar to those in DKA. Results: Values are expressed as mean f s.e. clearance index = clearance relative to antipyrine clearance. [BOHB] b’M) I.0
2.5 5.0 7.5
Flux (pnol/min) 0.47 1.09 2.57 3.19
f f f f
0.07 0.16 0.43 0.44
Clearance (ml/min) 0.47 0.43 0.51 0.43
f f f f
0.07 0.06 0.09 0.06
Clearance index 39.14 36.65 40.97 36.44
Open circuit perfusions (n = 5) with increasing maternal [BOHB] resulted in a linear increase in the rate of transfer to the fetal side (FLUX); FLUX = 0.452 [B0HBl-_o.o18. Neither clearance nor clearance index changed with [BOHB]. In closed circuit perfusions (n = 3) with 5 mM BOHB, the fetal/maternal [BOHB] was not different from I (1.04 f 0.02, compared to I .68 f 0.04 for 50 mM leucine under similar conditions). Together these verify transfer by passive diffusion. In open circuit perfusions at 5 mM maternal [BOHB], the cotyledon extracted 5.33 f 0.69 pmol/min (I I .4 per cent) from the maternal side, retained 2.76 f 0.81 pmol/min (5.9 per cent) and transferred 2.57 f 0.43 pmol/min (5.5 per cent) to the fetal side [BOHB] > IO mM were toxic to the cotyledon. transfer of BOHB by the human placenta is by passive Conclusions: (I) Maternal-t-fetal diffusion. (2) [BOHB] double those seen in DKA are toxic to the perfused cotyledon. (3) The placenta may store and/or metabolize some BOHB.
FETAL TO MATERNAL TRANSPORT OF OXYTOCIN ACROSS THE DUAL PERFUSED HUMAN PLACENTA A. Malek, M. J. Meadows, F. C. Miller 8z D. Mattison (Department of Obstetrics and Gynaecology, University of Arkansas for Medical Sciences, Little Rock, AR, USA and Division of Human Risk Assessment, National Centre for Toxicological Research, Jefferson, AR, USA) Fetal hormone signals to the maternal organism may play a role in parturition. For example, the anencephalic human and sheep fetus typically have prolonged gestation. Although the putative fetal signal remains to be defined, oxytocin (OX) has been suggested to fulfil that role. Fetal umbilical artery OX concentrations (I 5-40 pg/ml) are higher than umbilical vein concentrations (4-12 pg/ml) and peripheral maternal concentrations are even lower (I-IO pg/ml). Circulating concentrations of OX are low, or absent, in the anencephalic fetus. In addition, injection of OX into umbilical vessels has been suggested to shorten the third stage of labour and enhance separation of retained placenta. These data suggest that fetal OX may play a role in parturition. If fetal OX is to play a role, one possible route may involve transport across the placenta into the maternal circulation. To explore this question, we have conducted a series of experiments in which OX was injected as a bolus or infused into the fetal circulation and measured in the maternal circulation of the dually perfused term human placenta. In the experiments reported here, [3H] OX and [I ‘C] inulin (IN) were simultaneously infused into the fetal artery (FA) for ~oomin. OX and IN concentrations were assessed in MV, FV, MA and FA by liquid scintillation counting. In two experiments little IN or OX was transferred into
.4bstrmts: European Placenta Group
5’5
the maternal circulation. In one experiment substantial amounts of both IN and OX were transferred into the maternal circulation. In the third experiment intermediate amounts of both were transferred into the maternal circulation. If MV (IN) is plotted against MV (OX) the data points form a straight line with intercept not significantly different from o and a slope of approximately I, (r = 0.96). These data suggest that OX transfer from fetal to maternal circulation is not different from IN transfer. If the fetal circulation is intact, little OX would reach rhe maternal circulation. However, in the presence of fetal to maternal leaks, substantial and undefined quantities of fetal OX may have access to the maternal circulation. These data suggest that a putative role for fetal OX in the initiation of labour must involve a route other than access to the maternal circulation across the placenta. In addition, given that OX is a hypotensive agent, clinical misadventure may result from umbilical OX injection to shorten the third stage of labour.
6E4-
5E4
-
0
IE4
2E4
3E4 F4C]
4E4
5E4
6E4
inulin cpm
ENERGY PRODUCTION BY THE DUALLY PERFUSED TERM HUMAN PLACENTA IN VITRO: [“‘PI NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY AT 2.0 AND 4.7 TESLA A. Malek, R. K. Miller, D. R. Mattison, R. Bryant, M. Panigel & L. Neth (Departments of Obstetrics and Gynaecology, and Biophysics, University of Rochester, Rochester, NY, USA, Department of Obstetrics and Gynaecology, University of Arkansas, and National Centre for Toxic Research, Little Rock, AR, USA) The placenta is responsible for fetal well being, which requires high energy production for active transport and protein synthesis. Previous investigations have suggested that placental ATP remains constant or decreases after initiation of perfusion. Those ATP levels were determined after freeze clamping which, unfortunately, requires termination of perfusion. In contrast, we have assessed placental energy generation by measuring ATP and inorganic phosphate (Pi) during in vitro perfusion with modified M199 tissue culture medium using [3rP] nuclear magnetic resonance (NMR) spectroscopy at 2.0 Tesla (T) and 4.7 T. At higher magnetic field strengths (4.7T) adjacent resonance lines are better separated and signal to noise ratios higher. Perfusion conditions included: (i) control, up to IO h; (ii) ischemia, produced by halting the perfusion pumps up to 4 h; and (iii) metabolic inhibition, produced by