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PARATHYROID HORMONE PEPTIDE ACTIVATES PLACENTA by benbenzhou

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PARATHYROID HORMONE PEPTIDE ACTIVATES PLACENTA

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									Experimental Physiology, (1991), 76, 297-300
Printed in Great Britain


   PARATHYROID HORMONE-(1-34) PEPTIDE ACTIVATES
CYCLIC ADENOSINE 3',5'-MONOPHOSPHATE IN THE HUMAN
                    PLACENTA
   J. M. A. WILLIAMS, D. R. ABRAMOVICH*, C. G. DACKEt., T. M. MAYHEW
                                         AND K. R. PAGE§
 School of Biomedical Sciences, University of Aberdeen, Aberdeen AB9 lAS, * Department of Obstetrics
    and Gynaecology, Aberdeen Maternity Hospital, Foresterhill, Aberdeen AB9 2ZB and t School of
            Pharmacy and Biomedical Sciences, Portsmouth Polytechnic, Portsmouth P01 2DF
             (MANUSCRIPT RECEIVED 2 DECEMBER 1990, ACCEPTED 21 DECEMBER 1990)

                                               SUMMARY
   Dually perfused human term placental lobules were exposed to forskolin, bovine parathyroid
   hormone (bPTH(1-34)) and human parathyroid hormone related-peptides, hPTHrP(1-34),
   hPTHrP(67-86)NH2 or PTHrP(107-138) for 15 min in the presence of 3-iso-butyl-1-methyl-
   xanthine (IBMX); control lobules were exposed to IBMX alone. Homogenates of these tissues
   were then assayed for cyclic adenosine 3',5'-monophosphate (cyclic AMP) and results
   normalized per mg of protein. Exposure to forskolin or bPTH(1-34) on both sides, and exposure to
   bPTH(1-34) at a concentration of 30 nm on the maternal side of the placenta or 120 nm on the fetal
   side of the placenta, significantly enhanced tissue cyclic AMP production compared with tissue
   exposed to IBMX alone. Exposure to hPTHrP(1-34), hPTHrP(67-86)NH2 and hPTHrP(107-138)
   at a concentration of 30 nm on both sides of the placenta had no significant effect upon tissue
   cyclic AMP production.

                                            INTRODUCTION
During the later stages of human pregnancy, the fetus is hypercalcaemic compared with
the mother. This process is mediated by a Ca2+-ATPase system sited in the basal
membrane of the placental trophoblast (Williams, Abramovich, Dacke, Mayhew & Page,
1991). The control of transplacental fluxes of calcium and phosphate may involve
parathyroid hormone (PTH) (Allgrove, Adami, Manning & O'Riordan, 1985; Barlet,
Davicco & Coxam, 1990) or parathyroid hormone-related peptide (PTHrP) (Rodda,
Kubota, Heath, Ebeling, Moseley, Care, Caple & Martin, 1988). PTH responses in many
tissues involve cyclic adenosine 3',5'-monophosphate (cyclic AMP) as a second
messenger system. We now report changes in placental tissue cyclic AMP production
following exposure to PTH or PTHrP fragments.
                                            METHODS
Normal human term placentae were perfused with Krebs Ringer (KR) solution containing 2-4 mM-Ca2+
(Abramovich, Dacke, Elcock & Page, 1987). In each experiment, two lobular areas were perfused
simultaneously; one, randomly chosen, served as the experimental lobule and the other as the internal
control.

                                 § To whom reprint requests should be sent.




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298                                J. M. A. WILLIAMS AND OTHERS

  Each experiment lasted 45 min, consisting of 30 min equilibration followed by a 15 min experimental
period when the KR supplying the experimental lobule was replaced with KR modified by the additions
indicated in Fig. 1A and B. In all experiments except k, 100 AM-3-iso-butyl-1-methyl-xanthine (IBMX)
was present, and bovine serum albumin (0.5 % w/v) was present in all except experiment a. The KR
supplying control lobules and contralateral circulations in experiments b, d, e andf was replaced in the same
manner with KR of the same composition as the experimental lobule but with the omission of peptide or
forskolin. Forskolin, bPTH(1-34) and IBMX were obtained from Sigma Chemical Co., UK, and the
hPTHrP fragments from Peninsula Laboratories, UK.
  At minute 45, tissue samples (approx. 1 g wt) were taken from both lobules and treated with microwaves
(40 s at 350 W) in a domestic microwave oven to fix tissue cyclic AMP (Nahorski, Hunt, Rogers, Jones &
Martin, 1976). Samples were then immediately homogenized in 4 ml ice-cold phosphate buffer containing
100 pM-IBMX to prevent cyclic AMP breakdown by tissue phosphodiesterase. Homogenates were
stored at -20 OC until analysis. Tissue cyclic AMP was determined by use of a protein binding kit
(Amersham, code TRK 432) and values normalized per mg of total protein (Biorad protein assay, cat. no.
500-0002). Results are expressed as a percentage of the cyclic AMP production in the internal control
treated with IBMX alone except for experimentsj and k (see legend to figure).

                                          RES ULTS
Exposure to 10 gM-forskolin on both the fetal and the maternal side of the placenta
significantly enhanced tissue cyclic AMP by 223 % compared with IBMX-treated
controls (Fig. lAa). At a dose of 30 nM, bPTH(1-34) had a similiar but smaller effect
when perfused through both sides simultaneously or through the maternal side of the
placenta alone (Fig. lAb and Ac). When only the fetal side of the placenta was perfused,
the same dose of bPTH(1-34) had little effect (Fig. lAe) but a larger dose (120 nM)
did significantly enhance tissue cyclic AMP levels (Fig. lAd). Perfusion with
hPTHrP(1-34) at a concentration of 120 nm on the fetal side or 30 nm on both sides
simultaneously, also enhanced cyclic AMP production (Fig. lAf and Ag); but responses
were variable and consequently the increases were not statistically significant.
Exposure to hPTHrP(107-138) and hPTHrP(67-86)NH2 did not enhance cyclic AMP
levels: indeed, the latter peptide appeared to decrease cyclic AMP (Fig. lAh and Ai).

                                              DIS CUS SION
These results clearly demonstrate that bPTH(1-34) and possibly hPTHrP(1-34) can
activate cyclic AMP production in human placental tissue. At term, PTH is present in
both the maternal and the fetal bloodstreams; the transplacental gradient of calcium
however correlates with the concentration of bioactive PTH (1 to 10 pM) in the fetal
blood (Allgrove et al. 1985). PTH regulates calcium transport in a number of non-
placental tissues via cyclic AMP and it produces a cyclic AMP-mediated decrease in
inorganic phosphate (Pi) uptake into human placental microvillous membrane vesicles
(Brunette, Auger & Lafond, 1989). It is therefore possible that PTH regulates
movements of both Ca2+ and Pi across the placenta by mechanisms involving cyclic AMP.
   The role of PTHrP in these processes is as yet unclear. Some studies indicate
that activity lies within PTHrP(1-34) (Barlet et al. 1990), while others indicate
PTHrP(67-86) to be important (Abbas, Pickard, Rodda, Heath, Hammonds, Wood,
Caple, Martin & Care, 1989; Care, Abbas, Pickard, Barri, Drinkhill, Findlay, White &




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                                     PTH ACTIVATES CYCLIC AMP IN THE HUMAN PLACENTA                                                                       299
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Drug:              Forskolin   bPTH       bPTH      bPTH       bPTH       hPTHrP     hPTHrP     hPTHrP    hPTHrP                            IBMX       bPTH
                               (I -34)    (1-34)    (1 -34)    (I -34)    (1 -34)    (I -34)   (107-138) (67-86) NH2                                  ( 1-34)
Side:               Both       Material    Both     Fetal      Fetal       Fetal      Both       Both      Both                              Both     Both
Dose:              10pLM       30   nM    30 nM    120    nM   30   nM    120   nM   30 nM      30 nM     30 nm                             10 M     30 nM

Fig. 1A, cyclic AMP production in placental lobules following treatment with forskolin (a), bPTH(1-34)
  (b-e) or hPTHrP fragments (f-i) expressed as mean (with S.E.M.) percentage of control production (i.e. in
  lobules perfused with IBMX alone). B, cyclic AMP production in placental lobules treated with IBMX
  (j) or bPTH(1-34) (k), expressed as mean (with S.E.M.) percentage of control production (i.e. in lobules
  perfused with normal KR alone). In j 300 % is equivalent to 100 % in a (i.e. the IMBX control
  production). Statistical comparisons are by Student's paired t test. * P <0-05, ** P <0-01 (two-
  tailed); t P < 0-05 (one-tailed). Figures in parentheses give number of lobule pairs tested.

Caple, 1990). The present results indicate that PTHrP(1-34) may activate cyclic AMP
production and, by analogy with PTH, play a role in the regulation of placental Ca2+
and Pi transport; however, variability of responses prevents a firm conclusion being
drawn. PTHrP(67-86) and PTHrP(107-138) apparently do not activate placental cyclic
AMP production suggesting that a messenger system other than cyclic AMP must
mediate any putative actions which they have on Ca2+ and Pi transport in this tissue.
        Support from Action Research is gratefully acknowledged.

                                                                         REFERENCES
ABBAS, S. K., PICKARD, D. W., RODDA, C. P., HEATH, J. A., HAMMONDS, R. G., WOOD, W.                                                                         I.,
  CAPLE, I. W., MARTIN, T. J. & CARE, A. D. (1989). Stimulation of ovine placental calcium transport
  by purified natural and recombinant parathyroid hormone-related protein (PTHrP) preparations.
  Quarterly Journal of Experimental Physiology 74, 549-552.
ABRAMOVICH, D. R., DACKE, C. G., ELCOCK, C. & PAGE, K. R. (1987). Calcium transport across the
  isolated dually perfused human placental lobule. Journal of Physiology 382, 397-410.




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300                             J. M. A. WILLIAMS AND OTHERS
ALLGROVE, J., ADAMI, S., MANNING, R. M. & O'RIORDAN, J. L. H. (1985). Cytochemical bioassay of
  parathyroid hormone in maternal and cord blood. Archives of Disease in Childhood 60, 110-115.
BARLET, J. P., DAVICCO, M.-J. & COXAM, V. (1990). Synthetic parathyroid hormone-related
  peptide(1-34) fragment stimulates placental calcium transfer in ewes. Journal of Endocrinology 127,
  33-37.
BRUNETTE, M. G., AUGER, D. & LAFOND, J. (1989). Effect of parathyroid hormone on P04 transport
  through the human placenta microvilli. Pediatric Research 25, 15-18.
CARE, A. D., ABBAS, S. K., PICKARD, D. W., BARRI, M., DRINKHILL, M., FINDLAY, J. B. C.,
  WHITE, I. R. & CAPLE, I. W. (1990). Stimulation of ovine placental transport of calcium and
  magnesium by mid-molecule fragments of human parathyroid hormone-related protein. Experimental
  Physiology 75, 605-608.
NAHORSKI, S. R., HUNT, N. H., ROGERS, K. J., JONES, P. & MARTIN, T. J. (1976). Studies in vivo
  on the effects of parathyroid hormone upon kidney cyclic adenosine 3',5'-monophosphate content using
  rapid tissue fixation by microwave irradiation. Hormone and Metabolic Research 8, 311-316.
RODDA, C. P., KUBOTA, M., HEATH, J. A., EBELING, P. R.,MOSELEY, J. M., CARE, A. D.,
  CAPLE, I. W. & MARTIN, T. J. (1988). Evidence for a novel parathyroid hormone-related protein in
  fetal lamb parathyroid glands and sheep placenta: comparisons with a similar protein implicated in
  humoral hypercalcaemia of malignancy. Journal ofEndocrinology 117, 261-271.
WILLIAMS, J. M. A., ABRAMOVICH, D. R., DACKE, C. G., MAYHEW, T. M. & PAGE, K. R. (1991).
  Inhibitor action on placental calcium transport. Calcified Tissue International 48, 7-12.




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