THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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This ís confirmed by Bolander et aI (t9?B) that in placentâl
explants, hPL synthesis remained constant while hCG synthesis
increases with cont,inued incubation. These sÈudíes
suggested that. a factor from the mother or fetus has been
elimínated from placental explants vrhich normally stimulat.es
hPL secretion.
fn contrast to hcc synthesis, addition of cAMp to
term placental slices díd not increase synthesis of hpL
(Friesen et aL, 1969; Handwerger et al , l9?3; Belleville
et aL, J"97 41 . Other potential regulators (insulin, progesterone,
cortisol, and prostaglandin F2.) were also found to be hrithout
effect by these authors. prostagl-andins E2 and F2¿ and
the catecholamines have been found by other investigators
to depress the synthesis and release of labelled protein by
placental slices !'rith a preferential effect on hpt (Belleville
et aI , 1974; Kraincanic et a1 n 1975). The inhibitory effect
of prostaglandin F2¿ observed by the Kraincanic!s group can
be correlated with the reduction in plasma hpl, observed
in patients undergoing therapeutic abortion $/ith this agent
(Speroff et al , 1972; ylikorkala and pennanen, 1923).
ft is interesting that catecholamines (dopamine ) have
the abíJ.ity to suppress the secretion of hpL in vitro,
whereas dopamine-antagonist elevated the secretion of hpl.
These studies suggest. that the secretion of hpl, might be
sirùilar to the secretion of prolactin from the pituitary
under the control of catecholamines. However I thé above
findings have not been substantiated.