THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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metabolic factors may influence hpÏ, output by the pl_acent,a.
Although so¡ne investÍgators (Spellacy eÈ a1 , 1966, crumbach
et al, 1968; Fairweather, 1971 ; Ajabor and yen, 1972; Tyson
et al , 1974) found no change in hpl, levels due to glucose
administration to pregnant hromen, others (Burt et aI, L970;
spellacy et al , 1971a; Gaspard et aI , 1973, Lg74) observed
a significant faIl. ConverseLy, hypogJ_ycemia has been
found to elevate hpL levels (Kim and Felig, 1921 ; Spellacy,
1971 ; Gaspard et, al_, 1974t Tyson et aI , l"97La,b, 19741 .
On the other hand, hPL l"evel,s in pJ_asma appear to be
unaffected by the free fatty acid. concentrations in the
blood (Morris et aI, 1974t caspard et a1 , l_9?5) or by
PGFe2 and PGF2a (Keller et al_, ].972r, although the latter
may affect hcc output.
ix) Biological effects and physiological roles of hpl.,:
This hormonê appears to have three major
effects during pregnancy, all directed toward mãternal metabolism.
First, it is luteotropic, as evidence¿l by its stimulation
of progesterone and estrogen secretion by the corpus luteum
of hypophysectomized pseudopregnant. rats, an effect that
is potentiated by administration of hpl, and hCG together
(Josimovich, 1968b). Thus, hPL secretion during the
second Èrimester of human pregnancy may enhance the action
of hCG on the corpus luteum. However, attempts to
demonstrate such an action in pregnant women have not been
successful (Stock et aI, 1971).
Second, placental lactogen stimulates milk
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