Placental Lactogen Secretion during Prolonged-Pregnancy in the Rat: The Ovary Plays a Pivotal Role in the Control of Placental Function.

Abstract

The serum of rats at mid-pregnancy contains at least 2 distinct placental lactogen (PL)-like substances tentatively termed placental lactogen-alpha (PL-alpha) and placental lactogen-beta (PL-beta) (Endocrinol Japon 38: 533-540, 1991). We have investigated the secretory patterns of three placental lactogens (PL-alpha, PL-beta and placental lactogen-II) during normal pregnancy and in two prolonged-pregnancy models. Pregnancy was prolonged by the introduction of new corpora lutea by inducing ovulation on day 15 of pregnancy by successive treatments with PMSG (30 IU/rat, sc on day 12) and hCG (10 IU/rat, iv on day 14), and in the second model by progesterone implants on day 15 of pregnancy. During normal pregnancy, each of the 3 PLs exhibited only one secretory peak in the serum; PL-alpha and PL-beta on day 12 and placental lactogen II (PL-II) on day 20. Interestingly, in the rats with new sets of corpora lutea, serum PL-alpha and PL-beta levels began to increase again on day 18 and showed peaks on day 20 for PL-alpha and on day 22 for PL-beta. In this model, the initiation of PL-II secretion was not affected, but high levels were maintained until day 26, when parturition occurred. In rats receiving either PMSG or hCG, the secretory patterns of the PLs were similar to as those during normal pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

A cDNA Encoding a New Member of the Rat Placental Lactogen Family, PL-I mosaic (PL-Im).

“…Previously, we reported that there were at least two distinct PL-like substances in mid-pregnant rat serum, PL-I and PL-a (molecular masses of 45-50 and 55-60 kDa respectively) [14,15], although the structure of PL-a has not been determined. PL-a was recognized preferentially by antiserum All-86, which was specific to the hydrophilic region of PL-II, and the recognition site of the PL-a core protein appeared to be analogous to PL-II rather than to PL-I [28].…”

“…The PRL surges following mating, which is induced by cervical stimulation, is necessary to initiate and maintain the progesterone secretion function of the corpus luteum. PL is a primary candidate for the luteotrophic factor of gestation, in view of the observations that PRL secretion ceases at mid-pregnancy following the initiation of PL secretion [33] and PLs are able to bind to the ovarian PRL receptor [14,15,28]. Mid-pregnancy-specific PLs appear to be peculiar to the rat, mouse and hamster [7,17], while PL expression occurs predominantly during late pregnancy in other species.…”

“…Sephadex G-100 gel-filtration analysis of mid-pregnant rat serum and placentas revealed a broad elution profile of PL activity [1,13], which we separated into two substances by high-performance liquid chromatography gelfiltration [14,15]. Thus, the PL activity in midpregnant serum does not depend upon a single molecular type, but involves at least two molecular types, PL-I (molecular mass 45-50 kDa) and PL-a (55-60 kDa) [14,15]. These PLs were demonstrated to be N-glycosylated proteins, as they were sensitive to several glycosidases [14,15].…”

“…Thus, the PL activity in midpregnant serum does not depend upon a single molecular type, but involves at least two molecular types, PL-I (molecular mass 45-50 kDa) and PL-a (55-60 kDa) [14,15]. These PLs were demonstrated to be N-glycosylated proteins, as they were sensitive to several glycosidases [14,15]. PRL, GH and PLs appear to have evolved from a single ancestral gene by gene-duplication and sequence divergence [16].…”

Characterization of Rat Mid-Pregnancy-Specific Placental Lactogen Produced by Baculovirus / Insect Cell Expression System

“…The member of the placental PRL family has been assumed to be one of the luteotropic factors during pregnancy after placentation [13]. In accord with this concept, the mid-pregnancy-specific PLs are secreted again in late pregnancy and are associated with the prolonged secretion of progesterone from the corpora lutea beyond the normal pregnancy period in the prolonged pregnancy model, which is developed by induction of a new set of corpora lutea following successive treatment with PMSG and hCG at mid-pregnancy [1,27]. The present study clearly demonstrated that recPL-Im has luteotropic activity in a primary culture of luteal cells of pregnant rat.…”