Effect of pregnancy-specific protein B on luteal cell progesterone, prostaglandin, and oxytocin production during two stages of the bovine estrous cycle.

This experiment was designed to evaluate the effects of pregnancy-specific protein B (PSPB) on luteal cell progesterone (P4), PGF2 alpha, PGE2, and oxytocin secretion. Corpora lutea were collected during the mid (d 10 to 12; n = 5) or late luteal (d 17 to 18; n = 5) stage of the estrous cycle. Large and small cells (1.5 x 10(5)/well) were treated with PSPB (0, 2.5, or 5.0 micrograms) and LH (0, 50, or 100 ng) in a 3 x 3 factorial arrangement. Cells were incubated for 18 h before adding treatments; after treatments, medium was collected at 6 and 12 h. During the 18-h pretreatment period, P4, PGF2 alpha, PGE2, and oxytocin production was similar between the prospective treatment groups. The PSPB did not affect P4 production. Stage of the cycle (stage) x time interaction (P < .001) indicated that mid-stage luteal cells produced more P4 than late-stage cells; regardless of stage, P4 decreased with time. The time x LH interaction (P < .001) revealed that at 6 and 12 h the 50- and 100-ng doses of LH increased P4 to greater than the 0-ng dose. Production of PGF2 alpha by mid-stage cells was similar among the three PSPB treatments; however, PGF2 alpha production by late-stage cells increased (P < .01) in response to the 5.0-micrograms dose of PSPB. The LH did not affect PGF2 alpha production. Late-stage luteal cells produced more (P < .001) PGF2 alpha than mid-stage cells during the 18-h pretreatment period and at 6, but not 12, h.(ABSTRACT TRUNCATED AT 250 WORDS)