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Placental lactogen not growth hormone and prolactin regulates secretion of progesterone in vitro by the 40-45 day ovine corpus luteum of pregnancy

100%

Wierzchos E., Gregoraszczuk E. L., Zieba D., Murawski M., Gertler A.

Folia Biologica

2000

vol. 48

issue 1-2

19-24

The study was designed to compare the direct effect of three prolactin-like hormones on steroidogenesis of ovine luteal cells collected at day 40-45 of pregnancy. 100 ng/ml of ovine placental lactogen or 100 ng/ml of ovine growth hormone or 100 ng/ml of ovine prolactin were added to the media of luteal cell cultures. After 48 h incubation, all cultures were terminated and the media were frozen until further steroid analysis. To determine to what extent growth hormone (GH), prolactin (PRL) and lactogen (PL) regulate the activity of 3$-HSD, an enzyme involved in progesterone synthesis, the classical steroidal competitive inhibitor of 3$-HSD trilostane, was investigated for its effects on basal and GH-, PRL-, and PL-stimulated progesterone biosynthesis since there is a possibility that the luteotropic effect of these hormones are mediated via 3$-HSD. oPL resulted in an increase of progesterone secretion in a statistically significant manner, while GH or PRL had no effect on progesterone secretion. A decrease in progesterone secretion as an effect of 100 mM trilostane was observed in all culture types. An explanation for the luteotropic effect of PL and the lack of this effect for GH is that the GH receptor associates with a different molecule within the ovarian tissue and forms a heterodimeric receptor for PL, and the possibility that physiological effects of native oPL may be mediated through its binding to specific PL receptors, which have low affinities for oGH and oPRL.

The central oxytocin pulse generator: a pacemaker for the ovarian cycle

63%

McCracken J. A., Custer E. E., Eldering J. A., Robinson A. G.

Acta Neurobiologiae Experimentalis

1996

vol. 56

issue 3

819-832

During luteolysis in sheep, episodic pulses of oxitocin (OT), contributed by the neurophysis and the corpus luteum (CL), stimulate uterine luteolytic pulses of prostaglandin (PG) F2alpha via endometrial OT receptors.To distinquish relative contributions of neurophysical and luteal OT, overoctomized sheep were given estradiol-17 beta (E) and progeterone (P) to simulate levelas during the cycle.In intact sheep, luteectomy was performed to exclude the CL as a source of OT and initiate P withdrawal.IN overiectomized sheep, E (mug/h for 12 to 36h) superimposed on basal E (0.05 mug/h) caused a series of 4 to 6 episodes of high frequency pulses of OT, each episode lasting 1 to 2 h at intervals of 3 h, and commencing at 24 h.Withdrawal of P (500 mug/h), superimposed on basal E in ovariectomized sheep, oe luteectomy in intact sheep, evoked similar episodes of high frequency pulses of OT begining at 24h.We conclude that (1) an increase in E levels, or the return of E actin following P withdrawal, causes intermittent increases in tyhe frequency of the central OT pulse generator, (2) high frequency pulses of OT initiate subluteolytic levels of uterine PGF2 alpha which trigger a supplemental release of luteal OT; (3) luteal OT amplifies the secretion of uterine PGF2 alpha which initiates luteolysis and causes more luteal OT to be secreted; and (4) in addition to the established hypothalmic-antrior pituitarty-gonadal axis for initiating the ovarian cycle (via the gonadotrophins), there is now evidence for a hypothalmic-posterior pituitary-gonadal axis for terminating the ovarian cycle (via OT).

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1 Acta Neurobiologiae Experimentalis

1 Folia Biologica

1 2000

1 1996

1 Custer E. E.

1 Eldering J. A.

1 Gertler A.

1 Gregoraszczuk E. L.

1 McCracken J. A.

1 Murawski M.

1 Robinson A. G.

1 Wierzchos E.

1 Zieba D.

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Placental lactogen not growth hormone and prolactin regulates secretion of progesterone in vitro by the 40-45 day ovine corpus luteum of pregnancy

The central oxytocin pulse generator: a pacemaker for the ovarian cycle