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1

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
EN
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.
2

Gonadotropins and sex hormones modulate interrenal function in soft-shelled turtle

88%
Ray P. P., Maiti B. R.
Folia Biologica
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2002
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vol. 50
|
issue 3-4
115-120
EN
The aim of the current work was to investigate the role of gonadotropins and female sex hormones on interrenal activity in soft-shelled turtles, Lissemys punctata punctata. 1) FSH treatment (3 mug/100 g body wt daily for 10 days) caused interrenal hypertrophy with increased nuclear diameter, raises of acid phosphatase and alkaline phosphatase concentrations, and depletions of cholesterol (except the free fraction) and ascorbic acid levels from the interrenal gland. However, LH treatment (3 mug/100 g body wt daily for 10 days) failed to produce any perceptible change in the interrenal activity. The combined treatments of FSH and LH (3 mug each/100 gm body wt daily for 10 days) produced no further change beyond that of FSH alone. 2) Estrogen treatment with the low dose (25 mug/100 g body wt daily for 10 days) had no effect, but with higher doses (50 mug or 100 mug/100 gm body wt daily for 10 days) is caused interrenal stimulation by inducing the same manifestations to those of FSH. The degree of manifestations was higher with the higher dose (100 mug daily) than that of the moderate dose (50 mug daily). Progesterone treatment with the low dose (25 mug / 100 g body wt daily for 10 days) had no significant effect, but with the moderate (50 mug daily) and higher (100 mug daily) doses suppressed interrenal activity by showing the reverse changes to those of estrogen. The degree of manifestations was higher with the higher dose than that of the moderate one. The combined treatments of estrogen and progesterone (100 mug each/100 g body wt daily for 10 days) caused interrenal stimulation but to a lesser extent than that of estrogen alone. The findings are briefly discussed.
3
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Neural systems mediating the negative feedback actions of estradiol and progesterone in the ewe

63%
Goodman R. L.
Acta Neurobiologiae Experimentalis
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1996
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vol. 56
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issue 3
727-741
EN
The ewe shows a marked seasonal variation in the effect of ovarian steroids on pulsatile GnRH secretion.In the breeding season progesterone inhibits GnRH pulse frequency, while estradiol suppresses puilse amplitude.In anestrus, both steriods inhibit pulse frequency.The effects of progestrone in both seasons are mediated by endogenous opioid peptides (EOP) that act in the preoptic area (POA) and medial basal hypothalmus (MBH).However, knife cut studies indicate that actions in the MBH are most important.Moreover, blockade of EOP receptors activates GnRH perikarya in the MBH, but not those in the POA.Thus interactions between EOP and GnRH neurons within the MBH may be critical for progesterone negative feedback.The neural systems mediating estradiol suppression of GnRH pulse amplitude in the breeding season are largely unknown, although alpha-adrenergic neurons nay be involved.The seasonal variation in inhibition of GnRH pulse frequency by estradiol is postulated to be mediated by a group of dopaminergic (DA) neurons that have three important properties: (1)they inhibit GnRH pulse frequency; (2) their activity is stimulated by estradiol; and (3) they are functional in anestrus, but not the breeding season.Recent work examining the effects of lesions of DA neyrone and the ability of estradiol to induce Fos inDA cells srongly suggest that DA neurons in the retrochiasmatic area (A15) and POA (A14) have all three characteristics.We thus propose that these DA neurons are responsible for the seasonal variation in the ability of estradiol to inhibit GnRH pulse frequency.
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