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The effect of corticotropin releasing factor (CRF) on the gonadotropin hormone releasing hormone (GnRH) hypothalamic neuronal system during preovulatory period in the ewe

100%

Polkowska J., Przekop F.

Acta Neurobiologiae Experimentalis

1997

vol. 57

issue 2

91-99

Effects of infusions of corticotropin releasing factor (CRF) into the 3rd ventricle of the brain of ewes during the proestrus on the immunoreactive (ir) gonadotropin hormone releasing hormone (GnRH) neuronal system, pituitary luteinizing hormone(LH) producing cells and LH concentrations in the blood plasma were studied. None of the CRF treated sheep displayed the estrous activity nor ovulated on the day of estrus (17th day of the cycle), and two days later when they were slaughtered. The GnRH center of CRF treated ewes situated in the preoptico septal area was well organized , but irGnRH stores in the median eminence were low in comparison to the controls (sheep from the late follicular phase of the estrous cycle). The feature and the number of LH cells in CRF treated ewes were typical for the preovulatory phase of the cycle but the plasma concentrations of LH did not exceed basal levels. These results suggest that CRF induced decrease of irGnRH stores in the nerve terminals of the ME can be responsible for the blockade of the preovulatory surge of GnRH/LH in the sheep.

Feedback action of estradiol on GnRH secretion during the follicular phase of the estrus cycle

75%

Karsch F. J., Evans N. P.

Acta Neurobiologiae Experimentalis

1996

vol. 56

issue 3

715-725

The pattern of GnRH secretion during the follicular phase of the estrus cycle of sheep is characterized by an initial marked in episodic secretion followed by a massive and sustained discharge - the preovulatory GnRH surge.Studies emploing a physiological model for the follicular phase have revealed that estradiol has profound and complex feedback effects on GnRH release during the preovulatory period.These include both quantitative efects on pulses and qualitative effects, in addition to inducting a preovulatory GnRH surge.In stimulating the surge, estradiol causes a highly characteristic change in the minute-to-minute pattern of GnRH in hypophyseal portal blood.Initially, a strictly episodic pattern gives way to one in which GnRH is consistently elevated between pulses.Then, following enhancement of both pulsatile and interpulse components, GnRH becomes extramely high and variable for the majority of the surge.From this point, a regular and well organized pulse pattern is not apparent.The characteristic time course of GnRH at surge onset provides insight into possible mechanistic changes in the GnRH neurosecretory system.Such changes include quantitative and qualitative alternations in the pulse generating mechanism, recruiment of a surge specific population of GnRH neurones, morphologic alternations in GnRH neurones , morphologic alternations in GnRH neurones and neighboring cells, and changes in efficiency or route of delivery of GnRH from its siet of release to the portal vasculature.These possibilities, while untested and speculative, provide a conceptual framework for future research.

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2 Acta Neurobiologiae Experimentalis

1 1997

1 1996

1 Evans N. P.

1 Karsch F. J.

1 Polkowska J.

1 Przekop F.

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The effect of corticotropin releasing factor (CRF) on the gonadotropin hormone releasing hormone (GnRH) hypothalamic neuronal system during preovulatory period in the ewe

Feedback action of estradiol on GnRH secretion during the follicular phase of the estrus cycle