FSH Progesterone
The fall of the fotossensibilidade determines low in the release of GnRH for hipotlamo and a subsequent fall in the release of LH and FSH for hipfise. The fall of FSH and LH and the low stimulaton of the layers of cells of the theca and the granular, where the andrognios, estrognios and progesterone are synthecized, cause the ovariana regression and compromise the evolution of the folculos. The low level of progesterone goes to make it difficult the LH release still more, therefore the progesterone wave is that it induces the LH release to unchain the ovulao. Thus being, during the hatching phase of the hen it ceases the position (ETCHES, 1996). In the reproductive cycle, the prolactina levels vary very of low at the moment of the fotoestimulao until moderate levels at the moment of the production peak. During the days that precede to the position of the last egg, it occurs a reduction of the secretion of progesterone and an increase of the prolactina secretion and the ovrio regride. The increase of the prolactina secretion occurs in consequncia of a reduction of the dopaminrgica activity and of an increase in the production of PIV (Polipeptdeo Vasoativo Intestinal) for hipotlamo.
The PIV has been considered as a factor stimulant of release of Prolactina (PRF) and the dopamina an inhibiting factor of the prolactina release (PIF) (RABBIT, 2006). Literature has demonstrated that the prolactina consequentemente induces one feedback negative on the secretion of GnRH for hipotlamo and of LH for hipfise, as well as the estrognio and the progesterone inhibits the synthesis of PIV for hipotlamo. Currently the hypothesis is accepted of that the hormone reduction esterides for the ovrios propitiates the appearance of hatching when allowing an increase of PIV and consequence increase of the prolactina secretion. In this way, the prolactina in high in the circulation of the bird, determines reduction of hipofisrio hipotalmico GnRH and LH for feedback negative, cause the ovariana regression and imposes the behavior of hatching.
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