Progesterone facilitates the LRH releasing action of oestrogen

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Abstract
: The effects of progesterone (P) on the release of LRH and LH were examined in a sequential double chamber superfusion system by superfusing the medial basal hypothalamus (MBH) and/or pituitaries excised randomly from cycling female rats. Addition of 10 μl of 10−6 m oestradiol (E2) to the first chamber resulted in a gradual and significant (60–160%) increase in LH release above the pre-injection level from the pituitary in series with MBH. Administration of 10−8 m P after 10−6 m E2 caused a prompt and marked increase (300%) of LH (P < 0.05), whereas 10−8 m P alone had no effect. Administration of 10−6 m E2, 10−8 m P or E2 plus P did not significantly change LH secretion from the pituitary superfused alone. The concentration of LRH in the efflux was significantly increased (150–200%) 150 min after 10−6 m E2 administration. P administration after E2 injection produced a prompt and significant increase of LRH and the increase of LRH (300–600%) was 2–3-fold that produced by E2. P alone had no effect. These data clearly indicate that P enhances E2-induced LH release by increasing LRH secretion from the MBH.

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