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  • Title: Stimulatory versus inhibitory effects of progesterone on estrogen-induced phasic LH and prolactin secretion correlated with estrogen nuclear and progestin cytosol receptor concentrations in brain and pituitary gland.
    Author: Barraclough CA, Camp P, Weiland N, Akabori A.
    Journal: Neuroendocrinology; 1986; 42(1):6-14. PubMed ID: 3941760.
    Abstract:
    The purpose of these studies was to determine the temporal requirements and time of day required for progesterone (P4) to amplify versus extinguish LH surges. The experimental animal model used in these studies was the 7-day ovariectomized rat (day 0) treated continuously with estradiol (E2) for 2-4 days (days 2, 3 or 4). In these studies we also examined the changes which occur in estrogen nuclear (ERn) and progestin cytosol (PRc) receptor concentrations in the preoptic area (POA), medial basal hypothalamus (MBH), corticomedial amygdala (CMA) and pituitary gland (PIT) associated with these physiological responses. When two P4 capsules (50 mg/ml) were placed subcutaneously at 09.00 h on day 2 and removed 3 h later (12.00 h), LH surges were amplified that afternoon. 24 and 48 h later (days 3, 4) phasic LH release reoccurred albeit in reduced concentrations compared to the LH values obtained in E2-treated rats on day 2. In contrast, if P4 capsules remained in situ for greater than 24 h, LH surges did not reappear on day 3. In a separate group of E2-treated rats, P4 capsules were placed subcutaneously at 15.00 h and removed at 21.00 h on day 2. Only minor increases in LH occurred on day 3 compared to E2-treated controls. Thus, both the duration of time and hour of day that the hypothalamo-pituitary unit is exposed to P4 seem important in determining which component of the biphasic LH response (amplification vs. inhibition) will occur.(ABSTRACT TRUNCATED AT 250 WORDS)
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