Abstract
Abstract
In a series of four experiments, the temporal development of acute inhibitory and delayed stimulatory effects of 17β-estradiol (E) on luteinizing hormone (LH) release by superfused rat anterior pituitary cells pulsed with gonadotropin-releasing hormone (GnRH) was studied. Dispersed anterior pituitary cells from ovariectomized rats were cultured on Bio-Beads for 3 days and then placed in columns and superfused for up to 24 hr. During superfusion, the cells were exposed to GnRH pulses (3 × 10-9 M, one 6-min pulse/hr). Cells treated with E (3 × 10-10 M) either before (only 24 hr prior to superfusion) or before and during superfusion released significantly (P < 0.05) more LH in response to the first few pulses of GnRH than cells treated with diluent. In contrast, cells treated with E only during superfusion initially released less GnRH-induced LH than cells treated with diluent. In a subsequent experiment, the inhibitory effect of E reached a maximum by 1.5 hr (P < 0.01), and then gradually disappeared after 4.5 hr. Cells superfused simultaneously with E and fixed “low”-dose GnRH (5 × 10-10 M) pulses did not exhibit enhanced LH responses with time to that dose of GnRH. However, E-superfused cells responded more than diluent-superfused cells to subsequent stimulation with a higher-dose GnRH pulse. Superfusion of cells with E for 16.5 hr in the absence of GnRH pulses also did not increase release of LH to low-dose (5 × 10-10 M) pulses of GnRH, yet did cause a transitory increase to subsequent high-dose (10-8 M) GnRH pulses. In conclusion, these results demonstrate the direct biphasic inhibitory then stimulatory effects of E on GnRH-induced LH release by superfused rat anterior pituitary cells. Expression of the stimulatory effect of E is related to the dose of GnRH.
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