In vivo LH-RH output of ovariectomized rats following estrogen treatment

In the present experiment we examined the effect of estrogen upon in vivo luteinizing hormone releasing hormone (LH-RH) release from the medial basal hypothalamus of freely moving ovariectomized female rats during the period of the LH surge. Ovariectomized females (10-20 day) received two subcutaneous injections of oil or estradiol benzoate (EB; 25 micrograms/rat) at 48 and 24 h prior to push-pull perfusion and were perfused between 10:00 and 18:00 h on the 3rd, day. Unexpectedly, the activity of the LH-RH pulse generator in ovariectomized rats was characterized by a very low mean LH-RH output. Administration of EB increased the activity of the LH-RH pulse generator as indicated by a significant increase in overall mean LH-RH release of EB- versus oil-treated females. In addition, EB-treated females demonstrated a diurnal variation in LH-RH release with marginal, but significant, increases in LH-RH release during the period of the LH surge (14:10-18:00 h) as compared with levels obtained between 10:00 and 14:00 h. This increase in the overall mean release during the period between 14:10 and 18:00 h appears to be attributable to an EB-induced increase in the frequency of LH-RH release, since the amplitude did not change between the two 4-hour sampling periods.(ABSTRACT TRUNCATED AT 250 WORDS)