Effect of Median Eminence Implants of LH on Pituitary LH of Female Rats1

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Abstract
The effect of implantation of LH (luteinizing hormone) into the median eminence (ME) area of mature intact female rats on pituitary and plasma LH was investigated. Eight to 10 days post implantation, the animals were sacrificed and LH was determined according to the Parlow method. Identical ME + LH experiments were performed at 5 different times. At no time was plasma LH detectable. For each separate experiment, there was a consistent and appreciable reduction in pituitary LH content of the LH-implanted animals, when compared to either their normal or sham-operated controls. ME implants of FSH (follicle-stimulating hormone) or ACTH, as well as amygdalar implants of LH, were without effect. The minimum average percentage of depression of pituitary LH of ME + LH rats was about 51% (range of all experiments=43-65). These animals demonstrated an anestrous state, yielding predominantly metestrous/diestrous smears. In spite of the large LH decrement, ovulation had occurred, as evidenced by corpora lutea formation. The results imply that the implanted LH may have induced a partial inhibition of pituitary LH synthesis, via a negative feedback effect on LH-RF, and that LH may therefore play a role (either singly or in combination with the ovarian steroids) in the regulation of its neural controller.