Adult, female rats hypophysectomized 12 to 14 days previously received pituitary homografts under the kidney capsule. Ten to 12 days later they were treated for 10 or 51 days with 5 μg synthetic LH releasing hormone (LH RH) in 8% gelatin solution sc twice daily or with the vehicle only as a control. The rats were sacrificed 2 to 4 hr after the last injection. Ten days treatment with LH RH did not change body or ovarian weight, serum LH, prolactin and estrogen levels, but increased serum FSH levels. Fifty one days' treatment with LH RH did not alter body weight or serum LH and prolactin but increased ovarian and uterine weight, as well as serum FSH and estrogen levels. The ovaries of the LH RH treated animals showed marked follicular stimulation. This was most striking in the rats treated for 51 days. Electron micrographs of the pituitary grafts showed the expected preponderance of prolacting cells which were not appreciably altered by the LH RH treatment. The most striking effect of LH RH was a stimulation of the FSH cells. This trophic effect was most pronounced in grafts from the rats treated with LH RH for 51 days. LH gonadotrophs were present in all grafts but, in general, they were relatively small and inactive in appearance. Serum prolactin was relatively high in all the animals.
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