Pituitaries transplanted under the renal capsule contain functional growth hormone (GH) secretors and suppress GH and prolactin release from individual eutopic pituitary cells.

The extent to which pituitary explants secrete GH requires clarification. In the present study GH release from ectopic pituitary tissue was assessed using the reverse hemolytic plaque assay. In addition, the effects of this tissue on eutopic GH and PRL release were simultaneously investigated. Anterior pituitary glands from adult female donor rats were grafted beneath the kidney capsule of adult male hosts. Four weeks later, this ectopic pituitary tissue and the eutopic pituitary glands of the host animals were removed, dispersed with trypsin, and subsequently assayed for GH and PRL release. Contrary to expectations, we found that 37% of the ectopic pituitary cells were GH secretors. Furthermore, these GH cells remained highly responsive to GRF (10(-7) M), which evoked a 7-fold increase (P less than 0.05) in mean GH plaque area. By comparison, only 28% of these ectopic cells secreted PRL, and this release was not consistently augmented by exposure to TRH (10(-7) M). In the second half of this study we found that the presence of ectopic pituitary tissue severely compromised the secretory capacity of the eutopic pituitary cells. More specifically, GH-releasing factor induced a 3-fold increase in GH secretion from the eutopic pituitary cells of sham-operated control animals, but it enhanced the release from cells of host animals by only 2-fold. Moreover, the response to TRH by the eutopic PRL cells from explant-bearing animals was curtailed to such an extent that it was not significantly greater (P greater than 0.05) than basal release in that group. We conclude that the potential of pituitary explant cells to release GH is far greater than previously believed and that this ectopic hormone production may inhibit hormone release from the eutopic pituitary cells.