There is considerable indirect evidence to support the view that growth hormone (GH) and prolactin are secreted by separate and distinct pituitary cells in mammals. This uni-hormonal concept of acidophil function has predominated for several years without serious challenge because a technique sufficiently sensitive to detect GH or prolactin secretion by single pituitary cells has not been available. Reverse hemolytic plaque assays enabling the detection of GH and/or prolactin secretion by individual cells have recently been developed in this laboratory and applied to this problem. Preliminary experiments with this method indicate that at least two types of acidophils exist within the pituitary glands of female rats: one type that secretes prolactin only and another that releases both GH and prolactin. The long-term objective of the proposed research is to unequivocally establish whether a single pituitary cell is capable of secreting GH and prolactin either simultaneously or at different times. In pursuit of this objective, I plan to confirm and expand my preliminary findings by: (1) further validating the use of reverse hemolytic plaque assays for GH and prolactin; (2) determining whether physiologic state influences the relative proportions of GH and prolactin secreting cells; (3) invetigating the acute effects of hypophysiotropic factors on the secretion of GH and prolactin by individual cells; and; (4) assessing the chronic influences of estrogen, the hypothalamus and specific regulatory factors on the possible interconversion of somatotropes and mammotropes. It is anticipated that the proposed studies will provide valuable information toward our basic understanding of GH and prolactin reguatory processes. Such knowledg eis essential for identifying the causes of GH and/or prolactin secreting adenomas of the pituitary.