Prolactin-induced cytologic changes in the mucosa of the pigeon crop during crop- "milk" formation.

Abstract

Light and electron microscope observations reveal two basic histo- and cytologic changes which take place in the pigeon crop during the course of prolaction administration to both sexes; (1) an increase in mitotic activity resulting in hyperplasia of the lateral lobes of the crop and (2) the accumulation of lipid in cells of these lobes. The latter process begins about twelve hours following prolactin injection. Histologic and cytochemical tests, as well as thin layer chromatographic analysis, reveal that these lipids may be classified as neutral unsaturated triglycerides. Tissues of control and prolactin-treated groups examined during the course of this study do not reveal any striking changes in organelle systems — aside from the accumulation of large lipid droplets. It does appear, however, that while ribosomes exist primarily as single units in non-stimulated cells, they appear primarily as polysomes in stimulated cells actively engaged in lipid synthesis. The origin of the cytoplasmic lipid inclusions is of interest. Morphologic evidence suggests that (1) they are not the result of cyto-pathologic changes, (2) they do not result from mitochondrial transformation and (3) they are not incorporated as discrete triglyceride micelles into these cells. The availability of precursors to the cell is dicussed in light of the observation that intercellular channels increase in width, and microvilli and desmosomes decrease in number throughout the experimental series. The incorporation of possible precursors into the cytoplasm may occur via two distinct classes of vesicles. One class is thought to arise through micropinocytotic activity. These vesicles have filamentous boundaries which are thought to render them specific for certain classes of compounds. The second class is somewhat larger in size and differs morphologically from micropinocytotic vesicles. These are thought to arise by the fusion of tips of microvilli and the plasma membrane, thus inpounding and internalizing materials from the intercellular canals into the cytoplasm.