Control of the pars intermedia of the lizard, Anolis carolinensis. II. Ultrastructure of the intact intermediate lobe.

The ultrastructure of the intermediate lobe of the hypophysis was studied in Anolis carolinensis with the use of a threefold aldehyde fixative. Lizards with a brown skin were selected. The possibility of two types of secretory cells is discussed; neither cell type is innervated. Type I cells are rarely found and contain dense granules approximately 0.3 micron in diameter; Type II cells vary widely in secretory activity. Most of the Type II cells contain a large number of dense secretory granules (up to about 1.3 micron in diameter) almost filling the cytoplasm. Rough endoplasmic reticulum (RER), Golgi apparatus and mitochondria are poorly developed. Only some of these cells show signs suggesting a high secretory activity, namely a well developed RER, Golgi apparatus and numerous mitochondria. In these cells the RER sometimes forms large intracisternal droplets (up to 7 micron in diameter). Two of the animals exhibited a more uniform, high secretory activity. Large (about 2 micron in diameter), pale vacuoles, probably of extracellular character, were found mostly in the vicinity of the perivascular septum. Their role in the release of MSH is discussed. The present data, which are discussed with reference to earlier findings (Forbes, 1972), form the morphological basis for an experimental study on regulation of MSH release (Larsson et al., 1979).