Evidence for a secretory process, distinct from that of the aqueous humour, in the ciliary epithelium of Macaca mulatta.

In the ciliary epithelium of normal Rhesus monkeys, groups or islands of cells are present in which an intense secretory activity takes place. This is distinct from activity in aqueous humour production. In these regions of the epithelium the cytoplasm of the nonpigmented cells contains a well developed rough endoplasmic reticulum, numerous Golgi complexes and secretory granules containing an amorphous material of variable density. This material is discharged by a process of exocytosis into the intercellular spaces between the facing apices of the nonpigmented and pigmented cells and from here it percolates into the intercellular spaces between pigmented cells. The endothelial cells of the fenestrated capillaries located underneath these regions of actively secreting nonpigmented cells frequently contain, in their cytoplasm, granules of moderately dense material, suggesting a transport from the ciliary body stroma into the blood stream. Upon stimulation with pilocarpine the secretory activity of the nonpigmented cells is greatly increased and the intercellular spaces of the epithelium, including the ciliary channels, are frequently dilated and contain abundant osmiophilic material. These morphological observations suggest that, in addition to actively transporting aqueous humour, the ciliary epithelium produces a secretory material that diffuses into the ciliary body stroma and possibly enters into the blood stream across the walls of the fenestrated vessels.