Structure of the nongranulated cells in the hypophyseal rostral pars distalis of cyclostomes and actinopterygians.

The structure of the nongranulated cells in the sea lamprey adenohypophysis and similar cells of the rostral pars distalis in a number of actinopterygian fishes was examined with the aim of determining the role(s) of these cells in pituitary function. A number of possible roles are proposed for the nongranulated cells. In salmonids and Amia calva the cells may be involved in the active movement of material into or from the follicle lumina. The structure of the nongranulated cells in in vitro cultured and in in vivo transplanted trout rostral pars distalis also suggests a phagocytotic role for these cell. In teleosts with a non-follicular rostral pars distalis the nongranulated cells and in the subsequent dispersal of the hormone (and/or carrier substance) into the peripheral circulation.