Epidermal tissue homeostasis. II. Cell pool size, cell birth rate and cell loss in toads deprived of the pars distalis of the pituitary gland.

Following removal of the pars distalis of the pituitary gland in toads, epidermal efflux from the stratum corneum recruitment cell pool (i.e. production of corneal layers) is greatly increased. In this investigation the cell birth rate is studied by means of the metaphase arrest technique, as a function of time after pars distalis ablation. The method allows assessment of the total cell production over 14 days after the operation, to be compared with the total efflux and changes in the epidermal cell pool size. Whereas in intact toads the rate of cell production exceeds that of cell loss by moulting by a factor of 2.7, the 'surplus' of cells neither being used for formation of corneal layers nor permanently accommodated within the living epidermis, a 'balance sheet' of efflux and influx indicates that following pars distalis ablation all cells produced are also used for the (excessive) formation of corneal cell layers. The observations lend further support to the hypothesis that controlled cell deletion is a tissue homeostatic mechanism complementary to controlled cell divisions.