[Periodization of the postnatal proliferative activity in the rat retinal pigment epithelium detected by a method of experimental microphthalmia].

The dynamics of postnatal proliferative activity (PA) in the retinal pigment epithelium (RPE) and of its dependence on the general eye growth factor (intraocular pressure) was studied by means of 3H-thymidine autoradiography and experimental microphtalmia (lens removal from the eyes of the 1 and 4 days old rats). The regulation of RPE growth by the intraocular pressure was shown to be connected with the control of the number of cells by means of stimulation of their entry in S phase. The number of binucleated cells, formed as a result of acytokinetic mitosis, reflected the minimal number of cells proceeded through the reproduction cycle and was a weighted average, constant for each age and RPE zone. The first period of PA coincided with the most intensive growth of scleral part (2 to 5 days after birth) and was characterized by independence from the intraocular pressure and differences in PA intensity in different RPE zones (the highest in the central zone and dorsal and temporal regions of the equatorial zone). The second period (5 to 11 days) was dependent from the intraocular pressure and characterized by the levelling and decrease of PA in all RPE zones. The postnatal PA in RPE was characterized by a long G2 phase and a short G1 phase. The functional importance of PA and mass polyploidization of cells in RPE is discussed in the light of G2 phase specificity for the differentiating effect of melanotropic hormones on the pigment cells.