Growth of the sphincter muscle and neuroepithelia of the iris and ciliary body in rat: Autoradiographic study

Cell proliferation in the sphincter muscle and neuroepithelia of the iris and ciliary body in pigmented 1–11-day old rats was studied using pulse and continuous labelling with [ 3H]-thymidine. The duration of the M phase was calculated by the colchicine method. Labelling indices were the highest between the third and fifth days and did not exceed 28·3% in the ciliary body, 10·8% in the iris and 14·1% in the sphincter muscle. This level of labelled nuclei was observed in the sphincter muscle up to the 8th day while in the neuroepithelia labelling indices start to decrease after the fifth day. The cell cycle time ( T) and population doubling time ( T 2) in the 5- and 8-day old rats were calculated. Three characters of the iris and ciliary body cells proliferation call for attention: (1) cell populations with a longer cell cycle (neuroepithelia of the ciliary body) multiply more intensively than those with a shorter cell cycle (neuroepithelia of the iris) due to the larger number of cells involved in proliferation, (2) cell populations multiplying with an equal intensity (both neuroepithelia of the iris, sphincter muscle) have different structures of the cell cycles mainly owing to the variation of G 1 phase, (3) the M phase is considerably prolonged by comparison with that of the neural retina. These peculiarities of proliferation were considered as a way of cell adaptation to the development of functional entity of the anterior part of the eye during the period of the most intensive growth of its components.