The structure and activity of the hypophysis of Rana temporaria in normal and in experimental conditions

Summary Volumetric, karyometric and histological studies were done on the pars distalis of the hypophysis of Rana temporaria, in normal and in experimental conditions.In the normal pars distalis, a gradient of activity of the P.A.S.-positive cells is described which shows a close relation with the blood supply. This relation strongly suggests the presence of a gradient of humoral factors which would influence the activity of the pars distalis. This gradient is not dependent on the influence of A.F.-positive neurosecretory fibres. In the P.A.S.-negative cells (O.G.-cells) a similar gradient could not be found. In transplants of pars distalis the gradient of activity is absent.There exists a striking difference between autotransplants and homotransplants of pars distalis in the eye, and also between autotransplants on the iris and autotransplants in the cornea.A parallelism between autotransplants of pars distalis on the iris and the pars distalis of animals deprived of their median eminence could be established. In both groups the pars distalis shows a similar decrease in volume. The glandular cells are well differentiated, but show a low activity. This low activity is most pronounced in the P.A.S.-cells. The normal variability in staining of the P.A.S.-cells has diminished: in general, the great majority of the P.A.S.-cells are P.A.S.-purples. The gradient of activity of the pars distalis has disappeared. The seasonal development of the gonads and of the secundary sexual characteristics is absent. This absence is probably not caused by a decrease of the total number of P.A.S.-cells of the pars distalis. It is probably due to the low activity of the P.A.S.-cells, which cannot be ascribed to the absence of the neurosecretory influence of the magnocellular preoptic nuclei.A preliminary note on the gradient of activity of the pars distalis has been published (Dierickx 1963c).