The identification of the thyrotropic cells in the adenohypophysis of the cichlid fish Cichlasoma biocellatum and the role of these cells and of the thyroid in osmoregulation

Summary In order to identify the thyrotropic cells in the pituitary gland of Cichlasoma biocellatum, adult animals were treated with thyroxine. Periodic acid Schiff (PAS)- and aldehyde fuchsin (AF)-positive, and Alcian blue (AB)-negative basophils in the meso-adenohypophysis as well as the thyroid were strongly inactivated by such treatment. Since other cell types in the adenohypophysis were not affected, it is concluded that the PAS-positive and AB-negative basophils in the meso-adenohypophysis are the thyrotrops. In normal animals the thyrotrops and the thyroid are very active. Propylthiouracil did not cause a further activation of TSH cells. Keeping the animals in 25% sea-water caused a strong inactivation of the prolactin cells, the thyrotrops and the thyroid. In deionized water the prolactin cells were stimulated, but the thyroid was less active than in controls. Injections of ovine prolactin did not enhance the activity of the thyroid in salt water animals. It is suggested that in Cichlasoma biocellatum prolactin does not have a direct stimulatory effect on the thyroid.Thanks are due to Prof. Dr. P. G. W. J. van Oordt for his continual interest and valuable suggestions, and to Dr. L. Boomgaart for correcting the english. We are indebted also to Messrs. H. van Kooten and E. van der Vlist for making the photographs. The National Institutes of Health, Bethesda, Maryland (U.S.A.) kindly presented the ovine prolactin.