Vasopressin Secretion by Cells of Hypophyseal Floor of Diencephalon Shown by Transplantation. ∗

Abstract

Since it is well established that vasopressin is produced by the neural portion of the hypophysis it is of interest to know when secretion starts and by what cells it is first produced. The derivatives of the infundibular process in the amphibian may be divided into the saccular wall, the lateral processes, the hypophyseal floor and the pars nervosa proper. Hormone production is usually attributed either to nerve endings or to pituicytes. It has been pointed out that secretion in tissue cultures of the posterior lobe by Geiling and Lewis 1 can not be attributed to nerve endings since they would have degenerated in such cultures. Similarly, nerve endings are eliminated in transplantations, which we 2 have made of the hypophysis in urodele embryos for they often do not have specific nerve connections but nevertheless secrete vasopressin.

The present experiments deal with the transplantation of the epithelial rudiment of the hypophysis together with the adjacent floor of the diencephalon but with no other components of the brain. For this work embryos of Ambystoma maculatum have been used at about Harrison's stage 31. The grafts were placed above and posterior to the pronephros in hosts of the same age. These transplants give rise to a vesicular pars sacculosa and the hypophyseal floor adjacent to the pars intermedia of the epithelial portion. These experiments and earlier ones 2 show that the vasopressin first appears about stage 43. This is indicated by vasoconstriction in animals carrying additional hypophyses as transplants and by vasodilation in hypophysectomized animals. Later, at about stage 45, correlated growth differences appear in which the gills are short and the tail fin narrow. 3 At these early stages there is, in the normal animal, no neuropilum beneath the hypophyseal floor and the pars nervosa proper has not yet developed. A similar situation is present in the transplants above described. Certainly it is unlikely that the squamous ependyma of the sacular wall of the infundibulum is secreting hormones. This places the responsibility for vasopressin secretion at this age upon the cells of the hypophyseal floor which are columnar and have considerable cytoplasm.