Ultrastructure of the Fetal Rat Adenohypophysis

Abstract

and sheep (between 43 and 53 days: Stokes & Boda, 1968). With a similar method, using antibodies conjugated with peroxidase, Nakane (1970) demonstrated the ultrastructural localization of several pituitary hormones in the adult rat. There are no similar electron microscopic studies on fetal rats to be found in the literature.The content of hormones in the fetal pituitary has also been demonstrated in bio-assay or with radio-immune assay methods. By transplantation of fetal pituitaries or injection of pituitary extracts into immature hypophysectomized tadpoles, Enemar (1960b) demonstrated the debut of hormone activities in pituitaries of fetal mice. With this technique, growth-promoting activity was demonstrated at 17.5 days. By in vitro culture of pituitaries and peripheral organs, the presence of hormone in the fetal pituitary may be demonstrated. In this way, Tixier-Vidal (1958) demonstrated the presence of thyrothrophin in the fetal chicken on the 7th day of gestation. Direct demonstration of pituitary hormone content by radio-immune assay has been performed in the fetal rat by Birge et al. (1967), who reported that STH was not present until the 19th day, the concentration then being 0.2 microgram per pituitary. Studies like these may give information on the presence and quantity of trophic hormones in the fetal pituitary, but, as has been emphasized by Moore (1950), conclusions cannot be drawn concerning the ability of the individual pituitary cell to release its hormones in the intact organism.The vascularization of the fetal pituitary is, from a functional point of view, of great interest in two respects, namely, the possible existence of regulatory mechanisms in the fetus between the hypothalamus and the adenohypophysis and also between the adenohypophysis and other organs. The development of the hypophyseal vascular system was thoroughly investigated in the mouse by Enemar (1961), who demon¬ strated in the light microscope that the primary capillary plexus has already developed and has nerve connection in eminentia mediana at 15.5 days, and that a neurovascular communication of adult type is organized by the 17.5 day stage. The appearance of the corresponding neurovascular communication has not been demonstrated in the rat, as far as is known from the literature, but the primary plexus is supposed to be present at the 15.5 to 16.5 day stage (Enemar, 1961). From this stage onwards, the adenohypophysis may be under the influence of hypothalamic centres.

Molecular weights of adrenocorticotropic hormone in extracts of anterior and intermediate-posterior lobes of mouse pituitary.

“…It is not yet known whether the higher molecular weight forms of ACTH are biosynthetic precursors to a (1-39); the role of proteolytic enzymes in modifying the molecular weight distribution observed in the separated lobes must be considered. Both the intermediate and anterior lobes of the pituitary differentiate from Rathke's pouch (43), so it will be interesting to investigate the development of differences between the ACTH in the two lobes.…”

Ontogenèse des hormones de l'axe somatotrope

“…Ainsi, les hormones hypothalamiques hypophysiotropes, dont la sécrétion est modulée par de nombreux facteurs périphériques ou centraux, rejoignent l'antéhypophyse en empruntant le système porte hypothalamo-hypophysaire. Les (Lubberhuizen, 1931 ;Nelson, 1933 ;Harrison et Shyrock, 1940 ;Kingsbury et Roemer, 1940 ;House, 1943 ;Schechter, 1971 ;Vitums, 1977) (Atwell, 1926 ;Daikoku, 1958a, b ;Falin, 1961 ;Conklin, 1968 ;Andersen et al, 19711 (Atwell, 1926 ;Daikoku, 1958a, b ;Falin, 1961 ;Conklin, 1968 ;Andersen et al, 1971 ;Dubois, 1971a, b l'antéhypophyse (Maillard, 1963 ; Dumont, 1965Dumont, , 1966Dubois, 1968 ;Yoshimura et al, 1970 ;Schechter, 1971 ;Fink et Smith, 1971 ;Svalander, 1974 ;Hemming et al, 1983Hemming et al, , 1986 Falin, 1961 ;Dubois et Dumont, 1965, 1966Conklin, 1968 ;Dubois, 1968. On a pu décrire les cellules orangeophiles ou PAS + (Magre et Dupouy, 1973).…”

“…Mais ce que l'on met en évidence n'est qu'une affinité tinctoriale ou un radical chimique. La microscopie électronique elle-même ne permet souvent de raisonner que par analogie avec ce que l'on peut observer chez l'adulte (Maillard, 1963 ; Dumont, 1965Dumont, , 1966Dubois, 1968Yoshimura et al, 1970 ; Smith, 1971 ;Schechter, 1971 ;Svalander, 1974 (Bresson et al, 1984) et 28 semaines (Bloch et al, 1983). A 31 semaines, les fibres à GRF s'observent dans l'émi-nence médiane ; à la naissance, elles sont très nombreuses (Bloch et al, 1983 (Paulin et al, 1976 ;Bugnon et al, 1977).…”

Pituitary-ovarian axis of rats from fetal to peripubertal period of life after intrauterine exposure to dexamethasone

“…Pod treće moždane komore u tom periodu čini šest do deset slojeva okruglih i ovalnih ćelija koje svojom proliferacijom obezbeñuju rast i izduživanje začetaka neurohipofize ka Ratkeovom džepu (Svalander, 1974). Kapilarna mreža, koja počinje da se formira izmeñu dva primordijuma i to anteriornog dela ventralnog diencefalona i Ratkeovog džepa zajedno sa aksonima neurona čija su tela smeštena u jedrima hipotalamusa, predstavljaja buduću spoljašnju zonu EM.…”

“…Pukotinaste meñućelijske veze zadržavaju se i prilikom deoba ćelija. Kontakt izmeñu začetka adenohipofize i neurohipofize je uspostavljen 13. fetalnog dana (Svalander, 1974). U sledećim danima, 14. i 15. dana razvoja fetusa, veza Ratkeovog džepa i usne duplje zadobija izgled kraniofaringealnog kanala koji se postepeno sužava, i na kraju iščezava.…”