Ultrastructural Changes of the Pars Tuberalis and Median Eminence of Rats Following Hypophysectomy

Kotsu, Tadao; Daikoku, Shigeo

doi:10.1679/aohc1950.34.167

Cited by 16 publications

(6 citation statements)

References 28 publications

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“…The remaining marginal epithelium shows very little structural change during the organogenetic period. The hypothesis that the pars tuberalis may have a regulating influence on the function of the pars distalis as suggested by Morato (1965) and supported by Kotsu Daikoku (1972) is compatible with these morphologic findings, but further studies are needed. From the posterior and dorsal part of the vesicle wall, the pars intermedia originates without the occurrence of undifferentiated primordial cells of the type seen in the rostro-ventral outgrowth from the vesicle.…”

Section: ) Cellular Differentiation During Embryonic Developmentmentioning

confidence: 56%

“…From the remaining pouch epithelium, the intermediate lobe and the marginal cells bordering the residual lumen develop. In adult rats, Oota & Kurosumi (1966) and Kotsu & Daikoku (1972) reported the presence of two types of cells in the pars tuberalis. These marginal cells accumulate glycogen in considerable quantities but contain no secretory granules.…”

Section: ) Cellular Differentiation During Embryonic Developmentmentioning

confidence: 99%

“…It has been demonstrated by Enemar (1963) that in the pars intermedia of the fetal mouse there is a melanophore-expanding substance (or substances) present, detectable by implantation into tadpoles, from the 16th day of pregnancy. Recently Kotsu & Daikoku (1972) in reviewing the subject concluded that the function of the pars tuberalis was unknown, and from their own ultrastructural studies in hypophysectomized adult rats they suggested that the pars tuberalis, unlike the pars distalis, might not be under hypothalamic control. An ultrastructural study of the pars tuberalis in the adult rat by Oota & Kurosumi (1966) demonstrated the presence of two types of cells, one of which contained granules.…”

Section: Introductionmentioning

confidence: 99%

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Ultrastructure of the Fetal Rat Adenohypophysis

Svalander¹

1974

Acta Endocrinologica

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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.

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Section: ) Cellular Differentiation During Embryonic Developmentmentioning

confidence: 56%

Section: ) Cellular Differentiation During Embryonic Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultrastructure of the Fetal Rat Adenohypophysis

Svalander¹

1974

Acta Endocrinologica

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“…The cells of the pars tuberalis are in intimate contact with neuronal terminals that may contact the individual cells (16). The density of gonadotropes in the pars tuberalis is greatest overlying the lateral median eminence, which also contains the largest numbers of LHRH neuronal terminals (7).…”

Section: Discussionmentioning

confidence: 99%

Mediation of the short-loop negative feedback of luteinizing hormone (LH) on LH-releasing hormone release by melatonin-induced inhibition of LH release from the pars tuberalis.

Nakazawa

Marubayashi

McCann

1991

Proc. Natl. Acad. Sci. U.S.A.

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The pineal hormone melatonin is thought to mediate the effects of the pineal gland on seasonal reproduction by altering the release of gonadotropins. The mechanism by which melatonin controls gonadotropin secretion has been ob- This concentration of melatonin also significantly reduced the release of LH into the medium. The increased release of LIIRH induced by melatonin (10 FM) was completely blocked by the addition of LH (50 ng/ml), which by itself had no sigicant effect on LHRH release. Rat LH antiserum (final dilution, 1:1800) significantly elevated LHRH output, whereas normal rabbit serum at a similar dilution had no effect. Finally, LHRH Melatonin, the pineal hormone, responds to seasonal changes in photoperiod to influence reproductive rhythms in seasonal breeders; however, the mechanism by which melatonin brings about its diverse effects is unknown (1). The development of a high-affinity high-specific-activity ligand, 2-[1251]iodomelatonin, has allowed the identification of melatonin-binding sites within the brain. The highest concentration of melatonin receptors occurs in the pars tuberalis of mammals (2-4), and it may be that this part of the vertebrate pituitary gland is not the nonfunctional lobe it was thought to be. The cells of this structure have many of the ultrastructural characteristics considered necessary for endocrine secretion (5). Furthermore, seasonal fluctuations in its cytological features, seemingly in concert with reproductive cycles, may represent the morphological expression of seasonal changes in its endocrine function (6). Luteinizing hormone (LH)-containing cells in the pars tuberalis of rats were first demonstrated through immunocytochemistry by Baker et al. (7), and it is noteworthy that the distribution of these cells corresponds to the distribution of terminals of the LH-releasing hormone (LHRH) neurons in the overlying median eminence. When the median eminencepars tuberalis was incubated in vitro in the presence of medium with a high potassium concentration, there was release of LH into the medium; LH release could also be stimulated by addition of LHRH (8). Although there is some evidence of LH in hypothalamic neurons, it appears that the largest amount of LH in the median eminence-pars tuberalis complex actually occurs in the gonadotrope-like cells in the pars tuberalis (21).The concept of short-loop feedback by which pituitary hormones inhibit their own release (9-11) is well established. The short-loop feedback of LH has been thought to be mediated either by LH neurons within the hypothalamus (11) or by retrograde flow of blood in the hypophyseal portal vessels that transport high concentrations of LH to the median eminence (12). We do not believe that either of these is the major mechanism for the LH negative short-loop feedback. Rather, we hypothesize that LH is released from the gonadotropes of the pars tuberalis and diffuses into the median eminence where it suppresses the release of LHRH from the terminals of the LHRH neurons either by a direct action or by...

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“…Severance of the pituitary stalk results in extensive degeneration of the hypothalamic hypophyseal nerve tract (Raisman, 1973 Kotsu andDaikoku, 1972). This is followed by a period of partial regeneration and considerable remodeling of the hypothalamus.…”

Section: Discussionmentioning

confidence: 99%