Experiments concerning the mechanism of pituitary colloid secretion

Colloid in the pituitary pars distalis of viscacha (Lagostomus maximus maximus): ultrastructure and occurrence in relation to season, sex, and growth

Randomly distributed extracellular colloidal accumulations were observed in the pars distalis of viscacha (Lagostomus maximus maximus). They were preferentially located in the peripheral zone of the gland and showed variability in shape and size. Two different types of colloidal accumulations were found by electron microscopy: 1) those surrounded by nongranulated follicular cells that correspond to characteristic follicles, and 2) those surrounded by granulated cells. In the follicles lined by nongranulated follicular cells, long, prominent microvilli and cytoplasmic processes protruded into the lumen. The frequency of these accumulations varies during the year in adult male animals, showing an increase in number during summer and a decrease during winter. The lowest value was registered in August (winter). The mean follicular diameter did not vary seasonally. The number of colloidal accumulations did not vary seasonally in adult female viscachas, but a significant difference in the mean follicular diameter between pregnant and non-pregnant females was observed. Pituitaries of immature animals contain fewer colloidal accumulations than those of adults. In fetuses, these accumulations were absent. The administration of melatonin provoked a decrease in the number of these structures. The numeric changes of the colloidal accumulations observed in this study are associated with: 1) the seasonal reproductive activity in adult males, and 2) the reproductive condition, body weight and sexual maturity in males and females. The fact that melatonin administration decreases the population of colloidal accumulations in males suggests participation of the pineal gland in these changes.

Rathke's pouch during autoimmune inflammation of the rat pituitary

Allergic adenohypophysitis was produced in rats by injection of anterior lobe tissue, Freund's adjuvant, and pertussis vaccine. In addition to the inflammatory changes in the parenchyma, fluid and inflammatory cells were found in the lumen of Rathke's pouch. The cells entered the lumen through small ulcers of the lining of the anterior wall of the pouch. Pituitaries with inflammation were increased in size and weight. The enlargement was caused mostly by dilation of Rathke's pouch with fluid and cells.

Human fetuin/alpha 2 HS glycoprotein in colloid and parenchymal cells in human fetal pituitary gland

An immunohistochemical study was undertaken, in an attempt to identify the acidic glycoprotein(s) present in colloid and in parenchymal cells in human fetal pituitary gland. As the colloid has been proposed to represent disintegrating cells, a series of antibodies against plasma glycoproteins and plasma proteins was applied; their presence intracellularly would generally be an indicator of plasma membrane leakage in dying parenchymal cells. In tissue sections from 9- to 20-week-old fetuses, the colloid showed prominent staining with an antibody to human fetuin/alpha 2 HS glycoprotein. Anti-alpha 2-HS glycoprotein labelled parenchymal cells in pars anterior and intermedia. Apart from a minor immunoreactivity for alpha 1 beta glycoprotein, no other plasma glycoprotein was seen in colloid or parenchymal cells. An antibody against bovine fetuin showed staining of the colloid and of some parenchymal cells in pars distalis and intermedia; the plasma and stroma of the pituitary gland were unstained. In contrast, the anti-human plasma protein antibodies all stained the stroma. The presence of alpha 2 HS glycoprotein in parenchymal cells and absence of other plasma glycoproteins imply integrity of the parenchymal cell plasma membrane. Thus, alpha 2 HS glycoprotein is either synthesized locally or taken up specifically in the parenchymal cells, which are proposed to participate in the formation of colloid. It is suggested that alpha 2 HS glycoprotein is part of a homeostatic system, which controls remodelling and physiological cell death during development.

Cystlike structures derived from the marginal cells of Rathke's cleft in rat pituitary grafts

Hemipituitary glands from 30 rats were isotransplanted under renal capsules. At 1, 2, 4, 7 and 20 days after transplantation, the grafts were examined by light and electron microscopy. Two days after transplantation, the central area of graft showed necrosis; however, the peripheral area, where marginal cells of Rathke's cleft were ingesting the remnants of necrotic glandular cells, survived. Four days after transplantation, mitotic figures of marginal cells were observed. Seven days after transplantation, the damaged area of the graft disappeared, and Rathke's cleft was completely lined by marginal cells. Remnants of necrotic glandular cells were not seen in intercellular spaces or in the cytoplasm of marginal cells. Cystlike structures formed in the grafts; some were connected to Rathke's cleft by narrow cavities. The cavity-lining cells of the cysts were agranular and similar to those that lined Rathke's cleft. At 20 days after transplantation, granular cavity-lining cells appeared. It is suggested that marginal cells of immature rats can differentiate into granular cells.

The origin of ciliated cell cysts of the anterior pituitary. An experimental study in the rat

Rats were decapitated and the heads were stored at 4 degrees C for 24 h. The anterior pituitaries were then removed and incubated for 5 days. On the 1st, 3rd and 5th days of incubation, explants were studied by electron microscopy and immunohistochemistry using antiserum against S-100 protein. In the explant many granulated cells underwent necrosis; folliculo-stellate (FS) cells formed many cyst-like structures (CLSs) and became squamous epithelioid cells (CLS-forming cells). After incubation for 5 days the explants were isotransplanted under the renal capsules of male rats in order to observe morphological changes in the CLSs. Immediately after transplantation, the CLSs were encircled by a basement membrane, but from the 8th to 14th day, ciliation occurred in CLS-forming cells and "ciliated cell cysts" were formed. The ciliated cells were immunostained with antiserum against S-100 protein. The present study suggests that FS cells are related to CLS formation and have the potential to trans-differentiate to ciliated cells.

Presence of alpha-melanocyte-stimulating hormone in bovine pituitary intraglandular colloid of intermediate lobe origin

Alpha-melanocyte-stimulating hormone (alpha-MSH), one of several peptide hormones originating in the intermediate lobe of the pituitary as proopiomelanocortin, was discovered in bovine pituitary intraglandular colloid by using radioimmunoassay. The quantity of alpha-MSH varied from 5 to 368 micrograms/mg protein in the three pools. The importance of this finding is discussed in light of the possibility that the colloid is a transport medium for alpha-MSH and other intermediate lobe hormones.

A quantitative study of pituitary colloid in the bat Myotis lucifugus lucifugus in relation to age, sex, and season

Extracellular colloid accumulations were examined in pituitary glands of adult and juvenile, male and female, little brown bats, Myotis lucifugus lucifugus (Chiroptera: Vespertilionidae), collected at various times during the annual reproductive cycle. Round or ovoid periodic acid-Schiff-reactive accumulations of colloid were scattered throughout the pars distalis, pars intermedia, and pars tuberalis. These accumulations were surrounded by processes of agranular "follicular" cells. The proportion of the volume of the pars distalis occupied by colloid (volume fraction) exhibited considerable variation among animals, ranging from 0.00 to 3.18% in the total sample of bats. Pituitaries of juvenile males, yearling males, and nonparous females contained significantly less colloid than those of parous females and adult males. The mean volume fraction for each of these groups suggested that colloid content increased progressively from birth through sexual maturity in this animal. In addition, the frequency distribution of colloid content measurements made in parous females and adult males provided indirect evidence that colloid continues to accumulate throughout life. No sexual dimorphism in colloid content was observed before or after sexual maturity, and colloid content did not fluctuate in relation to the annual reproductive cycle of either males or females.

The pituitary cleft of the rat: an electron microscopic study

The epithelium of the pituitary cleft and its colloid have been studied at the ultrastructural level in normal, adrenalectomized, castrated, dehydrated and lactating adult rats. Both control and experimental animals showed cells in different stages of degradation inside the cleft and mixed with the colloid. These exfoliated cells seems to have originated from the cleft's epithelium of the adjacent granular cells. In adrenalectomized and castrated rats the rostral epithelium of the cleft had large intercellular spaces that in some instances appeared to open directly into the cleft. Occasionally, the adenohypophysial canaliculi of the adrenalectomized rats were also seen connecting with the cleft. In lactating and castrated animals dark cells appeared more frequently in the rostral and caudal epithelium of the cleft. The results obtained suggest that the colloids is originated at least in part by involuted pituitary cells. There is also evidence that the follicular cavities of the Pars distalis and the cleft are continuous structures.

Dysontogenetic pituitary cysts (pituitary cachexia in childhood)

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