Light- and electron-microscopic immunocytochemistry of somatotropes in the anterior pituitary gland of European ferret, Mustela putorius furo

Morphology of the Pituitary Gland in Ferrets (Mustela putorius furo) with Hyperadrenocorticism

Pituitary tumours are the cause of hyperadrenocorticism in a variety of species, but the role of the pituitary gland in hyperadrenocorticism in ferrets is not known. In this species, the disease is mediated by the action of excess gonadotrophins on the adrenal cortex and is characterized by an excessive secretion of sex steroids. In this study, the pituitary gland of four healthy control ferrets, intact or neutered, and 10 neutered ferrets with hyperadrenocorticism was examined histologically following immunohistochemical labelling for adrenocorticotrophic hormone, alpha-melanocyte-stimulating hormone, growth hormone, thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, and prolactin. Immunohistochemistry revealed that somatotrophs, thyrotrophs and lactotrophs were the most abundant cell types of the pars distalis of the pituitary gland in the healthy ferrets. The distribution of corticotrophs was similar to that in the dog and man. In ferrets, as in dogs, the melanotrophic cell was almost the only cell type of the pars intermedia. Gonadotrophs were found in the pars distalis of neutered, but not intact ferrets. All the ferrets with hyperadrenocorticism had unilateral or bilateral alterations of the adrenal gland. In addition, in the pituitary gland of two of these ferrets a tumour was detected. These tumours were not immunolabelled by antibodies against any of the pituitary hormones, and had characteristics of the clinically non-functional gonadotroph tumours seen in man. In some of the other ferrets low pituitary immunoreactivity for gonadotrophic hormones was detected, which may have been due to the feedback of autonomous steroid secretion by the neoplastic transformation of the adrenal cortex. It is concluded that initially high concentrations of gonadotrophins resulting from castration may initiate hyperactivity of the adrenal cortex. The low incidence of pituitary tumours and the low density of gonadotrophin-positive cells in non-affected pituitary tissue in this study suggest that persistent hyperadrenocorticism is not dependent on persistent gonadotrophic stimulation.

Immunocytochemistry of the pars tuberalis of the pituitary gland in some Indian wild birds: a comparative study

Immunohistochemistry has been applied to the cells of the pars tuberalis (PT) of the pituitary gland of three species of Indian wild birds (Halcyon smyrnensis perpulchra, Lonchura striata striata, Dicrurus adsimilis macrocercus). As in the pars distalis (PD), five types of immunoreactive cells (gonadotropic, GTH; thyrotropic, TSH; lactotropic/prolactin, PRL; growth hormone/somatotropic, STH; and cortico-melanotropic, ACTH/MSH cells) are present in the PT of these birds. In addition to the GTH cells, immunoreactive TSH, PRL, STH, and ACTH/MSH cells are present in the avian PT. The GTH cells are the predominant cell population of the PT. Other immunoreactive cells, though less numerous, are also present, unlike their inconsistent occurrence in several mammalian PTs. Though immunologically related, the PT cells distinctly differ from their counterparts in the PD with regard to their morphology, intensity of immunoreaction, and cellular arrangement.

Immunoelectron microscopic study of the GH cell in the anterior pituitary gland of normal human fetus

BACKGROUND

Ultrastructural studies of growth hormone-producing cells (GH cells) in the anterior pituitary gland have been reported using several experimental animals. However, no attempt has yet been made to identify the ultrastructural heterogeneity of the GH cells within the human anterior pituitary gland. To this end, we employed immunogold electron microscopy to investigate the ultrastructural characteristics of GH cells in relation to gestational age in normal human fetuses.

MATERIALS

Based on ultrastructural characteristics, three distinct types of GH cells were identified by immunogold electron microscopy in the anterior pituitary glands of 34 normal human fetal pituitary glands. The age of the tissue samples ranged from 8 to 34 weeks.

RESULTS

The Type-I GH cell is a small, round cell with a narrow cytoplasm containing a few small secretory granules (268 nm in mean diameter). The GH cells designated Type-II are polygonal and contain medium-sized secretory granules (347 nm), profiles of rough endoplasmic reticulum (RER) arranged in parallel lamellae, and a Golgi complex which is frequently encountered but only in this cell type. The Type-III GH cell is polygonal, large, and contains numerous large spherical-shaped secretory granules (404 nm). The Type-I was the predominant cell type until about 20 weeks of gestation; its incidence decreased thereafter. In contrast, the Type-II and Type-III cells increased in number starting at 20 weeks of gestational age.

CONCLUSION

From these results, we suggest that Type-I is the most immature type of GH cell, Type-III the most mature, and the Type-II is intermediate in development. The marked difference in the incidence of each GH cell type between the first and second half of gestation appears to be a reflection of the development of the hypothalamic regulation of the anterior pituitary gland, which is reported to be established at around 20 weeks of gestation.