The cellular origins of corticotropin and melanotropin as revealed by immunochemical staining

Seasonal plasticity of the pituitary pars intermedia of the one-humped camel (Camelus dromedarius)

The pituitary pars intermedia of Camelus dromedarius is well developed and completely surrounds the pars nervosa. Two major groups of cells are present: endocrine (ec) and glial-like cells (glc). The ec group is composed of three morphologically distinct cell types. Type I, or polyhedral light cells (LC-I) and type II, or polyhedral dark cells (DC-II), have secretory granules of heterogeneous electron density whose size ranges from 170 to 300nm. Type III cells are elongated with homogeneous electron-dense secretory granules of 80-200nm. The glc make up an organized network, form follicles in the centrolobular zones and are positive for vimentin and S-100β immunolabelling. The nerve fibres penetrating the lobe are numerous, and can be classified into two types according to the membrane bound vesicles found in their endings (ne). Ultrastructural quantitative analysis revealed significant variations in PI elements between winter and summer seasons (F=8.014, p=0.006). DC-II cells characterized by developed biosynthetic machinery and a large pool of secretory granules storage are increased with the ne in winter. However, LC-I cells showing frequent cytoplasmic degranulation are predominant with glc in summer. Thus, important cellular remodelling occurs in the dromedary PI that may depend upon, or perhaps anticipate, external living conditions.

POMC mRNA levels in individual melanotropes and GFAP in glial-like cells in rat pituitary

In this study we demonstrated that individual melanotropes expressed differing levels of POMC mRNA. Interspersed among the melanotropes was a small population of process-bearing cells expressing GFAP. We compared cellular resolution and feasibility for quantitation of hybrids formed by oligonucleotide probes labeled with two different markers using in situ hybridization histochemistry. In hybridizations using [35S]-labeled probes the signal could not easily be assigned to individual melanotropes, although digoxigenin-labeled probes provided good cellular resolution. Heterogeneous staining intensities of individual melanotropes for POMC mRNA were measured, and relative quantitation of changes in POMC mRNA levels following interactions with the D2 dopamine receptor was performed. We combined in situ hybridization histochemistry with immunohistochemistry to demonstrate that cells within the lobe parenchyma not expressing POMC mRNA were immunoreactive for GFAP.

Immunohistochemical distribution of corticotropin-like intermediate lobe peptide (CLIP) immunoreactivity in the human brain

The immunocytochemical distribution of CLIP (corticotropin-like intermediate lobe peptide) or ACTH(18-39), a small biologically active peptide, was examined in the human brain, using a monoclonal antibody against this peptide. Groups of CLIP-immunoreactive cell bodies, small to medium size and bipolar or triangular in shape, were found in the basal hypothalamus extending from the retrochiasmatic region to the premammillary nuclei area. Immunoreactive fibers with varicosities, terminals and "pipe shape" structures, were distributed within the hypothalamus, limbic structures, the brainstem and spinal cord nuclei, forming a particularly rich network in the hypothalamus, the preoptic area, the septal region, the amygdala and the upper brainstem periaqueductal gray matter. The above neuroanatomical observations confirm and extend previous findings in animals, strengthening even more the possibility that this peptide may be involved in numerous behavioral, autonomic and physiological functions such as regulation of sleep-waking cycle, pain control and respiratory and cardiovascular regulation.

The morphological effects of dexamethasone on the pituitary-adrenal axis of the rat--a quantitative study

Adult Sprague-Dawley rats received a daily intraperitoneal injection of dexamethasone (100 or 200 micrograms/kg) for 2 or 6 weeks. Quantitative assessment of the anterior pituitary corticotroph population performed using the stereological measurement of volume density (Vv). An indirect assessment of corticotroph function was also made, based on adrenal weight and histology. Adrenal changes were consistent with dose-related inhibition of corticotroph function in all dexamethasone-treated animals. Immunopositive corticotrophs were easily identified and in no treatment group was corticotroph Vv significantly less than in the appropriate vehicle-injected control group. In male animals, there was a significant increase (P less than 0.05) in Vv with 100 micrograms/kg at both 2 and 6 weeks. These results suggest that it is possible to produce inhibition of corticotroph function by the administration of such doses of dexamethasone without causing a significant reduction in the anterior pituitary corticotroph population. This may be related to the mode of negative feedback of such a regime.

Adrenocorticotropic hormone (ACTH) in pituitary colloid and extrapituitary tissues

The level of ACTH in bovine pituitary intraglandular colloid (IGC/ACTH), the holocrine secretion of the marginal half of the intermediate lobe (IL) cells, was found to correlate with the concentration of this peptide in blood plasma (BP/ACTH), cerebrospinal fluid (CSF/ACTH), the paraventricular nuclei (PVN/ACTH) and the arcuate nuclei (AN/ACTH). The ACTH content in all sites was measured by radioimmunoassay (RIA). Although the IL is virtually avascular, the intraglandular lumen housing the IGC communicates nonetheless with the venous cavernous sinuses as well as the subarachnoid cerebral spinal fluid (CSF). Therefore, we content that the IGC serves as a transport medium whereby IL materials gain access to these extrapituitary sites.

Regulation of pro-opiomelanocortin gene transcription in individual cell nuclei

A nonrepetitive complementary RNA probe specific for an intervening sequence of the rat pro-opiomelanocortin (POMC) gene primary transcript was used to analyze the hormonal regulation of POMC gene transcription in individual cell nuclei in the rat pituitary by in situ hybridization. This probe recognized only full-length POMC heterogeneous nuclear RNA, as verified by Northern blots of pituitary RNA. When pituitary sections were hybridized with this 3H-labeled POMC intron A probe, silver grains were predominantly localized over the nuclei of cells that expressed POMC in the anterior and intermediate lobes. Adrenalectomy increased both the average grain density over corticotroph nuclei and the number of cells in the anterior pituitary with significant numbers of silver grains over their nucleus. Dexamethasone administration to intact or adrenalectomized rats results in the rapid (within 30 minutes) disappearance of silver grains over the nuclei of corticotrophs in the anterior lobe, suggesting that POMC gene transcription had been inhibited. However, adrenalectomy or dexamethasone administration did not alter the silver grain density over nuclei of intermediate lobe melanotrophs. Thus, this in situ hybridization assay utilizing an intervening sequence-specific POMC probe can measure rapid physiological changes in POMC heterogeneous nuclear RNA in individual cell nuclei.

Immunohistochemical demonstration of TSH-, LH- and ACTH-cells in the hypophysis of tadpoles of Xenopus laevis D

By use of the immunofluorescence technique TSH-, LH- and ACTH-cells were localized in the hypophysis of tadpoles of Xenopus laevis. The first signs of the activity of these cells were observed in early stages of the development, i.e., stage 39 for ACTH, and stage 42 for TSH and LH.

A quantitative approach to trace the corticotrophs in culture after adrenalectomy

Anterior pituitaries of adrenalectomized and sham operated adult rats were dispersed by trypsin and cultured for 4 and 8 days. Adrenalectomy caused a moderate increase in number of corticotrophs in both zero-time cell suspensions and cultures. There was a pronounced elevation of immunoreactive ACTH content in both cells and media and an enhanced secretory response to stimulation of cultures with stalk-median eminence extract containing cortiocotropin releasing (CRF) activity. Some cells identified as corticotrophs by a specific immunostaining incorporated tritiated thymidine into their nuclei suggesting their ability to enter the cell cycle. The relatively smaller increase in number of ACTH cells and the considerably higher ACTH producing capacity of the corticotrophs after adrenalectomy seem to be inconsistent with the quantal response model of hormone secretion recently introduced by Rodbard.

The utility of antisera to different synthetic adrenocorticotrophins (ACTH) and melanotrophins (MSH) for immunocytochemical staining of the dog pituitary gland

Using the immunoperoxidase technique and specific antisera to synthetic ACTH beta (1-24), ACTH beta (17-39) and bMSHbeta1, selective immunocytochemical staining was localized in a distinctive cell type in the pars distalis and pars tuberalis of the dog pituitary gland. Except for a rare cell, the pars distalis and pars tuberalis did not stain with an anti-bMSH alpha serum. In the pars intermedia immunoreactive cells containing ACTH beta(1-24), ACTHbetap(17-39), bMSHbeta and/or bMSH alpha were observed. The specificity and validity of the antisera were demonstrated by elimination of their immunostaining capacity after prior absorption with their respective antigens, while absorption with other antigens failed to decrease staining intensity. The cytoplasm of the ACTH/MSH cells showed a positive reaction to periodic-acid-Schiff and assumed a pale aniline blue colour, whilst the granules were stained with carmoisine L and acid alizarine blue. These ACTH/MSH cells were further differentiated from other functional cell types of the pars distalis on the basis of their typical cytological features, intraglandular distribution and by immunochemical double staining. It is concluded that ACTH and MSH beta were present and most probably produced by the corticomelanotrophs of the pars distalis and pars tuberalis. In addition to corticomelanotrophs analogous to those of the pars distalis and pars tuberalis, the pars intermedia showed many cells which contain MSH alpha alone or together with MSH beta and/or ACTH.

Incorporation of regulatory peptide hormones by individual cells of the adrenal cortex: prolactin-adrenocorticotrophin differences

Recent refinements in methodology now permit the study of endogenous peptide hormones in their individual target cells. The investigations reported here deal with the question of whether endogenous ACTH can be detected in its target cells in the highly active adrenal gland of the normally lactating rat. This question was examined with immunohistochemistry. ACTH was found in both cytoplasm and nuclei of adrenal glomerulosa cells. In cells of the fasciculata and reticularis layers of the adrenal cortex, it did not appear inside nuclei but was present in the cytoplasm and on the nuclear envelope. The distribution of ACTH was compared with and found to be different from that of PRL. PRL, confirming previous findings, was not detectable at all in glomerulosa cells and, in cells of the inner cortical zones, was present in both cytoplasm and nuclei. In neither case was hormone found in the adrenal medulla. The apparent feasibility of studying peptide regulators such as ACTH and PRL in their individual target cells may be a focal point for an acceleration of our understanding of how these peptides work.

Cytology and distribution of secretory cell types in the mouse hypophysis as demonstrated with immunocytochemistry

Since differential chemical staining has been unsatisfactory for demonstration of specific secretory cell types in the hypophyseal pars distalis of the mouse, the objective of this study was to determine whether the peroxidase-antiperoxidase immunocytochemical procedure might be more effective. Accordingly, representative sections from the hypophyses of 17 female and 15 male adult mice of the Swiss-Webster strain were immunostained, 16 antisera to 5 pituitary hormones or their subunits being utilized. Five secretory cell types were demonstrated. Somatotropes were ovoid to spheroidal and distributed quite generally in the gland except for the "sex zone" where they were scarce. Somatotropes were larger and more numerous in the male than in the female. Mammotropes were polyhedral and also generally distributed in the gland except for the "sex zone" where few were observed. Mammotropes were larger and more numerous in the female than in the male. Corticotropes were small, stellate and few. They were most common near the ventral surface of the gland and formed bilateral centromedial groups in the lateral wings. Thyrotropes were usually large and polyhedral. They were restricted almost solely to the ventral region of the pars distalis. Gonadotropes were polyhedral, and generally distributed, except for aggregation in the cephalomedian "sex zone." Most gonadotropes appeared to contain both luteinizing hormone and follicle-stimulating hormone. Thus, all secretory cell types recognized in other species can be demonstrated readily in the mouse hypophysis with immunocytochemistry.

An immunocytochemical study of human pituitary mammotropes from fetal life to old age

The objectives were to (a) describe the cytology and distribution of mammotropes in the human pituitary gland, (b) determine whether the mammotrope is a distinctive secretory cell type and (c) ascertain when it first appears in the fetal hypophysis. Identification of mammotropes was based primarily on the Sternberger peroxidase-antiperoxidase immunocytochemical method used with an antiserum to human prolactin. Hypophyses from 25 male and 6 female adults, and 21 fetuses ranging in gestational age from 6 to 23 weeks were studied. In the adult two morphological forms of mammotropes were observed. Mammotrope I possessed a small perikaryon that commonly was located centrally in parenchymal cell cords. From the perikaryon long cytoplasmic processes extended toward neighboring capillaries. Mammotrope I reached its highest incidence in the posterolateral zones of the pars distalis. Mammotrope II possessed a larger perikaryon with short processes; cells of this form were fewer and occurred chiefly in the anteromedian zone. Mammotropes with intermediate morphological features that prevented classification into categories I or II were common in some hypophyses. Both forms of mammotropes were present prepuberally (one 6-week and one 9-year-old male) and in adult males and females. Mammotropes were only slightly more prominent in females than males. Regression of mammotropes was evident in old age. Mammotropes were distinctly different from somatotropes, corticotropes, gonadotropes and thyrotropes. In the fetal hypophysis mammotropes appeared first at 14 weeks of gestational age and remaind few through 16.5 weeks. Their number increased greatly at 23 weeks.

Observations on the functional cytochemistry of pars intermedia of the rat hypophysis

Light and electron microscopic histochemical reactions were studied in the cells of pars intermedia of the rat. The possible correlations between enzymatic reactions and endocrine functions of these cells were discussed. By combined formaldehyde and chloral vapour treatment the cells of the pars intermedia exhibited a strong yellow fluorescence suggesting the presence of a peptide or peptides with NH2-terminal tryptophan. Masked metachromasia after acid hydrolysis was probably due to these peptides. Only a weak or no alpha-glycerophosphate dehydrogenase and nonspecific esterase activity was observed in the cells of pars intermedia compared to the cells of pars distalis suggesting low production rate of hormone synthesis. Specific and non-specific cholinesterases were demonstrated light and electron microscopically constantly in the cells bordering the lobules. These cells probably represent a certain type of glial cells. In the other cells the enzymatic activities varied markedly in intensity and distribution showing different ultrastructural localizations. Thus cholinesterase activities in the cells of pars intermedia reflect possibly different functional stages of the cells in their hormone production, storage and secretion processes.

Corticotroph cells in primary cultures of rat adenohypophysis: a light and electron microscopic immunocytochemical study

Monolayer cultures of trypsin-dispersed cells of the rat adenohypophysis were grown for 5 to 54 days. ACTH was localized by immunocytochemistry using an antiserum to synthetic ACTH1-28 prepared in rabbit and sheep anti-goat immunoglobulin coupled with peroxidase. ACTH content of the culture medium was measured by radioimmunoassay. Corttion time. The corticotrophs retained their essential morphological characteristics. Immunological staining was found in the secretory granules, some tubular or saccular structures, parts of the rough endoplasmic reticulum, and the cytoplasmic matrix. Immature secretory granules in the Golgi apparatus as well as some Golgi elements showed different degrees of immunoreactivity. In agreement with the high ACTH content of the culture medium the number, size and shape of the secretory granules, the active Golgi apparatus, the high amount of extragranular ACTH as well as pictures suggesting granule extrusion claim for a high ACTH synthesis and transport (and low ACTH storage) in the cultured corticotrophs.

Electron microscope studies on the intermediate lobe of the embryonic mouse

The development of the intermediate lobe of the hypophysis was studied in the embryonic C3H mouse; at least four glands from embryos of every gestational day from 15 to 19 were examined. In the 16 day-old embryo prospective secretory cells proliferate at the centre of the intermediate lobe anlage. At the same stage cylindrical cells bordering the hypophyseal cleft begin to reorganize into marginal cells. By the end of fetal life marginal cells are well differentiated. In the 17 day-old embryo a few granular inclusions appear in some centrally located cells. Secretory cells increase in number during the following two embryonic days. Some of these cells contain polymorphic populations of granular and vesicular inclusions by gestational day 19. The possibility of a dual formation of secretory inclusions is discussed. The result implies that the onset of granule-formation by these cells is not contemporaneous with the start of production of melanophore-expanding substances, the presence of which has been detected by earlier biological assays.

Light and electron microscope localization of binding sites of antibodies against ovine luteinizing hormone and its two subunits in rat adenohypophysis using peroxidase-labeled antibody technique

The binding sites of antisera generated in the guinea pig against ovine luteinizing hormone (oLH) and its two subunits (oLHalpha and oLHbeta) have been localized in rat anterior pituitaries taken from normal or castrated males and from ovariectomized females with the peroxidase-labeled antibody method, using light and electron microscopy. With the light microscope, the cells positive with antiserum to ovine luteinizing hormone (A-oLH) were violet after the Alcian blue-periodic acid-Schiff (AB-PAS) staining; they were also positive for A-oLHalpha and for A-oLHbeta and, from castrated males, they displayed an increased affinity for A-oLHbeta. Another cell type which was blue after the AB-PAS method reacted with the A-oLHalpha only; these cells, presumably thyrotropic cells, were retracted after castration and, besides their affinity for A-oLHalpha, acquired an affinity for A-oLHbeta. As seen through the electron microscope, two cell types were positive for A-oLH, A-oLHbeta, and A-oLHalpha and may be identified as luteinizing hormone-secreting cells. Type A cells were characterized by two classes of rounded, secretory granules. Type B cells were smaller and contained only small secretory granules. 1 mo after the rats were castrated the type A cells were hypertrophied and vacuolized. In both cases the secretory granules were the main sites of the antigenicity with the three antisera. A positive reaction was also found in the cytoplasm, particularly in hypertrophied cells from ovariectomized females and with A-oLHbeta. The cisternae of the rough endoplasmic reticulum were usually negative, except in highly degranulated cells from ovariectomized females and with A-oLHbeta.