Immunocytochemical distribution of somatotrophs in porcine anterior pituitary

Anatomy and histology of the Göttingen minipig adenohypophysis with special emphasis on the polypeptide hormones: GH, PRL, and ACTH

The pituitary is involved in the regulation of endocrine homeostasis. Therefore, animal models of pituitary disease based on a thorough knowledge of pituitary anatomy are of great importance. Accordingly, we aimed to perform a qualitative and quantitative description of polypeptide hormone secreting cellular components of the Göttingen minipig adenohypophysis using immunohistochemistry and stereology. Estimates of the total number of cells immune-stained for adrenocorticotrophic hormone (ACTH), prolactin (PRL), and growth hormone (GH) were obtained with the optical fractionator technique using Stereo Investigator software. Moreover, 3D reconstructions of cell distribution were made. We estimated that the normal minipig adenohypophysis contains, on average, 5.6 million GH, 3.5 million PRL, and 2.4 million ACTH producing cells. The ACTH producing cells were widely distributed, while the PRL and GH producing cells were located in clusters in the central and lateral regions of the adenohypophysis. The morphology of the hormone producing cells also differs. We visualized a clear difference in the numerical density of hormone producing cells throughout the adenohypophysis. The relative proportions of the cells analyzed in our experiment are comparable to those observed in humans, primates, and rodents; however, the distribution of cells differs among species. The distribution of GH cells in the minipig is similar to that in humans, while the PRL and ACTH cell distributions differ. The volume of the pituitary is slightly smaller than that of humans. These data provide a framework for future large animal experimentation on pituitary function in health and disease.

A new method for physical disector analyses of numbers and mean volumes of immunohistochemically labeled cells in paraffin sections

BACKGROUND

In the neurosciences, the physical disector method represents an established quantitative stereological method for unbiased sampling and counting of cells in histological tissue sections of known thickness. Physical disector analyses are conventionally performed using plastic-embedded tissue samples, because plastic-embedding causes a comparably low and definable shrinkage of the embedded tissue, and the thickness of thin plastic sections can be determined adequately. However, immunohistochemistry protocols often don't work satisfactorily in sections of plastic-embedded tissue.

NEW METHOD

Here, a new methodological approach is presented, allowing for physical disector analyses of immunohistochemically labeled cells in paraffin sections. The embedding-related tissue shrinkage is standardized by using defined tissue sample volumes and paraffin volumes, and the extent of tissue shrinkage can be determined accurately from the sample volumes prior to and after embedding. Co-embedding of polyethylene section thickness standards together with the tissue samples allows the precise determination of individual paraffin section thicknesses by spectral reflectance measurements.

RESULTS AND COMPARISON WITH EXISTING METHOD(S)

The applicability of the new method is demonstrated by physical disector analysis of immunohistochemically identified somatotroph cells in paraffin sections of porcine pituitary gland tissue. With consideration of individual shrinkage factors and section thicknesses, the cell numbers and mean volumes estimated in paraffin disector sections do not significantly differ from the results obtained by analyses of plastic-embedded pituitary tissue samples of the identical animals (2.4% average difference).

CONCLUSIONS

The featured method enables combination of paraffin section immunohistochemistry and physical disector analyses for unbiased quantitative stereological analyses of different cell types.

Linkage between growth retardation and pituitary cell morphology in a dystrophin-deficient pig model of Duchenne muscular dystrophy

OBJECTIVE

Human patients with Duchenne muscular dystrophy (DMD) commonly exhibit a short stature, but the pathogenesis of this growth retardation is not completely understood. Due to the suspected involvement of the growth hormone/insulin-like growth factor 1 (GH/IGF1) system, controversial therapeutic approaches have been developed, including both GH- administration, as well as GH-inhibition. In the present study, we examined relevant histomorphological and ultrastructural features of adenohypophyseal GH-producing somatotroph cells in a porcine DMD model.

METHODS

The numbers and volumes of immunohistochemically labelled somatotroph cells were determined in consecutive semi-thin sections of plastic resin embedded adenohypophyseal tissue samples using unbiased state-of-the-art quantitative stereological analysis methods.

RESULTS

DMD pigs displayed a significant growth retardation, accounting for a 55% reduction of body weight, accompanied by a significant 50% reduction of the number of somatotroph cells, as compared to controls. However, the mean volumes of somatotroph cells and the volume of GH-granules per cell were not altered. Western blot analyses of the adenohypophyseal protein samples showed no differences in the relative adenohypophyseal GH-abundance between DMD pigs and controls.

CONCLUSION

The findings of this study do not provide evidence for involvement of somatotroph cells in the pathogenesis of growth retardation of DMD pigs. These results are in contrast with previous findings in other dystrophin-deficient animal models, such as the golden retriever model of Duchenne muscular dystrophy, where increased mean somatotroph cell volumes and elevated volumes of intracellular GH-granules were reported and associated with DMD-related growth retardation. Possible reasons for the differences of somatotroph morphology observed in different DMD models are discussed.

Two types of rat pituitary somatotrophs secrete growth hormone with different biological and immunological profiles

OBJECTIVE

Two stable subpopulations of somatotrophs reside in the rat pituitary gland. We tested the hypothesis that one produced growth hormone (GH) with greater activity when tested in the tibial line bioassay (BGH) than the other, while differences in the activities between the two groups would be less dramatic when measured by immunoassay (IGH).

DESIGN

A series of studies using hypophysectomized rats, hollow fibers, treatments and culture models were used to differentiate differences in Type I and Type II anterior pituitary somatotrophs in both function and production of immunoactive and bioactive growth hormone.

RESULTS

We found that dense, Type II somatotrophs (>1.070g·cm^-3) differed markedly in their secretion patterns of IGH vs BGH in different In vitro and in vivo tests. In culture, Type II cells secreted five times as much BGH, and three fourths as much IGH as the less dense Type I cells. Production (storage and secretion) of BGH was 7-fold greater by Type II cells whereas IGH production was identical for the two cell types. Implantation of Type II cells into hypophysectomized rats significantly increased body weight, epiphyseal cartilage thickness, and muscle weight of the recipients; in contrast, Type I cells elicited only a small increase in body weight. Type I somatotrophs isolated from rats which had been previously fasted or insulin-treated subsequently showed only small, inconsistent changes in release relative to that from cells in the unfractionated cell population. However, release of BGH from the Type II cells was markedly decreased.

CONCLUSION

Both IGH and BGH should be considered in the elucidation of GH physiology.

Resistance exercise induces region-specific adaptations in anterior pituitary gland structure and function in rats

The anterior pituitary gland (AP) increases growth hormone (GH) secretion in response to resistance exercise (RE), but the nature of AP adaptations to RE is unknown. To that end, we examined the effects of RE on regional AP somatotroph GH release, structure, and relative quantity. Thirty-six Sprague-Dawley rats were assigned to one of four groups: 1) no training or acute exercise (NT-NEX); 2) no training with acute exercise (NT-EX); 3) resistance training without acute exercise (RT-NEX); 4) resistance training with acute exercise (RT-EX). RE incorporated 10, 1 m-weighted ladder climbs at an 85° angle. RT groups trained 3 days/wk for 7 wk, progressively. After death, trunk blood was collected, and each AP was divided into quadrants (ventral-dorsal and left-right). We measured: 1) trunk plasma GH; 2) somatotroph GH release; 3) somatotroph size; 4) somatotroph secretory content; and 5) percent of AP cells identified as somatotrophs. Trunk GH differed by group (NT-NEX, 8.9 ± 2.4 μg/l; RT-NEX, 9.2 ± 3.5 μg/l; NT-EX, 15.6 ± 3.4 μg/l; RT-EX, 23.4 ± 4.6 μg/l). RT-EX demonstrated greater somatotroph GH release than all other groups, predominantly in ventral regions (P < 0.05-0.10). Ventral somatotrophs were larger in NT-EX and RT-NEX compared with RT-EX (P < 0.05-0.10). RT-NEX exhibited significantly greater secretory granule content than all other groups but in the ventral-right region only (P < 0.05-0.10). Our findings indicate reproducible patterns of spatially distinct, functionally different somatotroph subpopulations in the rat pituitary gland. RE training appears to induce dynamic adaptations in somatotroph structure and function.

Immunohistochemical study of somatotrophs in pituitary pars distalis of male viscacha (Lagostomus maximus maximus) in relation to the gonadal activity

Somatotrophs were identified and quantified in pituitary pars distalis of male viscachas (Lagostomus maximus maximus) during the annual reproductive cycle, after the administration of melatonin, after castration and in different growth stages by immunohistochemistry and morphometric analysis. In adult male viscachas, the somatotrophs were distributed throughout the pars distalis during the reproductive cycle. They were oval, pyramidal or round in shape with a large round nucleus. The percentage immunopositive area, the major cellular diameter and the number of cells decreased during the gonadal regression period in relation to the values found in the reproductive period. The administration of melatonin did not provoke any variations of the morphometric parameters studied. On the contrary, a significant decrease in the percentage immunopositive area, in the major cellular diameter and in the number of somatotrophs in castrated viscachas was observed. The study of different growth stages showed that these morphometric parameters increased from immature to adult animals in the reproductive period. The results obtained suggested that the variations of the morphometric parameters of somatotrophs are more related to the gonadal development and activity than to a direct effect of melatonin.

Recent progress in histochemistry and cell biology: the state of the art 2005

Advances in the field of histochemistry, a multidisciplinary area including the detection, localization and functional characterization of molecules in single cells and complex tissues, often drives the attainment of new knowledge in the broadly defined discipline of cell biology. These two disciplines, histochemistry and cell biology, have been joined in this journal to facilitate the flow of information with celerity from technical advancement in histochemical procedures, to their utilization in experimental models. This review summarizes advancements in these fields during the past year.

Physiology of ghrelin and related peptides

Growth hormone (GH) released from pituitary under direct control of hypothalamic releasing (i.e., GHRH) and inhibiting (i.e., sst or SRIF) hormones is an anabolic hormone that regulates metabolism of proteins, fats, sugars and minerals in mammals. Cyril Bowers' discovery of GH-releasing peptide (GHRP-6) was followed by a search for synthetic peptide and nonpeptide GH-secretagogues (GHSs) that stimulate GH release, as well as a receptor(s) unique from GHRH receptor. GHRH and GHSs operate through distinct G protein-coupled receptors to release GH. Signal transduction pathways activated by GHS increase intracellular Ca2+ concentration in somatotrophs, whereas GHRH increases cAMP. Isolation and characterization of ghrelin, the natural ligand for GHS receptor, has opened a new era of understanding to physiology of anabolism, feeding behavior, and nutritional homeostasis for GH secretion and gastrointestinal motility through gut-brain interactions. Other peptide hormones (i.e., motilin, TRH, PACAP, GnRH, leptin, FMRF amide, galanin, NPY, NPW) from gut, brain and other tissues also play a role in modulating GH secretion in livestock and lower vertebrate species. Physiological processes, such as neurotransmission, and secretion of hormones or enzymes, require fusion of secretory vesicles at the cell plasma membrane and expulsion of vesicular contents. This process for GH release from porcine somatotrophs was revealed by atomic force microscopy (AFM), transmission electron microscopy (TEM) and immunohistochemical distribution of the cells in pituitary during stages of development.

News and views in Histochemistry and Cell Biology

Advances in histochemical methodology and ingenious applications of novel and improved methods continue to confirm the standing of morphological means and approaches in research efforts, and contribute significantly to increasing our knowledge about structures and functions in all areas of the life sciences from cell biology to pathology. Reports published during recent months documenting this progress are summarized in the present review.