Interrenal tissue, chromaffin cells and corpuscles of Stannius of Nile tilapia (Oreochromis niloticus).

Twenty-three fishes were used to study the structure and ultrastructure of interrenal tissue, chromaffin cells and corpuscles of Stannius of Nile tilapia. The interrenal tissue and chromaffin cells are present within the head kidney. The interrenal tissue is arranged in the form of highly convoluted cords, bordered by the lining endothelium of the adjacent sinusoids. It has no connective tissue capsule. The cytoplasm of the interrenal cells contains abundance of mitochondria, vacuoles and smooth endoplasmic reticulum, characterizing of steroid-producing tissues. Two types of chromaffin cells; noradrenaline (NA) cells and adrenaline cells (A) could be recognized by light microscope using chromaffin reaction, as well as by electron microscope they could be distinguished depending on the size and electron density of their granules. The corpuscles of Stannius are two in number and located on the dorsal aspect of the tail kidney. Each corpuscle is surrounded by thick connective tissue capsule. The parenchyma is divided into lobules, each of which is surrounded by distinct basal lamina and has a pseudo lumen. Depending on the presence of secretory granules and the relative abundance of cell organelles, three cell types could be recognized; granular cell, agranular cell (Type I) and agranular cell (Type II). In conclusion, the morphological and ultrastructural analysis of the endocrine tissues of the kidney of Nile tilapia has revealed only one type of interrenal cells, two types of chromaffin cells and three staged-cells of Stannius corpuscles.

Long-term storage of endocrine tissues at - 80°C does not adversely affect RNA quality or overall histomorphology.

BACKGROUND: Today, no consensus exists regarding how human tissues are best preserved for long-term storage. Very low temperature storage in liquid nitrogen is often advocated as the superlative method for extended periods, but storage in -80 degrees Celsius (-80°C) freezers, while sometimes debated, is a possible alternative. RNA is the most easily degradable component of a biological sample in a molecular biology context and the quality can reliably be measured. AIM: To investigate to what extent long-term storage of tissues in -80°C affects the RNA quality and overall histomorphology. The tissue storage period represents nearly three decades (1986-2013). METHODS: RNA extraction from 153 tissue samples with different storage periods was performed with the mirVana kit (Invitrogen). RNA integrity was assessed using an Agilent bioanalyzer to obtain RNA integrity numbers (RIN). Further, tissue representative testing using light microscopy was performed by two pathologists to assess tissue composition and morphology. RESULTS: RIN values were measured in all samples, showing a variability that did not correlate with the storage time of the tissues. Microscopically, all samples displayed acceptable tissue morphology regardless of storage time. CONCLUSION: Long-term storage in -80°C does not adversely affect the quality of the RNA extracted from the stored tissues, and the tissue morphology is maintained to a good standard.

Ultrastructural analysis of the dorsal body gland of the terrestrial snail Megalobulimus abbreviatus (Becquaert, 1948) / Análise ultraestrutural da glândula corpo dorsal do caracol terrestre Megalobulimus abbreviatus (Becquaert, 1948)

The ultrastructure of the reproductive gland, dorsal body (DB), of Megalobulimus abbreviatus was analysed. Electron microscope immunohistochemistry was used to detect FMRFamide-like peptides in the nerve endings within this gland. Nerve backfilling was used in an attempt to identify the neurons involved in this innervation. In M. abbreviatus, the DB has a uniform appearance throughout their supraesophageal and subesophageal portions. Dorsal body cells have several features in common with steroid-secreting gland cells, such as the presence of many lipid droplets, numerous mitochondria with tubular cristae and a developed smooth endoplasmic reticulum cisternae. Throughout the DB in M. abbreviatus numerous axonal endings were seen to be in contact with the DB cells exhibiting a synaptic-like structure. The axon terminals contained numerous electron-dense and scanty electron-lucid vesicles. In addition, the DB nerve endings exhibited FMRFamide immunoreactive vesicles. Injection of neural tracer into the DB yielded retrograde labelling of neurons in the metacerebrum lobe of the cerebral ganglia and in the parietal ganglia of the subesophageal ganglia complex. The possibility that some of these retrograde-labelled neurons might be FMRFamide-like neurons that may represent a neural control to the DB in M. abbreviatus is discussed.

Foi analisada a ultraestrutura da glândula reprodutiva corpo dorsal (CD) de Megalobulimus abbreviatus. Imunoistoquímica para microscopia eletrônica foi utilizada para detectar peptídeos relacionados ao tetrapeptídeo FMRFamida nas terminações axonais existentes nessa glândula. Foi utilizada marcação neuronal retrógada com o intuito de localizar os neurônios envolvidos nesta inervação. O CD de M. abbreviatus possui um aspecto uniforme em toda sua extensão, tanto na porção supraesofágica como subesofágica. As células do CD possuem várias características de glândulas esteroidogênicas, tais como a presença de inúmeras gotículas lipídicas, numerosas mitocôndrias com cristas tubulares e cisternas bem desenvolvidas de retículo endoplasmático liso. Por toda a extensão do CD de M. abbreviatus foram encontradas numerosas terminações axonais fazendo contatos estruturalmente semelhantes a sinapses com as células do CD. As terminações axonais continham grande número de vesículas eletrodensas e esparsas vesículas eletrolúcidas. As terminações axonais no CD apresentavam vesículas com conteúdo imunorreativo à FMRFamida. A injeção de traçador neural no CD resultou em marcação retrógrada de neurônios no metacérebro dos gânglios cerebrais e nos gânglios parietais do complexo ganglionar subesofágico de M. abbreviatus. É discutida a possibilidade de que estes neurônios identificados por marcação retrógrada possam representar a via de controle neural do CD de M. abbreviatus, cujo mediador químico seria um neuropeptídeo relacionado à FMRFamida.

Ultrastructural analysis of the dorsal body gland of the terrestrial snail Megalobulimus abbreviatus (Becquaert, 1948).

The ultrastructure of the reproductive gland, dorsal body (DB), of Megalobulimus abbreviatus was analysed. Electron microscope immunohistochemistry was used to detect FMRFamide-like peptides in the nerve endings within this gland. Nerve backfilling was used in an attempt to identify the neurons involved in this innervation. In M. abbreviatus, the DB has a uniform appearance throughout their supraesophageal and subesophageal portions. Dorsal body cells have several features in common with steroid-secreting gland cells, such as the presence of many lipid droplets, numerous mitochondria with tubular cristae and a developed smooth endoplasmic reticulum cisternae. Throughout the DB in M. abbreviatus numerous axonal endings were seen to be in contact with the DB cells exhibiting a synaptic-like structure. The axon terminals contained numerous electron-dense and scanty electron-lucid vesicles. In addition, the DB nerve endings exhibited FMRFamide immunoreactive vesicles. Injection of neural tracer into the DB yielded retrograde labelling of neurons in the metacerebrum lobe of the cerebral ganglia and in the parietal ganglia of the subesophageal ganglia complex. The possibility that some of these retrograde-labelled neurons might be FMRFamide-like neurons that may represent a neural control to the DB in M. abbreviatus is discussed.

The frontal gland in workers of Neotropical soldierless termites.

The presence of the frontal gland is well established in termite soldiers of Rhinotermitidae, Serritermitidae, and Termitidae. It is one of their main defensive adaptations or even an exclusive weapon. The gland was also occasionally reported in alate imagoes, but never in the worker caste. Here, we report the first observation of a frontal gland in workers of several Neotropical and one African species of Apicotermitinae. The ultrastructure of Aparatermes cingulatus and Anoplotermes nr. subterraneus is described in detail. In these two species, the gland is well-developed, functional and consists of class 1 secretory cells. The presence of envelope cells, wrapping the gland, is an unusual feature, as well as the presence of several zonulae adherens, connecting neighbouring glandular cells. The frontal gland of workers is homologous to this organ in soldiers and imagoes, as evidenced by the same position in the head and its connection to the same muscle. However, the defensive role of the frontal gland in workers remains to be confirmed.

Fine structure of the antennal glands of the ant nest beetle Paussus favieri (Coleoptera, Carabidae, Paussini).

The antennae of the ant nest beetle Paussus favieri are studied by using both SEM and TEM. In the myrmecophilous genus Paussus, these structures are composed of three joints: scape, pedicel and a wide third joint, the "antennal club", resulting from the fusion of antennomeres A3-A11 (flagellum). The antennal club shows an exceptional glandular activity, with the presence of pores mostly crowded in special hairless cuticular areas, surrounding the base of single setae, grouped at the base of tufts of setae, or positioned inside deep pockets that store the secretions, with filiform material arising from them. The surface of A1 and A3 are covered by mechanoreceptors, modified to spread the glandular exudates, while the chemoreceptors are restricted to the apex of the club. The fine structural analysis shows a great number of antennal glands, that can be referred to three main typologies: type A (GhA) bi-cellular, composed of a large secretory cell and a small duct cell, positioned close to the antennal surface; type B (GhB), tri-cellular, composed of two secretory cells and one duct cell, less frequent and positioned deep inside the antennal club; type C (GhC), rare, located deeply within the antennal lumen, in the vicinity of the trophocytes. This complexity indicates that more than one substance could be released from the antennae. Possible functional aspects of the secretions dealing with symbiotic interaction with the host ants are discussed.

Automated microscopic quantification of adipogenic differentiation of human gland stem cells.

Detection of differentiation in general and adipogenesis specifically is conventionally practised by taking only the few cells into account which are visible in the field of view provided by optical microscopy using high-resolution objectives. Other methods of quantification of adipogenic differentiation such as real time PCR, measurement of glycerophosphate dehydrogenase activity or adipogenesis assays only provide integral information lacking spatial resolution and information on the fraction of differentiated cells. Here we used high-resolution scanning and automated image processing to automatically analyze and quantify cell numbers in the range of 20,000. For optimisation of the approach, human gland stem cells (GSC) were differentiated to the adipogenic phenotype comprising inclusion of lipid vesicles. Oil red O and 4',6'-diamidino-2-phenylindole (DAPI) staining made it possible to derive the number of differentiated cells in relation to the total number of cells. For evaluation of the image processing software we verified our results using adipogenesis assay and phase contrast based cell counting. We developed a method of determining differentiation efficiencies covering the range from 10% down to 100ppm with the same image processing and an identical set of parameters, matching the results of the adipogenesis assay. Our approach is based on a statistically significant number of cells and shows high sensitivity taking into account the heterogeneous differentiation pattern of adipogenesis in GSC and other stem cells.

Aquaporin 1 is important for maintaining secretory granule biogenesis in endocrine cells.

Aquaporins (AQPs), a family of water channels expressed in epithelial cells, function to transport water in a bidirectional manner to facilitate transepithelial fluid absorption and secretion. Additionally, AQP1 and AQP5 are found in pancreatic zymogen granules and synaptic vesicles and are involved in vesicle swelling and exocytosis in exocrine cells and neurons. Here, we show AQP1 is in dense-core secretory granule (DCSG) membranes of endocrine tissue: pituitary and adrenal medulla. The need for AQP1 in endocrine cell function was examined by stable transfection of AQP1 antisense RNA into AtT20 cells, a pituitary cell line, to down-regulate AQP1 expression. These AQP1-deficient cells showed more than 60% depletion of DCSGs and significantly decreased DCSG protein levels, including proopiomelanocotin/pro-ATCH and prohormone convertase 1/3, but not non-DCSG proteins. Pulse-chase studies revealed that whereas DCSG protein synthesis was unaffected, approximately 50% of the newly synthesized proopiomelanocortin was degraded within 1 h. Low levels of ACTH were released upon stimulation, indicating that the small number of DCSGs that were made in the presence of the residual AQP1 were functionally competent for exocytosis. Analysis of anterior pituitaries from AQP1 knockout mice showed reduced prohormone convertase 1/3, carboxypeptidase E, and ACTH levels compared to wild-type mice demonstrating that our results observed in AtT20 cells can be extended to the animal model. Thus, AQP1 is important for maintaining DCSG biogenesis and normal levels of hormone secretion in pituitary endocrine cells.

Effects of water-borne copper on the Y-organ and content of 20-hydroxyecdysone in Eriocheir sinensis.

The effects of water-borne copper (Cu2+) (0.01, 0.10, 1.00, and 5.00 mg/L) on Y-organ (YO) microstructure and ultrastructure and on the content of 20-hydroxyecdysone (20-HE) in Eriocheir sinensis were studied using single gradient factor experiments. Results demonstrated that there was no significant difference in YO microstructure and ultrastructure when E. sinensis was exposed to 0.01, 0.10, and 1.00 mg/L water-borne Cu2+. However, exposure to 5.00 mg/L Cu2+ caused serious damage to the YO microstructure, with an obvious decrease in hemocoel and the disappearance of the basement membrane between cell fibers. In addition, there was an intumescence of cells around the hemocoel, the cell nucleus became enlarged or even rounded, and some cells around the hemocoel crumpled with only the cell nucleus isolated or even huddled in the hemocoel. Similarly, effects of water-borne Cu2+ on the YO ultrastructure were observed: obvious enlargement and rounding of the cell nucleus, high heterochromatinization of the nucleus chromatin, disappearance of the YO cell membrane in some severely damaged cells, and varied damage in cellular organelles, such as the disappearance of cristae in mitochondria and disruption of the nucleus membrane. The hemocyte nucleus showed considerable heterochromatinization. In addition, when the Cu2+ concentration increased, the content of 20-hydroxyecdysone (20-HE) decreased in all Cu2+ treatment groups (P < 0.05). Results of this study indicate that high water-borne Cu2+ concentration impaired the basic structure of YO, which is regarded as the secretion site of 20-HE, and hence decreased the content of 20-HE in hemolymph. Therefore, molting frequency as well as the growth of E. sinensis is inhibited when exposed to high concentrations of water-borne Cu2+.

Calcium homeostasis in low and high calcium water acclimatized Oreochromis mossambicus exposed to ambient and dietary cadmium.

The effects of cadmium administered via ambient water (10 microg/l) or food (10 microgCd/fish/day) on plasma calcium, corpuscles of Stannius and bony tissues of Oreochromis mossambicus acclimated to low calcium (0.2 mM) and high calcium (0.8 mM) water were studied for 2, 4, 14 and 35 days. In low calcium water acclimated fish, ambient cadmium induced significant hypocalcemia, while the structure and morphometry of type-1 and type-2 cells of corpuscles of Stannius were not affected on day 2 and 4. Subsequently on day 14 and 35, recovery of plasma calcium to normal levels was observed followed by a decrease in corpuscles of Stannius index (CSI), cell size, volume of granular endoplasmic reticulum (p < 0.05) of type-1 cells in both, fish exposed to ambient or dietary cadmium. The type-2 cells were not affected. In high calcium water acclimated fish both, ambient and dietary cadmium caused a significant reduction of plasma calcium levels on day 2 and 4. In these fish, there was a significant transient increase in the size of corpuscles of Stannius on day 4, followed by recovery on day 14 and 35. Ultrastructural observations of corpuscles of Stannius revealed that cadmium did not cause any cellular damage on type- and type-2 cells during 35 days exposure. In low or high calcium water acclimatized tilapia exposed to ambient or dietary cadmium had no effect on the calcium and phosphate composition of the scales, operculum and vertebrae. Thus, it is unlikely that recovery of hypocalcemia was due to the dissolution of calcium from bony tissues. This study also revealed that cadmium does not mediate stimulation of the corpuscles of Stannius gland, and that high Ca2+ water had a protective effect against ambient and dietary cadmium.

Release mechanism of sex pheromone in the female gypsy moth Lymantria dispar: a morpho-functional approach.

A morpho-functional investigation of the sex pheromone-producing area was correlated with the pheromone release mechanism in the female gypsy moth Lymantria dispar. As assessed by male electroantennograms (EAG) and morphological observations, the pheromone gland consists of a single-layered epithelium both in the dorsal and ventral halves of the intersegmental membrane between the 8th and 9th abdominal segments. By using the male EAG as a biosensor of real-time release of sex pheromone from whole calling females, we found this process time coupled with extension movements of the ovipositor. Nevertheless, in females in which normal calling behavior was prevented, pheromone release was detected neither in absence nor in presence of electrical stimulation of the ventral nerve cord/terminal abdominal ganglion (TAG) complex. Tetramethylrhodamine-conjugated dextran amine stainings also confirm the lack of any innervation of the gland from nerves IV to VI emerging from the TAG. These findings indicate that the release of sex pheromone from the glands in female gypsy moths is independent of any neural control exerted by the TAG on the glands, at least by way of its three most caudally located pairs of nerves, and appears as a consequence of a squeezing mechanism in the pheromone-producing area.

Dense-core granules in neuroendocrine cells and neurons release their secretory constituents by piecemeal degranulation (review).

The term piecemeal degranulation (PMD) refers to a slow releasing process mediated by vesicular transport of stored secretory granule contents. This form of cell secretion was first proposed for basophils, mast cells and eosinophils, but evidence has begun to accumulate that PMD also occurs in dense-core granules of neuroendocrine cells and neurons. This review summarizes the electron-microscopic evidence that has been gathered in support of this view and also discusses the possible physiological significance of PMD in this class of secretory organelles in comparison with 'full fusion' and 'kiss-and-run' exocytosis.

Hormone complement of the Cancer productus sinus gland and pericardial organ: an anatomical and mass spectrometric investigation.

In crustaceans, circulating hormones influence many physiological processes. Two neuroendocrine organs, the sinus gland (SG) and the pericardial organ (PO), are the sources of many of these compounds. As a first step in determining the roles played by hemolymph-borne agents in the crab Cancer productus, we characterized the hormone complement of its SG and PO. We show via transmission electron microscopy that the nerve terminals making up each site possess dense-core and/or electron-lucent vesicles, suggesting diverse complements of bioactive molecules for both structures. By using immunohistochemistry, we show that small molecule transmitters, amines and peptides, are among the hormones present in these tissues, with many differentially distributed between the two sites (e.g., serotonin in the PO but not the SG). With several mass spectrometric (MS) methods, we identified many of the peptides responsible for the immunolabeling and surveyed the SG and PO for peptides for which no antibodies exist. By using MS, we characterized 39 known peptides [e.g., beta-pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide, and red pigment-concentrating hormone] and de novo sequenced 23 novel ones (e.g., a new beta-PDH isoform and the first B-type allatostatins identified from a non-insect species). Collectively, our results show that diverse and unique complements of hormones, including many previously unknown peptides, are present in the SG and PO of C. productus. Moreover, our study sets the stage for future biochemical and physiological studies of these molecules and ultimately the elucidation of the role(s) they play in hormonal control in C. productus.

The pancreas of the naked mole-rat (Heterocephalus glaber): an ultrastructural and immunocytochemical study of the endocrine component of thermoneutral and cold acclimated animals.

Endocrine cell distribution within the islets of Langerhans may vary both between species and under different energetically demanding conditions such as cold acclimation. The naked mole-rat, Heterocephalus glaber, lacking an effective insulatory pelage, is effectively a poikilotherm, yet it shows a typical mammalian cold-acclimation response by substantially increasing food intake to meet higher energy requirements when housed at lower temperatures. The endocrine component of the pancreas of thermoneutral and cold-acclimated naked mole-rats was thus characterized using immunocytochemistry and ultrastructural analyses. Four distinct endocrine cells were identified: alpha (glucagon-producing), beta (insulin-producing), delta (somatostatin-producing), and PP (pancreatic polypeptide-producing) cells. Distribution of these cells differed from that of other rodents, in that beta cells formed the mantle while alpha cells formed the core of the islets. This distribution may contribute to the observed insulin insensitivity of this species, as indicated in abnormal responses to glucose tolerance tests. Insulin-producing cells, however, were more numerous than glucagon-producing cells. This ratio was unchanged with cold acclimation. Immunoreactivity of alpha and beta cells was more intense in cold-acclimated than in thermoneutral animals, possibly indicative of a change in hormonal production in animals housed at a lower temperature.

Androgenic gland cell structure and spermatogenesis during the molt cycle and correlation to morphotypic differentiation in the giant freshwater prawn, Macrobrachium rosenbergii.

The freshwater prawn Macrobrachium rosenbergii shows three male morphotypes: blue-claw males (final stage having high mating activity), orange-claw males (transitional stage showing rapid somatic growth), and small males (primary stage showing sneak copulation). This morphotypic differentiation is considered to be controlled by androgenic gland hormone, which is probably a peptide hormone. However, its physiological roles are not fully understood. In the present study, we examined the correlation of androgenic gland cell structure to spermatogenic activity and morphotypic differentiation histologically in M. rosenbergii. spermatogenic activity showed close correlation to the molt cycle in orange-claw males and small males. spermatogonia increased in number in the late premolt stage, becoming spermatocytes in the postmolt stage, and spermatocytes differentiated into spermatozoa in the intermolt and early premolt stages. Ultrastructure of the androgenic gland was additionally compared among the molt stages, but, distinct histological changes were not observed in relation to spermatogenesis during the molt cycle. On the other hand, among the three morphotypes, the androgenic gland was largest in the blue-claw males, containing developed rough endoplasmic reticulum in the cytoplasm. These results suggest that, during spermatogenesis which is related to the molt cycle, the androgenic gland hormone is at rather constant levels and plays a role in maintaining spermatogenesis rather than directly regulating the onset of a specific spermatogenesis stage and that, during the morphotypic differentiation, the androgenic gland is most active in the blue-claw males and plays a role in regulating the observed high mating activity in M. rosenbergii.

Effects of adrenaline administration on the interrenal gland of the newt, Triturus carnifex: evidence of intraadrenal paracrine interactions.

The existence of paracrine control of steroidogenic activity by adrenochromaffin cells in Triturus carnifex was investigated by in vivo adrenaline (A) administration. The effects were evaluated by examination of the ultrastructural morphological and morphometrical features of the tissues as well as the serum levels of aldosterone, noradrenaline (NA), and adrenaline. In March and July, adrenaline administration reduced aldosterone release (from 187.23 +/- 2.93 pg/ml to 32.28 +/- 1.85 pg/ml in March; from 314.60 +/- 1.34 pg/ml to 87.51 +/- 2.57 pg/ml in July) from steroidogenic cells. The cells showed clear signs of lowered activity: they appeared full of lipid, forming large droplets. Moreover, adrenaline administration decreased the mean total number of secretory granules in the chromaffin cells in July (from 7.74 +/- 0.74 granules/microm(2) to 5.14 +/- 1.55 granules/microm(2)). In this period T. carnifex chromaffin cells contain almost exclusively NA granules (NA: 7.42 +/- 0.86 granules/microm(2); A: 0.32 +/- 0.13 granules/microm(2)). Adrenaline administration reduced noradrenaline content (4.36 +/- 1.40 granules/microm(2)) in the chromaffin cells, enhancing noradrenaline secretion (from 640.19 +/- 1.65 pg/ml to 1030.16 +/- 3.03 pg/ml). In March, adrenaline administration did not affect the mean total number of secretory vesicles (from 7.24 +/- 0.18 granules/microm(2) to 7.25 +/- 1.97 granules/microm(2)). In this period the chromaffin cells contain both catecholamines, noradrenaline (3.88 +/- 0.13 granules/microm(2)), and adrenaline (3.36 +/- 0.05 granules/microm(2)), in almost equal quantities; adrenaline administration reduced adrenaline content (1.74 +/- 0.84 granules/microm(2)), increasing adrenaline release (from 681.27 +/- 1.83 pg/ml to 951.77 +/- 4.11 pg/ml). The results of this study indicate that adrenaline influences the steroidogenic cells, inhibiting aldosterone release. Adrenaline effects on the chromaffin cells (increase of noradrenaline or adrenaline secretion) vary according to the period of chromaffin cell functional cycle. The existence of intraadrenal paracrine interactions in T. carnifex is discussed.

Piecemeal degranulation as a general secretory mechanism?

In this article we review the ultrastructural findings, functional aspects, and biological significance of piecemeal degranulation (PMD), a unique secretory pathway that has been described in basophils, mast cells, and eosinophils. Recent ultrastructural data suggestive of PMD in enteroendocrine cells of the gastrointestinal tract and chromaffin cells of the adrenal medulla are also presented and discussed. Further research on PMD in secretory cells of the endocrine and exocrine glands, as well as in neurons, is recommended, since the current data indicate that PMD has a broader spectrum of expression than was hitherto reported. The identification of the PMD phenotype in different cell types (e.g., basophils, mast cells, eosinophils, enteroendocrine cells, and adrenal chromaffin cells) suggests that PMD is a unique degranulation model for paracrine and endocrine secretion. Further investigation will clarify whether PMD can be considered as a general mechanism for the slow release of bioactive stored materials by granulated secretory cells.

Response by the corpuscles of Stannius to hypotensive stimuli in three divergent ray-finned fishes (Amia calva, Anguilla rostrata, and Catastomus commersoni): cardiovascular and morphological changes.

In accordance with their vital role in cardiovascular physiology () corpuscles of Stannius (CS) from two teleosts and an holostean species showed marked and consistent degranulation and exocytotic responses to hypotensive stimuli. In eels (Anguilla rostrata LeSueur) acute blood withdrawal (hypovolemic hypotension) was followed by a prompt decrease in cardiac output (CO) and dorsal aortic pressure (P(DA)), a compensatory tachycardic response and an increase in systemic vascular resistance (R(SYS)). Isovolemic hypotension induced by papaverine i.v., led to a similar, but more prolonged, decrease in P(DA) but the heart rate (HR) continued to accelerate, thereby counterbalancing the severe and persistent decrease in R(SYS). Both hypovolemic and isovolemic hypotension were followed by a significant depletion of cytoplasmic granules from eel CS even though plasma concentrations of Ca, Mg, Na(+), and K(+) were normal. In an ancient holostean fish, the bowfin, Amia calva and a generalized teleost fish, Catastomus commersoni, the number of cytoplasmic granules decreased by 39% and 54%, respectively, 120 min after the acute withdrawal of 8 ml kg bw(-1) of blood. These findings suggest that a primary role of the CS is to release cytoplasmic granules containing renin or isorenin into the blood circulation, in response to hypotension and/or hypovolemia.

Electron microscopic studies of the corpuscles of Stannius of an airbreathing teleost (Heteropneustes fossilis).

The ultrastructure of the corpuscles of Stannius (CS) of Heteropneustes fossilis reveals a homogenous cellular composition characterized by only one cell type, with large secretory granules and abundant ribosomal endoplasmic reticulum. These cells are comparable to the type 1 cell described in the CS of other teleosts; type 2 cells, whose presence is ubiquitous in the CS of freshwater species are absent in H. fossilis. Our data on the CS of H. fossilis demonstrate that not all freshwater species possess type 2 cells in their CS and these are not essential for life in freshwater