Immuno-electron microscopy of formation,degradation and exocytosis of the ovulation neurohormone in Lymnaea stagnalis

Summary The cerebral caudodorsal cells (CDC) of the pulmonate snail Lymnaea stagnalis are involved in the control of egg laying and associated behaviour by releasing various peptides. One of these is the ovulation hormone (CDCH). The cellular dynamics of this peptide have been studied using an antiserum raised to a synthetic portion of CDCH comprising the 20–36 amino acid sequence. With the secondary antibody-immunogold technique, specific immunoreactivity was found in all CDC. Rough endoplasmic reticulum and Golgi apparatus showed very little reactivity as did secretory granules that were in the process of being budded off from the Golgi apparatus. However, secretory granules that were being discharged from the Golgi apparatus, were strongly reactive. Secretory granules within lysosomal structures revealed various degrees of immunoreactivity, indicating their graded breakdown. Large electrondense granules, formed by the Golgi apparatus and thought to be involved in intracellular degradation of secretory material, were only slightly reactive. In the axon terminals secretory granules released their contents into the haemolymph by the process of exocytosis. The exteriorized contents were in most cases clearly immunopositive.The possibility has been discussed that CDCH is cleaved from its polypeptide precursor within secretory granules during granule discharge from the Golgi apparatus; subsequently, the mature secretory granules would be transported towards the neurohaemal axon terminals where they release CDCH into the haemolymph. Superfluous secretory material would be degraded by the lysosomal system including the large electron-dense granules.     

THE CYTOLOGY OF THE NORMAL PARATHYROID GLANDS OF MAN AND VIRGINIA DEER : A Light and Electron Microscopic Study with Morphologic Evidence of Secretory Activity

The normal parathyroids of six humans and a Virginia deer were studied by light and electron microscopy. The parenchyma of the deer parathyroid is composed of uniform chief cells, which contained 100 to 400 mµ electron-opaque, membrane-limited granules, presumed to be secretory granules, in addition to the usual cytoplasmic organelles. Desmosomes are present between adjacent cells, and rare cilia are observed protruding from the chief cells into the intercellular space. The human parathyroids contain chief cells in two phases—active and inactive—as well as oxyphil cells. Active chief cells have a large Golgi apparatus, sparse glycogen, numerous secretory granules, and rare cilia. Inactive chief cells contain a small Golgi apparatus, abundant glycogen, and few secretory granules. Both forms have the usual cytoplasmic organelles and, between adjacent cells, desmosomes. Oxyphil cell cytoplasm is composed of tightly packed mitochondria and glycogen granules, with rare secretory granules. Cells with cytoplasmic characteristics intermediate between chief and oxyphil cells, possibly representing transitional cells, have been observed. Secretory granules of both man and deer are composed of 100 to 200 A particles and short rods, and the granules develop from prosecretory granules in the Golgi region of the cell. The human secretory granules are smaller and more variable in shape than those of the deer. The granules are iron and chrome alum hematoxylin-positive, argyrophilic, and aldehyde fuchsin-positive, permitting light microscopic identification. They are also found in the capillary endothelial cells of the parathyroid and in its surrounding connective tissue. The secretory granules of the parathyroid cells can thus be followed from their formation in the Golgi apparatus almost to their extrusion into the blood stream.     

Ultrastructure of the sexual segments of the kidney in male and female lizards,Cnemidophorus l. lemniscatus (L.)

Summary Kidneys of adult male and female lizards were studied by electron microscopy, in order to understand the ultrastructure of the collecting duct and a differentiated part thereof, the sexual segment, which is an important accessory sexual organ. First portion of sexual segment in males: The cells are filled with large secretory granules of a wide range of opacities. The granular endoplasmic reticulum is abundant; basal formations of superimposed flat cisternae are frequent. Distended vesicles and microvesicles prevail in the supranuclear, well developed Golgi apparatus. Evidences indicate that secretion of these cells is holocrine. Second portion of sexual segment in males: All of the secretory granules are apical in location and relatively electron-opaque; they show a denser core. This core is formed by a substance which, after lying in contact with ribosomes, enters the secretory vesicles of the highly developed Golgi apparatus. A lighter substance is then condensed around it. The secretion of the granules is merocrine. The granular endoplasmic reticulum is very abundant in these cells, but basal ergastoplasmic formations are lacking. Sexual segment in females: The cells show features similar to those of the male first portion, but they are smaller. Undifferentiated collecting duct: Most of the cells are mucigenic. They have small ovoid, apical secretory granules. The density of the granules varies from cell to cell; when they are electron-lucent, they exhibit laminar or dotted opaque figures. Moderately developed Golgi apparatus and granular endoplasmic reticulum, as well as elongated mitochondria, occur in mucigenic cells. Intercalated among the latter are non-secretory cells. They have very abundant mitochondria, numerous microvilli, many pinocytic and smooth-membrane vesicles, whereas the organelles participating in synthetic processes are poorly developed; their function is most likely related to active solute transport.     

Morphological evidence for the presence of two cell types in the ependyma of the subcommissural organ of the snake,Natrix maura

Summary Two different types of ependymal cells were found in the subcommissural organ (SCO) of Natrix maura. Most secretory cells showed morphological features resembling the general structure and ultrastructure of cells in the SCO of other vertebrates. This report describes a second population of cells lining a portion of the dorsal groove of the SCO. These cells were not selectively stained by chromalum-hematoxylin and, under the electron microscope, they were characterized by scarce surface differentiations, sparse apical cytoplasm and short basal processes. Flat, parallel cisternae of the rough endoplasmic reticulum produced vesicles that appeared to be transported to the well-developed Golgi apparatus. Dense secretory granules about 200 nm in diameter were found in the Golgi region. Similar granules were seen in the vicinity of the apical plasma membrane; some of them opened toward the ventricle. All these characteristics clearly differentiate this cell group from the other secretory cells lining the SCO laterally and ventrally.     

Ultracytochemistry of glycoproteins in the eccrine nasolabial glands of the North American raccoon (Procyon lotor)

The distribution and quality of glycoproteins was studied by means of electron microscopic cytochemical methods, particularly lectin cytochemistry, in the secretory cells of the eccrine nasolabial glands of the North American raccoon (Procyon lotor). In the dark and clear glandular cells, complex glycoconjugates were demonstrable, predominantly, in secretory granules, the cisternae of the Golgi apparatus, the surface coat of the plasma membrane, and as glycogen particles. Secretory granules found in the dark cells contained a variety of saccharide residues, such as α-d-mannose, β-d-galactose, β-N-acetyl-d-glucosamine and sialic acid. Several sugars were also detectable in the surface coat of the plasma membrane and the Golgi apparatus.The results obtained may be helpful to understand the specific functions of the glandular secretions of the raccoon nasolabial glands. These could be, particularly, binding of water on the snout surface and protection against microbial hazards, to maintain the structural and functional integrity of the relatively thin snout epidermis in carnivores.     

Immuno-electron microscopy of sorting and release of neuropeptides in Lymnaea stagnalis

Summary The cerebral caudodorsal cells of the pulmonate snail Lymnaea stagnalis control egg laying and egglaying behavior by releasing various peptides derived from two precursors. The biosynthesis, storage, intracellular breakdown and release of three caudodorsal cell peptides were studied by means of immuno-electron microscopy using antisera raised to fragments of these peptides: (1) Caudodorsal Cell Hormone-I (CDCH-I; derived from precursor I), (2) Caudodorsal Cell Hormone-II (CDCH-II; from precursor II), and (3) -Caudodorsal Cell Peptide ( CDCP; from both precursors). After affinity purification of the antisera, the specificity of the sera was confirmed with dotting immunobinding assays. From the ultrastructural immunocytochemical data it has been concluded that the precursor molecules are cleaved at the level of the Golgi apparatus after which the C-terminal parts (containing CDCP) and N-terminal parts (containing CDCH-I or CDCH-II) are sorted and preferentially packaged into large electron-dense granules (MD 150 nm), respectively. Very probably, the content of the large electron-dense granules is degraded within the cell body. The immunoreactivity of the secretory granules increases during discharge from the Golgi apparatus, indicating further processing. At least a portion of the secretory granules contains all three peptides, as shown by double and triple immunopositive stainings whereas other granules appear to contain only one or two of these peptides. The caudodorsal cells release multiple peptides via exocytosis from neurohemal axon terminals into the hemolymph and from blindly ending axon collaterals into the intercellular space of the cerebral commissure (nonsynaptic release).     

Fine structure of the corpuscles of stannius in the toadfish.

The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.     

The ultrastructure of prolactin cells in the annual cyprinodont Cynolebias whitei during its life cycle

Summary Prolactin (PRL) cells were studied electron-microscopically and morphometrically in the annual cyprinodont fish, Cynolebias whitei during its life cycle. In prehatching larvae, PRL cells possessed small secretory granules, giant mitochondria and a well-developed Golgi apparatus. During hatching, no changes were observed in the volume density of the secretory granules, indicating that no increased release of PRL occurs at hatching. A significant change in the composition of PRL cells, i.e., the volume densities per cytoplasm volume of the different organelles, occurred between one day and one week of age. Thereafter, only minor differences were observed between age groups, indicating that no major changes occur in PRL cell activity during the lifespan of C. whitei. However, the volume density per cell volume of the nucleus decreased steadily with age during the lifespan. A comparison of the PRL cells in young and adult fish reared in fresh water (FW) with siblings reared from hatching in diluted sea water (1/3 SW) did not reveal any differences with respect to the volume densities of the organelles, including the secretory granules. However, significant differences were observed with respect to the diameter, electron-dense content and affinity to anti- PRL serum of the secretory granules. These differences indicate that, despite the similar volumetric composition of the PRL cells, their secretory granules contain a substantially higher concentration of PRL in FW-reared fish than in 1/3 SW-reared fish.     

Light and electron microscopic studies on the pars intermedia of the chameleon

Summary The neurointermediate lobe of the hypophysis in the Chameleon (Chamaeleo dilepis) was examined with light and electron microscopic methods, with special reference to the cytology of the pars intermedia (PI). The PI is the largest lobe of the hypophysis consisting of (1) dark cells with secretory granules ranging from 200–600 nm; (2) light cells, far fewer in number, containing granules 150–300 nm in diameter; (3) stellate, non-secretory cells. The secretory cells abut onto the perivascular basal lamina of the capillary sinusoids while their apical part borders an intercellular space. This surface of the cells often bears a cilium. The granules arise from the Golgi cisternae while small detached vesicles are found between circumscribed sites of the cell membrane and the Golgi apparatus. No nervous elements were found in the pars intermedia and it is assumed that the regulation of this lobe is purely humoral. This is supported by the presence of three types of nerve terminals in the pars nervosa: (a) terminals with large secretory granules and small vesicles; (b) terminals with dense-core vesicles and small vesicles; (c) terminals with small vesicles only. All of these are secretory as indicated by the presence of the synaptic semidesmosomes formed with the perivascular basal lamina.I would like to thank Mr. W.N. Newton for his skill and aid in all aspects of this work, Mr. A. Ansary for expert photographic assistance and the Central Pathology Laboratory, University of Dar es Salaam, for the electron microscopic facilities provided. Research sponsored by the University of Zambia Grants J02-18-00 and Medic 74/6     

The ultrastructure of mammary explants from virgin ovariectomized goats during hormone-induced lactogenesis

The effect of insulin (I), cortisol (F) and prolactin (P) on the ultrastructural morphology of epithelial cells of cultured mammary explants from virgin ovariectomized (OV-X) goats were studied. The epithelial cells showed little structural organization and were devoid of fat droplets and secretory protein granules at zero time of culture. The cytoplasm contained few profiles of smooth and rough endoplasmic reticulum and the Golgi apparatus was rudimentary. After being cultured in Waymouth's medium without added hormones the epithelial cells were indistinguishable from epithelial cells of uncultured explants. The addition of I induced changes mainly in the appearance of nucleoli. The nucleoli were enlarged and fibrillogranular areas with light spaces were observed. The most obvious cytological changes of epithelial cells of explants cultured in the presence of I and F are translocation of the nucleus into the basal cytoplasm, increase of rough endoplasmic reticulum, an increase in the size of the Golgi apparatus, presence of one or two lipid droplets and in some cells vacuoles with protein granules were present. Mitochondria were more abundant. The epithelial cells of explants cultured in the presence of I, F and P were characterized by the polarization of organelles within the cytoplasm and by the formation and release of protein granules and small and large fat droplets. The cell nucleus was in the basal cytoplasm, the Golgi apparatus was supranuclear. The rough endoplasmic reticulum was extensively developed and formed large sacs. Golgi vacuoles contained protein granules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural enzyme-cytochemical study of the intrinsic glandular cells in the corpus cardiacum of Locusta migratoria: relation to the secretory and endocytotic pathways,and to the lysosomal system

Summary Ultrastructural aspects of the secretory and the endocytotic pathways and the lysosomal system of corpus cardiacum glandular cells (CCG cells) of migratory locusts were studied using morphological, marker enzyme, immunocytochemical and tracer techniques. It is concluded that (1) the distribution of marker enzymes of trans Golgi cisternae and trans Golgi network (TGN) in locust CCG cells corresponds to that in most non-stimulated vertebrate secretory cell types; (2) the acid phosphatase-positive TGN in CCG cells is involved in sorting and packaging of secretory material and lysosomal enzymes; (3) these latter substances are produced continuously; (4) at the same time, superfluous secretory granules and other old cell organelles are degraded; (5) the remarkable endocytotic activity in the cell bodies and the minor endocytotic activity in cell processes are coupled mainly to constitutive uptake of nutritional and/or regulatory (macro)molecules, rather than to exocytosis; (6) plasma membrane recycling occurs mainly by direct fusion of tubular endosomal structures with the plasma membrane and little traffic passes the Golgi/TGN; and (7) so-called cytosomes arise mainly from autophagocytotic vacuoles and represent a special kind of complex secondary lysosomes involved in the final degradation of endogenous (cell organelles) and exogenous material.     

Ageing adipokinetic cells in Locusta migratoria: an ultrastructural morphometric study

Summary A morphometric study was made of the ultrastructure of adipokinetic cells in resting adults of Locusta migratoria at 3, 23, and 43 days after imaginal ecdysis. The nucleus, rough endoplasmic reticulum, and Golgi apparatus enlarge with age, which indicates that the synthesis and packaging of secretory substances increases during ageing. The size of the storage compartment, consisting of secretory and ergastoplasmic granules, does not increase earlier than 23–43 days after imaginal ecdysis. The lysosomal compartment markedly enlarges between 3 and 23 days; later on, the growth of this compartment, especially of autophagosomes, is less prominent. This suggests that lysosomal destruction initially compensates for the production of new secretory granules, assuming that exocytosis of secretory granules by adipokinetic cells is insignificant in resting locusts. Afterwards, lysosomal destruction may no longer be sufficient to prevent over-production of secretory granules, as is suggested by the increase in the number of these granules between 23 and 43 days. This coincides with the appearance of a considerable number of large ergastoplasmic granules, which represent a spatially more efficient form of storage of secretory material than the much smaller secretory granules. The increase with age in the amount of secretory products indicates that the biosynthetic activity of the adipokinetic cells is not (finely) tuned to their releasing activity.     

Control of the pars intermedia of the lizard,Anolis carolinensis

Summary The ultrastructure of the intermediate lobe of the hypophysis was studied in Anolis carolinensis with the use of a threefold aldehyde fixative. Lizards with a brown skin were selected. The possibility of two types of secretory cells is discussed; neither cell type is innervated. Type I cells are rarely found and contain dense granules approximately 0.3 m in diameter; Type II cells vary widely in secretory activity. Most of the Type II cells contain a large number of dense secretory granules (up to about 1.3 m in diameter) almost filling the cytoplasm. Rough endoplasmic reticulum (RER), Golgi apparatus and mitochondria are poorly developed. Only some of these cells show signs suggesting a high secretory activity, namely a well developed RER, Golgi apparatus and numerous mitochondria. In these cells the RER sometimes forms large intracisternal droplets (up to 7 m in diameter). Two of the animals exhibited a more uniform, high secretory activity. Large (about 2 m in diameter), pale vacuoles, probably of extracellular character, were found mostly in the vicinity of the perivascular septum. Their role in the release of MSH is discussed. The present data, which are discussed with reference to earlier findings (Forbes, 1972), form the morphological basis for an experimental study on regulation of MSH release (Larsson et al., 1979).Supported by grants from the Swedish Natural Science Research Council (to P. Meurling) and the Royal Physiographic Society of LundThe authors are indebted to Mrs. Ingrid Hallberg, Mrs. Kirsten Thörneby and Mrs. Lena Sandell for valuable technical assistance and to Miss Inger Norling for photographic aid     

A comparative ultrastructural study of ‘glue’ production and secretion of the salivary glands in different species of theDrosophila melanogaster group

Summary Salivary gland cells of members of theDrosophila melanogaster group (from four different subgroups) were examined electron microscopically and histochemically during the late larval period of development. The secretory product, which is supposed to be utilized as glue at the time of puparium formation, appears, by analogy to Palade and Jamieson's results, to be synthesized partially in the rough endoplasmic reticulum (RER) and partially in the Golgi complex. The latter is also the usual site of the packaging of the product into secretory granules, except in the case of one of the secretory granule components ofD. lucipennis. The phylogenetic relationships among the subgroups, implied by the morphological appearance of the secretory granules, fit well with the existing phylogenetic relationships within the group. The secretory granules of each species have their own morphological features; granules of species of the same subgroup share some of these features. Secretion occurs from the cells via exocytosis during which the morphology of the secretory granules changes. Light microscope examination of PAS (Periodic Acid-Schiff reaction) stained glands shows a strong positive reaction in most species, with the exception of the species of thesuzukii subgroup which show a weak, or a negative reaction (D. rajasekari). Electron histochemical localization of polysaccharides in the secretory granules was possible inD. melanogaster and the species of theananassae subgroup.     

Lectin-binding pattern in parotid acinar cells

Summary The localization of complex carbohydrates in the Golgi apparatus, secretory granules and plasmalemma of mouse parotid acinar cells was studied using the fracture-labelling method. The hexose residues of glycoconjugates were identified using ferritin conjugated with Wheat Germ Agglutinin (WGA-), Ricinnus Communis Agglutinin II (RCA-II-), Phaseolus Vulgaris Agglutinin (PHA-) and Limulus Polyphemus Agglutinin (LPA-). We found that the tracture-labelling method allows not only the labelling of membrane faces but also analysis of the compartment's content that is exposed during the fracturing of the tissue. Our results revealed differences in the hexose residues located in the Golgi apparatus, secretory granules and the apical and lateral plasmalemma. Numerous binding sites for WGA-, PHA-and RCA-II-ferritin were demonstrable in the Golgi apparatus. In secretory granules, the WGA-and RCA-II-ferritin binding sites were most numerous, while LPA-ferritin binding sites were very rate. The density of the binding sites for PHA-ferritin showed considerable variation in secretory granules. The apical plasmalemma exhibited a high density of binding sites for all of the lectins used. In the lateral plasmalemma, LPA-ferritin was not bound, and there were fewer binding sites for WGA-, RCA-H-and PHA-ferritin.     

The fine structure of the stomach mucosa of the llama (Llama guanacoe)

Summary The epithelium of the fundic region mucosa of the hind stomach in the Llama guanacoe has been studied using morphological and histochemical methods. Morphology suggests that solute and water absorption may occur in the epithelium of the surface and of the foveolae, although this absorption can not be estimated because of the extensive secretion of the gastric glands. The same cells of the surface and foveolar epithelium show numerous secretory granules. The glands reveal neck cells, chief cells, a large number of oxyntic cells, four types of endocrine cells (A-like, ECL, D and EC), brush cells and wandering cells. PAS and Alcian blue reactions for light microscopy suggest a secretion of neutral and acidic mucosubstances in the surface and foveolar epithelium, of neutral mucosubstances only in the neck cells. Periodic acid-thiocarbohydrazide silver proteinate (PA-TCH-SP) reaction for electron microscopy confirms the presence of neutral mucosubstances within the secretory granules of the surface, foveolar and neck epithelial cells. In all these cells, the reaction product is also evident within sacculi and vesicles of the maturing surface of the Golgi apparatus. A positive PA-TCH-SP reaction also occurs on the membrane (and not on the contents) of the Golgi apparatus (maturing surface) and of the secretory granules of the chief cells as well as on the membrane of the Golgi apparatus and of apical vesicles and tubules of the oxyntic cells. In addition, silver granules slightly enhance the electron density of the contents of the secretory granules in the endocrine cells. Morphological and histochemical findings are discussed and compared with results described by others for monogastric mammals.     

An ultrastructural study of the clitellar epithelium of the earthworm Metaphire posthuma (vail.)

The ultrastructure of clitellar epithelium of Metuphire posthuma revealed mainly three types of secretory cells. Most prominent among these are the large slender granular cells which contain a large number of secretory granules filling in the entire columncr region of the cell. The secretory granules are 2-4mu in diameter with a limiting membrane and containing numerous tiny vesicles in a matrix of varying electron density. Basolateral rough endoplasmic reticulum and extensive Golgi cisternae were seen interspersed with the secretory granules. The Golgi cisternae in these cells were quite prominent extending all around the secretory granules. The secretory granules of type 2 cells are spheroid bodies with motley appearance due to varying electron density of the matrix. The immature granules contain fibrillar material. Type 3 cells contained electron lucent membrane-bound mucous like secretory granules which are reticulated with filamentous materials. All the three cell types open to the exterior at the cuticular region which is characterised by the presence of numerous microvilli.     

Effects of secretory stimulation on the Golgi apparatus and GERL of rat parotid acinar cells

The structure and cytochemistry of the Golgi apparatus and GERL of rat parotid acinar cells was studied after in vivo secretory stimulation with isoproterenol. Discharge of mature secretory granules was complete within 1 hr after isoproterenol injection, but immature granules in the Golgi region or near the lumen were not released. At early times (1-5 hr) after isoproterenol, acid phosphatase (AcPase) activity was markedly increased in GERL and immature secretory granules compared to uninjected controls. GERL appeared increased in extent and numerous continuities with immature granules were observed. Reaccumulation of mature secretory granules was first evident at 5 hr, and was almost complete by 16 hr after isoproterenol. Thiamine pyrophosphatase (TPPase) activity, normally restricted to the trans Golgi saccules, was frequently present in immature granules during this time. Narrow cisternae resembling GERL, occasionally in continuity with immature granules, also contained TPPase reaction product. By 16-24 hr after stimulation, the activity and distribution of AcPase and TPPase were similar to control cells. These results demonstrate the dynamic nature of the Golgi apparatus and GERL in parotid acinar cells, and emphasize the close structural and functional relationship between these two structures.     

Electron-immunocytochemical localization of calcitonin and calcitonin-gene-related peptide in human c cells of the thyroid

A preembedding immunocytochemical technique enabled us to demonstrate normal human parafollicular (C) cells at the electron-microscopic level. The normal human C cells had numerous large secretory granules with a diameter of approximately 200 nm, well-developed rough endoplasmic reticulum and Golgi complex in their cytoplasm. Calcitonin immunoreactivity and calcitonin-gene-related peptide (CGRP) immunoreactivity were present only in the C cells whose secretory granules were heavily labeled. Both calcitonin and CGRP immunoreaction deposits were seen in the cytosol but not in the cisterna of endoplasmic reticulum, Golgi apparatus or mitochondrial matrix. The two peptides produced from a single calcitonin gene were stored in the secretory granules of the C cells.     

Effects of prolonged maternal fast on the pancreas of 18–21-day-old foetal rats

Summary After maternal fasting for 72 h the pancreatic cells of 18-day-old foetal rats show a conspicuous enrichment in secretory material, with an increase of pancreatic insulin concentration and a marked development of the rough endoplasmic reticulum and the Golgi apparatus.The morphometric analysis shows that the intracytoplasmic migration of the secretory granules is inhibited, principally inside the cell web. Consequently the number of secretory granules fused with plasma membrane decreases and this is associated with a decreased foetal plasma insulin.The difference in the ultrastructural aspect of the cells of foetuses from fasting mothers and of foetuses from fed mothers is less conspicuous at 19 days of gestation and progressively disappears at 20 and 21 days.The modifications in ultrastructural aspect and in functional state are discussed.