Steroidogenic characteristics of the adrenal cortex of the mare studied by electron microscopy

The three concentric zones of the horse adrenal cortex (zonae glomerulosa, fasciculata and reticularis) showed marked interpenetration and exhibited a different relative development according to their position in the gland. Whereas the three cortical zones each had a specific histological structure, the ultrastructure of their cells showed a certain qualitative homogeneity. The differences corresponded essentially to the relative abundance of the constituents which are generally considered typical of steroidogeneous cells: mitochondria with vesicular cristae, smooth endoplasmic reticulum and lipid droplets. Their importance increased progressively from the zona glomerulosa to the zona reticularis. In this zone, the presence of gap and septate-like cell junctions, and mitochondria with vesicular cristae in close proximity to a smooth endoplasmic reticulum with numerous dilated tubules, suggested that steroidogenesis may be the most active. Ultrastructural findings were indicative of only quantitative differences between the steroidogenic capacities of the three zones of the mare adrenal cortex.     

Stereological analysis of the guinea pig adrenal: effects of dexamethasone and ACTH treatment with emphasis on the inner cortex

This paper describes the morphological responses of adult male guinea pig adrenals to dexamethasone (DEX) and adrenocorticotrophic hormone (ACTH), in both qualitative and quantitative terms. Most organelles and inclusions are affected, but their responses often vary in the different cell types examined: zona fasciculata externa and interna, and zona reticularis. Following DEX the volume of lipid droplets increases in cells of zona fasciculata externa but decreases in zona reticularis; smooth endoplasmic reticulum decreases in fasciculata externa but increases in reticularis. Following ACTH, exactly the opposite occurs. This strongly suggests differing functions for these subcellular entities in each cell type, particularly for the smooth reticulum, as well as for the cells themselves. The volume of the Golgi complex markedly decreases following DEX in all cells but increases only in zona fasciculata interna and zona reticularis following ACTH. These deeper cortical cells are known to secrete at least one sulfated steroid, dehydroepiandrosterone sulfate, and these changes in the Golgi complex strengthen the suggestion that the Golgi plays a role in sulfation of steroids. Mitochondrial volume and number decrease in all cells following DEX, supporting their role in steroidogenesis. Further decreases in their volume, accompanied by increases in their number following ACTH, may be related to a proliferation of mitochondria in response to ACTH. Changes in peroxisome volume and number, following DEX and ACTH, suggest a possible role for these organelles in steroid cell metabolism. Lysosomes decrease in volume in all cells following ACTH. This does not support the recently suggested concept that they play a role in steroid secretion.     

Stimulation of the adrenal gland of the mongolian gerbil after ovariectomy

The effect of ovariectomy on the adrenal gland was studied in the Mongolian gerbil. Castration stimulated cells in the zona fasciculata as well as those in the region between the zona fasciculata and zona reticularis. No alterations occurred in the zona reticularis. The width of the intermediate region was enlarged, the cells were hypertrophic and contained an increased number of concentric whorls of rough endoplasmic reticulum. Smooth endoplasmic reticulum was hypertropic in cells of the zona fasciculata and intermediate region. Many mitochondria in cells of the intermediate region were larger than those in controls. Stimulation of cellular ultrastructure is directly correlated with a significant elevation in plasma cortisol in ovariectomized gerbils.     

Spontaneous or experimentally induced formation of a special zone in the adrenal cortex of the adult brush-tailed possum (Trichosurus vulpecula)

The cytology and ultrastructure of the hypertrophied special zone, which is formed spontaneously in the adrenal cortex of adult female brush-tailed possums (Trichosurus vulpecula), was compared to the adrenocortical tissue in adult males in which the special zone, normally absent, was induced following castration alone or by additional treatment with follicle-stimulating hormone (FSH). The special zone in females was situated between the zona fasciculata and the zona reticularis, the latter being a rudimentary zone in this species. Special zone tissue extended as a broad band parallel to and on one side of the adrenal medulla. In the luteal phase of the reproductive cycle, the special zone cells showed ultrastructural features commonly associated with steroidogenic tissues, with many mitochondria and compact masses of smooth endoplasmic reticulum. Cytoplasmic lipid inclusions were rarely observed. In lactating females, however, the special zone cells exhibited cytological and ultrastructural features suggestive of a transformation in their morphology broadly divided into two types of cells: (1) cells at the periphery of the special zone (closest to the zona fasciculata) showed variable quantities of lipid inclusions, mitochondria with dispersed cristae, and segregation of the smooth endoplasmic reticulum into compact masses; (2) cells within the more central regions showed an increasing abundance of lipid inclusions which in many cells became the dominant feature of the cytoplasm. These special zone cells contained very little smooth endoplasmic reticulum and their mitochondria contained few cristae together with amorphous granular material within the matrix. In castrated males, special zone tissue developed between the zona fasciculata and the zona reticularis, appearing initially as focal islands of cells (8 months postcastration) and later (11 months postcastration) expanding into a single zone, probably via the proliferation and differentiation of adjacent cells of the zona fasciculata and longitudinal growth of the special zone. Similar focal aggregations of special zone cells were induced after 14 days of FSH treatment given to 2-month castrated males. In all castrated and FSH-treated castrated males, the ultrastructure of special zone cells was similar to that of special zone cells in luteal-phase female possums. The findings suggest that the formation and cellular composition of the special zone is associated with changes in the pituitary-gonadal axis and that FSH plays a primary role in the differentiation of this tissue.     

Effect of acute heat stress on rat adrenal cortex — a morphological and ultrastructural study

The stereological structure of rat adrenal gland was analysed by light and electron microscopy after an acute (60 min) exposure to high ambient temperature (38°C). Under these conditions a significant increase in plasma corticotrophin (ACTH), serum corticosterone and aldosterone levels were observed. Histological and stereological investigation at light microscopy showed significant decrease in volume density of capsule and zona glomerulosa, increase in volume of fasciculata cells, and decrease of numerical density of zona fasciculata cells and mean diameter of blood vessels. At the ultrastructural level, volume density of nuclei and mitochondria of zona glomerulosa cells were significantly increased and that of lipid droplets decreased. Volume density of mitochondria of fasciculata cells was significantly increased, while number of lipid droplets per μm² of cell was reduced. In the cells of zona reticularis significant increase in the number of lipid droplets was found. The response of zona glomerulosa may be interpreted as immediate reaction to dehydration, while alterations detected in zona fasciculata, which were less extensive, were related to purely stressogenic effects of high ambiental temperature.     

An ultrastructural, morphometric and autoradiographic study of the effects of 7,12-dimethylbenzanthracene on the rat adrenal cortex.

The effects of chronic treatment (up to 9 consecutive days) with 7,12-dimethylbenzathracene (DMBA) on the adrenal glands of adult male Wistar rats were investigated. Morphometry showed that DMBA provokes atrophy of the zona reticularis which was due to the decrease in both cell volume and number. The zona fasciculata showed only a decrease in the cell volume, whereas the zona glomerulosa did not display any significant changes. Autoradiography demonstrated that DMBA induces a significant increase in the number of mitoses and "S" phase cells in the zona glomerulosa and outer zona fasciculata, which may be interpreted as a repair mechanism of the DMBA-provoked slight necrosis in the inner adrenocortical layers. The mechanism(s) underlying the cytotoxic effect of DMBA is discussed in the light of our ultrastructural observations showing that the chemical causes a decrease in the volume of the mitochondrial and nuclear compartments and in the surface of smooth endoplasmic reticulum as well as an increase in the volume of the lipid compartment.     

OSMIUM STAINING OF ENDOPLASMIC RETICULUM AND MITOCHONDRIA IN THE RAT ADRENAL CORTEX

The zona fasciculata of the rat adrenal cortex synthesizes and secretes glucocorticoids. As observed after aldehyde fixation, the cells in this zone contain an extensive endoplasmic reticulum (ER), a small Golgi apparatus, a moderate number of lipid droplets, and abundant mitochondria with tubulovesicular cristae. Numerous areas within the endoplasmic reticulum and mitochondrial cristae appear clear. In addition, a small percentage of mitochondria encompasses large, clear areas. After immersion of finely minced adrenal cortex in unbuffered 2% OsO₄ (40–48 hr at 40°C), deposits of osmium are seen within the Golgi apparatus, the entirety of the ER, and occasionally within mitochondria. In some mitochondria, the deposits are within cristae; in others, within vacuoles; in still others, in both cristae and vacuoles. These localizations correspond best to the clear areas found in aldehyde-fixed tissue. Osmium is not deposited in lipid droplets, in bar-containing inclusions, in mitochondrial matrix inclusions, or in the peripheral, outer mitochondrial spaces. Addition of zinc-iodide to OsO₄ increases the amount of Golgi apparatus and mitochondrial staining. Adrenocorticotropin (ACTH) does not affect the localization of deposits; hypophysectomy decreases mitochondrial staining. This study (a) emphasizes the necessity for electron microscopic confirmation of osmium localization when this technique is used as a Golgi apparatus stain; and (b) suggests that the ER-staining pattern may be consistent in cells actively synthesizing steroids or steroid-like compounds.     

PEROXISOMES IN INNER ADRENOCORTICAL CELLS OF FETAL AND ADULT GUINEA PIGS

Abundant membrane-bounded granules, 0.1–0.45 µm in diameter, occur among the elements of the smooth-surfaced endoplasmic reticulum in zona fasciculata and zona reticularis adrenocortical cells of guinea pigs. Acid phosphatase cannot be cytochemically demonstrated in them, and they are therefore distinct from lysosomes. Incubation in medium containing 3,3'-diaminobenzidine results in dense staining of the granules, identifying them as peroxisomes. These small peroxisomes increase in number as fetal adrenocortical cells differentiate, and they appear to arise from dilated regions of endoplasmic reticulum. They maintain interconnections with the smooth endoplasmic reticulum and with one another.     

Cytochemical and fine structural analysis of oogenesis in the gastropod, Ilyanassa obsoleta

An analysis of differentiating oocytes of the gastropod, Ilyanassa obsoleta, has been made by techniques of light and electron microscopy. Early previtellogenic oocytes are limited by a smooth surfaced oolemma and are associated with each other by maculae adhaerentes. Previtellogenic oocytes are also distinguished by a large nucleus containing randomly dispersed aggregates of chromatin. Within the ooplasm are Golgi complexes, mitochondria and a few cisternae of the rough endoplasmic reticulum. When vitellogenesis begins, the oolemma becomes morphologically specialized by the formation of microvilli. One also notices an increase in the number of organelles and inclusions such as lipid droplets. During vitellogenesis there is a dilation of the saccules of the Golgi complexes and cisternae of the endoplasmic reticulum. Associated with the Golgi complexes are small protein-carbohydrate yolk precursors encompassed by a membrane. These increase in size by fusing with each other. The “mature” yolk body is a membrane-bounded structure with a central striated core and a granular periphery. At maturity a major portion of the ooplasmic constituents such as as mitochondria and lipid droplets occupy the animal region while the bulk of the population of yolk bodies are situated in the vegetal hemisphere. The follicle cells incompletely encompass the developing oocyte. In addition to the regularly occurring organelles, follicle cells are characterized by the presence of large quantities of rough endoplasmic reticulum and Golgi complexes whose saccules are filled with a dense substance. Associated with the Golgi saccules are secretory droplets of varied size. Amongst the differentiating oocytes and follicle cells are Leydig cells. These cells are characterized by a large vacuole containing glycogen. A possible function for the follicle and Leydig cells is discussed.     

Ultrastructure of the cells of the ovarian interstitial gland in hypophysectomized rats

Summary The fine structure of the interstitial gland of the ovary was studied in hypophysectomized rats and in hypophysectomized rats after denervation of the ovary or stimulation of the ovarian plexus. Hypophysectomized rats were used to eliminate gonadotropic influences on interstitial cells. In hypophysectomized rats, there was a large amount of intercellular space and cells had irregularly shaped nuclei and a large nuclear-cytoplasmic ratio. Prominent cytoplasmic features included small mitochondria with an electron-dense matrix, rough and smooth endoplasmic reticulum, polysomes and large osmiophilic lipid droplets. Interstitial cells from stimulated ovaries had reduced intercellular space and a reduced nuclear-cytoplasmic ratio. Mitochondria had tubular cristae; smooth endoplasmic reticulum-surrounded lipid droplets, and large polysomes were present. After section of the ovarian plexus, intercellular space was increased and filopodia were numerous. Cytoplasmic features included mitochondria with a dense matrix and indistinct cristae, large electronlucent lipid droplets, and variously sized multivesicular structures. These observations suggest that stimulation of the ovarian plexus in hypophysectomized rats causes regressed cells to assume the fine structural features of active steroidogenic cells. In contrast, interruption of the ovarian nerve supply causes a qualitative and quantitative increase in ultrastructural features characteristic of regressed steroidogenic cells. These responses of interstitial gland cells to denervation and stimulation provide morphological evidence for a functional role for the adrenergic nerves to this ovarian compartment.     

Effects of tropic hormones on ultrastructure and synthesis of androgens in adrenals of male pseudohermaphrodite rats

Summary Ultrastructural and biochemical study of the adrenals in the pseudohermaphrodite (tfm) rat reveals hypertrophic adrenocortical cells. The cytoplasm of the cells in the zonae fasciculata and reticularis contains an exceptionally well developed smooth endoplasmic reticulum closely applied to mitochondria and lipid droplets. Mitochondria are more numerous than in normals and have especially abundant tubular cristae. More lipid droplets (appearing as empty vacuoles) are surrounded by pleomorphic mitochondria.The incubation study indicates that the capacity of rat adrenal cortex of producing androgens is greater in tfm than in normal animals. Hypophysectomy and castration result in a significant decrease in androgen biosynthesis by tfm rat adrenals and cause a reduced concentration of plasma testosterone. Administration of tropic hormones to hypophysectomizedcastrated rats appears to stimulate their adrenal androgenesis. It is suggested that in tfm rats the higher than normal luteinizing hormone (LH) together with adrenocorticotropic hormone (ACTH) stimulates the hypertrophy of cellular organelles in the adrenal cortex and causes an accompanying increase in androgenic steroids which may be responsible, at least in part, for the increased level of plasma androgens.     

A comparative morphometric analysis of the effects of thyroxine and ACTH on the zona fasciculata of rat adrenal cortex.

The effects of thyroxine and ACTH on the ultrastructure of cells of the adrenal zona fasciculata were studied by morphometric analysis and compared by two-way analysis of variance. The results indicate that the effects of thyroxine and ACTH are different and independent. The statistically significant differences in effect of thyroxine and ACTH are: thyroxine causes an increase in the volume fraction of mitochondria and a decrease in the volume fraction of endoplasmic reticulum independent of ACTH; thyroxine causes a decrease in surface density of mitochondria and endoplasmic reticulum in the absence of ACTH, but in the presence of ACTH this effect is moderated by an interaction of throxine and ACTH. There were no statistically significant effects of either thyroxine or ACTH on volume fraction or surface density of liposomes.     

Cytological differentiation of the interrenal tissue of the Japanese quail,Coturnix coturnix

Summary As reported for several other avian species there are clearly distinguishable subcapsular (SCZ) and inner (IZ) zones of interrenal tissue in the Japanese quail. The SCZ contains large columnar cells (type I) with rounded nuclei, polymorphic mitochondria with shelf-like cristae, and relatively small numbers of lipid droplets. The IZ contains two and possibly three types of cells. Type II consists of large columnar cells with moderately dense cytoplasm containing large numbers of lipid droplets and many rounded mitochondria with tubular cristae. Smooth endoplasmic reticulum (SER) and Golgi apparatus are well developed; coated vesicles occur in the Golgi area and at the cell surface. Type-III cells occur in IZ and especially in its more peripheral areas. They are columnar cells with strikingly clear cytoplasm (in comparison with type II) containing mitochondria with plate-like cristae and tubular SER. Type-IV cells are sparsely distributed in IZ and occur rarely in SCZ. Type IV may be a degenerating phase of type III.After adenohypophysectomy or section of portal vessels type-I cells atrophy somewhat with a decrease in lipid droplets; type-II cells, also atrophy with conspicuous increase in size and number of lipid droplets, enlargement of mitochondria, and gradual disappearance of SER; type-III cells decrease in number whereas type-IV cells increase.After injection of ACTH, type-I cells enlarge and their mitochondria, SER and Golgi apparatus become more conspicuous; there is a decrease in lipid droplets in type-II cells and a development of SER, polysomes and Golgi apparatus; there is also a decrease in lipid droplets and a development of SER in type-III cells after injection of 2IU ACTH and an almost complete disappearance of lipid droplets after 4IU ACTH; type-IV cells increase in number.The investigation reported herein was supported by Scientific Research Grants from the Ministry of Education of Japan to Professor Mikami; and by grants from the Japan Society for the Promotion of Science, the National Science Foundation (USA), and the Graduate School Fund of the University of Washington to Professor Farner     

Possible relationship between the activity of the adrenal gland and the subcommissural organ in the lizard Lacerta s. sicula raf.

Summary In order to study the possible functional relationship between the adrenal gland and the subcommissural organ (SCO) in the lizard Lacerta s. sicula Raf., ACTH was administered to some specimens of this species in January when both the adrenal gland and the subcommissural organ have a very low activity. In comparison to untreated controls, the adrenals of animals treated with ACTH showed clear signs of stimulation, presenting enlarged blood vessels, very few lipid droplets, numerous polymorphic mitochondria and abundant tubular smooth endoplasmic reticulum. In addition, a distinct increase in secretory material was observed in the subcommissural cells of specimens treated with ACTH. These cells showed large cisternae of the rough endoplasmic reticulum filled with granular material in the basal region, numerous secretory granules of two types in the apical region and a reduced number of microvilli on the free cell surface. These findings, together with the results of preceding studies, lead the authors to the consideration that steroid hormones might play a role in the regulation of the secretory activity of the SCO.     

CYTOLOGICAL ALTERATIONS RELATED TO STIMULATION OF THE ZONA GLOMERULOSA OF THE ADRENAL GLAND

The structure of the zona glomerulosa of the rat adrenal gland stimulated by sodium restriction has been studied by light and electron microscopy. The major changes observed during the course of the experiment in stimulated glands involve cytoplasmic droplets, mitochondria, and the endoplasmic reticulum. There is a progressive decrease in the number of cytoplasmic droplets of low electron opacity. Numerous, greatly elongated mitochondria containing parallel arrays of tubules are noted. These tubules extend from within the mitochondria through gaps in the mitochondrial-limiting membranes into the cytoplasm. In addition, amorphous intramitochondrial deposits, possibly aldosterone precursors, are seen. Increased amounts of smooth-surfaced endoplasmic reticulum, often showing complex arrangements, are another feature of the stimulated zona glomerulosa. Other alterations include the presence of large numbers of dense bodies as well as cytoplasmic droplets of high electron opacity. These observations are discussed in relation to the biosynthesis of aldosterone.     

Ultrastructure of the indifferent gonad in male and female pig embryos.

Pig embryos aged 24 days were obtained from artifically inseminated sows for ultrastructural study of the indifferent gonads. Sex was identified by chromosome analysis. The gonads are composed in both sexes of three different tissues: the surface epithelium, the gonadal blastema and the mesenchyme. The surface epithelial cells contained elongate mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, fine filaments and coated vesicles. The primitive cords were continuous with the surface epithelium and the interior of the gonad was occupied by blastema cells. They had prominent nucleoli, elongate mitochondria, granular endoplasmic reticulum, the Golgi complex, free polysomes, some lipid droplets and occasionally circular smooth membrane profiles resembling the agranular endoplasmic reticulum. Individual primordial germ cells were seen in all parts of the gonad. They were roundish with prominent nucleoli, globular mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, coated vesicles, lipid droplets and dense bodies. Degenerating cells and cells having pseudopods were also encountered. In comparison to the gonad at the age of 22 days, the primordium had grown into a longitudinal roundish protrusion and the number of primoridal germ cells had increased. Histological and ultrastructural observations showed that the pig gonads at the age of 24 days were similar in both sexes.     

Studies of the fine structure of ovarian interstitial tissue

Summary The fine structure of ovarian steroid-producing cells of the domestic fowl as seen after administration of steroids is described. Diaethylstilboestrol, estradiol and hydroxyprogesterone were given as intramuscular injections for a 28-days period. The main cytoplasmic changes of the steroid-producing cells were an increase in the number and the size of lipid droplets due to a possible expansion of the endoplasmic reticulum and a confluence of the smooth endoplasmic reticulum and the lipid droplets. The mitochondria became paler, markedly reduced in size and number, and contained less cristae. The Golgi apparatus became smaller and tended to disappear. The most prominent nuclear changes were irregular outline of the nuclear membrane, shrinkage of the nucleus, formation of pseudo-inclusions, decreased number of nuclear bodies with a tendency to vacuolization and small nucleoli. These alterations have never been demonstrated in ovarian steroid-producing cells before, and they are consistent with atrophic changes observed in steroid-producing cells in other organs. The present study substantiates the view that the thecal gland must be concerned with endocrine function. The possible functions of the different cell types of the thecal gland are discussed.     

Histochemical and ultrastructural analysis of developing adipocytes in the fetal pig

Histochemical and ultrastructural aspects of adipocyte differentiation in subcutaneous tissue of fetal pigs were analyzed in a longitudinal study. A matrix of collagen fibers surrounding adipocytes developed after the establishment of a distinct and continuous PAS-positive basement membrane. The degree of plasma membrane invagination and specialization was positively correlated with the extent of basement membrane and collagen matrix formation. Close spatial relationships between narrow, smooth endoplasmic reticulum, plasma membrane invaginations, the surface of lipid droplets and mitochondria were observed in differentiating adipocytes. Histochemical and ultrastructural criteria for the identification of preadipocytes are: (1) perivascular location; (2) mitochondria localized in the Golgi zone; (3) cytosolic glycogen; (4) rough endoplasmic reticulum with cisternae uniformly and approximately 600 A wide; (5) free ribosomes and few polysomes, and (6) lipid droplets encased by microfilaments. These criteria permitted clear distinction from obvious fibroblasts and macrophages. Other stromal cells were morphologically abnormal. Occasionally, adipocytes and perivascular cells exhibited close intercellular contacts that were morphologically distinct from intercellular contacts between contiguous endothelial cells.     

The status of the corpus luteum during pregnancy in Miniopterus schreibersii (Chiroptera: Vespertilionidae) with emphasis on its role in developmental delay

Summary Developmental delay is correlated with torpor in the temperate zone bent-winged bat, Miniopterus schreibersii (latitude 37° S) as a period of pre-implantation delay (delayed implantation) followed by a short post-implantation delay (delayed development). During this time, the number of steroidogenic organelles in luteal cytoplasm is greatly reduced compared with normal embryogenesis, and granular endoplasmic reticulum is prominent. Nidation, which occurs while the animals are hibernating, is not accompanied by marked changes in luteal ultrastructure, although the number of lipid droplets decreases somewhat. Progesterone rises slightly but not significantly; however, a pre-nidation decrease in high 17-estradiol levels may play a role in implantation. Following implantation, the conceptus remains delayed at the blastocyst stage for several weeks. During this time the bats remain torpid and the only change in luteal cell ultrastructure is an increase in smooth endoplasmic reticulum as differentiation begins toward the trilaminar stage. At the end of developmental delay hypertrophy of the luteal cell begins and mitochondria and lipid droplets increase, markedly. By this time arousal from hibernation has occurred, placentation takes place, and normal development is underway. At placentation, smooth endoplasmic reticulum reaches its maximum in luteal cytoplasm; estrogen and progesterone levels peak about 6 weeks later. For the remaining 2 months of gestation, signs of luteolysis appear. These observations suggest that the corpus luteum of developmental delay, though suboptimally functional, is prolonged in its luteinization by the arrival of winter when the bats enter torpor. The capacity for maximal steroidogenesis is acquired at the end of winter, some weeks after implantation, when arousal occurs and normal development ensues.     

Effects of alpha-amanitin on the fine structure of adrenal fasciculata cells in the young rat

The administration of 0.2 micrograms/g/bw of alpha-amanitin to approximately 20 g rats provoked the following nuclear modifications in rat adrenal fasciculata cells at 60 min: chromatin condensation, nucleolar fragmentation, increase in the number of PCG and clumping of ICG in the center of the nucleus. At longer time intervals (2.5 and 4.5 hr) these alterations were more evident, but at 24 hr the nuclear structure was back to normal with the exception of a persistent increased number of PCG. After injection of 0.75 micrograms/g/bw and at 2.5 hr, there was pulverization of condensed chromatin, fragmentation and partial segregation of the nucleolus with increased density of the fibrillar component. Cytoplasmic alterations were severe including cap-shaped mitochondria with electron-dense matrix surrounding lipid droplets, reduced endoplasmic reticulum of vesicular type and clusters of microvesicles with dense content in the Golgi trans-area. At 24 hr, the nuclear and cytoplasmic morphology returned to normal. These findings are interpreted as the morphological counterpart of a disturbance of extranucleolar and nucleolar RNA synthesis, as well as of lipid and lipoprotein metabolism, brought about by the drug.