Giant lysosomes in the renal proximal tubules--a morphological characteristic of DBA/2 and DBA/1 mouse kidneys.

The DBA/2Cr mouse is characterized by the presence of giant lysosomes located in the proximal convoluted tubules of males and proximal straight tubules of females. However, it remains unclear whether these giant lysosomes in the proximal tubules are characteristic of DBA/2Cr specifically, or are common to other DBA/2 substrains and DBA/1. The present study investigated the morphology of kidneys from DBA/2CrSlc, DBA/2JJcl, DBA/2NCrj and DBA/1JNCrj mice of both sexes. Giant lysosomes in the renal proximal tubules were found to represent common morphological characteristic of both DBA/2 and DBA/1JN.     

Lectin-histochemical and -cytochemical study of periodic acid Schiff-positive lysosome granules as a histological feature of the female mouse kidney

Renal proximal straight tubules (PST) of the female mouse contain periodic acid Schiff-positive lysosome granules. An excellent example of this is found in the kidneys of female DBA/2Cr mice. In the present study, lectin-histochemistry showed that lectin-positive granules occur in the PST of DBA/2Cr mice. Out of twenty-one lectins studied, the granules bound WGA, s-WGA, LEL, STL, DSL, GSL-II, VVL, RCA-I, ECL, PSA, LCA and PHA-E. Such granules were also observed in the proximal convoluted tubules (PCT). In addition, heterogeneous binding to the SBA or DBA was observed in the PST. Lectin-cytochemistry for s-WGA, STL, VVL, RCA-I, ECL and PSA, showed that: 1) lysosomes bind a higher level of s-WGA or STL than VVL, RCA-I, ECL or PSA; 2) PSA binding is similar in PST and PCT; 3) there are many PCT lysosomes that are negative for s-WGA, STL, VVL, RCA-I, and ECL lectin binding; and 4) s-WGA binding is highly specific to the lysosomes of the PST. Based on the binding specificities of each lectin, it was suggested that the mannose content of PST and PCT lysosomes is similar, and that PST lysosomes have a high level of N-acetylglucosamine, N-acetylgalactosamine, galactose or galactosyl (beta 1, 4) N-acetylglucosamine.     

Expression of Bcl-2 and Bax in mouse renal tubules during kidney development

Bcl-2 and Bax play an important role in apoptosis regulation, as well as in cell adhesion and migration during kidney morphogenesis, which is structurally and functionally related to mitochondria. In order to elucidate the role of Bcl-2 and Bax during kidney development, it is essential to establish the exact location of their expression in the kidney. The present study localized their expression during kidney development. Kidneys from embryonic (E) 16-, 17-, 18-day-old mouse fetuses, and postnatal (P) 1-, 3-, 5-, 7-, 14-, 21-day-old pups were embedded in Epon. Semi-thin serial sections from two E17 kidneys underwent computer assisted 3D tubule tracing. The tracing was combined with a newly developed immunohistochemical technique, which enables immunohistochemistry on glutaraldehyde fixated plastic embedded sections. Thereby, the microstructure could be described in detail, and the immunochemistry can be performed using exactly the same sections. The study showed that Bcl-2 and Bax were strongly expressed in mature proximal convoluted tubules at all time points, less strongly expressed in proximal straight tubules, and only weakly in immature proximal tubules and distal tubules. No expression was detected in ureteric bud and other earlier developing structures, such as comma bodies, S shaped bodies, glomeruli, etc. Tubules expressing Bcl-2 only were occasionally observed. The present study showed that, during kidney development, Bcl-2 and Bax are expressed differently in the proximal and distal tubules, although these two tubule segments are almost equally equipped with mitochondria. The functional significance of the different expression of Bcl-2 and Bax in proximal and distal tubules is unknown. However, the findings of the present study suggest that the mitochondrial function differs between mature proximal tubules and in the rest of the tubules. The function of Bcl-2 and Bax during tubulogenesis still needs to be investigated.     

OCCURRENCE OF PHAGOSOMES AND PHAGO-LYSOSOMES IN DIFFERENT SEGMENTS OF THE NEPHRON IN RELATION TO THE REABSORPTION, TRANSPORT, DIGESTION, AND EXTRUSION OF INTRAVENOUSLY INJECTED HORSERADISH PEROXIDASE

The size, number, and location of lysosomes, phagosomes, and phago-lysosomes in different segments of the proximal and distal tubules, in the collecting tubules, and in invading macrophages of the kidneys of rats were compared by staining lysosomes (acid phosphatase) red, and phagosomes (injected horseradish peroxidase) blue in separate sections, and by staining phago-lysosomes purple by successive application of the reactions for the two enzymes in the same sections. It was concluded from these observations that the absorption of the foreign protein from the lumen and its gradual digestion in large phago-lysosomes took place mainly in the cells of the proximal convoluted tubules of the outer cortex. Several segments of the proximal convoluted tubules were distinguished on the basis of differences in the size and location of the phago-lysosomes and the amounts of peroxidase ingested. The distal tubules showed, in addition to moderate numbers of phago-lysosomes, many small phagosomes in the apical and basal zones of the cells. Moderate numbers of phagosomes and phago-lysosomes were observed in the cells of the collecting tubules. Macrophages showing very large phago-lysosomes were seen in the peritubular capillaries of the medulla, after injection of peroxidase. When high doses of peroxidase were administered, enlarged phago-lysosomes, parts of which seemed to be extruded into the lumen, were formed in the terminal segments of the proximal convoluted tubules.     

Role of TASK2 potassium channels regarding volume regulation in primary cultures of mouse proximal tubules

Several papers reported the role of TASK2 channels in cell volume regulation and regulatory volume decrease (RVD). To check the possibility that the TASK2 channel modulates the RVD process in kidney, we performed primary cultures of proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) from wild-type and TASK2 knockout (KO) mice. In KO mice, the TASK2 coding sequence was in part replaced by the lac-Z gene. This allows for the precise localization of TASK2 in kidney sections using beta-galactosidase staining. TASK2 was only localized in PCT cells. K+ currents were analyzed by the whole-cell clamp technique with 125 mM K-gluconate in the pipette and 140 mM Na-gluconate in the bath. In PCT cells from wild-type mice, hypotonicity induced swelling-activated K+ currents insensitive to 1 mM tetraethylammonium, 10 nM charybdotoxin, and 10 microM 293B, but blocked by 500 microM quinidine and 10 microM clofilium. These currents were increased in alkaline pH and decreased in acidic pH. In PCT cells from TASK2 KO, swelling-activated K+ currents were completely impaired. In conclusion, the TASK2 channel is expressed in kidney proximal cells and could be the swelling-activated K+ channel responsible for the cell volume regulation process during osmolyte absorptions in the proximal tubules.     

Beige granules as a cell marker for clonal analysis in kidney and liver of mouse aggregation chimaeras, and three-dimensional reconstruction from serial paraffin sections

Anomalous giant granules of beige (bg) mice have been used as a cell marker in the study of cell lineage of mast cells. Similar granules are known to exist in other tissues including kidney proximal tubules and liver parenchymal cells. In the present study, these granules were found to give yellow or orange autofluorescence when the tissue had been fixed with formaldehyde and embedded in paraffin. Thus, the granules can be used as a cell marker that can be visualized in serial paraffin sections without any specific histochemical staining. Chimaeric mice were produced by aggregation of 8-cell-stage embryos of beige (C57BL/6J-bgJ/bgJ) and A/J strains. The chimaeric liver showed beige cell patches with complicated shapes, although the patches frequently conformed to the shape of parenchymal cell cord or plate structures. In chimaeric kidney, beige cells formed coherent patches in the proximal tubules. The tubules were found to contain more than one clone. The patches frequently had long extended shapes suggesting growth of the clone along the tubule axis. Three-dimensional image reconstruction from the serial paraffin sections was carried out with the aid of a computer-assisted image analysis system, resulting in a clearer image of the patch shape.     

Cellular differentiation in the kidneys of newborn mice studies with the electron microscope

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

CELLULAR DIFFERENTIATION IN THE KIDNEYS OF NEWBORN MICE STUDIED WITH THE ELECTRON MICROSCOPE

The structure of the kidney of the Swiss albino mouse changes progressively during the first 2 weeks after birth. Cells proliferate to form new nephrons, cells differentiate by acquiring specialized membranous components, and certain cytological features which are present at birth diminish in abundance or disappear. The differentiation of the cells of the cortical tubules has been studied using the light and electron microscopes. The tubules are partially and variably differentiated at birth. During the first 2 weeks after birth the brush border develops in the proximal tubules by the accumulation of numerous microvilli on the apical cell margins. Basal striations develop in proximal and distal tubules as an alignment of mitochondria, the result of what appears to be progressive interlocking of adjacent fluted cells. The mitochondria increase in number and size, accumulate homogeneous matrix, and acquire small, very dense granules. The collecting ducts develop tight pleating of the basal cell membranes, and dark cells containing numerous small cytoplasmic vesicles and microvilli appear. At birth there are dense irregular cytoplasmic inclusions presumed to be lipide in renal cells, the cytoplasmic granules of Palade are abundant, and there are large round bodies in the cells of the proximal tubules. The lipide inclusions disappear a few days after birth, and the cytoplasmic granules of Palade diminish in abundance as the cells differentiate. The large round bodies in the proximal tubules consist of an amorphous material and contain concentrically lamellar structures and mitochondria. They resemble the cytoplasmic droplets produced in the proximal tubules of adult rats and mice by the administration of proteins. The large round bodies disappear from the proximal tubules of infant mice during the first week after birth, but the concentric lamellar structures may be found in adult mice.     

Histopathology of streptozotocin-induced diabetic DBA/2N and CD-1 mice

Histopathological examinations were carried out on female DBA/2N and CD-1 mice which were autopsied 4 and 12 weeks after six daily intraperitoneal injections of streptozotocin (SZ). Histopathological changes related to SZ treatment were found in the pancreas, liver and kidneys. Little difference was observed between the two strains in the histological changes of the pancreas (a decrease in size of the islets, and degranulation and a decrease in the number of B cells) and liver (hypertrophy of hepatocytes and cytoplasmic invagination into hepatocyte nuclei). With regard to the changes in the kidneys, DBA/2N mice showed characteristic inclusions positive to periodic acid-Schiff reagent in the distal tubule epithelial cells, while CD-1 mice showed remarkable luminal dilatation and epithelial cell deformation of distal tubules. SZ-induced diabetes had no influence on the development of spontaneous cardiovascular lesions in DBA/2N mice under the present experimental conditions.     

小熊猫肾脏和输尿管的组织学研究

小熊猫的肾脏呈蚕豆形,表面光滑不分叶,只有1个肾锥体和1个肾盏,无肾盂。肾脏皮质内可见皮质迷路和髓放线。皮质迷路内有近曲小管、远曲小管和肾小体等结构。髓放线内有近端小管直部和远端小管直部。髓质可分为外髓和内髓两个区域。外髓有较多的集合管断面,少量的远端小管直部和细段,较多的直小血管束。内髓部位有大量的细段和乳头管。各种泌尿小管之间有少量的疏松结缔组织构成的间质,间质内有丰富的毛细血管。输尿管横切面呈圆形或卵圆形,管腔呈不规则的裂隙状。管壁由粘膜、肌肉层和外膜组成。并与大熊猫肾脏和输尿管的组织结构作了比较研究。     

Renal carbonic anhydrase activity in DBA/2FG-pcy/pcy mice with inherited polycystic kidney disease.

DBA/2FG-pcy/pcy (D2-pcy) mice are a hereditary murine model of slowly progressive polycystic kidney disease (PKD) and characterized by the persistent excretion of acidic urine, in association with polyuria, after weaning. In this study, the activity of carbonic anhydrase (CA) and it histological distribution in the kidney of D2-pcy mice were investigated by immunohistochemistry. Significantly higher CA activity was detected in the cytosolic, but not membrane, fraction of kidney homogenates in 5-week-old D2-pcy mice than in age-matched, control DBA/2 (D2) mice, and a more rapid rate of urine acidification was noted in 11-week-old mice when acetazolamide, an inhibitor of the enzyme, was administered orally. By immunohistochemistry for the major renal CA isoenzyme (CA II), epithelial cells in the distal straight tubules and the cortical collecting ducts were stained intensely, whereas those of the proximal convoluted tubules had only weak and diffuse staining. The glomeruli, the proximal straight tubules and the ascending thin limb of Henle's loop were almost free from staining. In the cells lining cysts and/or dilated tubules, CA II activity was well preserved, although the staining intensity was considerably reduced in fully-flattened, lining cells of cysts, but no difference was found between D2-pcy and D2 mice in any segmental localization of renal CA II activity. From these results it seems that D2-pcy mice in the early stages of the cystic disease continue to secrete excess protons through the CA-mediated reaction that is stimulated for regulation of acid-base balance in the distal portion of the nephron and the collecting duct in kidney. It also suggests that monitoring urine pH may be useful in predicting the effects of early interventions on the progression of slowly developing renal cysts.     

Metaphase-specific cell death in meiotic spermatocytes in mice

Apoptosis of male germ cells is a widespread but little-understood phenomenon in many animal species. The elucidation of its mechanisms could be useful in the understanding of male infertility. We have examined the distribution of dying cells with the terminal transferase-mediated nick-end labeling (TUNEL) method and by an electron-microscopic procedure in the testes of 10 mouse strains, viz., C57BL/10 (B10), SL/NiA (SL), C57BL/6 (B6), C3H/He (C3H), BALB/c (BALB), DBA2 (DBA), CBA/J (CBA), MRL/MpJ(-)+/+ (M+), MRL/MpJ-lpr/lpr (lpr), and wild-type NJL mice (Mus musculus musculus). In the testes of the B10, NJL, SL, B6, C3H, BALB, DBA, and CBA mice, very few TUNEL-positive cells are distributed in the seminiferous tubules, whereas in the testes of the M+ and lpr mice, many TUNEL-positive cells, which are restricted to stage XII seminiferous tubules, have been identified. The most important finding is that many metaphases of meiotic spermatocytes show a marked TUNEL-positive reaction. Some metaphases show apoptotic morphology electron-microscopically. These results suggest that the testes of MRL strains will provide a useful model for the study of the mechanism of metaphase-specific apoptosis in meiotic spermatocytes.     

The use of silver nitrate as a vital stain,and its distribution in several mammalian tissues as studied with the electron microscope

After chronic administration of a dilute solution of silver nitrate in drinking water to rats, mice, and guinea pigs, granular deposits of metallic silver were detected in electron micrographs of the kidney, liver, thyroid, and pancreas. The silver deposits were in the form of extremely dense, angular particles with sharp outlines. They varied from aggregates a few microns in diameter down to granules at the limit of resolution of the electron microscope. The principal sites of deposition were (1) basement membranes, especially those of the renal glomeruli, proximal convoluted tubules, and various glands, and those associated with vascular endothelium, and (2) the cytoplasm of fixed and free macrophages. Both in Kupffer cells lining hepatic sinusoids and in the wandering macrophages of other tissues, the silver was segregated in discrete vacuoles. In addition, granular deposits were observed in occasional vesicular structures in the proximal convoluted tubules of the kidney, the hepatic cells, and the pancreatic acinar cell. These structures, in favorable preparations, contained an outer double layered membrane and internal folds similar to those of mitochondria, from which they appear to have been derived. The significance of these findings in heavy metal poisoning and in cellular physiology is briefly discussed.     

THE USE OF SILVER NITRATE AS A VITAL STAIN, AND ITS DISTRIBUTION IN SEVERAL MAMMALIAN TISSUES AS STUDIED WITH THE ELECTRON MICROSCOPE

After chronic administration of a dilute solution of silver nitrate in drinking water to rats, mice, and guinea pigs, granular deposits of metallic silver were detected in electron micrographs of the kidney, liver, thyroid, and pancreas. The silver deposits were in the form of extremely dense, angular particles with sharp outlines. They varied from aggregates a few microns in diameter down to granules at the limit of resolution of the electron microscope. The principal sites of deposition were (1) basement membranes, especially those of the renal glomeruli, proximal convoluted tubules, and various glands, and those associated with vascular endothelium, and (2) the cytoplasm of fixed and free macrophages. Both in Kupffer cells lining hepatic sinusoids and in the wandering macrophages of other tissues, the silver was segregated in discrete vacuoles. In addition, granular deposits were observed in occasional vesicular structures in the proximal convoluted tubules of the kidney, the hepatic cells, and the pancreatic acinar cell. These structures, in favorable preparations, contained an outer double layered membrane and internal folds similar to those of mitochondria, from which they appear to have been derived. The significance of these findings in heavy metal poisoning and in cellular physiology is briefly discussed.     

Kallikrein localization in rodent salivary glands and kidney with the immunoglobulin-enzyme bridge technique.

Kallikrein has been localized in rodent kidney and salivary glands by means of an immunoglobulin-enzyme bridge technique. In sections of kidney, anti-kallikrein antibodies bound to the apical region of certain distal tubule segments in the cortex, to reabsorption droplets of proximal convoluted tubules, and to certain duct segments in the papilla. In salivary glands of both male and female rats and mice, and apical rim of most striated duct cells of submandibular, parotid and sublingual glands and granular tubules of submandibular glands exhibited immunoreactivity. Granular intercalated duct cells in female submandibular glands also displayed immunostaining for kallikrein. Phenylephrine administration resulted in loss of immunoreactive granules from the granular convoluted tubule cells of male mouse submandibular gland. This response was paralleled by a biochemically demonstrable decrease in kallikrein-like tosylarginine methyl ester (TAME) esterase activity.     

Sex and strain differences in the brush border and PAS-positive granules and giant bodies of the mouse renal S3 segment cells.

We recently demonstrated sexual dimorphism in the S3 segment of the ICR mouse kidney, as differences in periodic acid Schiff (PAS) staining on the brush border and the number and size of PAS-positive granules. However, whether these sex dependent features in the S3 segment of the mouse kidney occur only in the ICR strain or are a general feature also observed in other strains is unclear. In the present study, we examined the renal S3 segment of the ICR, BALB/c, C57BL/6, C3H/He and DBA/2 mice strains, which are commonly used in laboratory experiments. PAS staining of the brush border in females of all strains was more intense than that of males, and PAS-positive granules were detected in all females. In male groups, PAS-positive granules were detected in the DBA/2 strain only, but their number was very few. In addition, PAS-positive giant bodies, larger than the nuclear size, were detected in females except those of the C57BL/6 strain. Histometrical investigation demonstrated apparent strain differences in a number of PAS-positive granules and PAS-positive giant bodies. The ultrastructural and cytochemical investigations suggest that the PAS-positive granules and PAS-positive giant bodies were multilamellar lysosomes. We propose that the present findings are significant for comparative morphology in laboratory animal science.     

鸡肾发生的组织学观察

采用组织学方法和电镜技术,对9个不同发育时期的鸡(Callus domestiaus)胚胎进行了观察.通过对鸡胚胎肾组织发生过程的观察,探讨鸡胚中肾的发生与退化,后肾的发生、分化规律和特点.结果表明,孵育到第16期在中肾前端附近出现一些中肾小泡.孵育到第18期形成中肾小管.孵育到第26期,中肾小管的盲端内陷,原始的肾小囊和肾血管球形成,中肾小管显著伸长并迂回曲折.孵育到第33～37期,体前后部中肾组织均已形成完整的肾单位.第37～46期体前部至后部的中肾组织依次退化.孵育到第26期从泄殖腔附近发出的输尿管芽向生后肾组织侵入生长,生后.肾组织产生许多生后肾小泡.第33期出现肾小囊和肾小管,肾小管伸长并发生折叠,出现集合小管、近端小管和远端小管的形态分化.第37～46期肾小体逐渐发育成熟,肾小管继续分化出现细段.鸡的中肾具有排泄功能.鸡后肾的发生与分化存在明显的时间差异.肾单位的分化中,同一胚龄肾组织内可存在不同发育阶段的肾小体,集合小管分化较早,诱导近端小管和远端小管分化,细段分化较迟.     

Electron microscopic immunohistochemical localization of components of Na+-cotransporters along the rat nephron

The localization of Na+-cotransport proteins in cortex and outer medulla of rat kidney was investigated with five monoclonal antibodies. Recently, it was found that these antibodies altered Na+-D-glucose cotransport and/or Na+-dependent high affinity phlorizin binding in pig kidney cortex and that three of these antibodies interacted also with Na+-cotransporters for lactate, L-alanine and/or L-glutamate (Koepsell, H., K. Korn, A. Raszeja-Specht, S. Bernotat-Danielowski, D. Ollig, J. Biol. Chem. 263, 18,419-18,429 (1988]. In pig and rat the monoclonal antibodies bind to two brush-border membrane polypeptides with identical molecular weights and isoelectric points of 75,000 and pI 5.5, and 47,000 and pI 5.4. These polypeptides have been previously identified as components of the porcine renal Na+-D-glucose cotransporter (Neeb, M., U. Kunz, H. Koepsell, J. Biol. Chem. 262, 10,718-10,727 (1987] and may also be part of other Na+-cotransporters. The electron microscopic localization of antibody binding was demonstrated by protein A-gold labeling on ultrathin plastic sections. Three antibodies bound to brush-border membranes of proximal convoluted and straight tubules. In the proximal convoluted tubules all antibodies reacted with apical endocytic vacuoles, apical dense tubules and lysosomes. Since dense tubules are supposed to originate from endocytic vacuoles and to fuse with brush-border membranes the data suggest recycling of Na+-cotransporters in the proximal convoluted tubule. In the outer medulla two antibodies bound to apical membranes of descending thin limbs (DTL) of short loops of Henle and to apical and basal membranes of DTL of long loops of Henle. Three antibodies bound to apical membranes of collecting ducts. These data indicate that Na+-cotransporters or homologous proteins exist beyond the proximal tubule.     

Membrane traffic after inhibition of endocytosis in renal proximal tubules

This study was performed to examine quantitatively the cellular organelles involved in membrane recycling after inhibition of luminal endocytosis in renal proximal tubules. Paraffin oil was microinfused into rat renal proximal convoluted tubules to prevent luminal endocytosis. After 1-2 hr the kidneys were fixed by perfusion and prepared for electron microscopy. Segment 1 proximal tubules infused with paraffin oil and control tubules from the same kidney were studied. In addition we examined proximal tubules from kidneys fixed by immersion 30 sec after removal of the kidney. In the oil-infused tubules the large endocytic vacuoles (greater than 0.5 micron) disappeared, the amount of small endocytic vacuoles (less than 0.5 micron) was reduced to about 10%, and the amount of dense apical tubules was significantly increased. The dense apical tubules were very seldom seen connected to the apical plasma membrane in controls but this was occasionally observed in tubules fixed by immersion and relatively often in oil-infused tubules. An ultrastructural morphometric analysis substantiated and extended the qualitative observations and provided quantitative estimates of volumes and surface areas for large endocytic vacuoles, lysosomes, mitochondria, small endocytic vacuoles, and dense apical tubules in control and experimental tubules. The results strongly support the suggestion that the dense apical tubules located in the apical cytoplasm represent the vehicle for the recycling of membrane from endocytic vacuoles back to the plasma membrane, and show that in renal proximal tubule cells small and large endocytic vacuoles are transformed into dense apical tubules when endocytosis is stopped.     

Immunocytochemical localization of epidermal growth factor in mouse submandibular gland.

The cellular and subcellular localization of epidermal growth factor in the submandibular glands of male and female adult mice was established by immunoperoxidase techniques. In light microscopic preparations epidermal growth factor was found exclusively in the granular convoluted tubules of the gland. The intensity of staining for epidermal growth factor varied from cell to cell, and some cells apparently were negative. The pattern of staining was similar in the glands of male and female mice; however, the granular convoluted tubules are androgen-responsive, and thus more extensive and composed of larger cells in males. In thin sections epidermal growth factor was most heavily concentrated in the secretion granules of the granular convoluted tubule cells. Within a given cell there was variation in intensity of staining of individual secretion granules, with some granules appearing minimally reactive or negative. The only other cell component with deposits of reaction product was the ribosomes.