On the regional histology and histochemistry of the epididymis of the camel (Camelus dromedarius).

Distinct morphological regions, initial, middle and terminal segments, were distinguishable histologically; the middle segment was further subdivided into proximal, intermediated and distal parts. PAS-positive, diastase-resistant reaction was detected in the blood vessels, subepithelial tissue and stereocilia of all segments. Acid phosphatase was demonstrated in the epithelial cells with the highest activity being in the proximal part of the middle segment. Non-specific esterase gave a similar reaction but the strongest activity was in the terminal segment. Alkaline phosphatase, adenosine triphosphatase and adenosine monophosphatase were of similar activity in the subepithelial tissue, blood vessels, stereocilia and luminal contents; the strongest reaction occurred in the middle segment. Lactate, succinate, glutamate and glucose-6-phosphate dehydrogenases were examined; LDH was more active than the others particularly in the terminal segment. Some reaction was found in the epithelial cells, subepithelial tissue and luminal contents.     

Enzyme histochemistry of the sheep uterus during the oestrous cycle

Enzyme histochemical techniques were applied to frozen sheep uteri from different stages of the oestrous cycle. The localization and activities of succinate, lactate, glucose-6-phosphate, and isocitrate (NADP+) dehydrogenases and acid and alkaline phosphatases were studied in the luminal and glandular epithelia, caruncle and myometrium. Enzyme activity in the sections was scored on a scale of 0--5. In general the enzyme activity in the uterine caruncles and epithelia was higher than in the myometrium. The myometrium did not show any alkaline phosphatase activity and isocitrate dehydrogenase (NADP+) activity was negligible. The low activities of acid phosphatase and lactate dehydrogenase and the moderate levels of glucose-6-phosphate and succinate dehydrogenases in the myometrium were constant. The caruncular tissue showed high levels of phosphatases and glucose-6-phosphate dehydrogenase, moderate levels of lactate and succinate dehydrogenases, and low levels of isocitrate dehydrogenase (NADP+) throughout the oestrous cycle. Much lower phosphatase and isocitrate dehydrogenase (NADP+) levels were found in the epithelium of deep glands compared with superficial glands. The high activity of acid and alkaline phosphatases in the luminal epithelium and the superficial glands was constant from mid-cycle to ovulation, but a significant decrease was observed immediately after ovulation. The level of dehydrogenases in epithelia was generally high and did not change during the oestrous cycle.     

The ultrastructural localization of membrane ATPase in rat thin limbs of the loop of Henle.

The cytochemical distribution of nonspecific membrane ATPase activity in the epithelial membranes of the thin limbs of the loops of Henle of rat nephrons was studied at the ultrastructural level. Membrane ATPase activity was localized in the luminal, lateral, and (to a lesser extent) basal membranes of only the outer medullary segment of the thin descending limbs of long nephrons (Type II epithelium). The reaction product was lacking in the thin limb of short nephrons (Type I epithelium) as well as in the inner medullary descending (Type III epithelium) and ascending (Type IV epithelium) segments of the thin limbs of long nephrons. These data reinforce the concept of thin limb heterogeneity and may indicate a specialized role for the outer medullary segment of thin descending limbs of long nephrons in the concentrating mechanism.     

Microfluorometric study of glucose-6-phosphate and malate dehydrogenases in histologically defined areas of the uterus in cyclic and pregnant ewes

Activities of glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49; G6PDH) and malate dehydrogenase (E.C. 1.1.1.37; MDH) were determined fluorometrically in freeze-dried sections of the sheep uterus during the estrous cycle and pregnancy. Samples (0.2–0.3 μg) from the luminal epithelium, uterine glands, maternal caruncles, fetal cotyledons and intercotyledonary trophoblast were assayed in a small aliquot (5 μl) of the reaction medium under oil.Activity of G6PDH in the luminal epithelium, uterine glands and maternal caruncles did not change during the estrous cycle. Activity of MDH in the uterine glands did not change during the cycle, but in the luminal epithelium and maternal caruncles highest activities were found on day 9 and day 2 post-estrus, respectively.The enzyme activities in the fetal tissues were lower than in the maternal tissues. In all maternal tissues, MDH and G6PDH activities decreased during early pregnancy, but after implantation, the activities increased significantly. In fetal tissues G6PDH activity increased, whereas MDH activity decreased during the second half of gestation. These results suggest an increased rate of pentose shunt activity in both maternal and fetal tissues, and an increased rate of Krebs' cycle activity in the maternal but not in the fetal tissues.     

Localization of AQP5 during development of the mouse submandibular salivary gland

Aquaporin 5 (AQP5) is known to be central for salivary fluid secretion. A study of the temporal-spatial distribution of AQP5 during submandibular gland (SMG) development and in adult tissues might offer further clues to its unknown role during development. In the present work, SMGs from embryonic day (E) 14.5–18.5 and postnatal days (P) 0, 2, 5, 25, and 60 were immunostained for AQP5 and analyzed using light microscopy. Additional confocal and transmission electron microscopy were performed on P60 glands. Our results show that AQP5 expression first occurs in a scattered pattern in the late canalicular stage and becomes more prominent and organized in the terminal tubuli/pro-acinar cells towards birth. Additional apical membrane staining in the entire intralobular duct is found just prior to birth. During postnatal development, AQP5 is expressed in both the luminal and lateral membrane of pro-acinar/acinar cells. AQP5 is also detected in the basal membrane of acinar cells at P25 and P60. In the intercalated ducts at P60, the male glands show apical staining in the entire segment, while only the proximal region is positive in the female glands. These results demonstrate an evolving distribution of AQP5 during pre- and postnatal development in the mouse SMGs.     

Histological localization of hydrolases in the epididymis of the dog]

Localization and activity of five hydrolases (alkaline phosphatase, adenosine triphosphatase, acid phosphatase, nonspecific esterase and leucylamino-peptidase) were evaluated histochemically in the epididymides of mature dogs. In the ductuli efferentes, cilia and apical parts of the epithelial cells displayed high activity of alkaline phosphatase and adenosine triphosphatase. Strong activity of acid phosphatase, nonspecific esterase and leucylamino-peptidase was present in the basal and supranuclear zones of the epithelium of the ductuli efferentes. Stereocilia of all three segments of the ductus epididymidis showed a high activity of alkaline phosphatase. Positive adenosine triphosphatase reaction was confined to the stereocilia of the initial segment. A complex pattern of acid phosphatase activity was observed in the middle segment. The subdivision of the middle segment in four subsegments was therefore suggested. In the epithelium of the initial segment only a few nonspecific esterase-positive cells were seen. The infranuclear and basal areas of the epithelium in the middle segment and the supranuclear zone of the terminal segment displayed distinct nonspecific esterase activity. The possible contribution of the hydrolases to the function of the epididymis is discussed.     

Epithelial phenotypes in the developing human prostate.

An intermediate population has been identified among prostate glands called transiently amplifying (TA) cells, which are characterized by coexpression of basal and luminal cytokeratins (CKs), high proliferation, and lack of p27 expression. These cells are rare in the normal adult prostate and increase in pretumoral conditions, but their importance in the developing gland remains unknown. We analyzed fetal prostates for the expression of CKs (5/6, 18, 19) and factors involved in proliferation and apoptosis: p63, Ki67, p27, epidermal growth factor (EGFR), Bcl2, androgen receptor (AR). Immunostaining was performed on a tissue microarray, including 40 prostates from fetuses aged 13-42 weeks and normal prostate tissue from 10 adults. In both solid buds and the basal compartment of canalized glands, cells expressed p63, CK5/6, CK19, CK18, BCL2, EGFR and were p27 negative. Luminal cells of fetal canalized glands continue to express CK19, EGFR, and BCL2, without p27 expression. In contrast, adult epithelial luminal cells showed diffuse AR and p27 expression, without CK19, BCL2, and EGFR staining. Proliferation was high and diffuse in fetal glands and rare and restricted to basal cells in adult glands. These results indicate that most fetal epithelial prostatic cells exhibit the phenotype of TA cells, suggesting their regulatory function in prostate development.     

中华鳖肾脏的组织化学特性研究

利用光镜组织化学反应对中华鳖肾单位的结构和组织化学特性进行了详细的观察和分析。结果表明,中华鳖肾脏为分叶形的实质器官,肾小叶由被膜和实质组成,实质无髓质和皮质之分,但可以区分为外侧区和内侧区。外侧区嗜酸性,主要分布有近端小管和集合管。内侧区呈弱嗜酸性,肾小体、颈段、中间段和远端小管主要分布在内侧区。肾小球PAS反应呈阳性,但其琥珀酸脱氢酶(SDH)弱阳性,碱性磷酸酶(ALPase)、Na+/K+-ATPase和阿利新兰(AB)反应为阴性。足细胞酸性磷酸酶(ACPase)反应呈阳性。近端小管刷状缘嗜伊红,PAS反应以及ALPase、ACPase和Na+/K+-ATPase酶反应呈阳性,而SDH弱阳性。中间段、远端小管、集合管弱嗜酸性,SDH阳性。中间段Na+/K+-ATPase弱阳性。远端小管细胞侧面呈PAS阳性,腔面显示AB阳性。集合管胞质含有许多ACPase阳性颗粒,腔面呈PAS强阳性,AB阳性。甲苯胺兰(TB)染色可见集合管腔面有阳性颗粒,肾小管上皮含有亮、暗两种细胞。上述组化反应和分布结果表明,鳖的肾小管细胞类型较多,近端小管在原尿的重吸收中起主要作用,远端小管和集合管具有分泌黏液作用。中华鳖肾单位的结构与组化特性不仅与哺乳类和鸟类有一定差异,也与其他爬行动物不完全相同。       

Glyceraldehyde-3-phosphate dehydrogenase is a major protein associated with the plasma membrane of retinal photoreceptor outer segments

A major 38-kDa protein associated with bovine rod outer segment plasma membranes, but not disk membranes, has been identified as glyceraldehyde-3-phosphate dehydrogenase on the basis of its N-terminal sequence and specific enzyme activity. This enzyme was extracted from lysed rod outer segments or isolated rod outer segment plasma membrane with 0.15 M NaCl and purified to homogeneity by affinity chromatography on a NAD(+)-agarose column. A specific activity of 90-100 units/mg of protein is within the range of activity obtained for glyceraldehyde-3-phosphate dehydrogenase isolated from other mammalian cells. Enzyme activity measurements indicate that this enzyme makes up approximately 2% of the total rod outer segment protein and over 11% of the plasma membrane protein. Protease digestion and binding studies on purified rod outer segment plasma and disk membranes suggest that glyceraldehyde-3-phosphate dehydrogenase reversibly interacts with a protease-sensitive plasma membrane-specific protein of rod outer segments. The finding that glyceraldehyde-3-phosphate dehydrogenase is present in large quantities in rod outer segments suggests that at least some of the energy required for the synthesis of ATP and GTP for phototransduction and other processes of the outer segment is derived from glycolysis which takes place within this organelle.     

Cytochemical studies on the localization of 5'-nucleotidase in the acinar cells of the rat salivary glands.

The cytochemical localization of 5'-nucleotidase (5'-AMPase), and its validity, were investigated in parotid and submandibular acinar cells of a rat. Biochemical determinations showed that adequate treatment with glutaraldehyde could minimize the loss of enzymatic activity, and that 5'-AMPase and non-specific alkaline phosphatase (beta-GPase) possessed different pH optima. The cytochemical distribution of the reaction products from the 5'-AMPase activity was distinct from those of beta-GPase. 5'-AMPase activity was localized on the surface membranes of acinar, ductal and myoepithelial cells of both salivary glands. beta-GPase activity was evenly distributed on the entire plasma membranes of myoepithelial cells and on the basal plasmalemma of acinar cells. The reaction products, which appeared on the luminal and lateral plasma membranes of the acinar cells, were presumed to reflect the presence of 5'-AMPase, while those on the myoepithelial surface and basal plasma membranes of the acinar cells demonstrated both 5'-AMPase and beta-GPase. The results indicate that 5'-AMPase activity can be utilized as a reliable marker enzyme of plasma membranes in the salivary acinar cells.     

The microscopic anatomy of the oesophagus, stomach and intestine of the channel catfish, Ictalurus punctatus

An anatomical study of the digestive tract of the channel catfish revealed that the oesophageal mucosa was longitudinally folded and that secondary folds were occasionally located on the primary longitudinal folds. The infoldings were more numerous near the stomach. The stratified squamous epithelium covering the folds was made up of a basal layer, large mucous cells and simple squamous cells on the surface. The epithelium on the side of the folds consisted primarily of mucous secreting cells. Taste buds were observed between mucous cells on the apical portion of the oesophageal folds and were more prevalent in the cranial part of the oesophagus. The remaining layers of the oesophagus were: a lamina propria-submucosa, tunica muscularis and adventitia or serosa.
The J-shaped stomach had two regions: a large sac-shaped region containing gastric glands and a smaller, nonglandular pyloric region. The large rugae of the stomach became gradually smaller near the pylorus. There was a well developed pyloric sphincter. The mucosa included a simple columnar epithelium, a lamina propria and adventitia or serosa.
The intestine could be differentiated into a thick ascending segment, a descending segment, a thin convoluted segment and a thicker terminal segment, the rectum. Many mucosal folds containing branched villi characterized the ascending segment of the intestine. The descending and convoluted segments contained fewer folds with shorter and less-branching villi and were smaller in diameter and thinner walled. Descending and convoluted segments were also mildly convoluted and accounted for 80% of the total length of the intestine. An intestinal valve with a sphincter marked the beginning of the rectum. There was an approximately four-fold increase in the thickness of the tunica muscularis of the terminal segment of the intestine.     

Glycolytic enzymes and a GLUT-1 glucose transporter in the outer segments of rod and cone photoreceptor cells

The presence of glycolytic enzymes and a GLUT-1-type glucose transporter in rod and cone outer segments was determined by enzyme activity assays, glucose uptake measurements, Western blotting, and immunofluorescence microscopy. Enzyme activities of six glycolytic enzymes including hexokinase, phosphofructokinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, pyruvate kinase, and lactate dehydrogenase, were found to be present in purified rod outer segment (ROS) preparations. Immunofluorescence microscopy of bovine and chicken retina sections labeled with monoclonal antibodies against glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and lactate dehydrogenase have confirmed that these enzymes are present in rod and cone outer segments and not simply contaminants from the inner segments or other cells. Rod outer segments were also found to contain glucose transport activity as detected by 3-O-[14C]methylglucose uptake and exchange. The glucose transporter had a Km of 6.3 mM and a Vmax of 0.15 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for net uptake and a Km of 29 mM and a Vmax of 1.06 nmol of 3-O-methylglucose/s/mg of ROS membrane protein for equilibrium exchange. These Km values for net uptake and equilibrium exchange are similar to values obtained for human red blood cells and are characteristic of GLUT-1-type glucose transporter. The transport was inhibited by both cytochalasin B and phloretin. Western blot analysis and immunofluorescence microscopy using type-specific glucose transporter antibodies indicated that both rod and cone outer segment plasma membranes have a GLUT-1 glucose transporter of Mr 45K as found in red blood cells and brain microsomal membranes. Solid-phase radioimmune competitive inhibition studies indicated that rod outer segment plasma membranes contained 15% the number of glucose transporters found in human red blood cell membranes and had an estimated density of 400 glucose transporter per micron2 of plasma membrane. These studies support the view that outer segments can generate energy in the form of ATP and GTP by anaerobic glycolysis to supply at least some of the energy requirements for phototransduction and other metabolic processes.     

K+-Cl- Cotransporter-3a Up-regulates Na+,K+-ATPase in Lipid Rafts of Gastric Luminal Parietal Cells

Gastric parietal cells migrate from the luminal to the basal region of the gland, and they gradually lose acid secretory activity. So far, distribution and function of K+-Cl(-) cotransporters (KCCs) in gastric parietal cells have not been reported. We found that KCC3a but not KCC3b mRNA was highly expressed, and KCC3a protein was predominantly expressed in the basolateral membrane of rat gastric parietal cells located in the luminal region of the glands. KCC3a and the Na+,K+-ATPase alpha1-subunit (alpha1NaK) were coimmunoprecipitated, and both of them were highly localized in a lipid raft fraction. The ouabain-sensitive K+-dependent ATP-hydrolyzing activity (Na+,K+-ATPase activity) was significantly inhibited by a KCC inhibitor (R-(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]acetic acid (DIOA)). The stable exogenous expression of KCC3a in LLC-PK1 cells resulted in association of KCC3a with endogenous alpha1NaK, and it recruited alpha1NaK in lipid rafts, accompanying increases of Na+,K+-ATPase activity and ouabain-sensitive Na+ transport activity that were suppressed by DIOA, whereas the total expression level of alpha1NaK in the cells was not significantly altered. On the other hand, the expression of KCC4 induced no association with alpha1NaK. In conclusion, KCC3a forms a functional complex with alpha1NaK in the basolateral membrane of luminal parietal cells, and it up-regulates alpha1NaK in lipid rafts, whereas KCC3a is absent in basal parietal cells.     

Histomorphological changes in the oviduct of the mallard (Aves: Anatidae)

Studies on histomorphometrical changes in different segments (infundibulum, magnum, isthmus, shell gland and vagina) of oviduct of mallard, Anas platyrhynchos during active and quiescent phases of the reproductive cycle have been made. The absolute and per cent length and width of each segment showed a marked change. The magnum showed an increase of 280 per cent. Of all the histological parameters studied the number and height of mucosal folds and mucosal epithelium showed more marked increase in all segments of oviduct. The size of tubular glands and frequency of ciliated and secretory cells were studied in relation to oviductal activity.     

Immunohistochemical localization of Zn-alpha 2-glycoprotein in normal human tissues

The Zn-alpha 2-glycoprotein (Zn-alpha 2-GP) is present at a high concentration in the seminal plasma and at significant levels in other human body fluids. Its precise localization, however, has remained unclear, as well as its physiological and pathological significance. The present study reports the immunohistochemical localization of this protein in normal adult human tissues. Localization of the reactive product to anti-human plasma Zn-alpha 2-GP antibody was demonstrated in the following cells: luminal and basal cells of the prostate gland, luminal epithelial cells of the acini and of some ducts of the mammary glands, luminal cells of the secretory portion of the eccrine and apocrine sweat glands, serous cells of the salivary, tracheal, and bronchial glands, acinar cells of the esophageal glands, exocrine acinar cells of the pancreas, hepatocytes of the liver, and epithelial cells of the proximal and distal tubules in the kidney. The present results suggest that Zn-alpha 2-GP exerts some unknown but fairly widespread exocrine function and may be produced in the various epithelial cells tested. Hepatocytes are also suggested to be a source of the protein in the blood plasma.     

An ultrastructural study of the submandibular glands of the squirrel monkey, Saimiri sciureus

In squirrel monkey (Saimiri sciureus) the position of submandibular glands in the neck, on either side of the trachea, more closely resembles that of rodents than that of other primates. The glands exhibit seromucous acini and mucous tubules with seromucous demilunes. Electron microscopy shows basal cytoplasmic folds and well-developed intercellular tissue spaces and canaliculi only in relation to seromucous cells. Greatly dilated cisternae of the granular endoplasmic reticulum and prominent Golgi membranes are characteristic of the mucous cells. The secretory granules of seromucous and mucous cells are morphologically distinct and indicate chemically different products for the two cell types. Histochemically, the seromucous cell shows the presence of acid mucosubstance as indicated by the PAS and Alcian blue techniques. Preliminary studies showed no appreciable quantity of amylase in submandibular glands. The intercalated duct cell is juxtaposed with the acinar cell or mucous tubule cell. Short luminal microvilli, prominent Golgi complexes and scant apical granules are notable features of intercalated duct cells. Four cell types compose the striated ducts, viz., granular light cells, agranular dark cells, vesiculated dark cells, and basal cells. Peripheral nerves are found in five different locations: in the connective tissue (interstitial), between adjacent myoepithelial and mucous-secreting cells, in the intercellular space between adjacent secretory cells, and between basal plications of striated ducts and between adjacent myoepithelial and intercalated duct cells.     

Oxidative enzyme histochemistry of the chick esophagus and proventriculus

Succinic dehydrogenase, NAD and NADP diaphorases, choline oxidase, d-amino acid oxidase, α-glycerophosphate dehydrogenase, glutamic dehydrogenase, lactic dehydrogenase and aldolase were identified histochemically in the esophagus and proventriculus of the developing chick embryo. In general, the deep glands of the proventriculus reacted more strongly than the epithelium and mucous glands of the esophagus to the tests. The intensity of the enzymatic activity seems correlated with the number of mitochondria and metabolic activity of the cells.     

Reproduction in the male honey possum (Tarsipes rostratus: Marsupialia): the epididymis

The epididymis of the adult honey possum, Tarsipes rostratus, is enclosed by a heavily pigmented tunica vaginalis and lies with the testis in a prominent prepenile scrotum. It is connected to the testis by a single ductus efferentis and is lined by approximately equal numbers of cuboidal ciliated and principal cells. It is unusual for marsupials in having no well-defined compartments or fibrous septae and in having extensive convolutions of the duct only at the caudal flexure. Three principal functional zones (initial, middle, and terminal segments) were identified in the epididymis, based on epithelial type and ultrastructural evidence of sperm maturation. Luminal diameter increases progressively throughout the tract, and epithelial height variations (from about 2 to 20 microns) are greatest in the terminal segment. The epithelium itself is remarkably low (maximum of 21.6 microns) compared with that seen in the epididymis of other mammals. The thickness of the peritubular smooth muscle coat increases close to the junction of the epididymis and ductus deferens. Sperm concentrations were estimated from counts of sperm nuclei and thus can be no more than approximations. The figures are consistent, however, with a rapid increase in concentration in the initial segment, indicating extensive fluid resorption. Sperm concentrations appear to peak in the distal zone of the terminal segment, although sampling problems and wide variations in count make such a conclusion only tentative. Principal and basal cells are the predominant cell types in the epididymal epithelium. Basal cells are most abundant in the initial and distal middle segment. Principal cells show structural evidence of active exchange with the luminal contents and have abundant apical stereocilia, the structure of which depends on the epididymal zone. Other cell types occur less commonly in the epithelium. Lipid-rich and phagocytic principal cells are restricted to the middle and distal zones of the middle segment, respectively. Clear cells, restricted to the terminal segment, and halo cells were found in very low numbers. As in some other marsupials, principal cells (possibly specialized for this function) selectively remove cytoplasmic droplets and probably other cellular debris from the luminal contents. In Tarsipes, however, this process is not very efficient, and many discarded droplets pass through to the terminal segment where they form large masses of debris associated with aggregates of degenerating spermatozoa.     

Visual cycle: Dependence of retinol production and removal on photoproduct decay and cell morphology

The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exposure to light. Initial steps, the liberation of all-trans retinal and its reduction to all-trans retinol by retinol dehydrogenase (RDH), take place in photoreceptors. We performed comparative microspectrophotometric and microfluorometric measurements on a variety of rod and cone photoreceptors isolated from salamander retinae to correlate the rates of photoproduct decay and retinol production. Metapigment decay rate was spatially uniform within outer segments and 50-70 times faster in the cells that contained cone-type pigment (SWS2 and M/LWS) compared to cells with rod-type pigment (RH1). Retinol production rate was strongly position dependent, fastest at the base of outer segments. Retinol production rate was 10-40 times faster in cones with cone pigments (SWS2 and M/LWS) than in the basal OS of rods containing rod pigment (RH1). Production rate was approximately five times faster in rods containing cone pigment (SWS2) than the rate in basal OS of rods containing the rod pigment (RH1). We show that retinol production is defined either by metapigment decay rate or RDH reaction rate, depending on cell type or outer segment region, whereas retinol removal is defined by the surface-to-volume ratio of the outer segment and the availability of retinoid binding protein (IRBP). The more rapid rates of retinol production in cones compared to rods are consistent with the more rapid operation of the visual cycle in these cells.     

Carbonic anhydrase in the monkey kidney

The distribution of carbonic anhydrase in the kidney of the cynomolgus monkey was studied by the histochemical method of Hansson. Glomeruli and Bowman's capsule were inactive. Convoluted proximal tubules showed high enzyme activity at the brush border and the basolateral membranes and the cytoplasm. Straight proximal tubules were less intensely stained. In nephrons with long loops of Henle, the descending thin limb contained weak enzyme activity, whereas the ascending thin limb was inactive. The thick limb of Henle's loop displayed most enzyme activity at the luminal cell border. In distal convoluted tubules enzyme activity was restricted to the basal part of the cells. In the late distal tubule, intercalated cells appeared among the "ordinary" distal cells and contained abundant cytoplasmic enzyme. Many intensely stained intercalated cells were also found in the cortical and outer medullary segments of the collecting duct, intermingled with more weakly stained chief cells. In the inner medullary segment of the collecting duct, enzyme activity gradually disappeared. Many capillaries were clearly stained for enzyme activity. The capillary staining apparently varied with that of the kidney tubules; virtually all capillaries in the cortex, but very few in the inner medulla, were stained. The distribution of carbonic anhydrase in the kidney tubules of the monkey is very similar to that in man and in the rat, but the primate kidney differs from the rat kidney by the presence of capillary enzyme activity. The functional importance of this difference is not clear at present.