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PubMed2005

Molecular cloning of several rat ABC transporters including a new ABC transporter, Abcb8, and their expression in rat testis.

Several members of the ABC transporter superfamily play an important role in testicular physiology and defence against anticancer drugs. Using a reverse transcription-polymerase chain reaction strategy with degenerate primers and rat testis RNA as template, we have looked for the presence of other members of this superfamily. Of the six partial cDNA found, five corresponded to ABC transporters already known -Mdr1b, Mrp1, Tapl/Abcb9, Umat/Abcb6 and Sur2/Abcc9- and one presented a strong homology with mouse and human ABCB8. Using a 5' and 3' RACE approach, we cloned the full-length cDNA and found that the predicted protein presented 92% and 80% homology with the mouse and human proteins respectively. Strong expression of rat abcb8 was found in heart, brain and testis when compared with liver, lung and spleen. In the testis, rat abcb8 was expressed both in the somatic Sertoli cells and peritubular cells and in the germline (spermatogonia and pachytene spermatocytes). Furthermore, Umat/Abcb6 was very highly expressed in the testis (high amounts in meiotic pachytene spermatocytes and low amount in post-meiotic early spermatids). In conclusion, we confirm the presence of several ABC transporters in the testis and also provide evidence of the presence of Abcb8 in the organ.

ATP-Binding Cassette Transporters↗
PubMed1990

A novel testis-specific 105-kDa protein related to the 90-kDa heat-shock protein.

Brain 90- and 100-kDa heat-shock proteins (HSP90 and HSP100) were purified and antibodies against them prepared. The two antibodies were very specific and did not cross-react with each other. In rat, immunoblotting with the anti-HSP90 antibody showed the most abundant presence of HSP90 in testis as well as brain, compared with lung, liver, spleen, kidney, cardiac muscle, ovarium and uterus. The anti-HSP90 antibody showed the presence of a new 105-kDa protein in rat testis. This novel 105-kDa protein was also detected in brain at a very low concentration but not in HeLa cells or other organs including the uterus and ovarium. The testis 105-kDa protein was purified from rat testis; although it was clearly separable from HSP90 by two-dimensional gel electrophoresis, Q-Sepharose and hydroxyapatite column chromatographies, the properties of this protein were very similar to HSP90. The similarity was higher than 60% on peptide mapping with trypsin digestion, the 105-kDa protein cross-reacted with anti-HSP90 antibody, both were bound similarly to heparin-Sepharose gel and both are located in the cytosol fraction. When the 105-kDa protein was fractionated by HPLC, a molecular mass of 195 kDa was calculated, indicating that it is composed of two identical subunits, similarly to HSP90. The 105-kDa protein did not react with the anti-HSP100 antibody. There was a slight similarity between the 105-kDa protein and HSP100 on the peptide mapping. HSP100 was present in the microsomal fraction as well as in the cytosol. It is concluded that the 105-kDa protein is a testis-specific and HSP90-related protein.

Animals↗
PubMed1994

cDNA sequence and structure of a gene encoding trout testis high-mobility-group-1 protein.

Perchloric acid extraction of trout testis nuclei revealed the presence of two large high-mobility-group (HMG) proteins, HMG-T1 and HMG-T2. The sequence of a complete cDNA (1407 bp) for trout testis HMG-1 protein (referred as to HMG-T1) has been determined. The deduced HMG-T1 protein contains 203 amino acids with more than 86% similarity to mammalian HMG-1 proteins. A single-sized mRNA for HMG-T1 has been detected by Northern-blot analysis consistent with the size derived from the HMG-T1 cDNA. Amplification of human and trout genomic DNAs by polymerase chain reaction using primers specific for trout and human HMG-1 cDNAs revealed that unlike the human genome, which contains predominantly intronless HMG-1 sequences, intronless HMG-T1 sequences were not found in the fish genome. Southern-blot analysis suggested that the trout testis HMG-1 gene is encoded by at least two sequences with high similarity. A gene encoding HMG-T1 protein has been isolated from a trout testis genomic library and by PCR of trout genomic DNA (3879 bp). The trout testis HMG-1 gene is organized into five exons (four exons corresponding to the protein-coding region) and its exon/intron boundaries are identical to those of the human HMG-2 gene [Shirakawa, H. & Yoshida, M. (1992). J. Biol. Chem. 267, 6641-6645] suggesting the evolution of HMG-1 and HMG-2 genes from a common ancestor.

Amino Acid Sequence↗
PubMed1995

Distribution and activity of calcineurin in rat tissues. Evidence for post-transcriptional regulation of testis-specific calcineurin B.

Calcineurin (CN), a Ca2+/calmodulin-regulated phosphatase 2B, plays an important role in many biological processes including T-cell signal transduction. In the present study, the distribution and activity of CN were investigated in rat tissues. CN has a wide tissue distribution, as measured by enzyme-linked immunosorbent assay. CN concentrations are 0.2-0.6 micrograms/mg protein in most tissues, while the brain contains 3-10-fold higher concentrations. Immunohistochemical analyses using a monoclonal antibody to CN B subunit reveals that CN is not evenly distributed but concentrated in specific cells, especially in the brain, kidneys and testis. The specific enzymic activity of CN in tissues is around 10 pmol.min.mg protein-1, except in brain and liver (60 pmol.min-1.mg protein-1 compared to 3.6 pmol.min-1.mg protein-1). The immunosuppressants cyclosporin A and tacrolimus, but not rapamycin, inhibit the phosphatase activity of CN derived from most tissues tested, while CN activity from liver was resistant to cyclosporin A. Furthermore, transcripts and protein of the common CN B subunit and of the testis-specific form of CN B subunit were analyzed. The common CN B subunit transcripts and protein are detected in all tissues. Transcripts for the 'testis-specific' CN B subunit are also found in brain, lung, thymus and heart, while the protein is only detected in testis. This indicates that the testis-specific CN B subunit gene expression is regulated at both transcriptional and posttranscriptional levels. The findings demonstrate that CN is a widely distributed protein phosphatase and that its activity is regulated in a tissue-specific manner.

Amino Acid Sequence↗
PubMedDate not supplied

Presence of luteinizing hormone receptor binding inhibitor (LH-RBI) in ovine testis.

Luteinizing hormone receptor binding inhibitor (LH-RBI has been isolated from the aqueous extracts of ram testis using Sephadex column chromatography. Sephadex G-75 fraction I was found to inhibit the binding of I125 LH to rat testis receptors. Further purification of Sephadex G-75-I fraction on G-200 column gave four fractions (I-IV), the maximum inhibitory activity to inhibit I125 LH binding to rat testis receptor was associated with the fraction I only. Fraction II gave marginal inhibition only, whereas fractions III and IV did not have any inhibitory effect on I125 LH binding to rat testis receptors. Our findings suggest that LH-RBI isolated from ram testis is a protein having molecular weight more than 10,000 Daltons.

Animals↗
PubMedDate not supplied

A quantitative morphological study of age-related changes in the donkey testis in the period between puberty and senium.

The testis of the donkey was used as a model to study age-related changes in the period between puberty and senium. From the age of 1.5 years to the middle of sexual maturity (5 to 6 years) a number of histophysiological features, all indicative of the spermatogenetic efficiency, increase continuously. Then without a longer-lasting plateau of maximal performance these features undergo continuous retrogression. Thus, the adult testis is an organ in permanent change. During its progressive period (1.5 to 5 years) the average testicular and tubular volumes treble. The increase in tubular volume is due to an increase in tubular length (from 700 m to 1600 m per testis) and tubular diameter (from 205 microns to 250 microns). Parallel to this growth, the spermatogenetic efficiency of the seminiferous epithelium rises: the number of germ cells entering meiosis increases and the cell loss by apoptosis or exfoliation decreases. During the following regressive period of the testis (5-10 years) seminiferous epithelial height and tubular diameter are again gradually reduced to 70 microns and 205 microns, respectively. The absolute number of Sertoli cells per testis decreases continuously from puberty onwards. The tubular lamina propria thickens with advancing age and at the age of 10 years, displays long irregular projections into the seminiferous epithelium.

Aging↗
PubMed2005

Significance of determining the point of reperfusion failure in experimental torsion of testis.

BACKGROUND: Experimental studies of the use of free radical scavengers in ischemic/reperfusion (I/R) injury following detorsion of the torted testis have yielded conflicting results due to differences in the period of ischemia used. The authors studied I/R injury in the rabbit model, to define the point beyond which there is reperfusion failure. METHODS: Ischemia/reperfusion injury of the testis was created in 3-6-month-old male New Zealand white rabbits by cross-clamping the left spermatic cord for periods of ischemia lasting 0, 15, 30, 60, 90, 120 and 180 min. There were eight animals per experimental group. The right testis served as internal control. Both testes were harvested after 24 h of reperfusion in four animals and after 3 months in the remaining four animals for each group. Testicular malondialdehyde (MDA), a measure of free radical damage, was determined by using the thiobarbituric acid reaction on testicular homogenates. Johnsen score was used to assess morphological damage caused by the ischemia. RESULTS: After 24 h of reperfusion, the mean testicular MDA in the control right testes at 0, 15, 30, 60, 90, 120 and 180 min was 2.1, 2.5, 2.9, 2.4, 2.1 and 1.9 nmol/mg protein, respectively. The mean left testicular MDA at corresponding ischemic periods was 1.6, 2.0, 3.9, 10.0, 4.4, 6.1 and 1.0 nmol/mg protein, respectively. The maximum left testicular MDA was at 60 min (10.0 nmol/mg protein), following which the level dropped significantly to 1.0 nmol/mg protein at 180 min. At 3 months, the mean Johnsen scores for left testes subjected to 0, 60, 120 and 180 min ischemia were 9.4, 8.8, 2.3, 3.5, respectively. CONCLUSION: The results suggest that following ischemia of up to 60 min in the rabbit testis, adequate reperfusion is possible, but ischemia lasting beyond 60 min results in inadequate reperfusion leading to irreversible damage. Thus, in experiments for assessing the effect of antioxidants on I/R injury of the testis in rabbits, periods up to 60 min of ischemia should be regarded as optimum to observe an effect.

Animals↗
PubMed1988

Undescended testis: how history and examination may influence treatment.

This paper reports a prospective study of 114 boys with 126 undescended testes. The aims were to identify the position of the testis in the first year of life, to document cases of apparent ascent of the testes following a scrotal position in infancy, and to determine whether knowledge of the position of the testis in infancy might be used as a guide in later management. In 92 instances the position of the testis at birth, at 6 weeks and at 1 year of age was recorded; 84 were considered undescended and eight were in the scrotum. There was no clear indication of the position of the testis in the remaining 34. When the position of the testis was known to be undescended from birth to the end of the first year, response to hormonal therapy was disappointing. However, when there was a history of prior descent or when there was no clear information about the position in the first year of life, response to hormonal therapy was rewarding (57%) and this therapeutic modality is recommended prior to surgery for this group of patients.

Age Factors↗
PubMed1988

Is the incidence of testis cancer related to trauma or temperature?

The position of the testes reduces their temperature but makes them vulnerable to trauma. Patients with testis cancer frequently report prior testicular trauma, but this trauma may have triggered diagnosis of the tumor rather than been aetiological. In this study, the frequencies of various prior traumatic and temperature exposures in 259 patients with testis cancer were compared with their frequencies in two sets of control patients who did not have testis cancer. Particular effort was made to prevent bias. Testis cancer was not significantly associated with any temperature or trauma exposure and the confidence limits of the findings excluded substantially raised risks. The evidence suggests that raised temperatures and traumas commonly encountered in everyday life are not important risk factors for testis cancer. The possible aetiological roles of extreme trauma sufficient to cause atrophy, and of the trauma and raised temperature which can occur in cryptorchidism, however, need investigation by other methods.

Adolescent↗
PubMed1988

Detection and localization of immunoreactive alcohol dehydrogenase protein in the rat testis.

Alcohol dehydrogenase in the testis metabolizes ethanol and a variety of physiological substrates such as dihydrotestosterone and vitamin A. Studies of the localization of enzyme activity in the testis have revealed its presence in either interstitial cells or seminiferous tubules alone or in both places. The purpose of this study was to detect and localize immunoreactive alcohol dehydrogenase in the testis. The testis enzyme had similar antigenicity than the liver enzyme as demonstrated by double immunodiffusion and inhibition titration using antibody to the liver enzyme. The concentration of immunoreactive enzyme protein was 1.7 +/- 0.1 micrograms/mg of cytosol protein in the testis as compared with 9.3 +/- 0.3 micrograms/mg of cytosol protein in the liver. Isoelectric focusing revealed eight isoenzyme bands. Only the three bands with the highest isoelectric points precipitated with antibody to liver alcohol dehydrogenase. By immunohistochemistry using this antibody, the enzyme was localized principally to the Leydig cells which are also the site of steroidogenesis. The presence in the seminiferous tubules of isoenzymes of lower isoelectric point, which do not react with the antibody to the liver enzyme, can not be excluded.

Alcohol Dehydrogenase↗
PubMed2005

High doses of nandrolone decanoate reduce volume of testis and length of seminiferous tubules in rats.

Anabolic-androgenic steroid (AAS) compounds rank among the drugs most widely abused with the goal of improving athletic ability, appearance, or muscle mass. It has been shown that these compounds have adverse effects on human and animal physiology and sperm quality, but quantitative structural changes of the testis have received less attention. The present study was conducted to evaluate the effects of nandrolone decanoate, which is one of the AAS compounds, on testis weight and volume, diameter and length of seminiferous tubules in rats by unbiased stereological methods. Adult rats were divided into three groups. The first comprised control rats; the second and third groups received low and high doses of nandrolone decanoate for 14 weeks. The rats were then left untreated for 14 weeks. After removal of the testis, stereological study of these tissues showed that the mean volume of testis and length of the seminiferous tubules in the animals that received high doses of nandrolone decanoate were reduced approximately 32% (p<0.01) and approximately 31% (p<0.04), respectively, in comparison with the control group. It can be concluded that the high doses of nandrolone decanoate produce structural changes in the rat testis that remain 14 weeks after stopping injection of the drug.

Anabolic Agents↗
PubMed1997

The testis: the witness of the mating system, the site of mutation and the engine of desire.

There is now abundant evidence in a wide range of mammalian and non-mammalian species to show that the relative size of the testis and the morphology of the spermatozoa are infallible predictors of the mating system. Species with the largest testis/body weight ratios and the best spermatozoa have a multi-male or promiscuous mating system in which sperm competition operates. Judged by these criteria, men were not designed to be promiscuous. There is increasing evidence in humans to show that most spontaneous mutations of the germ line occur in the testis. Because these provide the variability on which natural selection can operate, the testis holds the key to evolution. Genes on the Y chromosome that control male fertility are particularly prone to mutations, perhaps because of the mutagenic metabolites produced by the metabolically active testis. Testicular descent into a scrotum, and cooling by countercurrent heat exchange between the spermatic artery and vein may have evolved as a way of holding the mutation rate in check. The hormones secreted by the testis, which control libido and aggression, ensure that these male mutations are disseminated as widely as possible throughout the population.

Animals↗
PubMed2006

The expression and significance of CATSPER1 in human testis and ejaculated spermatozoa.

AIM: To investigate the distribution of cation channel of sperm 1 (CATSPER1) protein and the presence of CATSPER1 mRNA in human testis and ejaculated spermatozoa. The influence of anti-human CATSPER1 antibody upon human sperm motility was used to evaluate the function of human CATSPER1 and to estimate its possible use as a target for immunocontraception. METHODS: Human ejaculated sperm from normozoospermic donors (n = 12) and liquid nitrogen frozen human testis were used for the study of mRNA and protein expression of CATSPER1 by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry, respectively. Spermatozoa from normozoospermic donors (n = 12) were individually processed using a swim-up procedure and were then incubated with CATSPER1 antibody at final concentrations of 20, 4 and 0.8 microg/mL. After 1, 2 and 6 h incubation, progressive motility and fast progressive motility were measured by means of computer-assisted semen analysis. RESULTS: CATSPER1 transcript was detected in both human testis and each human ejaculated semen sample. CATSPER1 protein expressed in the membrane of spermatid and was localized in the principal piece of the sperm tail. The application of CATSPER1 antibody at all concentrations significantly inhibited both progressive motility and fast progressive motility after 1, 2 and 6 h incubation, and significant dose-dependent changes were observed. CONCLUSION: CATSPER1 is meiotically and post-meiotically expressed in human testis tissue. CATSPER1 mRNA in human ejaculated spermatozoa could be a more feasible target for study and infertility screening than testis biopsy. In addition, our results suggest that human CATSPER1 could be a possible target for immunocontraception.

Antibodies↗
PubMed2006

Immunohistopathology of the contralateral testis of rats undergoing experimental torsion of the spermatic cord.

AIM: To evaluate the immunohistopathological changes in the contralateral testis of rats after an experimental spermatic cord torsion. METHODS: Male Sprague-Dawley rats of 45-50 days old were subjected to a 720 degree unilateral spermatic cord torsion for 10, 30 and 80 days (experimental group, E), respectively or sham operation (control group, C). Histopathology of the contralateral testis as well as germ cell apoptosis were studied using the Terminal Deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling (TUNEL) technique. The number of testicular lymphocytes, mast cells and macrophages, and the expression of tumor necrosis factor-alpha (TNF-alpha) and its receptor (TNFR1) in testicular cells of the contralateral testis were quantified by histochemistry and immunohistochemistry. TNF-alpha concentration in testicular fluid was determined by ELISA. RESULTS: In the contralateral testis of rats from the E group, the maximal degree of damage of the germinal epithelium was seen 30 days after torsion. At this time we observed in the E group vs. the C group increases: (i) the number of testicular T-lymphocytes; (ii) the number of testicular mast cells and macrophages; (iii) the percentage of macrophages expressing TNF-alpha; (iv) TNF-a concentration in testicular fluid; (v) the number of apoptotic germ cells; and (vi) the number of TNFR1+ germ cells. CONCLUSION: Experimental spermatic cord torsion induces, in the contralateral testis, a focal damage of seminiferous tubules characterized by apoptosis and sloughing of germ cells. Results suggest humoral and cellular immune mediated testicular cell damage in which macrophages and mast cells seem to be involved in the induction of germ cell apoptosis through the TNF-alpha/TNFR1 system and in the modulation of the inflammatory process.

Animals↗
PubMed2004

Xenobiotic and endobiotic transporter mRNA expression in the blood-testis barrier.

A major function of xenobiotic and endobiotic transporters is to move a wide range of organic substances across cell membranes. Sertoli cells play an important role in protecting developing germ cells by forming a physiological barrier, limiting exposure to potentially toxic substrates, or conversely, facilitating uptake of xenobiotics within the testis. The aim of this study was to quantitatively determine the constitutive expression of various transporters in isolated Sertoli cells from adult Sprague-Dawley rats. The following mRNA levels were measured in isolated Sertoli cells by the branched DNA signal amplification method, multidrug resistance (Mdr) protein 1a, 1b, and 2; multiple drug resistance protein (Mrp) 1, 2, 3, 4, 5, 6, 7, and 8; sodium taurocholate cotransporting polypeptide; bile salt excretory protein; ileal bile acid transporter; AbcG5 and AbcG8; organic anion transporting polypeptide (Oatp) 1, 2, 3, 4, 5, 9, and 12; prostaglandin transporter (Pgt); testis-specific transporter (Tst) 1 and Tst2; organic anion transporter (Oat) 1, 2, 3, and K; organic cation transporter (Oct) 1, 2, 3, N1, and N2; divalent metal transporter (Dmt) 1, Menke's, and Wilson's; zinc transporter (Znt) 1; equilibrative nucleoside transporter (Ent) 1 and 2; concentrative nucleoside transporter (Cnt) 1 and 2; and peptide transporter (Pept) 1 and 2. Levels were also determined in whole testis, liver, kidney, and ileum to provide a reference for determining relative expression levels. Mrp8, Tst1 and 2, and Ent1 and 2 were expressed in Sertoli cells at higher levels than in liver, kidney, or ileum, whereas Mrp1, 5, and 7, Mdr2, Oatp3, Oat2, OctN2, Dmt1, Menke's, Wilson's, and Znt1 were all significantly expressed in Sertoli cells, but Sertoli cell expression was not the tissue of highest expression. The remaining transporters were expressed at low levels in isolated Sertoli cells. Additionally, expression levels of Mrp1, Mrp7, Mrp8, Tst1, Tst2, OctN2, Wilson's, Znt1, Ent1, and Ent2 were greater in isolated Sertoli cells than in whole testis. Constitutive expression of transporters in Sertoli cells may provide an insight into the range of xenobiotics that can potentially be transported by Sertoli cells and thereby provide a mechanistic under standing of blood-testis barrier function.

Animals↗
PubMed1996

Directional dominance and a developmental model for the expression of the Tda testis-determining autosomal trait of the mouse.

The POSCH-2 Y chromosome from the poschiavinus variety of Mus musculus domesticus causes incomplete testis development in the recessive autosomal background of the C57BL/6J laboratory mouse strain. Testis development is normal with the POSCH-2 Y in its native strain background as well as in some strains of the laboratory mouse such as DBA/2J. The phenotype or expression of XY gonadal hermaphroditism in a C57BL/6J strain, which was constructed to be consomic for the POSCH-2 Y, is a threshold trait in which liability is normally distributed and thresholds in the development of the testis define the probability of observing XY embryos with different combinations of ovaries, ovotestes, and testes. The difference in this testis-determining autosomal or Tda trait between the C57BL/6J and DBA/2J strain pair has been demonstrated to be multigenic. We conducted a survey among different strains of the laboratory mouse by test mating females with C57BL/6J.Y-POS males that are consomic for the POSCH-2 Y. We identified five groups of strains with significantly different response of XY gonadal hermaphroditism in their XY-POS F1 test embryos. In test embryos, four groups of strains produced gonadal hermaphroditism with different distributions of the types of gonad that appear to have the same variance or shape of a normally distributed liability, but the means of the distributions are at different locations on a scale of gonadal development. The fifth group of strains produced only tests in the test embryos. Several additional matings produced results suggesting that a model of dominance, in the direction of more complete testis development, could interpret the strain differences. The differences in response to the POSCH-2 Y chromosome among the five groups of strains may represent the phenotypes of the genetic recombinants in the Tda trait that were suggested previously by a segregation analysis between C57BL/6J and DBA/2J. The strains may also provide the tools to further dissect the allelic differences and locus determinants of the Tda trait.

Animals↗
PubMed1991

Microvascular pressure distribution in the hamster testis.

Convective transport is a critical element in the regulation of steroidogenesis and spermatogenesis in the testis. Steroid hormones are distributed to their target cells within seminiferous tubules via interstitial fluid. The movement of interstitial fluid and lymph, which transports protein hormones and many of the substrates required for spermatogenesis and steroidogenesis, is driven by capillary filtration. Despite the importance of convective transport in testicular function, however, the mechanisms regulating transvascular exchange in the testis are unknown. As a first step in understanding this process, we measured directly the microvascular hydrostatic pressure distribution in the hamster testis (pentobarbital sodium, 70 mg/kg ip). Using a servo-null transducer, intravascular pressure was measured in all vessel types accessible beneath the surface of the testis of 19 animals. Systemic arterial pressure averaged 89 +/- 2 (SE) mmHg. The most significant observations were that mean capillary pressure was extremely low (10.1 +/- 0.8 mmHg) and remarkably constant (range 8.2-13.3 mmHg), despite a 45 mmHg range in systemic mean arterial pressure among the animals observed. The maintenance of a low hydrostatic pressure in testicular capillaries may serve to sustain fluid filtration at a rate that prevents washout of essential solutes while preserving convective transport. Unfortunately, the anatomical and functional characteristics that determine this unique microvascular environment may also expose the testis to significant pathological risks. For example, the large pre- to postcapillary resistance ratio observed suggests that testicular capillaries must be highly susceptible to increases in venous pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Escherichia coli enterotoxin receptors: localization in opossum kidney, intestine, and testis.

The distribution of receptors for Escherichia coli enterotoxin were examined in opossum kidney, intestine, and testis. E. coli enterotoxin stimulated guanosine 3',5'-cyclic monophosphate (cGMP) production in renal cortex, testis, and small intestinal mucosa but had only a small effect in the colon. Atrial natriuretic factor enhanced the cGMP content of renal cortex and small intestine but had no effect on testis or colon. The enterotoxin receptors were observed to be localized in proximal tubules, to epithelial cells of crypts and villi of small intestine, to crypts of colon, and in seminiferous tubules. Both convoluted and straight portions of proximal tubules exhibited specific binding sites for 125I-labeled enterotoxin. Glomeruli and distal tubules did not have receptors. Binding of 125I-enterotoxin to brush-border membranes of kidney cortex or intestinal mucosa and to testis membranes was markedly temperature dependent. The binding affinities of these receptors for E. coli enterotoxin were similar (i.e., IC50 approximately equal to 0.4-0.5 nM). Daily administration of 20 micrograms of enterotoxin intramuscularly to opossums increased urine cGMP excretion with no apparent changes in urine volume, Na+, or K+ excretion. Thus receptors for heat-stable enterotoxins are localized to proximal tubules of kidney and to enterocytes and seminiferous tubules of intestine and testis, respectively. Apical membranes may be the site of enterotoxin receptors in these epithelia.

Animals↗