Anatomical study of the seminal vesicle system for transurethral seminal vesiculoscopy.

Because of a general lack of knowledge regarding the precise anatomy of the seminal vesicle system, efforts to use transurethral seminal vesiculoscopy (TSV) are currently constrained. We investigated 26 normal adult male specimens. Contrast medium was injected into the seminal vesicle system in 18 specimens and the openings of the ejaculatory ducts were examined with an operating microscope. India ink was injected into the urethra in four specimens to investigate the function of the ejaculatory duct valve. Another four specimens were examined histologically to identify the anatomical relationships of the seminal vesicle system. We found that the openings of the ejaculatory ducts were covered by the ejaculatory duct valve, which could be classified into two types and acted as a one-way valve. The apex of the seminal colliculus together with the right and left openings of the ejaculatory ducts formed a shape resembling an isosceles triangle. This could be used to locate the openings of the ejaculatory ducts during TSV. The ejaculatory ducts can be classified into two types according to their course. During surgery, efforts must be made to protect the ejaculatory duct valve. During inspection or surgery, the second segment and the angles of the ejaculatory ducts, particularly in Type Ib and Type II cases, require particular attention. Clin. Anat. 32:244-252, 2019. © 2018 Wiley Periodicals, Inc.

Transcriptome analysis to identify genes for peptides and proteins involved in immunity and reproduction from male accessory glands and ejaculatory duct of Bactrocera dorsalis.

In the male reproductive system of insects, the male accessory glands and ejaculatory duct (MAG/ED) are important organs and their primary function is to enhance the fertility of spermatozoa. Proteins secreted by the MAG/ED are also known to induce post-mating changes and immunity responses in the female insect. To understand the gene expression profile in the MAG/ED of the oriental fruit fly Bactrocera dorsalis (Hendel), that is an important pest in fruits, we performed an Illumina-based deep sequencing of mRNA. This yielded 54,577,630 clean reads corresponding to 4.91Gb total nucleotides that were assembled and clustered to 30,669 unigenes (average 645bp). Among them, 20,419 unigenes were functionally annotated to known proteins/peptides in Gene Orthology, Clusters of Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes pathway databases. Typically, many genes were involved in immunity and these included microbial recognition proteins and antimicrobial peptides. Subsequently, the inducible expression of these immunity-related genes was confirmed by qRT-PCR analysis when insects were challenged with immunity-inducible factors, suggesting their function in guaranteeing fertilization success. Besides, we identified some important reproductive genes such as juvenile hormone- and ecdysteroid-related genes in this de novo assembly. In conclusion, this transcriptomic sequencing of B. dorsalis MAG/ED provides insights to facilitate further functional research of reproduction, immunity and molecular evolution of reproductive proteins in this important agricultural pest.

[Semen expulsion under the ureterocystoscope].

OBJECTIVE: To determine the exact location of the opening of the ejaculatory duct in men and provide some basic anatomical evidence for seminal vesiculoscopy and the treatment of ejaculatory duct obstruction. METHODS: We performed ureterocystoscopy for 21 male patients aged 26 - 47 years with hematuria (n = 12), hematospermia (n = 2), glandular cystitis (n = 6), and anejaculation after radical resection of rectal carcinoma (n = 1), and meanwhile, with the consent of the patients, massaged the prostate and ejaculatory duct and observed the outlet of the expelled fluid. Under the microscope, we described the fluid samples with sperm as the expulsion from the ejaculatory duct. RESULTS: Ureterocystoscopy showed that the exact anatomical sites of the expulsion of prostatic fluid and semen in the patients were the side and lower side of the prostatic utricle opening above the verumontanum and the ventral side of the verumontanum. Quantities of sperm were found in the expulsion fluid of 13 of the patients, and no expulsion, including semen, was seen from the prostatic utricle opening. CONCLUSION: Anatomically, the ejaculatory duct openings of males are located at the two sides of the verumontanum adjacent to the opening of the prostatic utricle, rather than in the prostatic utricle above the verumontanum.

New myotropic and metabotropic actions of pyrokinins in tenebrionid beetles.

Pyrokinins are a large family of insect neuropeptides exhibiting pleiotropic activity, but are predominantly myostimulatory hormones. In this study, four pyrokinins Tenmo-PK-1 (HVVNFTPRLa), Tenmo-PK-2 (SPPFAPRLa), Tenmo-PK-3 (HLSPFSPRLa) and Zopat-PK-1 (LPHYPRLa) from the neuro-endocrine system of two tenebrionid beetles, Tenebrio molitor and Zophobas atratus, were tested in homologous bioassays to evaluate their putative myotropic and glycaemic actions. The four investigated bioassays systems (the heart, oviduct, ejaculatory duct and hindgut) revealed species-specific and organ-specific myotropic actions for the pyrokinins tested. In most bioassays with both beetles, the peptides showed myostimulatory properties with different efficacy. However, the T. molitor heart is not sensitive to Tenmo-PK-1, Tenmo-PK-2 and Tenmo-PK-3, and one of the peptides Tenmo-PK-1, is myoinhibitory on the oviduct. Tenmo-PK-2, which is also present in Z. atratus, exerted an inhibitory effect on the contractions of the heart and ejaculatory duct muscles in this beetle. Such myoinhibitory properties of pyrokinins in insects are shown here for the first time. Only one of the peptides tested, Tenmo-PK-2, stimulated a hyperglycaemic response in the haemolymph of larvae of T. molitor and Z. atratus, and this effect suggests a possible additional metabotropic function of this peptide in beetles. The differences in the myotropic and glycaemic responses to pyrokinins suggest that these peptides modulate contractions of muscles from visceral organs and free sugar levels in the haemolymph of the beetles, through complex and species-specific mechanisms.

Gene expression in the efferent ducts, epididymis, and vas deferens during embryonic development of the mouse.

The tissues of the male reproductive tract are characterized by distinct morphologies, from highly coiled to un-coiled. Global gene expression profiles of efferent ducts, epididymis, and vas deferens were generated from embryonic day 14.5 to postnatal day 1 as tissue-specific morphologies emerge. Expression of homeobox genes, potential mediators of tissue-specific morphological development, was assessed. Twenty homeobox genes were identified as either tissue-enriched, developmentally regulated, or both. Additionally, ontology analysis demonstrated cell adhesion to be highly regulated along the length of the reproductive tract. Regulators of cell adhesion with variable expression between the three tissues were identified including Alcam, various cadherins, and multiple integrins. Immunofluorescence localization of the cell adhesion regulators POSTN and CDH2 demonstrated cell adhesion in the epithelium and mesenchyme of the epididymis may change throughout development. These results suggest cell adhesion may be modulated in a tissue-specific manner, playing an important role in establishing each tissue's final morphology.

Ultrastructure of male reproductive accessory glands and ejaculatory duct in the Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae).

Ultrastructure of male reproductive accessory glands and ejaculatory duct in the Queensland fruit fly (Q-fly), Bactrocera tryoni, were investigated and compared with those of other tephritid flies. Male accessory glands were found to comprise one pair of mesodermic glands and three pairs of ectodermic glands. The mesodermic accessory glands consist of muscle-lined, binucleate epithelial cells, which are highly microvillated and extrude electron-dense secretions by means of macroapocrine transport into a central lumen. The ectodermic accessory glands consist of muscle-lined epithelial cells which have wide subcuticular cavities, lined with microvilli. The electron-transparent secretions from these glands are first extruded into the cavities and then forced out through small pores of the cuticle into the gland lumen. Secretions from the two types of accessory glands then flow into the ejaculatory duct, which is highly muscular, with epithelial cells rich in rough endoplasmic reticulum and lined with a thick, deeply invaginated cuticle. While there are some notable differences, reproductive accessory glands of male Q-flies generally resemble those of the olive fruitfly, Bactrocera oleae, and to a lesser extent the Mediterranean fruit fly, Ceratitis capitata.

Segment boundaries of the adult rat epididymis limit interstitial signaling by potential paracrine factors and segments lose differential gene expression after efferent duct ligation.

The epididymis is divided into caput, corpus and cauda regions, organized into intraregional segments separated by connective tissue septa (CTS). In the adult rat and mouse these segments are highly differentiated. Regulation of these segments is by endocrine, lumicrine and paracrine factors, the relative importance of which remains under investigation. Here, the ability of the CTS to limit signaling in the interstitial compartment is reviewed as is the effect of 15 days of unilateral efferent duct ligation (EDL) on ipsilateral segmental transcriptional profiles. Inter-segmental microperifusions of epidermal growth factor (EGF), vascular endothelial growth factor (VEGFA) and fibroblast growth factor 2 (FGF2) increased phosphorylation of mitogen activated protein kinase (MAPK) in segments 1 and 2 of the rat epididymis and the effects of all factors were limited by the CTS separating the segments. Microarray analysis of segmental gene expression determined the effect of 15 days of unilateral EDL on the transcriptome-wide gene expression of rat segments 1-4. Over 11,000 genes were expressed in each of the four segments and over 2000 transcripts in segment 1 responded to deprivation of testicular lumicrine factors. Segments 1 and 2 of control tissues were the most transcriptionally different and EDL had its greatest effects there. In the absence of lumicrine factors, all four segments regressed to a transcriptionally undifferentiated state, consistent with the less differentiated histology. Deprivation of lumicrine factors could stimulate an individual gene's expression in some segments yet suppress it in others. Such results reveal a higher complexity of the regulation of rat epididymal segments than that is generally appreciated.

Effect of serotoninergic and cholinergic nervous systems and corresponding neurotransmitters on heart function and motor activity of pelvic smooth muscle organs.

Serotonin potentiated vagal negative chronotropic effect in rabbits and increased the synergistic action of autonomic nervous structures on cardiac function in frogs. Acetylcholine in low doses produced a positive chronotropic effect in frogs, which was related to activation of intracardiac adrenergic neurons. Simultaneous activation of the serotoninergic and cholinergic system suppressed heart function, but increased motor activity of pelvic smooth muscle organs.

Signal transduction in the ductuli efferentes testis of the rat: inhibition of fluid reabsorption by cyclic adenosine 3', 5'-monophosphate.

It is important to identify the signal transduction pathway involved in the regulation of fluid reabsorption by the ductuli efferentes of the testis because they reabsorb most of the fluid leaving the testis and are essential for male fertility. Microperfusion studies of the ducts in vivo showed that 0.1 or 1.0 mM dibutyryl (db)-cGMP in the perfusate had no effect on fluid reabsorption, but 0.1 mM db-cAMP significantly reduced fluid reabsorption, 0.25 mM abolished reabsorption, and 0.5-1.0 mM caused secretion. The inhibitory effect of db-cAMP was reversible. Although the presence of db-cAMP in the perfusate did not affect the concentration of Na+ in the collectate, the concentrations of K(+) and Cl(-) increased, indicating that their transport is at least partly regulated by cAMP. Including the phosphodiesterase inhibitor pentoxifylline in the perfusate decreased fluid reabsorption by the ducts in a dose-dependent manner, and it also increased the concentration of cAMP (5.5-fold) in collectate. Pentoxifylline also increased the production of cAMP (4-fold) by ducts incubated in vitro. It is concluded that cAMP, but probably not cGMP, is an intracellular messenger regulating fluid reabsorption in the efferent ducts.

Cystatin E1 and E2, new members of male reproductive tract subgroup within cystatin type 2 family.

The family of type 2 cystatin proteins is a class of cysteine proteinase inhibitors that function as potent inhibitors of papain-like cysteine proteinases. Recent studies have suggested that cystatins in the male reproductive tract subgroup may perform functions distinct from those of typical cystatins. The objective of the present study was to identify and characterize the expression of new gene members of the cystatin family 2 in mouse male reproductive tissues. Two new members of cystatin family 2, named mouse Cystatin E1 and mouse Cystatin E2 (mCST E1 and mCST E2, respectively), were identified in mice by searching the National Center for Biotechnology Information database for proteins containing homology to known type 2 cystatins. Human CST E1 has recently been reported independently under the name CST 11. The deduced amino acid sequences of these genes have significant homology with the family 2 cystatins, including four conserved cysteine residues at the C-terminus. Similar to other male reproductive subgroup cystatins, the inhibitory motifs are not well conserved in these genes. Northern blot analyses showed that both genes were highly expressed only in the epididymis. In situ hybridization demonstrated that both genes were restricted in their expression to the epithelial cells of the caput and that the highest expression was localized to the initial segment of caput epididymis. Northern blot analyses and in situ hybridization showed that both mCST E1 and E2 mRNA decreased after castration, and treatment with testosterone propionate (T) did not maintain expression of these genes. In fact, T treatment further repressed the expression of these genes in the epididymis following castration. Efferent ductule ligation resulted in a dramatic decrease of epididymal expression of mCST E1 and E2. The expression of mCST E1 mRNA was up-regulated by 17 beta-estradiol (E) administration for 7 days postcastration, whereas no recovery of mCST E1 mRNA level was detected after 14 days of E treatment. Combined E and T (E+T) treatment for 1 and 2 wk reduced the mCST E1 transcripts. The expression of mCST E2 mRNA was maintained by E administration for both 7 and 14 days after castration, whereas treatment of both T and E repressed the expression of mCST E2. Although both mCST E1 and E2 share significant homology with family 2 cystatins, including similar distribution in tissues and localization in epididymis, these genes may have different functions, because their regulation involves different hormones and, probably, other testicular factors.

Ductus ejaculatorius peptide 99B (DUP99B), a novel Drosophila melanogaster sex-peptide pheromone.

We have characterized a glycosylated, 31 amino-acid peptide of 4932 Da isolated from Drosophila melanogaster males. The mature peptide contains a sugar moiety of 1184 Da at a NDT consensus glycosylation site and a disulfide bond. It is synthesized in the male ejaculatory duct via a 54 amino-acid precursor containing an N-terminal signal peptide and Arg-Lys at the C-terminus which is cleaved off during maturation. The gene contains an intron of 53 bp and is localized in the cytological region 99B of the D. melanogaster genome. The peptide is therefore named DUP99B (for ductus ejaculatorius peptide, cytological localization 99B). The C-terminal parts of mature DUP99B and D. melanogaster sex-peptide (ACP70A) are highly homologous. Injected into virgin females, DUP99B elicits the same postmating responses as sex-peptide (increased oviposition, reduced receptivity). These effects are also induced by de-glycosylated native peptide or synthetic DUP99B lacking the sugar moiety. Presence of the glycosyl group, however, decreases the amount needed to elicit the postmating responses. Homologies in the coding regions of the two exons of DUP99B and sex-peptide, respectively, suggest that the two genes have evolved by gene duplication. Thus, we consider these two genes to be members of the new sex-peptide gene family.

Dual role of the Pax gene paired in accessory gland development of Drosophila.

The Drosophila Pax gene paired encodes a transcription factor that is required for the activation of segment-polarity genes and proper segmentation of the larval cuticle, postembryonic viability and male fertility. We show that paired executes a dual role in the development of male accessory glands, the organ homologous to the human prostate. An early function is necessary to promote cell proliferation, whereas a late function, which regulates the expression of accessory gland products such as the sex peptide and Acp26Aa protein, is essential for maturation and differentiation of accessory glands. The late function exhibits in main and secondary secretory cells of accessory glands dynamic patterns of Paired expression that depend in both cell types on the mating activity of adult males, possibly because Paired expression is regulated by negative feedback. The early Paired function depends on domains or motifs in its C-terminal moiety and the late function on the DNA-binding specificity of its N-terminal paired-domain and/or homeodomain. Both Paired functions are absolutely required for male fertility, and both depend on an enhancer located within 0.8 kb of the downstream region of paired.

Role of male accessory glands in spermatodesm reorganization in Orthoptera Tettigonioidea.

A preliminary examination of the spermatodesms of Orthoptera Tettigonioidea revealed a structure that is similar in individuals of the same sex but very different in specimens of opposite sex. This reorganization would seem to take place inside the spermatophore during transit from the male to female genital tracts. The results of incubating spermatodesms with the secretions of glandular extract (GE) obtained from male accessory glands, known to be involved in forming the spermatophore wall, revealed changes in the spermatodesm 'cap' that are comparable to those occurring in vivo. Moreover, incubation of spermatodesms with the extracts obtained separately from tubules of the 1st and 2nd orders (GE1, GE2) established that GE2 alone modifies the spermatodesms, thus excluding the possible implication of 1st order tubules in the rearrangement process. In conclusion, data from incubations of spermatodesms with the single fractions obtained by submitting GE2 to gel-filtration FPLC show that only the peak 4 maintains intact the biological activity of GE2, SDS-PAGE analysis of the fraction corresponding to peak 4 revealed a greater protein content of 29 kD, which also appears to a lesser degree in fraction 3. This material is responsible for a partial dismantling of the 'cap' in the incubated spermatodesms.

Estrogen receptor alpha has a functional role in the mouse rete testis and efferent ductules.

Previous studies of the estrogen receptor-alpha knockout (alpha ERKO) in the male mouse demonstrate that the rete testis and efferent ductules are targets of estrogen. Because the alpha ERKO mouse lacks a functional estrogen receptor alpha (ER alpha) throughout development, it was not known whether the morphological and physiological abnormalities observed in the alpha ERKO male were due to developmental defects or to dysfunctions concurrent with the lack of ER alpha in the tissue. This study was designed to determine if treatment of normal wild-type (WT) mice with the pure antiestrogen, ICI 182,780, (ICI) could reproduce the morphological characteristics seen in alpha ERKO mice. Thirty-day-old male mice were treated for 35 days with either castor oil or ICI. Age-equivalent alpha ERKO mice were used for comparison. Light microscopic examinations of the reproductive tracts revealed dramatic changes in the efferent ductules of treated mice: a 1.7-fold increase in luminal diameter, a 56% reduction in epithelial cell height, a 60% reduction in brush boarder height of nonciliated cells, and an apparent reduction of the number of observable lysosomes and endocytotic vesicles. Testes of ICI-treated mice showed swollen rete testes area (6.5 times larger than control) and a 65% reduction in rete testis epithelium height. However, there were no significant changes in body and testis weights. These results indicate that ER blockage with ICI in WT mice results in morphological changes of the efferent ductules resembling those seen in alpha ERKO siblings of the same age. Based on this study, we conclude that ER alpha has a functional role in the mouse reproductive tract and the aberrant morphology observed in the efferent ductules of the alpha ERKO mouse is likely the result of a concurrent response to the lack of functional ER alpha, and not solely due to the lack of ER alpha during early developmental times.

Human ejaculatory duct: parameters of smooth muscle motor activity and modulatory role of autonomic drugs.

The contractile behaviour and effects of several autonomic drugs on the motor activity of human isolated ejaculatory ducts were investigated. Ejaculatory ducts exhibited spontaneous contractions characterised by an amplitude of 2.35 +/- 0.28 mN, a duration of 62. 9 +/- 3.72 s and a frequency of 0.64 +/- 0.014 waves min-1. Acetylcholine (10-5-10-4 m) induced a slight increase in basal tone and in the frequency of the contraction waves. These effects were suppressed by atropine (10-4 m). Noradrenaline (norepinephrine) increased the basal tone and frequency of spontaneous contractions in a dose-dependent manner. These responses were competitively inhibited by HEAT, a selective a1-adrenoceptor antagonist. These preliminary functional findings, indicating the presence of spontaneous motor activity of human ejaculatory ducts and its possible control by adrenergic agonists, suggests a physiological role for human ejaculatory duct in the propulsion of semen from the seminal vesicle towards the urethra.

Oestrogen in fluid transport in efferent ducts of the male reproductive tract.

This review focuses on the importance of oestrogen and oestrogen receptors in the male reproductive system, with a special interest in the newly discovered role of oestrogen in the regulation of fluid reabsorption in the efferent ductules of the testis. Early work on oestrogen synthesis indicated that Leydig and Sertoli cells were the only important cells in the production of this steroid in the adult testis. However, more recent work has shown that germ cells and spermatozoa also contain aromatase and produce oestrogen. The observation that germ cells synthesize oestrogen contributed to a new hypothesis that oestrogen in the lumen of the male reproductive tract targets the epithelial lining of efferent ductules and the epididymis. The location of nuclear oestrogen receptors in the male reproductive tract has also been investigated and it has been found that oestrogen receptor alpha is more abundant in the efferent ductules of the testis than in any other tissue of the male or female. In all species examined to date, oestrogen receptor alpha has been found to be abundant in the efferent ductules. The structure and function of the efferent ductules are taken into account as these tubules are responsible for the reabsorption of almost 90% of the luminal rete testis fluid. Thus, it was logical to hypothesize that oestrogen receptors play a role in the regulation of fluid reabsorption in efferent ductules. The oestrogen receptor alpha knockout mouse was used to help define this role of the receptor in males. In this animal model, the efferent ductules are altered markedly from a reabsorptive epithelium to a squamous epithelium devoid of lysosomes and endocytotic organelles. Although the separate roles for oestrogens and androgens in the regulation of fluid reabsorption are controversial and remain to be resolved, it is now established that loss of oestrogen receptor function in males interferes with the resorptive function of efferent ductules, a function that is essential for fertility. Future studies will focus on the biochemical and physiological mechanisms involved in the regulation of water and ion movement by oestrogen in the male reproductive tract.

Shedding of a rat epididymal sperm protein associated with infertility induced by ornidazole and alpha-chlorohydrin.

The protein composition of epididymal fluid and sperm extracts of rats treated with the nitroimidazole compound ornidazole was investigated by two-dimensional gel electrophoresis. Epididymal luminal fluid from the corpus and cauda regions of male animals rendered infertile by ornidazole treatment contained a prominent protein (contraception-associated protein 1, CAP1) with a molecular mass of approximately 25 kDa and an isoelectric point (pI) of 5.8; it was not found in fluids, but was present in sperm, from fertile vehicle-fed rats. Infrared matrix-assisted laser desorption/ionization mass spectrometry indicated that the molecular mass of CAP1 was 20420+/-120 daltons. Analysis of 17 amino acids demonstrated 49% homology to a diuretic hormone from an insect (Acheta domesticus). Densitometric quantitation of CAP1 on silver-stained gels indicated its presence in greater amounts in cauda than in corpus fluid from treated animals, whereas fluid from the rete testis lacked CAP1. In vitro incubations of tissue from the caput, corpus, and cauda epididymidal regions with [35S]methionine gave no hint that CAP1 was a secretion product of the epididymal epithelium. The absence of CAP1 from luminal fluid obtained from the sperm-depleted corpus epididymidis of efferent duct-ligated ornidazole-fed rats suggested a spermatozoal origin. CAP1 was present in spermatozoa from the caput epididymidis but not from the rete testis in control animals. Less CAP1 was present in detergent extracts of cauda sperm from ornidazole-treated rats than in sperm from control animals, suggesting a contraceptive-related displacement of protein from sperm to fluid. The association of ornidazole- and alpha-chlorohydrin-induced infertility with the presence of CAP1 in epididymal fluid, probably originating from spermatozoa, suggests a critical role for this protein in fertilization.

In vivo microperfusion of the ductuli efferentes testis of the rat: flow dependence of fluid reabsorption.

Individual ducts from the initial zone of the efferent ducts of the rat were microperfused in vivo using a double cannulation procedure, which allowed the recovery of perfused fluids for analysis and determination of the rate of fluid reabsorption from the perfused duct. The ducts were perfused at rates from 0.025 to 0.4 microliters min-1 with either Krebs-Ringer bicarbonate (KRB) solution or the native rete testis fluid (nRTF) that perfuses the ducts in situ. Reabsorption of KRB solution increased linearly with a perfusion rate of between 0.025 and 0.1 microliter min-1 (from 17.4 +/- 1.5 to 34.3 +/- 3.2 nl (10 mm duct)-1 min-1), then increased no further. Reabsorption of nRTF increased linearly between 0.025 and 0.2 microliters min-1 (from 17.7 +/- 1.5 to 61.4 +/- 13.5 nl (10 mm duct)-1 min-1) and then declined. The reabsorption rate from nRTF perfusates was significantly higher than from KRB perfusates. As a proportion of the luminal perfusate, reabsorption declined from 73.0 +/- 6.0 to 7.4 +/- 3.0% (10 mm duct)-1 for KRB solution and from 73.1 +/- 6.0 to 4.1 +/- 1.3% (10 mm duct)-1 for nRTF. There was no significant change in the concentration of either Na+ or Cl- in KRB solution or nRTF during perfusion through the efferent ducts, indicating that the reabsorption of these ions was isomolar. However, the reabsorption of K+ from nRTF occurred at a greater rate than that of water, and the initial [K+] declined from 17.2 +/- 0.4 mM in nRTF perfusates to 5.7 +/- 0.5 mM in collectates (perfusion rate, 0.1 microliter min-1) to achieve equilibrium with blood plasma (4.7 +/- 0.4 mM). The osmotic pressure of both KRB and nRTF perfusates equilibrated with blood plasma, indicating a high permeability of the epithelium to water. The results of this study provide further evidence that fluid reabsorption in the efferent ducts is isosmotic, or close to isosmotic, and have shown that, as in the homologous proximal kidney tubule, reabsorption is dependent on luminal flow rate. In contrast to the proximal tubule, however, reabsorption in the efferent ducts is not maintained as a constant proportion of the perfusion load. It is concluded that microperfusion in vivo provides a useful technique for studying fluid reabsorption in the efferent ducts of the rat.