Angiotensin II receptors, AT1 and AT2 in the rat epididymis. Immunocytochemical and electrophysiological studies

Function and therapeutic potential of G protein-coupled receptors in epididymis

Infertility rates for both females and males have increased continuously in recent years. Currently, effective treatments for male infertility with defined mechanisms or targets are still lacking. G protein-coupled receptors (GPCRs) are the largest class of drug targets, but their functions and the implications for the therapeutic development for male infertility largely remain elusive. Nevertheless, recent studies have shown that several members of the GPCR superfamily play crucial roles in the maintenance of ion-water homeostasis of the epididymis, development of the efferent ductules, formation of the blood-epididymal barrier and maturation of sperm. Knowledge of the functions, genetic variations and working mechanisms of such GPCRs, along with the drugs and ligands relevant to their specific functions, provide future directions and a great arsenal for new developments in the treatment of male infertility.

Renin Angiotensin System, COVID-19 and Male Fertility: Any Risk for Conceiving?

The current knowledge concerning the connection between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the renin-angiotensin system (RAS) system in the male reproductive apparatus is still limited, so dedicated studies are urgently required. Concerns about the male fertility consequences of SARS-CoV-2 infection have started to emerge, since epidemiologic studies observed that this coronavirus affects male patients more frequently and with increased severity, possibly because of the hormone-regulated expression of angiotensin-converting enzyme 2 (ACE2) receptor. A disturbance in fertility is also expected based on studies of the previous SARS-CoV infection, which targets the same ACE2 receptor when entering the host cells. In addition, bioinformatics analyses reveal the abundant expression of ACE2 receptor in the male reproductive tissues, particularly in the testis. It has been proposed that pharmacological intervention favoring the angiotensin-(1-7)/ACE2/Mas receptor pathway and increasing ACE2 expression and activity could greatly prevent inflammatory lesions in this area. Finally, in laboratories performing assisted reproductive technologies it is recommended that more attention should be paid not only to sperm quality but also to safety aspects. Data about the potential infectivity of seminal fluid are in fact conflicting and do not exclude risks for both personnel and patients. The potential infectivity of SARS-CoV-2 in reproductive male tissues should be strongly considered and further investigated for the proper management of in vitro fertilization procedures.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

Transepithelial projections from basal cells are luminal sensors in pseudostratified epithelia

Basal cells are by definition located on the basolateral side of several epithelia, and they have never been observed reaching the lumen. Using high-resolution 3D confocal imaging, we report that basal cells extend long and slender cytoplasmic projections that not only reach toward the lumen but can cross the tight junction barrier in some epithelia of the male reproductive and respiratory tracts. In this way, the basal cell plasma membrane is exposed to the luminal environment. In the epididymis, in which luminal acidification is crucial for sperm maturation and storage, these projections contain the angiotensin II type 2 receptor (AGTR2). Activation of AGTR2 by luminal angiotensin II, increases proton secretion by adjacent clear cells, which are devoid of AGTR2. We propose a paradigm in which basal cells scan and sense the luminal environment of pseudostratified epithelia and modulate epithelial function by a mechanism involving crosstalk with other epithelial cells.

Role of the AT1A receptor in the CO2-induced stimulation of HCO3- reabsorption by renal proximal tubules

The proximal tubule (PT) is major site for the reabsorption of filtered HCO(3)(-). Previous work on the rabbit PT showed that 1) increases in basolateral (BL) CO(2) concentration ([CO(2)](BL)) raise the HCO(3)(-) reabsorption rate (J(HCO(3))), and 2) the increase that luminal angiotensin II (ANG II) produces in J(HCO(3)) is greatest at 0% [CO(2)](BL) and falls to nearly zero at 20%. Here, we investigate the role of angiotensin receptors in the [CO(2)](BL) dependence of J(HCO(3)) in isolated perfused PTs. We found that, in rabbit S2 PT segments, luminal 10(-8) M saralasin (peptide antagonist of ANG II receptors), lowers baseline J(HCO(3)) (5% CO(2)) to the value normally seen at 0% in the absence of inhibitors and eliminates the J(HCO(3)) response to changes in [CO(2)](BL). However, basolateral 10(-8) M saralasin has no effect. As with saralasin, luminal 10(-8) M candesartan (AT(1) antagonist) reduces baseline J(HCO(3)) and eliminates the [CO(2)](BL) dependence of J(HCO(3)). Luminal 10(-7) M PD 123319 (AT(2) antagonist) has no effect. Finally, we compared PTs from wild-type and AT(1A)-null mice of the same genetic background. Knocking out AT(1A) modestly lowers baseline J(HCO(3)) and, like luminal saralasin or candesartan in rabbits, eliminates the J(HCO(3)) response to changes in [CO(2)](BL). Our accumulated evidence suggests that ANG II endogenous to the PT binds to the apical AT(1A) receptor and that this interaction is critical for both baseline J(HCO(3)) and its response to changes in [CO(2)](BL). Neither apical AT(2) receptors nor basolateral ANG II receptors are involved in these processes.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Pressor and intra-renal effects of angiotensins I and II, and noradrenaline, in anaesthetized and conscious sheep

The pressor and intra-renal actions and effects of octa - and deca-peptides angiotensins II and I and of the catecholamine noradrenaline, in anaesthetized and conscious sheep, are considered. The halothane anaesthetic substantially lowers pressor sensitivity to both peptides but does not influence their ability to liberate K(+) ions into the circulating plasma. In comparison with angiotensin II, both angiotensin I and noradrenaline -- with direct presentation to the kidney -- are ineffective in decreasing intra-renal blood flow. However, with left ventricular injection, both pressor compounds immediately increase the blood pressure, as does angiotensin II. Combined doses of the decapeptide and catecholamine are thus highly effective in raising the blood pressure while having a minimal effect on blood flow through the kidney. This overall situation could provide a basis for treating clinical shock, especially regarding septicaemia and septic shock. The lowered hind-limb blood flow, with administration of the pressor compounds into the femoral artery, contrasts strongly with the raised flow resulting from intravenous injection. Experimental procedures to establish, or otherwise, relevant hypothetical situations are detailed.

Angiotensin II stimulates DNA synthesis of rat pancreatic stellate cells by activating ERK through EGF receptor transactivation

Although angiotensin II (Ang II) is known to participate in pancreatic fibrosis, little is known as to the mechanism by which Ang II promotes pancreatic fibrosis. To elucidate the mechanism, we examined the action of Ang II on the proliferation of rat pancreatic stellate cells (PSCs) that play central roles in pancreatic fibrosis. Immunocytochemistry and Western blotting demonstrated that both Ang II type 1 and type 2 receptors were expressed in PSCs. [3H]Thymidine incorporation assay revealed that Ang II enhanced DNA synthesis in PSCs, which was blocked by Ang II type 1 receptor antagonist losartan. Western blotting using anti-phospho-epidermal growth factor (EGF) receptor and anti-phospho-extracellular signal regulated kinase (ERK) antibodies showed that Ang II-activated EGF receptor and ERK. Both EGF receptor kinase inhibitor AG1478 and MEK1 inhibitor PD98059 attenuated ERK activation and DNA synthesis enhanced by Ang II. These results indicate that Ang II stimulates PSC proliferation through EGF receptor transactivation-ERK activation pathway.

Effects of angiotensin II on rat pancreatic stellate cells

The aim of the study was to identify pancreatic stellate cells (PSCs) as a potential target of angiotensin II (ATII) action because recently a local renin-angiotensin system (RAS) has been described in the pancreas. PSCs were isolated from male Wistar rats and investigated for ATII receptor expression and ATII-induced calcium transients, contractions, proliferation, and alpha-smooth muscle actin expression. Quiescent and activated PSCs expressed the ATII receptor subtype AT1 but not AT2. Addition of ATII led to a rapid elevation of intracellular calcium ([Ca]i). The sensitivity toward ATII with respect to calcium transients did not change during the transdifferentiation process. In activated PSCs, ATII dose dependently induced PSC cell contraction. Furthermore, ATII induced an activation of the c-Jun-N-terminal kinase (JNK) and extracellular regulated kinase (Erk), which was inhibited after intracellular calcium chelation by BAPTA-AM. The p38 mitogen-activated protein kinase (p38) was also activated by ATII. BAPTA-AM itself induced p38 activation, which was not further enhanced by ATII. ATII stimulated PSC proliferation, while PSC transdifferentiation, as indicated by alpha-smooth muscle actin expression and collagen type I secretion, was not enhanced. The data suggest that PSCs are targets of ATII action with potential pathophysiological relevance.

Epididymal phenotype in luteinizing hormone receptor knockout animals and its response to testosterone replacement therapy

Previous studies reported that epididymis contains functional LH receptors. The LH receptor knockout mice, which have epididymal phenotypes, gave us an opportunity to test the hypothesis that testosterone replacement alone may not be sufficient to reverse phenotypes to wild-type epididymis. The morphological phenotype in knockout animals includes a decrease in luminal diameter of the proximal and distal caput and cauda epididymis, the absence of clear and halo cells in the epithelial lining, a decrease in the height of principal cells and the number of cells containing cilia, a decrease in cilia length, and a change from basal to central location of nuclei in the principal cells. The biochemical phenotype includes a decrease in periodic acid-Schiff reaction product, reflecting the glycogen and glycoprotein synthesis and secretion, a decrease in androgen receptor (AR) and estrogen receptor (ER)beta, and an increase in ERalpha levels. Twenty-one-day testosterone replacement therapy in 30-day-old knockout animals reversed some, but not all, morphological and biochemical phenotypes. Those that did not reverse include luminal diameters of proximal and distal caput and cauda epididymis, the percentage of ciliated principal cells in caput epididymis, and nuclear AR localization. In summary, while our results reaffirm that androgens are important for normal epididymal morphology and function, they indicate that LH could be required for certain facets of epididymal morphology and/or function.

A locally generated angiotensin system in rat carotid body

Previous studies have shown the existence of functional angiotensin II receptors in rat carotid body, which directly alters the carotid chemoreceptor afferent nerve activity. Moreover, chronic hypoxia could result in an enhanced sensitivity of chemoreceptor afferent activity via an AT(1) receptor-mediated calcium signaling in the carotid body. In the present study, the localization and expression of angiotensinogen, the obligatory component for an intrinsic, angiotensin-generating system, were investigated by in situ hybridization histochemistry, immunohistochemistry, RT-PCR, Western blot and Northern blot analysis. In situ hybridization showed the expression of angiotensinogen within the glomus cells of the carotid body. Double immunostaining of angiotensinogen and tyrosine hydroxylase, an immunohistochemical marker for type I glomus cells, elucidated that angiotensinogen protein was specifically localized to the lobules of type I cells. Consistently, RT-PCR and Western blot analysis confirmed the expression of angiotensinogen mRNA and protein, respectively. On the other hand, renin mRNA was not detected using RT-PCR and Northern blot analysis whereas angiotensin-converting enzyme (ACE) mRNA was detected in the carotid body. These data suggest that a locally generated angiotensin system is operated in the carotid body, which might be linked to a renin-independent biosynthetic pathway. Such an intrinsic, angiotensin-generating system and its local regulation by chronic hypoxia should be important in the modulation of cardiopulmonary adaptation in the hypoxic ventilatory response and the electrolyte as well as water homeostasis.

Physiological and enzymatic properties of the ram epididymal soluble form of germinal angiotensin I-converting enzyme

The 94-kDa ram epididymal fluid form of the sperm membrane-derived germinal angiotensin I-converting enzyme (ACE) was purified by chromatography, and some of its enzymatic properties were studied. For the artificial substrate furanacryloyl-L-phenylalanylglycylglycine (FAPGG), the enzyme exhibited a Michaelis constant (K(m)) of 0.18 mM and a V(max) of 34 micromoles/(min x mg) and for hippuryl-L-histidyl-L-leucine a K(m) of 2.65 mM and a V(max) of 163 micromoles/(min x mg) under the defined standard conditions (300 mM NaCl and 50 mM Tris; pH 7.5 and 8.3, respectively). The FAPGG hydrolysis was decreased by 82.5% and 67.5% by EDTA and dithioerythritol, respectively, and was totally inhibited by specific ACE inhibitors such as captopril, P-Glu-Trp-Pro-Arg-Pro-Glu-Ile-Pro-Pro, and lisinopril. Optimum activity for FAPGG was with pH 6.0, 50 mM chloride, and 500 microM zinc. Under the various conditions tested, bradykinin, angiotensin (Ang) I, Ang II, and LHRH were competitors for FAPGG. Bradykinin and angiotensin I were the best competitors. The enzyme cleaved Ang I into Ang II, and the optimal conditions were with pH 7.5 and 300 mM chloride. The relationship between the carboxypeptidase activity in seminal plasma and the prediction of fertility of young rams was also studied. These results indicated a correlation between sperm concentration and ACE activity in semen but showed no statistically significant correlation between such activity and fertility of the animal. Finally, we tested the role of ACE in fertilization; no difference in the in vitro fertilization rate was observed in the presence of 10(-4) M captopril.

Chronic hypoxia induced down-regulation of angiotensinogen expression in rat epididymis

The presence of an intrinsic renin-angiotensin system (RAS) in the rat epididymis has been previously established by showing the expression of several key RAS components, and in particular angiotensinogen, the indispensable element for the intracellular generation of angiotensin II. In this study, the possible involvement of this local epididymal RAS in the testicular effects of chronic hypoxia was investigated. Semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR), Western blotting and by in situ hybridization histochemistry of the rat epididymis were used to show changes in localization and expression of angiotensinogen. Results from RT-PCR analysis demonstrated that chronic hypoxia caused a marked decrease (60%) in the expression of angiotensinogen mRNA, when compared with that in the normoxic epididymis. Western blot analysis demonstrated a less decrease (35%) in the expression of angiotensinogen protein. In situ hybridization histochemistry showed that the reduced angiotensinogen mRNA in chronic hypoxia was specifically localized to the epididymal epithelium from the cauda, corpus and caput regions of the epididymis; a distribution similar to that of normoxic rats. It was concluded that chronic hypoxia decreases the transcriptional and translational expression of angiotensinogen, and thus local formation of angiotensin II, in the rat epididymis.

High-affinity binding of T3 to epididymis nuclei

Thyroid hormones play an important role in epididymal function. Hypothyroid animals experience a significant decrease in the number and forward motility of sperm and a remarkable impairment of epididymal morphology. However, it is yet unknown if such activity is due to direct actions of iodothyronines on the target epididymis. The eventual identification of T3 receptors in the nucleous of epididymal cells becomes relevant. For this reason, the authors searched for specific high-affinity binding of T3 to these nuclei. Twenty prepuberal male Wistar rats were used. The testes and epididymis were approached as one unit through a scrotal incision. The fat-free epididymides were subjected to standard techniques to prepare the nuclei for incubations with 125I-T3 concentrations, ranging from 0.5 x 10(-9) to 2.0 x 10(-11) M. Calculations of association constants and binding capacities were performed according to Scatchard. A single binding site with a Ka of 3.06 +/- 0.6 x 10(9) M(-1) or Kd of 3.26 +/- 0.6 x 10(10) M and a maximal binding capacity of 0.11 +/- 0.02 pmol T3/microg DNA were observed. It is concluded that these nuclei contain a specific T3 receptor. This finding strongly suggests that thyroid hormones have direct effects on the epididymis.

Testicular hormonal regulation of the renin-angiotensin system in the rat epididymis

Evidence for the existence of an intrinsic angiotensin system based on locally formed angiotensinogen as a precursor for angiotensin production has been demonstrated in the rat epididymis. The data strongly support the presence of an epididymal renin-angiotensin system (RAS) which may be important for epididymal and sperm functions. In the present study, the effects of castration and testicular hormonal replacement on the expression of RAS components from the rat epididymis are investigated at the gene and protein levels. Results from northern blot and western blot analyses consistently showed that the expression of angiotensinogen mRNA and protein was apparently abolished by castration whereas their expression was completely restored to control levels when the castrated rats were hormonally replaced with either testosterone alone or with combined testosterone and estradiol. Northern blot did not detect any signal for angiotensinogen mRNA while western blot could detect a weak signal for angiotensinogen protein when the castrated rats were replaced with estradiol alone. Renin could be detected neither in control, castrated nor hormonally replaced rats. Moreover, the expression of angiotensin II receptor, type I (AT1) was almost abolished by castration as demonstrated by northern blot and reverse transcription-polymerase chain reaction. These data indicate that the expression of RAS by the rat epididymis at the levels of its precursor angiotensinogen and its receptor AT1, is subject to the regulation of testicular hormones and its expression appears to be predominantly testosterone-dependent.

Activation of local renin-angiotensin system by chronic hypoxia in rat pancreas

Previous studies have provided evidence that several key elements of renin-angiotensin system (RAS) are present in the rat pancreas, notably angiotensinogen, which is mandatory for intracellular generation of physiologically active angiotensin II. The data support the existence of an intrinsic RAS, which may be important for pancreatic blood flow and ductal anion secretion. In the present study, the effect of chronic hypoxia on the expression of RAS components, particularly at the levels of its precursor angiotensinogen and its receptor subtypes AT(1) and AT(2), were investigated in the rat pancreas. Results from western blot and semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) analyses unequivocally showed that chronic hypoxia caused a marked increase in angiotensinogen both at the protein and gene levels when compared with that in the normoxic pancreas. However, results from RT-PCR showed that there was a differential effect of chronic hypoxia on the expression of AT(1) and AT(2) receptor subtypes, which exhibited subtype-specific changes in gene expression. For AT(1), chronic hypoxia did not cause a significant change in mRNA expression for AT(1a) but a significant increase in mRNA expression for AT(1b). For AT(2), chronic hypoxia caused a marked increase in its mRNA expression. The increased expression of RAS component genes by chronic hypoxia and its significance of changes may be important for physiological and pathophysiological aspects of the pancreas.

Angiotensinogen expression by rat epididymis: evidence for an intrinsic, angiotensin-generating system

Previous studies have suggested the presence of an intrinsic renin-angiotensin system (RAS) in the rat epididymis with functions in epididymal activity and sperm maturation. In the present study, the localization and expression of angiotensinogen, the component of the RAS which is indispensable for intracellular angiotensin generation, were investigated by immunochemistry, hybridization histochemistry and by reverse-transcriptase polymerase chain reaction (RT-PCR). Western blot analysis of protein from the epididymis confirmed the presence of angiotensinogen with the expected molecular mass of about 60 kDa, in agreement with results from other tissues. Immunocytochemistry showed the regional localization of immunoreactivity for angiotensinogen in the rat epididymis. In situ hybridization histochemistry further demonstrated the expression of angiotensinogen mRNA by the epididymal epithelium in a region-specific manner along the length of the rat epididymis. RT-PCR confirmed that the rat epididymis expresses angiotensinogen mRNA. On the other hand, mRNA of renin was not detected in the rat epididymis using Northern blot and RT-PCR analyses. The present study strongly supports the existence of an intrinsic, angiotensin-generating system based on locally formed angiotensinogen as a precursor for angiotensin production. This epididymal RAS may have paracrine or autocrine roles in mediating the epididymal and sperm functions.

A 105- to 94-kilodalton protein in the epididymal fluids of domestic mammals is angiotensin I-converting enzyme (ACE); evidence that sperm are the source of this ACE

SDS-PAGE analysis of luminal fluid from the ram testis and epididymis revealed a protein of about 105 kDa in the fluid in the caput epididymal region. The molecular mass of this fluid protein shifted from 105 kDa to 94 kDa in the distal caput epididymidis and remained at 94 kDa in the lower regions of the epididymis. The possible sperm origin of this protein was suggested by the decrease in intensity of a 105-kDa compound on the sperm plasma membrane extract and by its total disappearance from the fluid of animals with impaired sperm production caused by scrotal heating. The 94-kDa protein was purified from ram cauda epididymal fluid, and a rabbit polyclonal antiserum was obtained. This antiserum showed that membranes of testicular sperm and sperm from the initial caput were positive for the presence of an immunologically related antigen. The protein was immunolocalized mainly on the flagellar intermediate piece, whereas in some corpus and caudal sperm, only the apical ridge of the acrosomal vesicle was labeled. The purified protein was microsequenced: its N-terminal was not found in the sequence database, but its tryptic fragments matched the sequence of the angiotensin I-converting enzyme (ACE). Indeed, the purified 94-kDa protein exhibited a carboxypeptidase activity inhibited by specific blockers of ACE. All the soluble seminal plasma ACE activity in the ram was attributable to the 94-kDa epididymal fluid ACE. The polyclonal antiserum also showed that a soluble form of ACE appeared specifically in the caput epididymal fluid of the boar, stallion, and bull. This soluble form was responsible for all the ACE activity observed in the fluid from the distal caput to the cauda epididymidis in these species. Our results strongly suggest that the epididymal fluid ACE derives from the germinal form of ACE that is liberated from the testicular sperm in a specific epididymal area.

Angiotensin II: a reproductive hormone too?

It has long been known that angiotensin II (Ang II) can affect reproductive tissues such as the uterus. However, the existence of a local renin-angiotensin system (RAS) in female as well as male reproductive tissues is a relatively recent observation. Of great interest is the discovery that all components of the RAS are present in the ovary, that the ovary secretes components of the RAS into the bloodstream, and that the ovary itself is responsive to Ang II. Recent studies suggest that the primary role of Ang II in the ovary is to cause atresia in non-ovulatory follicles; however, there is also compelling data to suggest that Ang II facilitates ovulation. Male reproductive structures also contain all of the components of the RAS, gonadotropins regulate the activity of these components, and these tissues have Ang II receptors. Of great interest is the expression of testis-specific angiotensin-converting enzyme (ACE), which is located on germ cells. Recent studies using gene knock-out techniques indicate that testis ACE plays an important role in male fertility. However, the overall significance of the RAS for normal reproductive function remains questionable. There is now a body of evidence implicating the RAS in pathophysiologies associated with reproductive function, which gives rise to the possibility that drugs acting on the RAS might ameliorate some of these disorders. Considerable work remains to determine the role of Ang II in reproductive functions.

Functional expression of sperm angiotensin II type I receptor in Xenopus oocyte: modulation of a sperm Ca2+-activated K+ channel

In addition to Ca2+ and K+ fluxes, angiotensin II (Ang II) has been shown to influence sperm motility. The present study investigated the involvement of angiotensin II type 1 receptor (AT1) in mediating the modulatory effect of Ang II on a sperm Ca2+-activated K+ channel expressed in Xenopus oocytes injected with RNAs of spermatogenic cells. Ang II at a concentration of 1 microM was found to potentiate the ionomycin-induced current, previously demonstrated to be mediated by a 'Maxi' Ca2+-activated K+ channel. However, at higher concentration, 20 microM, Ang II was found to suppress the ionomycin-induced current. Both potentiating and inhibitory effects of Ang II were blocked by losartan, a specific antagonist of AT1 receptors. Immunohistochemical studies further confirmed the presence of AT1 receptors in spermatogenic cells while expression of AT1 receptor mRNA was demonstrated by RT-PCR. These results suggest that Ang II may influence sperm motility as well as other sperm function by acting on AT1 receptors, and exerting potentiating and inhibitory effects on the Ca2+-activated K+ channels.

Differential gene expression of angiotensin II receptor subtypes in the epididymides of mature and immature rats

Previous studies have suggested that epididymal and sperm functions are subject to control by a local renin-angiotensin II system (RAS) in the rat epididymis. Type-1 angiotensin II receptor, AT1 and type-2 receptor, AT2 were localized in epididymal epithelium, indicating that RAS may act in a paracrine or autocrine fashion to regulate fluid secretion, probably through the basally placed membrane-bound AT1 protein as revealed by immunocytochemical and electrophysiological studies. In the present work, the expression of the angiotensin II receptor subtypes in the rat epididymis was showed by western blot analysis and reverse-transcription polymerase chain reaction (RT-PCR) using specific primers for the angiotensin II receptor subtypes. Western blot analysis showed the expression of AT1 receptor in the rat epididymis. Results from RT-PCR, using specific primers based on the corresponding angiotensin II receptor subtype genes for AT1a, AT1b and AT2 , demonstrated the differential expression of mRNAs from these receptor subtypes in the epididymides of mature and immature rats. Both the genes for AT1a and AT1b, but not that for AT2, are predominantly expressed in the epididymides of mature rat. In contrast, only AT1a and AT2 were highly expressed in the epididymides of immature rat. These results suggest that the expression of type-1 and type-2 angiotensin II receptor subtypes are developmentally regulated. Type-1 subtype may play a role in regulation of electrolyte and fluid transport in mature rat whereas type-2 subtype may be important in growth and development in the immature rat.

Immunohistochemical localization of angiotensin II in the mouse pancreas

Previous studies have suggested the presence of a tissue renin-angiotensin II system in the pancreas. These studies were based on the observation of several key components of the renin-angiotensin II system using molecular biological, biochemical and pharmacological approaches. In the present study, angiotensin II was localized immunohistochemically in the mouse pancreas using an indirect immunoperoxidase-staining technique. The results showed that angiotensin II-like immunoreactivity was localized predominantly in the endothelial cells of pancreatic blood vessels and the epithelial cells of pancreatic ducts from a subgroup of the vessels and ducts. Compared with those found in the pancreatic blood vessels and ductal system, a less pronounced immunoreactivity for angiotensin II was also observed in the acinar cells and in the smooth muscle layers overlying the pancreatic ducts as well as the blood vessels. However, no angiotensin II-like immunoreactivity was detected in the islet cells. Taken together with previous findings, the present results suggest a local angiotensin II-forming system in the mouse pancreas, which may be a significant autocrine or paracrine modulator of diverse pancreatic functions, including regulation of pancreatic blood flow and pancreatic anion secretion.