ABSTRACT

In order to investigate the role of renin angiotensin in the epididymis, angiotensin-converting enzyme (ACE) activity and angiotensin I (AI) and angiotensin II (AII) concentrations were measured in the male reproductive tract and blood serum of the rat. High ACE activity was detected in the rat epididymis, with a major part of the activity being associated with epididymal spermatozoa. When spermatozoa were prevented from entering the epididymis by efferent duct ligation, the ACE activity in the epididymis was greatly reduced. The epithelial cells lining the epididymal duct were also shown to possess ACE activity which was dependent upon circulating androgens.

Treatment of male rats with captopril at a single oral dose (20 mg/kg) significantly inhibited the ACE activity in the blood serum but had no effect on the activity of the epididymal fluid. The intraluminal ACE was protected from the circulating captopril by the blood–epididymis barrier. Long-term treatment with captopril (20 mg/kg per day, 8 weeks), however, caused an increase in blood serum ACE activity but was without effect on intraluminal ACE. The fertility and fecundity of male rats after treatment were apparently normal.

The concentrations of AI and AII were high in the epididymal plasma and epididymal cell when compared with the respective concentrations in blood serum. The intraluminal AII concentration found (13 nmol/l) was close to the threshold concentrations that stimulate anion (and fluid) secretion in cultured epididymal epithelium in vitro. The high intraluminal AII concentration could not have been derived from the testicular fluid or spermatozoa since the rete testis fluid and sperm contained little AII. When spermatozoa were prevented from entering the epididymis by efferent duct ligation, the AII concentration of the epididymal plasma was almost completely abolished, indicating that intraluminal AII was formed endogenously in the epididymal lumen by sperm ACE. We propose that ACE released by epididymal spermatozoa converts AI (formed from the epididymal epithelial cells) to AII which plays a paracrine role in regulating electrolyte and fluid transport through apical membrane angiotensin receptors.

Journal of Endocrinology (1990) 125, 457–465

ABSTRACT

Monolayer cell cultures formed from the rat cauda epididymidis exhibited renin-like and angiotensin-converting enzyme (ACE) activities and contained immunoreactive angiotensin I (AI) and angiotensin II (AII). Renin-like activity, determined indirectly by radioimmunoassay of generated AI at a near-neutral pH of 6·0, was demonstrated in the cell lysate but was almost undetectable in the serum-free cell culture medium, suggesting that renin expression in epididymal cells is an intracellular phenomenon. In contrast, both AI and AII were detected in the cell lysate and cell culture medium. The level of AI was enhanced by pretreating the cells with the ACE inhibitor captopril (100 nmol/l). Incubating the cell monolayers with thoroughly washed sperm cells obtained from the intact cauda epididymides of rats increase (P < 0·01) the AII content of the cell culture medium, with a parallel decline (P < 0·01) in the AI concentration. However, adrenaline (0·23 μmol/l), which was found to stimulate electrogenic anion secretion by cell monolayers grown on pervious supports, was without effect on the renin-like activity or concentration of angiotensins.

The ACE activity in cells was confirmed by its strong dependence on chloride ion and its susceptibility to inhibition by captopril (100 nmol/l). Enzyme activity was significantly (P < 0·005) higher in the culture medium than in the cell lysate and cell membrane fragments. Angiotensinogen, which is obligatory for an intrinsic renin-angiotensin system, is present in epididymal cells. Presumably, it is synthesized and processed in the cell cytosol by intracellular renin.

These findings in cultured cells provide further evidence for a local renin–angiotensin system in epididymal tissue and suggest a possible role of endogenous AII in the regulation of epididymal function.

Journal of Endocrinology (1991) 131, 287–293

ABSTRACT

A study was carried out to investigate the role of the calcitonin gene-related peptide (CGRP) in the regulation of electrolyte transport in the rat and human epididymis. In monolayer cultures derived from the rat cauda epididymal cells, CGRP stimulated the short-circuit current (SCC) in a dose-dependent manner with the EC₅₀ (concentration required to produce 50% of the response) at 15 nmol/l. This effect of CGRP was seen when the peptide was added to the basolateral aspect of the cells; apical addition having negligible effect. The CGRP-induced rise in the SCC was dependent on the presence of chloride in the bathing solution. Calcitonin had no effect on the SCC and did not affect the CGRP-induced rise in the SCC. The effect of CGRP on secretion was inhibited in a competitive fashion by the CGRP receptor antagonist CGRP(8–37). In contrast to bradykinin, angiotensin II and endothelin I, the effect of CGRP was independent of prostaglandin synthesis. Measurement of intracellular adenosine 3′:5′-cyclic monophosphate showed a time- and dose-dependent increase upon stimulation with CGRP. CGRP also stimulated the SCC in monolayers grown from the human epididymis. The current could be inhibited by apical application of the chloride channel blocker, diphenylamine-2-carboxylate. Immunoreactive CGRP was found in the epithelia of rat and human cauda epididymidis. It is suggested that CGRP may regulate the electrolyte and fluid secretion in the epididymis, thereby providing an optimal microenvironment for the maturation and storage of spermatozoa.

Journal of Endocrinology (1992) 133, 259–268

Abstract

Previous studies have demonstrated the existence of several key components of the renin–angiotensin system in the pancreas. In the present study, the localization of angiotensin II receptor subtypes, type I (AT₁) and type II (AT₂), in the mouse and the rat pancreas was studied by immunocytochemistry using specific antipeptide antibodies against the second extracellular loops of AT₁ and AT₂ receptors in conjunction with confocal laser scanning microscopy. In the mouse, immunoreactivity for AT₁ and AT₂ was observed predominantly in the endothelia of the blood vessels and the epithelia of the pancreatic ductal system. Similar distribution of immunoreactivity for AT₁ and AT₂ was also observed. However, the intensity of immunoreactivity for AT₁ and AT₂ was stronger in the rat than that found in the mouse pancreas. Much weaker immunostaining for both AT₁ and AT₂, as compared with that found in ductal regions, was also found in the acini of the rodent pancreas. Together with the previous findings, the present results suggest that AT₁ and/or AT₂ receptors may play a role in regulating pancreatic functions in the rodent.

Journal of Endocrinology (1997) 153, 269–274

ABSTRACT

Confluent monolayers cultured from the rat cauda epididymidis have been shown to respond to angiotensin I (AI) and angiotensin II (AII) when studied under short-circuit conditions and bathed on both sides with Krebs–Henseleit solution. Both the decapeptide AI and the octapeptide AII elicited transient increases in short-circuit current (SCC) when added to the basolateral as well as to the apical surfaces, with the effect of basolateral application greater than that of apical application. The maximal responses produced by AI and AII were similar with median effective concentrations of 20 to 80 nmol/l. The increase in SCC by AII was dependent upon extracellular Cl⁻ and was inhibited by addition of a Cl⁻ channel blocker, diphenylamine 2-carboxylate, to the apical surface. These patterns of activity suggest that the SCC responses to angiotensins result from electrogenic chloride secretion. Pretreating the monolayers with captopril (100 nmol/l), an angiotensin-converting enzyme (ACE) inhibitor, reduced the response to basolateral application of AI, but completely abolished the response to AI added apically. These results suggest that the response to apical addition of AI was due to conversion of AI to AII which interacts with apical angiotensin receptors. This conversion was mediated by ACE which has been detected in epididymal monolayers. Of the endogenous ACE activity, 86% was found to be inhibited by captopril (100 nmol/l).

Responses of the epididymal monolayers to angiotensins were mediated by specific angiotensin receptors. [Sar¹,Ile⁸]-AII, a specific antagonist of the AII receptor, completely inhibited the responses to AI and All but had no effect on the responses to bradykinin and endothelin. The effects of All were mediated by eicosanoid formation since piroxicam, a cyclooxygenase inhibitor, inhibited the AII-induced increase in SCC. This is the first study to demonstrate an effect of angiotensin on epididymal functions. We propose that angiotensin formed locally in the epididymis may play a role in the regulation of electrolyte and fluid transport.

Journal of Endocrinology (1990) 125, 449–456

Department of Physiology, Faculty of Medicine, University of Hong Kong, Li Shu Fan Building, Sassoon Road, Hong Kong

(Received 22 November 1977)

The rat testis secretes fluid (Tuck, Setchell, Waites & Young, 1970; Cheung, Hwang & Wong, 1977) which is reabsorbed by the epididymis (Crabo & Gustafsson, 1964; Levine & Marsh, 1971). In the cauda epididymidis, sodium chloride is reabsorbed isotonically with water and potassium is secreted into the ductal lumen (Wong & Yeung, 1977, 1978); these transport processes seem to have many characteristics typical of the processes occurring in the distal tubule of the kidney. Apart from electrolyte and water transport, proteins are also secreted into the ductal lumen. The epididymal epithelium actively maintains a definite milieu within the tubule in which the spermatozoa are maturing. In several transporting epithelia such as those of the toad bladder, frog skin, salivary and sweat glands, intestine and renal tubule (for references,

Abstract

The localization and distribution of angiotensin II (Ang II) in the rat epididymis was studied using immunohistochemical and RIA techniques. The immunohistochemical results showed that Ang II-like immunoreactivity progressively increased along the length of the rat epididymis (cauda>corpus>>caput) and was predominately localized in the basal region of the epididymal epithelium. Occasionally, immunostaining of lighter intensity was also found in the apical region. The concentration of Ang II in cultured rat cauda epididymal epithelial cells was further measured by RIA. In addition to that found in cultured epithelial cells, Ang II activity was also detected in the culture medium, suggesting a secretory role of the epithelium. These findings suggest that Ang II could be derived locally from epididymal epithelium and that it could play a role in local regulation of epithelial transport and, possibly, in the maintenance of sperm function as well, by exerting its paracrine and/or autocrine effect in various regions of the epididymis.

Journal of Endocrinology (1996) 149, 217–222

In adult rat testes, blood–testis barrier (BTB) restructuring facilitates the migration of preleptotene spermatocytes from the basal to the adluminal compartment that occurs at stage VIII of the epithelial cycle. Structural proteins at the BTB must utilize an efficient mechanism (e.g. endocytosis) to facilitate its transient ‘opening’. Dynamin II, a large GTPase known to be involved in endocytosis, was shown to be a product of Sertoli and germ cells in the testis. It was also localized to the BTB, as well as the apical ectoplasmic specialization (apical ES), during virtually all stages of the epithelial cycle. By co-immunoprecipitation, dynamin II was shown to associate with occludin, N-cadherin, zonula occludens-1 (ZO-1), β-catenin, junctional adhesion molecule-A, and p130Cas, but not nectin-3. An in vivo model in rats previously characterized for studying adherens junction (AJ) dynamics in the testes by adjudin (formerly called AF-2364, 1-(2,4-dichlorobenzyl)-1H-indazole-3-car-hohydrizide) treatment was used in our studies. At the time of germ cell loss from the seminiferous epithelium as a result of adjudin-induced AJ restructuring without disrupting the BTB integrity, a significant decline in the steady-state dynamin II protein level was detected. This change was associated with a concomitant increase in the levels of two protein complexes at the BTB, namely occludin/ZO-1 and N-cadherin/β-catenin. Interestingly, these changes were also accompanied by a significant increase in the structural interaction of dynamin II with β-catenin and ZO-1. β-Catenin and ZO-1 are adaptors that structurally link the cadherin- and occludin-based protein complexes together at the BTB in an ‘engaged’state to reinforce the barrier function in normal testes. However, β-catenin and ZO-1 were ‘disengaged’ from each other but bound to dynamin II during adjudin-induced AJ restructuring in the testis. The data reported herein suggest that dynamin II may assist the ‘disengagement’ of β-catenin from ZO-1 during BTB restructuring. Thus, this may permit the occludin/ZO-1 complexes to maintain the BTB integrity when the cadherin/catenin complexes are dissociated to facilitate germ cell movement.