The blood-borne renin-angiotensin system (RAS) is known best for its role in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, numerous tIssues show intrinsic angiotensin-generating systems that cater for specific local needs through actions that add to, or differ from, the circulating RAS. The male reproductive system has several sites of intrinsic RAS activity. Recent focus on the epididymis, by our laboratories and by others, has contributed important details about the local RAS in this tIssue. The RAS components have been localized morphologically and topographically; they have been shown to be responsive to androgens and to hypoxia; and angiotensin has been shown to influence tubular, and consequently, fluid secretion. Components of the RAS have also been found in the testis, vas deferens, prostate and semen. Angiotensin II receptors, type 1 and, to a lesser extent, type 2 are widespread, and angiotensin IV receptors have been localized in the prostate. The roles of the RAS in local processes at these sites are still uncertain and have yet to be fully elucidated, although there is evidence for involvement in tubular contractility, spermatogenesis, sperm maturation, capacitation, acrosomal exocytosis and fertilization. Notwithstanding this evidence for the involvement of the RAS in various important aspects of male reproduction, there has so far been a lack of clinical evidence, demonstrable by changes in fertility, for a crucial role of the RAS in male reproduction. However, it is clear that there are several potential targets for manipulating the activity of the male reproductive system by interfering with the locally generated angiotensin systems.

The classical concept of the renin-angiotensin system (RAS) is that of a blood-borne cascade, whose final and bioactive product, angiotensin II, plays an important endocrine role in the maintenance of blood pressure and electrolyte as well as fluid balance. In addition to this circulating RAS, there are an increasing number of studies to suggest the existence of a local angiotensin-generating system in several tissues. The so-called tissue RAS can act locally as a paracrine and/or autocrine factor in meeting specific needs for individual tissues and it can operate, in whole or in part, independently of the circulating counterpart. Recent studies on the expression and localization of key RAS components, particularly angiotensinogen and renin, have provided solid evidence for the existence of an intrinsic, angiotensin-generating system in the pancreas. The tissue RAS has a potential role in finely regulating exocrine and endocrine functions of the pancreas such as ductal anion secretion and islet hormonal secretion. Some of these effects may be exerted via the markedly vasoconstrictive effects of RAS. Of particular interest in this context are the recent epidemiological data showing that administration of angiotensin-converting enzyme inhibitors appears to be protective against the development of diabetes in hypertensive patients. Moreover, the upregulation of pancreatic RAS has been shown to occur during chronic hypoxia. The significance of changes in pancreatic RAS could have a potential role in acute pancreatitis, islet transplantation and in different shock states, by causing a further decrease of blood perfusion in the pancreas.

Previous studies have shown that the expression of the major components from a local pancreatic renin-angiotensin system (RAS) was upregulated after chronic exposure to oxygen deprivation (10% oxygen). In the present study, the reversibility of expression for the pancreatic RAS affected by chronic hypoxia was investigated in the pancreas. Rats were first subject to hypoxia for one Month and they were then returned to normoxic conditions for a varying period of time (1, 2, 3 and 4 weeks). The degree of recovery in the expression of RAS components was analyzed with standard curve-quantitative competitive-reverse transcription-polymerase chain reaction (SC-QC-RT-PCR), Western blot analysis and a specific assay for angiotensin-converting enzyme (ACE) activity. Results from SC-QC-RT-PCR showed that the upregulated expression of angiotensin II type 1 (AT(1)) receptor mRNA following chronic hypoxia could be completely restored to the control level after the rats were returned to the normoxic condition for 3 weeks. The reversibility of mRNA expression for angiotensin II type 2 (AT(2)) receptor and angiotensinogen was observed after the return to normoxic conditions for 2 and 3 weeks respectively when compared with that of their respective controls. Results from Western blot analysis further confirmed that the expression of AT(1) receptor protein was also reversible after return to normoxic conditions for 4 weeks. In addition, the activation of ACE activity returned to its normal level in a time-dependent manner. These data indicate that the upregulation of a local pancreatic RAS affected by chronic hypoxia could be recoverable. The significance of its reversibility and adaptability following chronic hypoxia may be of physiological relevance to the pancreas.