Effects of doxazosin on renin-angiotensin system-regulating aminopeptidase and vasopressin-degrading specific activities in male and female rat hypothalamus-pituitary-adrenal axis.

M Arrazola, MJ Ramirez-Exposito, MD Mayas, S Chica-Rodriguez, MJ Garcia, JM Martinez-Martos. Universidad de Jaén, Experimental and Clinical Physiopathology Research Group BIO296, Faculty of Experimental Sciences, University of Jaen, Jaen, Spain., Spain

The maintenance of cardiovascular and body fluid homeostasis requires mechanisms that regulate the total amount of water and sodium in the body and their appropriate regional and compartmental distribution. Most of these mechanisms are mediated through the hypothalamus-pituitary-adrenal (HPA) axis. Furthermore, local renin-angiotensin system (RAS) have been postulated in brain, pituitary and adrenal glands, and is responsible of the central regulation of the cardiovascular system and body water balance, the secretion of hypothalamus vasopressin (AVP) and the secretion of pituitary and adrenal gland hormones. On the other hand, doxazosin, a long-lasting alpha-1 adrenergic receptor blocker, is widely used to control hypertension and it has been very recently described that structural similarities exist among angiotensin receptor AT1 and alpha-1-antagonists, supporting the idea that alpha-1 antagonists could possibly block the AT1 receptor and vice-versa. The aim of the present work is to analyze the effects of doxazosin on RAS-regulating aminopeptidase and AVP degrading (AVP-DA) specific activities in the HPA axis in male and female Wistar rats, to determine its influence in the cardiovascular regulatory mechanisms mediated by these hormone systems, and to analyze the putative existence of gender differences. Thirty male and thirty female Wistar rats were used and randomly divided into four groups of fifteen animals each; Two groups (male and female doxazosin groups) were treated subcutaneously with 10 mg/Kg doxazosin during fifteen days and two groups (control male and control female) received the vehicle only. After treatment, hypothalamus, anterior pituitary, neurohypophysis, adrenal cortex and adrenal medulla were obtained and processed to obtain both soluble and membrane-bound fractions. Soluble and membrane-bound RAS-regulating aspartyl aminopeptidase (ASAP), aminopeptidase A (APA), aminopeptidase N (APN), aminopeptidase B (APB) and vasopressin-degrading (AVP-DA) specific activities were assayed fluorometrically using their corresponding aminoacyl-beta-naphthylamide as substrates. Data (expressed in picomoles/minute/mg of protein as mean±SEM) were analyzed using multiple analysis of variance (MANOVA). Post-hoc comparisons were made using Newman-Keul´s test. In hypothalamus, doxazosin decreased male soluble ASAP (50±7 vs 27±3), but increased female APA activity (89±13 vs 140±6). No changes were found in APN, APB or AVP-DA activities. In anterior pituitary, doxazosin increased male membrane-bound APA (69±15 vs 105±19) and decreased soluble ASAP (158±42 vs 52±6), and in females, increased membrane-bound ASAP (102±25 vs 238±34) and soluble APN (1193±234 vs 1875±242) activities. No changes were found in APB activity, but doxazosin modifies AVP-DA in the same way in males and females. In neurohypophysis, doxazosin increased membrane-bound APA in males (6±0.7 vs 10±0.4) but decreased it in females (10±0.6 vs8±0.1). Similar results were found with APN (16±1 vs 21±2 in males and 30±1 vs 18±1 in females). Moreover, soluble and membrane-bound APB and AVP-DA activities were higher in females. No changes were found in ASAP. In adrenal cortex, doxazosin decreased soluble APA in males (267±19 vs 249±19) and membrane-bound APA in females (202±9 vs 167±6). Soluble ASAP was also decreased with doxazosin only in males (71±5 vs 48±5). Similarly, soluble APB decreased in males (1477±88 vs 1045±52) and membrane-bound APB decreased in females (952±57 vs 756±44). Doxazosin did not modify AVP-DA in adrenal cortex. In adrenal medulla, doxazosin decreased soluble APA in males (55±4 vs 17±0.5), but increased it in females (15±0.4 vs 58±2). However, in both males and females, doxazosin decreased membrane-bound APA (147±3 vs 28±0.5 and 151±10 vs 110±3 respectively). Both soluble and membrane-bound ASAP decreased in males (92±2 vs 45±0.7 and 244±4 vs 106±2 respectively) and increased in females (35±0.6 vs 72±2 and 116±3 vs 183± 8 respectively). On the contrary, soluble APN and APB increased with doxazosin in both males (671±12 vs 979±17 and 1000±17 vs 1499±26 respectively) and females (658±19 vs 1016±14 and 803±21 vs 1363±17 respectively), although membrane-bound APN and APB increased only in females (848±25 vs 1459±24 and 1188±36 vs 1435±26 respectively). Doxazosin treatment also increased membrane-bound AVP-DA both in males (871±58 vs 1060±55) and females (829±45 vs 1654±78). We conclude that alpha-1-adrenergic receptor blockade modifies both RAS and AVP-DA at different levels of the HPA axis which indicate the existence of a putative mechanism of action of doxazosin to control blood pressure as angiotensin AT1 receptor antagonist. Furthermore, the effects of doxazosin on both peptide hormone systems show gender differences.