Alpha-1-adrenergic receptor blockade modifies insulin-regulated aminopeptidase (IRAP) activity in rat prostate and modulates oxytocin functions.

BACKGROUND: Oxytocin (OT) is one of the important paracrine factors that prostate synthesizes. OT maintains its resting tone and stimulates its contractile activity. However, the involvement of OT in modulating cell proliferation of the prostate is being investigated. In fact, alterations in OT concentrations accompany both benign prostatic hyperplasia/hypertrophy and carcinoma of the prostate. The enzyme Insulin-regulated aminopeptidase (IRAP) is the main responsible of OT levels regulation through its catabolism. To date, the long-acting selective α(1)-adrenergic receptor antagonist doxazosin is widely used to the treatment of BPH. Thus, our aim was to analyze the effects of doxazosin on IRAP specific activity and its putative effects on prostate OT regulation and functions. METHODS: Fifteen male Wistar rats were treated subcutaneously with 10 mg/Kg doxazosin during 15 days and fifteen controls were treated with the vehicle only. After the treatment period, prostate was removed to obtain soluble and membrane-bound fractions. Soluble and membrane-bound IRAP specific activities were assayed fluorometrically using leucyl-ß-naphthylamide as substrate. Prostate OT content was assayed by enzyme immunoassay. RESULTS: Doxazosin treatment significantly increased membrane-bound IRAP specific activity in rat prostate by 59.4%, whereas no changes were observed in the soluble fraction. Treatment with doxazosin also significantly increased OT concentration by 26.3%. CONCLUSIONS: In vivo administration of doxazosin to male rats modify both prostatic IRAP activity and OT levels. Because there is now evidence that OT plays a physiological role in the regulation of growth and muscular contractility within the gland, more attention should be paid to IRAP activity, which could represent a new target for the regulation of the functions of OT under physiological or pathological conditions such as BPH and prostate cancer.

A new approach regarding the treatment of preeclampsia and preterm labor.

Both preeclampsia and preterm delivery are important complications in pregnancy and are leading causes for maternal and perinatal morbidity and mortality. The underlying molecular mechanisms of both diseases remain unknown, thus treatments (beta2-stimulants and magnesium sulfate) are essentially symptomatic. Both molecules have molecular weights less than 5-8 kDa and cross the placental barrier thus exerting their effects on the fetus. In addition, the fetus produces peptide hormones that are highly vasoactive and uterotonic and increase in response to maternal stress and with continued development. Fetal peptides are also small molecules that inevitably leak across into the maternal circulation. Aminopeptidases such as placental leucine aminopeptidase (P-LAP) and aminopeptidase A (APA) are large molecules that do not cross the placental barrier. We have shown that APA acts as an antihypertensive agent in the pregnant spontaneously hypertensive rat by degrading vasoactive peptides and as a result returns the animal to a normotensive state. We have also noted that P-LAP acts as an anti-uterotonic agent by degrading uterotonic peptides, and as a result prolongs gestation in the pregnant mouse. Thus, P-LAP and APA represent promising agents for the treatment of preeclampsia and preterm labor by degrading bioactive hormones derived from the feto-placental circulation.

Effects of alpha1-adrenergic receptor blockade by doxazosin on renin-angiotensin system-regulating aminopeptidase and vasopressin-degrading activities in male and female rat thalamus.

The thalamus has connections with central autonomic centers involved in cardiovascular control and is enervated by noradrenergic fibers. The excitability of thalamic neurons is due to a reduction of ionic currents mediated by alpha(1)-adrenoceptors. The brain renin- angiotensin system (RAS) and the peptide hormone arginine-vasopressin (AVP) are also involved in the central control of blood pressure, and fluid and electrolyte homeostasis. It has been extensively reported that aminopeptidase A (APA), aminopeptidase B (APB), aminopeptidase N (APN), and vasopressin-degrading cystyl aminopeptidase activity (AVP-DA) play an important role in the regulation of the activity of angiotensins and AVP. We have analyzed the effect of alpha(1)-adrenoceptor blockade by doxazosin on RAS-regulating aminopeptidase activities and AVP-DA in soluble and membrane-bound fractions of male and female rat thalamus. Our results show that alpha(1)-adrenoceptors blockade by doxazosin does not modify the RAS through its degrading peptidases at thalamic level either in male or female rats. However, alpha(1)-adrenoceptors blockade shows gender differences in AVP-DA, increasing in males but not in females, supporting an increased capacity of males against females to degrade AVP and, therefore, to regulate cardiovascular homeostasis, under this pharmacological manipulation.

Oxytocin-induced prostaglandin E2 (PGE2) synthesis is regulated by progesterone via oxytocinase in Ishikawa cells.

Cell-surface oxytocinase inactivates oxytocin and regulates oxytocin stimulation. We reported that oxytocinase in human endometrial epithelial cells was secreted from the cell membrane in the mid-secretory phase and disappeared from the cell surface. On the other hand, the production in human endometrium of prostaglandins, which play important roles in the reproductive process, has been reported to be upregulated by oxytocin. We investigated whether progesterone affects cell-surface oxytocinase and oxytocin-induced prostaglandin E2 (PGE2) production in vitro. Progesterone induced secretion of oxytocinase into the culture medium, which resulted in a decrease in cell-surface oxytocinase. Production of PGE2 was increased slightly by oxytocin without progesterone, and significantly with progesterone. The inhibition of oxytocinase activity by amastatin had a similar effect to the loss of cell-surface oxytocinase caused by progesterone. It is therefore likely that the cell-surface oxytocinase of endometrial epithelial cells modified by progesterone plays an important role in the function of the human endometrium through PGE2.

Interleukin-1beta stimulates placental leucine aminopeptidase/oxytocinase expression in BeWo choriocarcinoma cells.

In addition to prostaglandins, inflammatory cytokines induce uterine contraction via oxytocin (OT). Placental leucine aminopeptidase (P-LAP), an oxytocinase that is identical to cystine aminopeptidase, destroys OT activity. Patients with spontaneous preterm delivery have higher concentrations of inflammatory cytokines and lower P-LAP activities than those with normal delivery. In addition, the P-LAP promoter region contains putative binding sites for cytokine-induced transcription factors. We therefore postulated that inflammatory cytokines suppress P-LAP expression and examined this notion using BeWo choriocarcinoma cells cultured in the presence of cytokines. However, interleukin-1beta (IL-1beta) increased P-LAP activity in a time- and dose-dependent manner. Furthermore, Western blot analysis showed a dose-dependent increase of P-LAP proteins. We also detected IL-1 type I receptor mRNA in BeWo cells by RT-PCR. Semi-quantitative RT-PCR and Southern blot analysis showed that IL-1beta also increased P-LAP mRNA, which was abrogated by prior exposure to cycloheximide. Luciferase assays did not reveal any regulatory regions that could explain IL-1beta-induced P-LAP mRNA accumulation within 1.1 kb upstream of the P-LAP gene. Immunohistochemical analysis of human placenta with chorioamnionitis demonstrated prominent P-LAP staining at sites of abundant inflammatory cell infiltration. These findings indicated that prolonged exposure to IL-1beta induces P-LAP in the trophoblasts, possibly via other de-novo protein synthesis, which contradicted our initial hypothesis.

[The use of clofelin for the treatment of arterial hypertension and for the anesthesia of labor]. / Izpolzvaneto na klofelina za lechenieto na arterialnata khipertoniia i obezboliavaneto na razhdaneto.

Fourteen women in labor with pregnancy of 39.1 +/- 1.1 gestational weeks and arterial hypertension (BSP of 183.4 +/- 12.4 and BDP of 90.6 +/- 14.3 mm Hg) were given chlopheline with a rate of infusion 0.0005, 0.001 mg/kg/hr for 120 min. Decrease of arterial pressure began at minute 15.7 +/- 0.3 after starting perfusion, and the hypotensive effect lasted for 300 minutes. At minute 360, a new dose of chlopheline was needed. Against the background of arterial hypertension, a decrease of BSP, BDP and P was observed, and the central hemodynamics remained unchanged within statistically reliable range. The changes observed in the hemodynamics did not affect labor activity and the fetus. The analgesic effect of chlopheline was favorable. Perfusion of chlopheline at a rate of infusion 0.0005, 0.001 mg/kg/hr is a choice to provide a bulk of positive hypotensive and analgesic affect on the woman in labor.