Unveiling the Angiotensin-(1-7) Actions on the Urinary Bladder in Female Rats.

Angiotensin-(1-7) is a peptide produced by different pathways, and regardless of the route, the angiotensin-converting enzyme 2 (ACE-2) is involved in one of the steps of its synthesis. Angiotensin-(1-7) binds to Mas receptors localized in different cells throughout the body. Whether angiotensin-(1-7) exerts any action in the urinary bladder (UB) is still unknown. We investigated the effects of intravenous and topical (in situ) administration of angiotensin-(1-7) on intravesical pressure (IP) and cardiovascular variables. In addition, the Mas receptors and ACE-2 gene and protein expression were analyzed in the UB. Adult female Wistar rats were anesthetized with 2% isoflurane in 100% O2 and submitted to the catheterization of the femoral artery and vein for mean arterial pressure (MAP) and heart rate (HR) recordings, and infusion of drugs, respectively. The renal blood flow was acquired using a Doppler flow probe placed around the left renal artery and the renal conductance (RC) was calculated as a ratio of Doppler shift (kHz) and MAP. The cannulation of the UB was performed for IP recording. We observed that angiotensin-(1-7) either administered intravenously [115.8 ± 28.6% angiotensin-(1-7) vs. -2.9 ± 1.3% saline] or topically [147.4 ± 18.9% angiotensin-(1-7) vs. 3.2 ± 2.8% saline] onto the UB evoked a significant (p < 0.05) increase in IP compared to saline and yielded no changes in MAP, HR, and RC. The marked response of angiotensin-(1-7) on the UB was also investigated using quantitative real-time polymerase chain reaction and western blotting assay, which demonstrated the mRNA and protein expression of Mas receptors in the bladder, respectively. ACE-2 mRNA and protein expression was also observed in the bladder. Therefore, the findings demonstrate that angiotensin-(1-7) acts in the UB to increase the IP and suggest that this peptide can be also locally synthesized in the UB.

Lateral Preoptic Area Neurons Activated by Angiotensin-(1-7) Increase Intravesical Pressure: A Novel Feature in Central Micturition Control.

Central micturition control and urine storage involve a multisynaptic neuronal circuit for the efferent control of the urinary bladder. Electrical stimulation of the lateral preoptic area (LPA) at the level of the decussation of the anterior commissure in cats evokes relaxation of the bladder, whereas ventral stimulation of LPA evokes vigorous contraction. Endogenous Angiotensin-(1-7) [(Ang-(1-7)] synthesis depends on ACE-2, and its actions on binding to Mas receptors, which were found in LPA neurons. We aimed to investigate the Ang-(1-7) actions into the LPA on intravesical pressure (IP) and cardiovascular parameters. The gene and protein expressions of Mas receptors and ACE-2 were also evaluated in the LPA. Angiotensin-(1-7) (5 nmol/µL) or A-779 (Mas receptor antagonist, 50 nmol/µL) was injected into the LPA in anesthetized female Wistar rats; and the IP, mean arterial pressure (MAP), heart rate (HR), and renal conductance (RC) were recorded for 30 min. Unilateral injection of Ang-(1-7) into the LPA increased IP (187.46 ± 37.23%) with peak response at ∼23-25-min post-injection and yielded no changes in MAP, HR, and RC. Unilateral or bilateral injections of A-779 into the LPA decreased IP (-15.88 ± 2.76 and -27.30 ± 3.40%, respectively) and elicited no changes in MAP, HR, and RC. The genes and the protein expression of Mas receptors and ACE-2 were found in the LPA. Therefore, the LPA is an important part of the circuit involved in the urinary bladder control, in which the Ang-(1-7) synthetized into the LPA activates Mas receptors for increasing the IP independent on changes in RC and cardiovascular parameters.

Oxytocin Reduces Intravesical Pressure in Anesthetized Female Rats: Action on Oxytocin Receptors of the Urinary Bladder.

Urinary bladder dysfunction affects several people worldwide and shows higher prevalence in women. Micturition is dependent on the Barrington's nucleus, pontine urine storage center and periaqueductal gray matter, but other brain stem areas are involved in the bladder regulation. Neurons in the medulla oblongata send projections to hypothalamic nuclei as the supraoptic nucleus, which synthetizes oxytocin and in its turn, this peptide is released in the circulation. We investigated the effects of intravenous injection of oxytocin (OT) on the urinary bladder in sham and ovariectomized rats. We also evaluated the topical (in situ) action of OT on intravesical pressure (IP) as well as the existence of oxytocin receptors in the urinary bladder. In sham female Wistar rats, anesthetized with isoflurane, intravenous infusion of OT (10 ng/kg) significantly decreased the IP (-47.5 ± 1.2%) compared to saline (3.4 ± 0.7%). Similar effect in IP was observed in ovariectomized rats after i.v. OT (-41.9 ± 2.9%) compared to saline (0.5 ± 0.6%). Topical administration (in situ) of 0.1 mL of OT (1.0 ng/mL) significantly reduced the IP (22.3.0 ± 0.6%) compared to saline (0.9 ± 0.7%). We also found by qPCR that the gene expression of oxytocin receptor is present in this tissue. Blockade of oxytocin receptors significantly attenuated the reduction in IP evoked by oxytocin i.v. or in situ. Therefore, the findings suggest that (1) intravenous oxytocin decreases IP due to bladder relaxation and (2) OT has local bladder effect, binding directly in receptors located in the bladder.

Unravelling the intravenous and in situ vasopressin effects on the urinary bladder in anesthetized female rats: More than one vasopressin receptor subtype involved?

Urinary bladder dysfunctions show high prevalence in women. We focused to investigate the intravenous and in situ (topic) vasopressin effects on the bladder and also to characterize the vasopressin receptor subtypes in the bladder. Adult female Wistar rats anesthetized with isoflurane underwent to the cannulation of the femoral artery and vein, and also urinary bladder for mean arterial pressure, heart rate and intravesical pressure (IP) recordings, respectively. Doppler flow probe was placed around the renal artery for blood flow measurement. After baseline recordings, intravenous injection of saline or vasopressin at different doses (0.25, 0.5, 1.0 ng/ml/kg of b.w.); or 0.1 ml of saline or 0.1 ml of vasopressin at different doses (0.25, 0.5, 1.0 ng/ml) was randomly dropped on the bladder. In another group of rats, the UB was harvest for gene expression by qPCR and also for protein expression by Western blotting of the vasopressin receptor subtypes. We observed that either intravenous or in situ vasopressin evoked a huge increase in the IP in a dose-dependent manner compared to saline, whilst no differences were observed in the cardiovascular parameters. The genes and the protein expression of V1a, V1b and V2 vasopressin receptors subtypes were found in the bladder. Intravenous injection of V1a or V2 receptor antagonist evoked a huge fall in IP and 30 min later, i.v or in situ vasopressin evoked responses on IP were significantly attenuated. Therefore, intravenous or in situ vasopressin increases the IP due to binding in V1a or V2 receptors localized in the bladder.

Renal and femoral venous blood flows are regulated by different mechanisms dependent on α-adrenergic receptor subtypes and nitric oxide in anesthetized rats.

Venous and arterial walls are responsive to sympathetic system and circulating substances, nevertheless, very few is known about the venous blood flow regulation simultaneously to arterial vascular beds. In this study, we compared the venous and arterial blood flow regulation in visceral and muscular beds upon injection of different doses of vasoactive drugs which act in arterial vascular beds. Anesthetized adult male Wistar rats underwent to right femoral artery and vein cannulation for hemodynamic recordings and infusion of drugs. Doppler flow probes were placed around the left renal artery and vein, and left femoral artery and vein to evaluate the changes in flood flow. Phenylephrine (PHE) injection (α1-adrenergic receptor agonist) elicited vasoconstriction in all arteries and veins. Intravenous prazosin (PZS) (1mg/kg, α1-adrenergic receptor blocker) caused renal artery vasodilation, but not in the other beds. Vasoconstrictor effect of PHE was abolished by PZS in all vascular beds, except in femoral vein. Phentolamine (PTL) injection (1mg/kg, α1/α2-adrenergic receptor blocker) produced renal artery vasodilation with no change in other beds. After PTL, the vasoconstriction evoked by PHE was abolished in all vascular beds. Sodium Nitroprusside (SNP), a nitric oxide donor, elicited vasodilation in all beds, and after PTL but not post PZS injection, SNP enhanced the vasodilatory effect in femoral vein. Our findings suggest that the vasoconstriction in renal and femoral veins is mediated by different subtypes of α-adrenoceptors. The nitric oxide-dependent vasodilation in femoral vein enhances when α2-adrenoceptors are not under stimulation, but not in the other vascular beds investigated.