Cyclical estrogen and free radical damage to the rabbit urinary bladder

Age-associated bladder and urethral coordination impairment and changes in urethral oxidative stress in rats

AIMS

We examined age-associated changes in bladder and urethral coordination involving the nitric oxide (NO)/soluble guanylyl cyclase (sGC) system, which induces urethral smooth muscle relaxation, and urethral ischemic/oxidative stress changes in rats.

MAIN METHODS

Sixteen female Sprague-Dawley rats were divided into young (3 months old) and middle-aged (12-15 months old) groups. Urethral activity was evaluated by simultaneously recording intravesical pressure under isovolumetric conditions and urethral perfusion pressure (UPP) under urethane anesthesia. Sodium nitroprusside (SNP, 0.1 mg/kg), an NO donor, and BAY 41-2272, a novel NO-independent stimulator of sGC (0.1 mg/kg), were administered intravenously to both groups. N-nitro-l-arginine methyl ester hydrochloride (l-NAME, 100 mg/kg) was also injected intravenously, to inhibit NO synthase activity in both groups. Staining for the ischemic marker, hypoxia-inducible factor-1α (HIF-1α), and the oxidative stress markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA), was performed on tissue sections of the urethra, in both groups.

KEY FINDINGS

Baseline UPP and UPP changes were significantly lower in middle-aged rats than in young rats. After administration of SNP and BAY 41-2272, baseline UPP and UPP nadir were significantly decreased in both groups. After administration of l-NAME, UPP change/bladder contraction amplitude in young rats was still lower than at baseline but was completely restored to control levels in middle-aged rats. Immunoreactivity of HIF-1α, 8-OHdG, and MDA was higher in middle-aged rats than in young rats.

SIGNIFICANCE

Age-associated ischemic and oxidative stress in the urethra might be correlated with impairment of the NO/sGC system and with coordination of the bladder and urethra.

Estrogen replacement is protective to the effect of in vitro hypoxia on female rabbit bladder and pelvic floor contractile response

Purpose

To explore the effect of estrogen replacement on pelvic floor and bladder contractile response to electrical field stimulation, following in vitro hypoxia in an animal model of surgical menopause.

Materials and Methods

Twelve female adult rabbits were divided into three groups: control, ovariectomy, and ovariectomy with estradiol replacement. At 4 weeks animals were euthanized. Bladder, coccygeus, and pubococcygeus were isolated. Tissues were equilibrated with oxygenated Tyrodes containing glucose and stimulated with electrical field stimulation. Tissues were then stimulated under hypoxic conditions for 1 hour using nitrogenated Tyrodes without glucose. Tissues were then re-oxygenated for 2 hours and stimulated.

Results

Pelvic floor required 10 times the stimulation duration (power) to achieve maximum contraction at 2 g baseline tension (10 ms duration) when compared to bladder (1 ms duration). Maximal tension generated was significantly greater for bladder than pelvic floor. Coccygeus and pubococcygeus were significantly less sensitive to the effects of hypoxia and had stable contractile response to field stimulation throughout the hour of hypoxia. Hypoxia resulted in progressive and rapid decline of bladder contractile strength. Following hypoxia, pelvic floor contractile recovery was superior to bladder. Improvement in the contractile response of both bladder and pelvic floor, during the period of post-hypoxia re-oxygenation, was significantly greater in ovariectomy animals treated with estradiol replacement.

Conclusions

Replacement of estradiol at time of ovariectomy reduced oxidative stress on tissue and was protective to the effects of hypoxia on pelvic floor and bladder contractile function.

The effect of in vitro oxidative stress on the female rabbit bladder contractile response and antioxidant levels

Introduction. There are several bladder dysfunctions that are associated with oxidative stress to the urinary bladder. Two experimental models are known to cause this type of bladder damage. The first is direct oxidative damage caused by hydrogen peroxide (H2O2). The second is oxidative damage caused by ischemia followed by reperfusion (I/R). The specific aim of this study is to directly compare these two models of oxidative stress. Methods. Six adult female NZW rabbits were divided into two groups of three rabbits each. Eight full thickness strips from three rabbit bladders were taken for in vitro ischemia/reperfusion physiological analysis, while eight strips from three rabbit bladders were taken for in vitro H2O2 physiological analysis. All tissue was analyzed for total antioxidant activity (AA) and malondialdehyde (MDA) levels. In addition, samples of the water baths were also analyzed for AA. Results. In vitro I/R reduced the response to field stimulation (FS) to a significantly greater extent than the inhibition of the response to carbachol. In vitro H2O2 decreased all responses to approximately the same degree. Total AA levels at higher concentrations of H2O2 for all bath fluids were significantly higher than controls. MDA levels were significantly elevated in both models of oxidative stress.

Calcium effects on superoxide dismutase and catalase of the rabbit urinary bladder muscle and mucosa

PURPOSE

Superoxide dismutase (SOD) and catalase are two important antioxidant mechanisms that work together to reduce free radical damage. Intracellular free calcium in smooth muscle can change rapidly and many enzymes can be affected. The sensitivity of SOD and catalase activity to calcium was determined in both rabbit bladder smooth muscle and mucosa.

MATERIALS AND METHODS

Calcium sensitivity was analyzed by determining SOD and catalase activity in muscle and mucosa at the following calcium concentrations: 0 (in the presence of 1 mM EGTA), 1 and 5 mM CaCl(2).

RESULTS

SOD: EGTA resulted in increased SOD activity of bladder smooth muscle, whereas both 1 and 5 mM calcium significantly decreased SOD activity. EGTA had no effect on SOD activity of the mucosa whereas 1 and 5 mM calcium decreased SOD activity of the muscle. Catalase: 1 mM calcium resulted in decreased catalase activity of the muscle and no change in the activity of the mucosa, whereas 5 mM calcium resulted in increased catalase activity of the mucosa but no change in the activity of the muscle.

DISCUSSION

Mucosa showed more SOD and catalase activity than the muscle. Both SOD and catalase showed differing sensitivities to EGTA and calcium.