Effects of acute adult and early-in-life bladder inflammation on bladder neuropeptides in adult female rats.

BACKGROUND: The purpose of the present study was to determine how acute adult and/or prior early-in life (EIL; P14-P16) exposure to bladder inflammation affects bladder content of calcitonin gene related peptide (CGRP) and substance P (SP). Estrous cycle influences were also studied in the adult-treatment conditions. METHODS: In Experiment 1, intravesical zymosan or isoflurane anesthesia alone was administered to adult female rats. Bladders and serum were collected 24 hours later during each phase of the estrous cycle. In Experiment 2, zymosan or anesthesia alone was administered EIL and as adults, with bladder tissue collection 24 h later. RESULTS: In general, Experiment 1 showed that bladder content of both CGRP and SP was increased by inflammation. This effect was significant when data were collapsed across all phases of the estrous cycle, but was only significant during proestrus when individual comparisons were made during each phase of estrous. Also, adult bladder inflammation significantly reduced estradiol levels. In Experiment 2, bladder content of CGRP and SP was significantly increased in rats receiving EIL and/or adult inflammation. Bladder weights were also significantly increased by inflammation. CONCLUSIONS: These data indicate that bladder CGRP and SP are maximally increased during the proestrus phase of the estrous cycle in inflamed adult female rats. EIL exposure to bladder inflammation alone can also produce an increase in CGRP and SP lasting into adulthood. Therefore, EIL experience with bladder inflammation may predispose an organism to experience a painful bladder disorder as an adult by increasing primary afferent content of CGRP and/or SP.

Opioid blockade and inflammation reveal estrous cycle effects on visceromotor reflexes evoked by bladder distention.

PURPOSE: Painful bladder disorders vary in intensity with the menstrual cycle in women. We evaluated the influence of the correlate in rats (the estrous cycle) on the nociceptive visceromotor reflex to bladder distention in the presence/absence of inflammation and of spinal opioid blockade. MATERIALS AND METHODS: We recorded visceromotor reflexes as electromyogram responses of the abdominal musculature to graded (10 to 60 mm Hg) bladder distention in anesthetized female rats in the presence of intrathecal saline or naloxone (10 µg) 1 day after receiving intravesical zymosan or anesthesia alone. RESULTS: In saline treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. When separated into phases, rats with bladder inflammation showed complex estrous cycle effects with significantly greater visceromotor reflexes to bladder distention during metestrus and proestrus than diestrus. In naloxone treated rats visceromotor reflexes to bladder distention were significantly greater in those with an inflamed vs a noninflamed bladder when examined together. Naloxone enhanced the overall magnitude of visceromotor reflexes to bladder distention in the inflamed and noninflamed conditions. The magnitude of visceromotor reflexes to bladder distention in noninflamed and inflamed conditions in the presence of naloxone was estrous phase dependent in the order, estrus >metestrus >diestrus >proestrus. Similar findings were apparent on analysis of data on responses at threshold intensity (30 mm Hg). CONCLUSIONS: Data suggest that circulating hormones present during the estrous cycle alter bladder reactivity and opioid modulatory systems to maintain constancy of input from the bladder to the central nervous system.

Effect of estrogen on bladder nociception in rats.

PURPOSE: We assessed the effect of ovariectomy and estrogen replacement on nociceptive responses to bladder distention in a rat model. MATERIALS AND METHODS: Female Sprague-Dawley rats (Harlan) underwent ovariectomy or sham surgery. Visceromotor responses (abdominal contractions) to bladder distention were determined 3 to 4 weeks later under isoflurane anesthesia. In rat subsets estrogen was chronically replaced with a subcutaneous estrogen pellet vs a placebo pellet or acutely replaced by subcutaneous injection 24 hours before testing. Effects of estrogen withdrawal were examined in another group of rats by implanting a pellet and explanting the pellet 24 hours before testing. Uterine weight was measured to assess the estrogen dose. RESULTS: Visceromotor responses to bladder distention were significantly less vigorous in ovariectomized rats vs controls. Acute estrogen replacement increased visceromotor responses in these rats but chronic estrogen replacement did not. Sudden chronic estrogen withdrawal resulted in increased visceromotor responses. Uterine weight was consistent with the physiological estrogen dose. CONCLUSIONS: Estrogen alone was not sufficient to produce increased nociceptive responses but an acute decrease in estrogen resulted in increased visceromotor responses. These data suggest that the pronociceptive effects of estrogen may be due to a mismatch between peripheral vs central and/or genomic vs nongenomic effects of the hormone, which occur during rapidly decreasing estrogen levels.

Serotonergic and noradrenergic facilitation of the visceromotor reflex evoked by urinary bladder distension in rats with inflamed bladders.

Bladder inflammation resulting from intravesical administration of zymosan significantly enhances the visceromotor reflex (VMR) evoked by urinary bladder distension (UBD). The present study examined whether intrathecal (i.t.) administration of receptor antagonists to either norepinephrine (NE) or serotonin (5-HT) altered this enhancement effect. I.t. administration of the non-specific 5-HT receptor antagonist methysergide (30 microg), the 5-HT(3) receptor antagonist ondansetron, or the 5-HT(1A) receptor antagonist WAY 100635 eliminated the enhancement effect produced by intravesical zymosan and also tended to reduce electromyographic (EMG) responses to UBD in non-inflamed rats. I.t. administration of either the non-specific NE receptor antagonist phentolamine (30 microg) or the alpha(1) antagonist WB 4101 also eliminated the enhancement effect, whereas i.t. administration of the alpha(2) antagonist yohimbine failed to significantly affect the enhancement effect. The effects of phentolamine and methysergide were not mediated by changes in bladder compliance. This is the first study to demonstrate that bladder hypersensitivity resulting from bladder inflammation is partly mediated by 5-HT and NE facilitatory effects. Based on these and previous findings we conclude that the net nociceptive response to bladder distension under conditions of bladder inflammation represents a complex interaction of facilitatory influences of spinal 5-HT and NE, and inhibitory influences of spinal opioids.