Prostaglandin agonists for increasing U&LP spontaneous phasic activity
Strips of U&LP exhibited spontaneous phasic contractions in the absence of any stimulation at a mean frequency of 3.26 ± 0.07 cycles per minute (cpm, n = 146). Treatment with PGE2 caused the most prominent increases to U&LP spontaneous contractile activity. When PGE2 (1 µM) was added to isolated tissues, spontaneous activity increased by 39.2% ± 6.7% (n = 38, p < 0.001, Figure 1). A greater concentration of PGE2 (10 µM) showed similar increases of 40.4% ± 9.6% to the U&LP spontaneous activity (n = 42, p < 0.001). Treatment with PGF2α showed smaller increases of 10.5% ± 4.6% to spontaneous activity when treated with 1 µM (n = 10, p < 0.05) and 13.3% ± 5.3% when treated with 10 µM (n = 14, p < 0.05). The addition of PGI2 (10 µM) increased spontaneous activity by 6.2% ± 1.6% (n = 8, p < 0.01) but had no effect at a lower concentration (1 µM, n = 8). The frequency was not significantly affected by PGD2 (1 - 10 µM, n = 12) or TXA2 (1 - 10 µM, n = 16).
The average amplitude of these spontaneous phasic contractions exhibited in U&LP strips in the absence of any stimulation was 0.57 ± 0.02 g (n = 146). In response to treatment with 1 µM PGE2, amplitude decrease of 0.14 ± 0.04 g (n = 38, p < 0.001, Table 1) were observed. Similar decreases of 0.16 ± 0.03 g were also observed in response to a higher PGE2 concentration (10 µM, n = 42, p < 0.01). Treatment with TXA2 (1 µM) showed a significant decrease in the amplitude by 0.28 ± 0.06 g (n = 8, p < 0.01), which was not observed at a higher concentration (10 µM, n = 6). The addition of PGI2 (10 µM) decreased amplitude of spontaneous activity by 0.14 ± 0.05 (n = 8, p < 0.05) but had no effect at a lower concentration (1 µM, n = 8). The amplitude of spontaneous contractions was not altered by the addition of either PGF2α (1-10 µM, n = 24) or PGD2 (1-10 µM, n = 12, Table 1). None of the decreases in the amplitude of spontaneous phasic contractions of the U&LP were significantly affected by the two different prostaglandin receptor agonist concentrations (1 µM and 10 µM).
Table 1: U&LP changes in the amplitude of phasic contractions in response to the five primary prostaglandin agonists (mean ± SEM).
|
1 µM of agonist
|
|
10 µM of agonist
|
|
Agonist
|
Absence (g)
|
Presence (g)
|
n
|
Absence (g)
|
Presence (g)
|
n
|
PGE2
|
0.53 ± 0.05
|
0.40 ± 0.03***
|
38
|
0.53 ± 0.04
|
0.37 ± 0.03**
|
42
|
PGF2α
|
0.30 ± 0.03
|
0.29 ± 0.01
|
10
|
0.51 ± 0.06
|
0.46 ± 0.08
|
14
|
TXA2
|
0.90 ± 0.16
|
0.62 ± 0.14**
|
8
|
0.75 ± 0.16
|
0.71 ± 0.25
|
6
|
PGD2
|
0.59 ± 0.10
|
0.46 ± 0.04
|
4
|
0.55 ± 0.08
|
0.43 ± 0.06
|
8
|
PGI2
|
0.64 ± 0.07
|
0.56 ± 0.07
|
8
|
0.57 ± 0.09
|
0.43 ± 0.06*
|
8
|
*p < 0.05, **p < 0.01, ***p < 0.001. Paired Student’s t-test.
Prostaglandin agonists in stimulating phasic contractions in detrusor
Total of 34% (n = 48) of the detrusor preparations that were set up in the organ baths exhibited spontaneous activity prior to the addition of any agonists. These contractions occurred at an average frequency of 2.03 ± 0.12 cpm (n = 48) with an average amplitude of 0.26 ± 0.02 g (n = 48). However, the majority of the detrusor preparations, that were otherwise quiescent developed spontaneous phasic contractions after the addition of the agonist.
Of those detrusor preparations that did not exhibit initial phasic activity during baseline: PGE2 (1 µM) sparked contractions in 68% of preparations (n = 19) and PGE2 (10 µM) in 69% (n = 22); PGF2α (1 µM) initiated contractions in in 56% (n = 5) and PGF2α (10 µM) in 88% (n = 7); TXA2 (1 µM) initiated contractions in 63% (n = 5) and TXA2 (10 µM) in 80% (n = 4); PGD2 (1 µM) initiated phasic activity in 50% (n = 2) and PGD2 (10 µM) in 75% (n = 6); and lastly PGI2 (10 µM) initiated contractions in 40% (n = 2) of preparations. This demonstrates the ability of prostaglandin agonists to induce spontaneous activity in otherwise quiescent detrusor tissue strips.
Prostaglandin agonists in stimulating tonic contractions in U&LP
All assessed prostaglandin agonists contracted the U&LP with the rank order of contractile response effectiveness as: PGE2 > PGF2α > TXA2 > PGD2 > PGI2. The addition of PGE2 (1 µM) to isolated U&LP induced tissue contractions, with increases of 1.01 ± 0.08 g (n = 38, p < 0.001) to the tonic contractions. When a greater concentration of PGE2 (10 µM) was selected, increases of 1.36 ± 0.09 g (n = 42, p < 0.001, Figure 2) were observed. Treatment with 1 µM PGF2α showed a small increase to tonic contractions of 0.15 ± 0.04 g (n = 10, p < 0.01) when compared to a higher concentration of 10 µM, which exhibited increases of 0.79 ± 0.06 g (n = 14, p < 0.001). The addition of two concentrations of TXA2 induced similar contractions, where tonic contraction increased by 0.70 ± 0.07 g when treated with 1 µM (n = 8, p < 0.001), and by 0.65 ± 0.12 g after treatment with 10 µM (n = 6, p < 0.001).
When PGD2 (1 µM) was added to the U&LP tissue preparations, tonic contractions increased by 0.19 ± 0.04 g (n = 4, p < 0.05, Figure 3). Treatment with a higher concentration of PGD2 (10 µM) exhibited increases of 0.63 ± 0.09 g (n = 8, p < 0.001). The addition of PGI2 showed small increases in tonic contractions of 0.11 ± 0.02 g in response to 1 µM PGI2 (n = 8, p < 0.001), and 0.22 ± 0.03 g in response to 10 µM PGI2 (n = 8, p < 0.001, Figure 3).
Prostaglandin agonists in stimulating tonic contractions in detrusor
All assessed prostaglandin agonists contracted the detrusor smooth muscle preparations with the rank order of contractile response effectiveness as: PGE2 > PGF2α > TXA2 > PGD2 > PGI2. In detrusor preparations, PGE2 (1 µM) increased the tonic contractions by 0.73 ± 0.09 g (n = 34, p < 0.001), whereas PGE2 (10 µM) nearly doubled the response, producing an average increase of 1.32 ± 0.13 g (n = 38, p < 0.001, Figure 4). Treatment with 1 µM PGF2α showed a small increase of 0.20 ± 0.05 g (n = 10, p < 0.01), whereas 10 µM of PGF2α increased the tonic contractions by 0.97 ± 0.14 g (n = 12, p < 0.001). When TXA2 was added, tonic contractions increased by 0.47 ± 0.12 g when treated with 1 µM (n = 8, p < 0.001), and by 1.03 ± 0.14 g (n = 6, p < 0.001, Figure 4) when treated with 1 µM TXA2.
PGD2 showed a small increase in the tonic contractions of 0.12 ± 0.04 g when 1 µM was added (n = 4, p < 0.05), and an increase of 0.36 ± 0.06 g when 10 µM PGD2 was added (n = 6, p < 0.01, Figure 5). PGI2 showed small increases in tonic contractions at both concentrations, showing an increase of 0.16 ± 0.02 g when treated with 1 µM (n = 8, p < 0.001), and 0.13 ± 0.03 g when treated with 10 µM PGI2 (n = 8, p < 0.001, Figure 5). The effects of prostaglandin agonists on tonic contractions of the detrusor smooth muscle were significantly different between the two concentrations (1 µM and 10 µM) for PGE2 (p < 0.001), PGF2α (p < 0.001) and PGD2 (p < 0.05).