Spasmogenic Actions of Frog Urotensin II on the Bladder and Ileum of the Frog, Rana catesbeiana

The effects of synthetic frog urotensin II on the motility of isolated smooth muscle strips of urinary bladder and ileum from the bullfrog Rana catesbeiana were investigated. The strips of bladder exhibited strong spontaneous contractions. Frog urotensin II produced a concentration-dependent increase in the frequency of contraction (EC₅₀ = 8.1 × 10^-9M) but had no significant effect on tension. Maximum stimulation (4 times the rate of spontaneous contractions) was produced by 10^-7M peptide. The ileal smooth muscle strips exhibited only weak spontaneous contractions but frog urotensin II produced concentration-dependent increases in both the frequency (EC₅₀ = 1.3 × 10^-9M) and the strength (EC₅₀ = 3.6 × 10^-9M) of contraction. The peptide had no effect on the motility of strips of rat urinary bladder and ileum. In both the frog bladder and ileum preparations, the effect of urotensin II was not affected by preincubation of the strips with atropine, tetrodotoxin, and somatostatin-14 but indomethacin produced a significant (P < 0.05) decrease in the strength of the contractions of the bladder (to 21 ± 6% of control values) and ileum (to 32 ± 13%). Arachidonic acid produced an increase in the frequency of contraction of the bladder and an increase in both the frequency and the strength of contraction of the ileum. The data demonstrate that urotensin II exercises a spasmogenic effect on amphibian smooth muscle that is similar to that of the peptide on teleost tissues. An involvement of prostaglandin synthesis in the spasmogenic action of urotensin II on frog bladder and ileum is indicated.