Generation and transmission of ovine ureteral contractions, with special reference to prostaglandins

The pattern of spontaneous rhythmic contractions was studied in isolated preparations from calyx, pelvic, middle and distal parts of the sheep ureter. The frequency of contractions was highest in intrarenal specimens (13.3 +/- 0.8 contractions min-I). The regional difference in contractions is consistent with proximal dominant pacemaker cells. In isolated rings, indomethacin (10(-5) M) inhibited and finally stopped rhythmic motility. After stoppage prostaglandin PGF2 alpha (10(-6)-10(-5) M) promptly re-established contractions in a manner characteristic of each specimen, apparently according to the pre-existent dominant pacemaker (frequency and pattern). This was demonstrated in a frequency analysis which showed a highly significant correlation of pacemaker frequencies before and after indomethacin. Experiments using dual recordings from both ends of a longitudinal preparation (tandem mode) showed that co-ordinated contractile waves travelling from one end to the other could be initiated with PGF2 alpha. These results have been interpreted to indicate that prostaglandins in ureteral smooth muscle play a predominant role in co-ordinating intercellular impulse transmission for which gap junctions could be responsible. The presence of such structures, as clearly demonstrated by an ultrastructural study, lends support to this hypothesis.