Physiology and pharmacology of the oviducts of Raja and Scyliorhinus

Abstract

1. In oviparous elasmobranchs the oviducts vary in structure and physiology according to how they carry the sperm upwards and the eggs down. The sperm are accompanied by a large volume of fluid secreted by the siphon. In some species this contains much 5-hydroxytryptamine (5HT), produced by a gland. The muscles of the oviducts are very sensitive to 5HT in Raja , which has such a gland, but not in Scyliorhinus , which has none. 2. The female Scyliorhinus draws the egg case down the duct by attaching tendrils to a rock or weeds and swimming round and round (Dodd 1983); the muscles of the lower oviduct and vagina are weak. 3. In Raja the egg case is buried in the sand or mud and there are powerful muscles in the lower oviduct and vagina. 4. In-vitro isolated strips of longitudinal or circular muscles of the lower oviduct of Raja give slow rhythmical contractions. 5-HT 10 -8 m increased the amplitude and frequency of contraction. The same response was induced by 8-OH-DPAT 5 x 10 -6 m (a 5-HT 1A receptor agonist) but not by 5 x 10 -6 m 2-methyl-5-HT (a 5-HT 3 agonist) or by 5 x 10 -6 m x-methyl-5-HT (a 5-HT 2 agonist). The response to 5-HT was partly blocked by methysergide 10 -6 m (a 5-HT 2 antagonist) but not by ketanserin 10 -5 m (a 5-HT 2 antagonist) or granisetron (BRL 43694) 10 -5 m (a5-HT 3 and 5-H T 4 antagonist). The receptor involved may therefore be of the 5-HT 1 or perhaps 5-HT 2 type. 5. Spontaneous contractions of the oviduct in Raja were inhibited by adrenalin 10 -6 m, and less strongly by noradrenaline 10 -6 m . 6. Substance P 10 -8 m produced increased amplitude and frequency of contraction. 7. Acetylcholine produced contraction only above a dose of 10 -6 m. 8. Strips of lower oviduct or vagina of Scyliorhinus canicula showed long periods of slight rhythmic activity punctuated by large rapid contractions at intervals of 10—40 min. 9. Similar large contractions occurred after addition of 5-HT at 10 -6 m but only in half the experiments and at high concentration, and with long delay. 10. Adrenalin produced large rapid contractions but only at a dose of 10 -7 M and above, and often after a long delay. 11. Substance P and acetylcholine also produced contraction, but the latter only at 10 -6 m . 12. Strips of the oviduct or vagina of either Raja or Scyliorhinus responded to a sudden stretch by a large contraction. 13. These findings are discussed in the light of the differences in sperm transport and egg laying in the two species.