A rapid in vivo bioassay of the ovulation hormone of Lymnaea stagnalis.

The neurosecretory caudo-dorsal cells (CDC) of the basommatopora Lymnaea stagnalis produce an ovulation hormone (CDCH), which is released at the periphery of the intercerebral commissure (COM). A rapid in vivo bioassay for CDCH has been established and is based on the dose-dependent relationship between the quantity of injected CDCH (COM-extract) and the number of snails responding with the first stages of the egg-mass production process, as determined 30 min after injection. Three types of scores can be distinguished: (1) no response (very low CDCH doses), (2) ovulation only (O), and (3) ovulation and packaging (O + P). With increasing CDCH doses the number of snails responding with O, O + P, and oviposition increases. It is shown that the O response first increases followed by a decrease, while simultaneously, the P response increases. This is caused by the fact that the packaging latency is dose dependent, i.e., at low doses it is greater than 30 min, whereas at higher doses it is less than 30 min. This agrees with the finding that at low doses the oviposition latencies are longer (ca. 20 min) than at higher doses. The size of the egg mass is not dose dependent. Several factors that influence the responses upon which the bioassay is based have been analyzed, i.e., refractory period, photoperiod, and day-to-day variability of the assay snails. Experiments relating to the development of a bioassay are reported. The half-life of injected CDCH appeared to be 30-40 min.