Effects of gonadotropin-releasing hormone agonists and dopamine antagonists on gonadotropin secretion and ovulation in Chinese loach, Paramisgurnus dabryanus

The analogs [D-Ala6, Pro9NEt]-luteinizing hormone-releasing hormone (LHRH-A) and [D-Arg6, Pro9NEt]-salmon gonadotropin-releasing hormone (sGnRH-A) were tested in the presence or absence of pimozide (PIM) or domperidone (DOM) for their ability to stimulate an increase in serum gonadotropin (GtH) levels and ovulation in preovulatory female loach. In the absence or presence of PIM or DOM, sGnRH-A was more active than LHRH-A in terms of stimulating serum GtH levels. PIM or DOM potentiated the activity of both peptides equally. PIM or DOM (5 μg/g body weight) plus 0.001 μg/g body weight of sGnRH-A were effective in stimulating serum GtH levels and a good rate of ovulation (50–70%). The most effective combination for inducing ovulation (100%) was sGnRH-A at 0001 μg/g body weight plus DOM at 5 μg/g body weight. LHRH-A at 0.001 μg/g body weight and PIM or DOM (5 μg/g body weight) were ineffective in inducing a good rate of ovulation. These results indicate that GnRH-A in the presence of DOM or PIM is effective in stimulating ovulation in loach at dosages about 10-fold less than for LHRH-A. The time to ovulation following injection of DOM plus sGnRH-A was highly predictable, in the range of 11–14 h postinjection.