Effects of LHRH and LHRH-A on plasma GtH levels and maturation/ovulation in the common carp, Cyprinus carpio, kept under various environmental conditions
Résumé
Experiments were carried out to determine if some environmental factors usually present in spawning ponds at the time of ovulation could potentiate the effects of LHRH or LHRH-A on the plasma level of GtH, oocyte maturation or ovulation in the common carp, Cyprinus carpio. In one experiment females were held in the absence of a male in cages placed in rearing ponds containing a dense population of unicellular algae; the cages touched the bottom but there was no vegetation inside the cages. When LHRH-A was given in two injections (the first 5 μg/kg, the second, 6 h later, 50 μg/kg) plasma GtH was increased and followed oocyte maturation. Ovulation occurred in 50% (3 of 6) of the females. In another experiment, using a similar LHRH-A treatment schedule, the females were held in aquaria with added vegetation to serve as a spawning substrate; in such a simplified environment the effect of LHRH-A was not potentiated. Similarly, the natural environment of spawning ponds including the presence of males was of no benefit to the response to low doses of LHRH or LHRH-A when the water temperature was low (12°C). These results suggest that some undetermined environmental factors besides vegetation present in a pond situation may potentiate the effect of LHRH-A, possibly via abatement of the action of an endogenous gonadotropin release-inhibitory factor.
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