Effects of synthetic LH-RH and analog on plasma gonadotropin levels and maturational response to 17 alpha Hydroxy - 20 beta - dihydroprogesterone

The effects of LH-RH and analog on the stimulation of gonadotropin (GtH) secretion have been studied in order to use them as priming, before inducing maturation with 17α-hydroxy-20β-dihydroprogesterone (17α-20βP) in the carp Cyprinus carpio. One injection of LH-RH (2 μg/kg body weight) or LH-RH analog (0.3 μg/kg) induces a transient rise in the plasma GtH concentration, but subsequent 17α-20βP treatment does not result in an increase in the number of oocytes with germinal vesicle breakdown or in ovulation. Two and three in ections of LH-RH or analog at the same dosages are followed by a stimulation of GtH secretion (to 30 ng/ml) which is maintained for 6–9 h, and lasts longer with LH-RH analog than with LH-RH. The same magnitude in the increase of GtH secretion is obtained with lower doses of LH-RH analog. Injection of 17α-20βP then increases the number of oocytes undergoing germinal vesicle breakdown and sometimes partial ovulation. Futher studies on the mechanism of action of GtH during priming hypophysation treatment are needed in order to develop a sequential treatment using: (1) priming by LH-RH or analog, (2) 17α-20βP induced maturation treatment