Effects of superovulation on endogenous LH secretion in cattle, and consequences for embryo production

Stimulation of follicular growth during superovulation is achieved by the i njection of FSH or compounds with high FSH-bioactivities. However, some LH- activity is required for follicle maturation. It is of relevance to evaluat e, therefore, the effect of superovulatory treatments on endogenous LH secr etion. Luteinizing hormone is secreted in discrete pulses, and the pattern of pulsatile LH secretion during superovulation is reviewed. Four of five p ublished studies have shown that LH pulse frequency is significantly reduce d by injection of eCG or FSH preparations. This suppression appears within 8 h of treatment Effects of superovulation on LH pulse amplitude are less c onsistent. The reasons for the decrease in pulse frequency have been invest igated, and although the answer is not definitive, it would seem that incre ased follicular estradiol, acting perhaps in synergism with progesterone, m ay play a role. Changes in plasma progesterone concentrations are not relat ed to changes in LH pulse frequency. What is the significance of decreased LH pulse frequency? We attempted to investigate this by inducing LH pulses during superovulation, but the result was a major reduction in ovulation ra te. More research is required to determine if modification of endogenous LH secretion can improve superovulatory responses. (C) 1998 by Elsevier Scien ce Inc.