Differential regulation of the gonadotropin storage pattern by gonadotropin-releasing hormone pulse frequency in the ewe

The differential control of gonadotropin secretion by GnRH pulse frequency may reflect changes in the storage of LH and FSH. To test this hypothesis, ovariectomized ewes passively immunized against GnRH received pulsatile injections of saline (group 1) or GnRH analogue: 1 pulse/6 h for group 2 or 1 pulse/h for group 3, during 48 h. Immunization against GnRH suppressed pulsatility of LH release and reduced mean FSH plasma levels (3.1 +/- 0.2 vs. 2.2 +/- 0.1 ng/ml before and 3 days after immunization, respectively). Pulsatile GnRH analogue replacement restored LH pulses but not FSH plasma levels. Low and high frequencies of GnRH analogue increased the percentage of LH-containing cells in a similar way (group 1 = 6.9 +/- 0.5% vs. group 2 = 10.5 +/- 0.8%, or vs. group 3 = 9.6 +/- 0.4%). In contrast, the rise of the percentage of FSH-containing cells was greater after administration of the analogue at low frequency than at high frequency (group 1 = 3.7 +/- 0.4% vs. group 2 = 8.4 +/- 0.2%, or vs. group 3 = 5.2 +/- 0.8%). Moreover, while GnRH pulse frequency had no differential effect on FSHbeta mRNA levels, LHbeta mRNA levels were higher under high than low frequency. These data showed that the frequency of GnRH pulses can modulate the gonadotropin storage pattern in the ewe. These changes may be a component of the differential regulation of LH and FSH secretion.