Regulation of Pulsatile Luteinizing Hormone Release During the Estrous Cycle and Pregnancy in the Rat

Luteinizing hormone (LH) secretion during the rat estrous cycle (Gallo, 1981; Higuchi and Kawakami, 1982; Fox and Smith, 1985) and pregnancy (Gallo et al., 1985) occurs in a pulsatile manner. Moreover, changes in the amplitude and frequency characteristics of this secretion take place with different stages of the 4-day estrous cycle and during different stages of gestation in this species. Plasma levels of estradiol (E2) and progesterone (P) also vary from stage to stage in the estrous cycle (Butcher et al., 1974; Kalra and Kalra, 1974b; Smith et al., 1975; Nequin et al., 1979) as well as during the different stages of pregnancy in the rat (Morishige et al., 1973; Taya and Greenwald, 1981; Bridges, 1984). The emphasis in our work is to study the neuroendocrine regulation of pulsatile LH secretion in a physiological context. Therefore, the aim of our experiments has been to first describe the normal changes that occur in LH pulse amplitude and frequency throughout the estrous cycle and pregnancy, and then to define the regulatory negative feedback roles of E2 and/or P during each 24-h interval of the rat estrous cycle, and during specific stages of gestation.