Acute and long-term changes in central and pituitary mechanisms regulating pulsatile luteinizing hormone secretion...

These experiments examined the time course of changes in the characteristics of pulsatile luteinizing hormone (LH) secretion that occur after ovariectomy (OVX) in the rat, and compared the response of the brain and pituitary to the absence of ovarian steroid negative feedback. The literature indicates that the brain could respond to OVX by altering the frequency and/or amplitude of the pulsatile luteinizing hormone releasing hormone (LH-RH) release which triggers pulsatile LH secretion, while the pituitary could respond by altering basal LH output and/or its response to LH-RH. In vivo experiments examined changes in mean blood LH levels, LH pulse amplitudes and pulse frequencies in control rats on diestrus 1 (D1) and at 7 h, 14 h, 1, 2 or 8 days, or 3 weeks following OVX. In addition, anterior pituitaries from rats on D1 or rats ovariectomized for 1, 2 or 8 days, or 3 weeks, were incubated in vitro with or without LH-RH to examine changes in both basal and LH-RH-induced LH release. Mean blood LH levels increased within 17-24 h following OVX. This acute, rapid elevation was due to increases in both LH pulse frequency and pulse amplitude. Blood LH levels continued to increase over a 3-week period. However, the long-term increase seen at 8 days or 3 weeks was not only due to increases in LH pulse frequency and amplitude, but also to dramatic increases in basal LH secretion. The frequency of pulsatile LH release was maximal within 8 days, with no further increases occurring over the next 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)