Changes in the characteristics of pulsatile luteinizing hormone secretion during the oestrous cycle and after ovariectomy and oestrogen treatment in female rats

Abstract

Changes in the characteristics of LH secretory pulses in female rats were determined in different hormonal conditions; during the oestrous cycle and after ovariectomy and oestrogen treatment. The frequency and amplitude of the LH pulses were stable during the oestrous cycle except at oestrus when a pattern could not be discerned because of low LH concentrations. These were significantly lower than those measured during other stages of the cycle. Mean LH concentrations and LH pulse amplitudes increased with time up to 30 days after ovariectomy. The frequency of the LH pulse was unchanged 4 days after ovariectomy when mean LH levels had already increased. The frequency increased 10 days after ovariectomy and then remained stable in spite of a further increase in mean serum LH concentrations. Oestradiol-17 beta injected into ovariectomized rats caused a decrease in LH pulse amplitude but no change in pulse frequency. One day after treatment with oestradiol benzoate no LH pulse was detectable, probably because the amplitude was too small. A generator of pulsatile LH release is postulated and an oestrogen effect on its function is discussed.

Influence of Estradiol and Progesterone on Pulsatile LH Secretion in 8-Day Ovariectomized Rats

“…D2-proestrous levels of E2 retain their suppressive action on LH pulse amplitude, D1-D2 levels of E2 + P combined remain effective in decreasing pulse frequency and DI-D2 levels of E2 are again ineffective in altering pulse frequency. In contrast, D2-proestrous E2 levels lose their suppressive action on LH pulse frequency, DI-D2 levels of P lose their action in decreasing pulse amplitude and DI-D2 levels of E2 gain the ability to suppress LH pulse amplitude.Luteinizing hormone (LH) secretion is pulsatile throughout the rat estrous cycle [17,18,21]. Recently, we reported that mean blood LH levels rapidly increased Received: April 15.…”

“…While some studies in long-term ovariectomized rats also indicated that E; can decrease both parameters of pulsatile LH secretion [2. 44], others indicate a suppressive effect of E2 only on LH pulse amplitude [20,21,42] or pulse frequency [30]. Moreover, physiological or pharmacological levels of P decreased LH secretion in acute but not long-term ovariectomized rats [6, 7, 12, 19, 20, 33, 35.…”

Role of Proestrous Progesterone Secretion in Suppressing Basal Pulsatile LH Secretion during Estrus of the Estrous Cycle

“…In addition, the proestrous surge of progesterone may be responsible for this suppression during estrus, since blocking progesterone secretion or blocking its action restores pulsatile LH secretion on estrus. We hypothesize that the proestrous surge of progesterone may cause an increase in endogenous opioid tone which then suppresses GnRH release and pulsatile LH secretion during estrus.During the rat estrous cycle, the pattern of tonic LH secre tion is pulsatile except on the day of estrus, when only infre quent LH pulses are observed [18, 20,21]. There is general agreement that the LH interpulse interval (about 50 min) is sim ilar during diestrus 1, diestrus 2 and the morning of proestrus [18, 20,21], suggesting that changes in the LH interpulse inter val are not a mechanism for the control of tonic LH secretion between diestrus 1 and proestrus.…”

“…There is general agreement that the LH interpulse interval (about 50 min) is sim ilar during diestrus 1, diestrus 2 and the morning of proestrus [18, 20,21], suggesting that changes in the LH interpulse inter val are not a mechanism for the control of tonic LH secretion between diestrus 1 and proestrus. However, the LH pulse am plitude has been reported to change among the days of the es trous cycle [18, 20,21], but not in parallel with changes in pi tuitary responsiveness to GnRH [13,25, 36], LH pulse ampli tude either decreases [ 18, 20] or does not change [21 ] between diestrus I and proestrus, whereas pituitary responsiveness to 1 Supported by a USPHS grant, NIH, HDI4643.Received: October 12, 1988 Accepted after revision: January 20, 1989 GnRH increases during this time [13,25, 36]. Changes in the secretory patterns of ovarian steroids during the estrous cycle have been described [8,24,30, 38] and may account for these data; that is, ovarian steroids may be acting on the hypothala mus to restrain GnRH pulse frequency and pulse amplitude, and acting on the pituitary to enhance pituitary responsiveness to GnRH [13,25,36].…”

“…There is general agreement that the LH interpulse interval (about 50 min) is sim ilar during diestrus 1, diestrus 2 and the morning of proestrus [18, 20,21], suggesting that changes in the LH interpulse inter val are not a mechanism for the control of tonic LH secretion between diestrus 1 and proestrus. However, the LH pulse am plitude has been reported to change among the days of the es trous cycle [18, 20,21], but not in parallel with changes in pi tuitary responsiveness to GnRH [13,25, 36], LH pulse ampli tude either decreases [ 18, 20] or does not change [21 ] between diestrus I and proestrus, whereas pituitary responsiveness to 1 Supported by a USPHS grant, NIH, HDI4643.…”