Changes in the pulsatile pattern of luteinizing hormone secretion during the XXXX estrous cycle.

@entity35 @entity1510 @entity1176
To ascertain whether changes in the pattern of @entity1176 release from the hypothalmus occur during the 4-day @entity35 estrous cycle, the pattern of LH release was characterized on each day of the estrous cycle, and the results were interpreted in light of the changes in pituitary responsiveness to @entity1176 previously described by this laboratory to occur during this time. Blood samples were taken from intact, freely moving @entity35 via venous catheters at 6- to 10-min intervals for 3-4 h. LH pulse height and LH interpulse interval were quantified on each day of the cycle, and the transition on the afternoon of proestrus from tonic LH release to the preovulatory LH surge was detailed. The effects on the pattern of LH release during estrus of small doses of @entity1176 (0.4 ng) and the continuous infusion of the opioid antagonist @entity1510 were also examined. Plasma LH concentrations (NIAMDD @entity35 LH-RP-1) were determined with a highly sensitive LH RIA. LH pulses were identified using the PULSAR algorithim. The LH interpulse intervals of 46 +/- 2 min on diestrous-1 day, 49 +/- 4 min on diestrous day 2, and 60 +/- 8 min on proestrus immediately before the LH surge were not significantly different. There were no changes immediately preceding the preovulatory LH surge on the afternoon of proestrus in either the LH interpulse interval or the LH pulse height. Instead, the transition from tonic LH secretion to the preovulatory LH surge was found to occur abruptly. These data suggest that an abrupt increase in @entity1176 secretion during the afternoon of proestrus initiates the dramatic rise in LH concentrations. The pattern of LH secretion during the day of estrus differed significantly from that on the other days of the cycle in that no LH pulses were observed. However, the administration of small pulses of @entity1176 elicited physiological elevations in LH release. Furthermore, the continuous infusion of @entity1510 to estrous @entity35 immediately stimulated a pulsatile pattern of LH secretion, with a LH interpulse of 56 +/- 4 min. These data indicate that the absence of LH pulses during estrus may result from a deficit in @entity1176 release. Similar modifications in @entity1176 release during the other days of the cycle were inferred from the observed changes in LH pulse heights. The LH pulse height of 21 +/- 3 ng/ml on diestrous day 2 was significantly less than the LH pulse height of 41 +/- 4 ng/ml on diestrous day 1 or 35 +/- 4 ng/ml on proestrus before the surge.(ABSTRACT TRUNCATED AT 400 WORDS)
