Reanalysis of the rat proestrous LH surge by deconvolution analysis

To evaluate the temporal mechanisms that give rise to the spontaneous proestrous surge of luteinizing hormone (LH) in the rat, we have applied deconvolution analysis to earlier immunoreactive LH concentration vs. time profiles obtained by sampling blood in proestrus at 2- to 3-min intervals in 10 animals over a span of 160-300 min. Six other animals were bled in 6-min intervals on day 1 of diestrus. Deconvolution analysis permitted us to calculate the number, duration, amplitude (maximal release rates), and mass of underlying LH secretory bursts and to simultaneously estimate basal secretion and the half-life of endogenous LH in each animal. Proestrous rats exhibited a significant increase in the number of computer-identified LH secretory bursts per hour (1.8 ± 0.2 vs. 1.1 ± 0.01 on diestrus, P < 0.01), with a corresponding reduction in the LH intersecretory burst interval from 61 ± 6.4 min (diestrus) to 25 ± 2.7 min (proestrus, P < 0.01). There was a remarkable 16-fold increase in the mass of LH secreted per burst, which rose from 72 ± 5.2 to 1,230 ± 200 ng/ml (P < 0.01). This resulted from a sixfold increase in LH secretory burst amplitude and a doubling of burst duration. The total amount of LH released in a burstlike fashion during the proestrous LH surge rose 20-fold, and calculated basal LH secretion increased to ~25% of this value. Of interest, the computed half-life of endogenous LH also increased from 10 ± 1.1 to 19 ± 3.7 min (P < 0.05). We conclude that there is a fourfold mechanistic basis (amplified LH secretory burst frequency and amplitude, increased basal secretion, and prolonged LH half-life) to account for the profound increases in blood LH concentrations attained in the preovulatory surge.