Analysis of luteinizing hormone and follicle-stimulating hormone release kinetics during a dynamic secretory event, the postpartum preovulatory surge in the rat, based on quantitative changes in stored and circulating luteinizing hormone and follicle-stimulating hormone and metabolic clearance data for these hormones.

The original objective of this study was to use available distribution volume (V) and deca constant (k) estimates for rat LH and FSH to determine the amounts of these hormones synthesized and released during a dynamic secretory event, the postpartum preovulatory surge. The problem was approached by 1) determining the approximate rates and durations of pituitary LH and FSH depletion during the surge, and 2) comparing observed plasma LH and FSH patterns with patterns calculated on the assumptions a) that the rates and durations of LH and FSH release would have to equal or exceed the rates and durations of LH and FSH depletion, and b) that the V and k estimates reported by Bogdanove and Gay (Endocrinology 84: 1118, 1969) would be applicable in this situation. The observed surges proved to be 3- to 10-fold smaller than the calculated patterns, suggesting either that depletion exceded release or that inappropriate values of V and/or k had been used in the calculations. Subsequent reexaminations of LH clearance kinetics (Campbell et al., accompanying reports) provided larger estimates for both VLH and kLH. Recalculation of the data, using these new parameters, eliminated the apparent discrepancy between depletion and release. On the basis of these direct comparisons of stored and circulating LH, it seems that a "half-life" shorter than 30 min and a distribution volume greater than 3 ml/100 g must be used to model the effects of variations in LH release on circulating LH in the rat.