Episodic LH Secretion in the Immature Male and Female Rat as Assessed by Sequential Blood Sampling

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Abstract
Using a repeated sampling method, the precise and detailed secretory pattern of luteinizing hormone (LH) was studied in the immature female rat. Animals which had been kept under controlled environmental conditions were implanted with a intracardiac cannula 1 day before, and sequential 50 .mu.l blood samples were collected every 10 min for a 4 h period at 24-27 days of age. The concentrations of LH in the whole blood were determined by radioimmunoassay. When an LH pulse was defined as a rapid increase in LH concentrations to the levels higher than 0.28 ng/ml (mean of minimally detectable amounts plus 2 SD), LH was secreted in a pulsatile fashion in both the female and male rats. Most animals showed 1 or 2 LH pulses over the 4 h sampling period, and the mean amplitudes were slightly but significantly higher in the female than in the male.