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Concentrations of LH in the serum were estimated in rats bled either once or twice during a 15-day period preceding first ovulation. In rats bled once (between 09.00 and 17.00 h) serum concentrations showed little change between 15 and 9 days before first ovulation and averaged 16 µg/l (days –15 to –9). A shift in LH level, to a mean of 31 µg/l, was seen on day –8, whereafter LH concentrations increased gradually. Basal LH values of < 10 µg/l were only found until day –4.

The finding that LH values increased with age was confirmed by data from rats bled twice with an interval of 3 days between bleedings. Furthermore, both in rats bled twice at 11.00 h and in rats bled twice at 15.00 h LH concentrations were significantly higher in the second sample.

Both morning (11.00 h) and afternoon (15.00 h) LH concentrations in rats bled once also indicated a rise in LH concentrations with age but it became apparent that only morning values showed a shift in LH concentration (from 15 to 42 µg/l) from day –9 to day –8. In contrast, mean afternoon values showed a gradual increase from day –15 on. From day –8 on the number of rats with LH values 50 µg/l increased, and from day –5 on they were more frequent at 15.00 than at 11.00 h.

Thus a clear increase in LH secretion, most likely of a pulsatile nature, was found in the female rat approaching puberty. The correlation in time and possible functional relationship with late-prepubertal follicular growth is discussed.

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				C. J. Guigon, S. Mazaud, M. G. Forest, S. Brailly-Tabard, N. Coudouel, and S. Magre Unaltered Development of the Initial Follicular Waves and Normal Pubertal Onset in Female Rats after Neonatal Deletion of the Follicular Reserve Endocrinology, August 1, 2003; 144(8): 3651 - 3662. [Abstract] [Full Text] [PDF]