Chronological Study on Changes in Luteinizing Hormone Release during Fasting and Refeeding in Ovariectomized Estrogen-primed Rats

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To investigate the effect of food manipulation on luteinizing hormone (LH) secretion, changes in pulsatile release of the hormone during the periods of 48h fasting and subsequent 24h refeeding, both started at noon, were examined chronologically in ovariectomized estrogen-primed rats fed in 14L-10D (lights on at 0500h) lighting condition, by taking plasma samples at intervals of 10 min for 6h in each animal. Diurnal pattern of LH secretion, being high in the afternoon and low in the morning, was observed in the free feeding group rats. The plasma concentration of LH started to decrease from 6-12h after the food deprivation and was kept low thereafter throughout the fasting period. Refeeding caused the prompt recovery of pulsatile release of LH and frequent occurrence of LH pulses which lasted for 6h or a little more. Frequent LH pulses were observed again on the morning of the next day in the refed rats, while the hormone release remained low at the same clock time in the freely fed animals. Suppression of the LH secretion by fasting seemed to be slightly alleviated on the third day of fasting. The sensation from digestive organs associated with fasting and refeeding may be the primary factor responsible for the change in LH secretion, and also the intervention of light-dark cycle in the mechanism was suggested.