Effect of estradiol and progesterone on daily rhythm in food intake and feeding patterns in Fischer rats

Author(s): Chai, J. K., Meguid, M. M., Laviano, A., Gleason, J. R., Yang, Z. J., Blaha, V.

Journal/Book: Physiol Behav. 1999; 68: the Boulevard Langford Lane, Kidlington, Oxford Ox5 1GB, England. Pergamon-Elsevier Science Ltd. 99-107.

Abstract: The product of meal number x meat size, over time, is food intake. Because estrogens modulate feeding activity via their action on the hypothalamus, and because there is a diurnal rhythm in the expression of cytoplasmic estrogen receptors and in estrogen binding activity, the present study examined the effects of ovariectomy and later hormone therapy on acute changes in body weight, and on the meal number-to-meal size relationship as reflected by food intake in the dark/light feeding patterns, in adult female rats in the intact state and after ovariectomy. Twelve female Fischer rats were randomized into ovariectomy and sham operation groups. A rat eater meter measured the feeding indexes for 15 days before and 25 days after ovariectomy, and later for 35 days with hormone therapy. We report: (a) mean body weight gain was linear before and up to ovariectomy, while exponential after ovariectomy; (b) increase in daily food consumption is mainly via an increase in food intake during the light phase; (c) light phase meal number remains unchanged, meal size significantly increases, with the resultant increase in overall food intake; (d) during the dark phase, meal size also significantly increases, but is accompanied by a proportional decrease in meal number, resulting in unchanged dark-phase food intake; and (e) estrogen restoration with either estradiol valerate or estradiol-progesterone combination, reversed the above changes. Data show that in the female Fischer 344 rat: (a) changes in daily rhythm in food intake are brought about by differential effects of the hormones on both meal size and meal number in both the total daily levels as well as in the dark-to-light distribution; (b) estadiol appears to have a tonic inhibitory effect on the light-phase meal size and a phasic effect on the dark phase meal size and number, but no significant effect on the light-phase meal number; and (c) in the Fischer rats, progesterone augments estradiol's effect on these indicies.

Note: Article Meguid MM, SUNY Hlth Sci Ctr, Univ Hosp, Dept Surg, Surg Metab & Nutr Lab, Neurosci Program, 750 E Adams St, Syracuse,NY 13210 USA

Keyword(s): female Fischer rats; ovariectomy; daily rhythm; food intake; meal number; meal size; OVARIECTOMIZED RATS; DIURNAL RHYTHM; BODY-WEIGHT; CIRCADIAN-RHYTHMS; SYRIAN-HAMSTERS; MEAL PATTERNS; FEMALE RATS; SHORT-TERM; LONG-TERM; BRAIN

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