Circadian and Menstrual Cycle Variation in Serum Ascorbic Acid Levels in Baboons

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Abstract
Serum levels of ascorbic acid were determined every 6 hours over a 36-hour period and every other day throughout complete menstrual cycles in five baboons. All baboons were normally cycling females exhibiting normal serum progesterone and estrogen patterns and changes in sex skin morphology. There was no evidence for a circadian rhythm in serum ascorbic acid levels since the relationship between ascorbic acid levels and sampling time over a 36-hour period was not statistically significant. Serum ascorbic acid levels throughout the menstrual cycle did not vary significantly although periovulatory levels tended to be lower and a positive significant (P < 0.05) regression coefficient was obtained during the luteal phase (Y = 85.99 + 1.49 (x), where Y is the mean concentration of ascorbic acid for five baboons in mg/100 ml serum expressed as a percentage of each individual baboons mean ascorbic acid concentration throughout the menstrual cycle studied and X is the day of the menstrual cycle). The disappearance (t½) of ascorbic acid from the serum after an intramuscular injection of 1 g L-ascorbic acid during the follicular, periovulatory and luteal phases was 70, 62 and 67 minutes, respectively. These times were not significantly different. In conclusion, when diet and environment were rigidly controlled and the periovulatory period was accurately timed as a marker during the menstrual cycle, there was no statistically significant relationship between physiologic levels of sex hormones and serum ascorbic acid levels.