Circadian variations of ovarian ascorbic acid depletion in response to luteinising hormone in the rat.

The ovarian ascorbic acid (OAA) was titrated, three hours after an I.V. injection of either saline or LH, administered to 46 day-old Sprague Dawley female rats pretreated with P.M.S., H.C.G., and estradiol benzoate (and undecylate). The rats were killed at specific times along the 24-hour scale (L.D. 12:12; L 06(00) to 18(00); Ambient temperature 24 degrees C +/- 2 degrees C). The OAA content varied with a statistically significant circadian rhythm in the controls. The minimum dose of LH effecting OAA depletion varied systematically with the circadian system phase. OAA depletion increases with the dose of LH, and also depends on the circadian time that the animal is killed; it is maximum at the same time that the OAA peak is found in the controls. The slope of the linear regression (quantity of OAA as a function of the logarithm of the LH doses administered) is always significant, but varies over the 24-hour span; in consequence the LH biological titration must be carried out rapidly, the optimal circadian time for killing the animals is about 16(30).