Interactions of ascorbic acid with prostaglandins

Samples of blood, urine and ovarian tissues of non-pregnant cycling guinea-pigs were obtained from day 3 before until day 2 after oestrus. In addition placental specimens were obtained from 49- to 62-day pregnant guinea-pigs. In a separate series of experiments blood samples of normally menstruating and dysmenorrhoeic women were collected daily during the last one week preceding and the first two days of the menstrual cycle. Plasma and tissue samples were analyzed simultaneously for ascorbic acid (AA) and prostaglandins (PGs) E2 and F2 alpha. The urine and leukocyte samples were estimated for AA only. The results demonstrate that the ovarian AA depletion at ovulation is not associated with a rise in urinary, plasma or leukocyte levels. From about the 8th week of pregnancy in the guinea-pig the placental levels of AA start to decline, while the concentrations of PGs start to rise. During the late luteal phase, the plasma of normally cycling women has a PGD2 alpha/PGE2 ratio of about 0.6. In the dysmenorrhoeic women this ratio varies from 0.9 to 1.3. In addition, the plasma and leukocyte levels of AA in the dysmenorrhoeic women are lower than the levels found in the normally cycling women. The results of both animal and human studies indicate that an inverse relationship exists between the levels of AA and the amount of PGF2 alpha synthesized and/or released in the body tissues. It is suggested that AA acts to control the ratio between PGF2 alpha and PGE2 and therefore forms an integral part of the adenyl/guanylate cyclase system. The mechanism for the fall in tissue ascorbic acid is however not known. The results suggest that this is due to increased break-down and/or rapid consumption of AA in the body tissues. In addition the reduction in placental tissue levels of AA near term could be due to its redistribution from maternal to foetal tissues.