Metabolic effects of combined oral contraceptive preparations

Mechanisms of hepatic fatty acid oxidation and ketogenesis during fasting

Fasting is part of many weight management and health-boosting regimens. Fasting causes substantial metabolic adaptations in the liver that include the stimulation of fatty acid oxidation and ketogenesis. The induction of fatty acid oxidation and ketogenesis during fasting is mainly driven by interrelated changes in plasma levels of various hormones and an increase in plasma nonesterified fatty acid (NEFA) levels and is mediated transcriptionally by the peroxisome proliferator-activated receptor (PPAR)α, supported by CREB3L3 (cyclic AMP-responsive element-binding protein 3 like 3). Compared with men, women exhibit higher ketone levels during fasting, likely due to higher NEFA availability, suggesting that the metabolic response to fasting shows sexual dimorphism. Here, we synthesize the current molecular knowledge on the impact of fasting on hepatic fatty acid oxidation and ketogenesis.

Tyrosine metabolism in users of oral contraceptives

Brain noradrenaline takes part in the regulation of several brain functions. The formation of brain noradrenaline depends on brain tyrosine (Tyr) levels, which associates with the ratio in plasma of Tyr to other large, neutral amino acids (LNAA). Tyr metabolism has been studied in users of the new generation combined oral contraceptives (OC) and comparable controls at the follicular, mid-cycle, and luteal phases of the menstrual cycle. OC users showed significantly increased plasma Tyr transaminase activity, and significantly decreased plasma Tyr and Tyr/LNAA levels at mid-cycle and luteal phase, whereas plasma total 3-methoxy-4-hydroxyphenylglycol (MHPG) was not affected. Following an oral protein load, the area under the curve in plasma of Tyr and Tyr/LNAA in OC users at the luteal phase were 43% and 29%, respectively, of control levels. The results suggest that the decreased Tyr availability to the brain in OC users may result in a substrate-limited reduction of brain noradrenaline formation, which, secondarily, may contribute to disturbances of mood, coping mechanisms, and appetite in susceptible subjects.