Fatty acid reesterification but not oxidation is increased by oral contraceptive use in women

Abstract

We evaluated the hypothesis that fatty acid reesterification would be increased during rest and exercise in the midluteal menstrual cycle phase and during oral contraceptive use, when ovarian hormone concentrations are high, compared with the early follicular phase. Subjects were eight moderately active, weight-stable, eumenorrheic women (24.8 +/- 1.2 yr, peak oxygen consumption = 42.0 +/- 2.3 ml.kg(-1).min(-1)) who had not taken oral contraceptives for at least 6 mo. Plasma free fatty acid (FFA) kinetics were assessed in the 3-h postprandial state by continuous infusion of [1-(13)C]palmitate and [1,1,2,3,3-(2)H]glycerol during 90 min of rest and 60 min of exercise at 45% and 65% peak oxygen consumption in the early follicular and midluteal menstrual cycle phases and during the inactive- and high-dose phases following 4 mo of oral contraceptive use. Plasma FFA rates of appearance, disappearance, and oxidation increased significantly from rest to exercise with no differences noted between menstrual cycle or oral contraceptive phases or exercise intensities. Compared with either menstrual cycle phase, oral contraceptive use resulted in an increase in plasma-derived fatty acid reesterification and a decrease in the proportion of plasma FFA rate of disappearance that was oxidized at rest and during exercise. Endogenous and exogenous synthetic ovarian hormones do not exert a measurable influence on plasma FFA turnover or oxidation at rest or during moderate-intensity exercise in the 3-h postprandial state when carbohydrate use predominates. The increase in whole body lipolytic rate during exercise noted previously with oral contraceptive use is not matched by an increase in fatty acid oxidation and results in an increase in reesterification. Synthetic ovarian hormones contained in oral contraceptives increase lipolytic rate, but fatty acid oxidation during exercise is determined by exercise intensity and its metabolic and endocrine consequences.

No effect of menstrual cycle phase on glycerol or palmitate kinetics during 90 min of moderate exercise

“…Only very recently have data been published from one study on the effect of menstrual cycle phase on exercise lipid kinetics. Results showed that in five eumenorrheic women, there were no differences in systemic glycerol (8) and NEFA (25) turnover between the follicular and ML phases of the menstrual cycle. The later study, however, assessed lipid kinetics in the follicular phase when estrogen was very low (Ͻ30 pg/ml), as was progesterone, and compared this with the luteal phase when both estrogen and progesterone were elevated.…”

“…Similar methodology has been employed to address the effect of oral contraceptives (OC) on lipid kinetics during exercise in eumenorrheic women. Results showed that 4 mo of OC use significantly increased systemic glycerol turnover (8) but had no effect on NEFA turnover, suggesting increased intracellular reesterification of NEFA (25). In addition, there was a significant decrease in the proportion of NEFA uptake that was oxidized (25), and because whole body lipid oxidation did not change, estimated TG-derived FFA oxidation was significantly increased.…”

“…Results showed that 4 mo of OC use significantly increased systemic glycerol turnover (8) but had no effect on NEFA turnover, suggesting increased intracellular reesterification of NEFA (25). In addition, there was a significant decrease in the proportion of NEFA uptake that was oxidized (25), and because whole body lipid oxidation did not change, estimated TG-derived FFA oxidation was significantly increased. In a novel study that used a gonadotropin-releasing hormone (GnRH) antagonist to acutely suppress endogenous hormone production, although exercise lipid kinetics were not measured directly, data showed a significant increase in circulating NEFA concentrations, suggesting increased lipolysis, after estrogen replacement (9).…”

“…Even though this snack had a low glycemic index, it would still have resulted in an insulin response sufficient to significantly suppress lipolysis and lipid utilization in the preexercise period. Furthermore, because insulin is a potent antilipolytic hormone, some carryover effect to the measures of lipid kinetics during exercise were likely, thus confounding any potential influence of the sex steroids (2,25). Hence the effect of normal cyclic fluctuations in the female sex steroids, on exercise lipid kinetics, warrants further investigation.…”

“…Glycerol kinetics and palmitate kinetics (representative of plasma NEFA turnover) were measured during 90 min of moderate-intensity exercise, after an overnight fast (12-13 h) in moderately active women. Measurements were made in the overnight-fasted state because this is more likely to elicit an effect of cycle phase vs. measures in the fed state (25). It was hypothesized that systemic NEFA turnover, and systemic glycerol turnover, would be greatest in the MF phase of the menstrual cycle, when estrogen is elevated but progesterone low, followed by the ML phase (high estrogen and progesterone), and lowest in the EF phase of the menstrual cycle (low estrogen and progesterone).…”