EFFECTS OF ORAL-CONTRACEPTIVES ON PLASMA NEUTRAL AMINO-ACIDS AND CHOLESTEROL DURING A MENSTRUAL-CYCLE

Objective: Concentrations of plasma neutral amino acids, i.e. threonin e, serine, asparagine, glycine, alanine, citrulline, alpha-aminobutyri c acid, valine, methionine, isoleucine, leucine, tyrosine, phenylalani ne, and tryptophan, and serum cholesterol, were determined at the foll icular (Day 4), mid-cycle (Day 16) and luteal (Day 25) phases of the m enstrual cycle in 15 users of the new generation of combined oral cont raceptives (OC), 11 on multiphase combined OC, and 17 controls. Result s: The controls showed a decrease in the sum of amino acids to 95% at mid-cycle and 90% in the luteal phase relative to the follicular phase , and a significant decrease in the tyrosine level at the luteal relat ive to the follicular phase. Since there was no significant difference between the two OC subgroups in the levels of the specified variables at either of the phases, the two groups were considered together. The sum of amino acids in the OC group decreased to 89% at mid-cycle and 91% at the luteal phase relative to the follicular phase, indicating l ess metabolic effect than reported for older OC formulations. Compared to the controls, the OC group showed significant increased threonine level at the luteal phase, decreased glycine levels at mid-cycle and t he luteal phases, decreased citrulline level at midcycle, and markedly decreased tyrosine levels at the mid-cycle and luteal phases. Neither total nor high density lipoprotein (HDL) cholesterol differed signifi cantly between the control and OC groups. Conclusion: The results sugg est that the metabolic effects of the new generation combined OC on ne utral amino acids and cholesterol are only modest to slight, except fo r the effect on tyrosine, the brain noradrenaline precursor, which may cause disturbances of various noradrenaline-mediated central function s in susceptible subjects.