The effect of various oestrogens and progestogens on the susceptibility of low density lipoproteins to oxidation in vitro.
OBJECTIVE
To investigate the effect of different oestrogens and progestogens, at various concentrations, on the oxidation of low density lipoproteins (LDL) in vitro.


METHODS
Oestradiol, oestrone, oestriol and equilin, as well as medroxyprogesterone acetate, norgestrel and norethisterone, were added to isolated male LDL, before it was oxidised in the presence of copper ions at 37 degrees C. The oxidation process was monitored spectrophotometrically by the production of conjugated dienes. The lag time to oxidation and the maximum rate of propagation of the reaction were used as measures of the resistance and susceptibility of the LDL to oxidation respectively.


RESULTS
The lag time was increased from 43.7 +/- 1.5 min (mean +/- SEM) for LDL without any added hormone, to 81.2 +/- 1.0 min by 1 microM oestradiol (P < 0.01), 77.9 +/- 4.6 min by 1 microM oestrone (P < 0.01), 67.6 +/- 6.2 min by 1 microM equilin (P < 0.01), and 51.8 +/- 2.8 min by 1 microM oestriol (P < 0.05). The maximum rate of propagation of the reaction was decreased from 0.23 +/- 0.01 nmol conjugated dienes/mg LDL-protein/min (mean +/- SEM) (control LDL) to 0.14 +/- 0.006 nmol/mg/min by oestradiol (P < 0.01), 0.15 +/- 0.009nmol/mg/min by oestrone (P < 0.01), 0.17 +/- 0.012 nmol/mg/min by equilin (P < 0.01) and 0.19 +/- 0.014 nmol/mg/min (P < 0.05) by oestriol. The progestogens alone had no antioxidant effect, nor did their addition to the oestrogens influence their antioxidant activity.


CONCLUSIONS
These results demonstrate that all oestrogens investigated have an inhibitory effect on LDL oxidation in vitro. The magnitude of this effect varied, being of the order oestradiol > oestrone > equilin > oestriol.
McManus
J
J
Department of Obstetrics and Gynaecology, Queen's University of Belfast, Northern Ireland.
McEneny
J
J
Young
I S
IS
Thompson
W
W
D004305:Dose-Response Relationship, Drug; D004967:Estrogens / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D015227:Lipid Peroxidation / Q000187:drug effects*; D008077:Lipoproteins, LDL / Q000187:drug effects*; D008297:Male; D011372:Progestins / Q000494:pharmacology*
D004967:Estrogens; D008077:Lipoproteins, LDL; D011372:Progestins