An ultramicro method for the estimation of plasma cholesterol.

A procedure is outlined for the ultramicro determination of total cholesterol that gives results in excellent agreement with classic methods. The determination requires 40 l. of plasma obtained from a finger-tip puncture and special handling of precipitated proteins. By the use of the described procedure plasma cholesterol levels have been estimated 4 times daily over a period of 8 weeks in young men undergoing rigorous physical training and 3 times daily in women during the menstrual cycle. A striking fall in total plasma cholesterol was observed in men following physical conditioning in contrast to controls, and a similar decrease was observed in women with normal menstrual cycles in contrast to women with an anovulatory menses. It is suggested that the total cholesterol decrease in the female coincides with the phase in the menstrual cycle when estrogen activity is maximal and that the lowering of total cholesterol in men, following physical conditioning, may be due to an increased production of endogenous androgens with a consequent increase in conversion of these steroids to estrogens.