Effect of protein deficiency on plasma progesterone levels during the menstrual cycle of adult rhesus monkeys

Abstract

Plasma progesterone levels in protein-deficient monkeys were determined by the competetive protein binding technique. The alternate day plasma samples from day 10 to the end of the menstrual cycle were analyzed. Of the 8 monkeys used, half were fed 20 % and the other half 10% protein diet (control diets) before the protein-deficient diet was provided. After a 6-month deficiency, all the monkeys were fed a 20% protein diet. On the control diets the monkeys showed a plasma progesterone rise on day 12, reaching a peak value of 5.5 ng/ml by the 18th day. These levels were maintained till day 20, when they gradually declined to 1 ng/ml before menstruation. During the deficient-diet feeding the monkeys showed a peak value of 2.4-4.0 ng/ml for the next 2-3 menstrual cycles. The cycles became shorter, the peak occurred a day earlier, and the progesterone level declined, sharply. Persistent low levels of progesterone were observed for the following 1-2 menstrual cycles, after which the monkeys had amenorrhea. Menstruation spontaneously appeared after 2- to 3-month feeding of control diet, by which time the body weight and serum protein values had improved. The progesterone levels and pattern gradually returned to normal. The findings are suggestive either of the deficient animal's incapacity to maintain corpora lutea or its failure to synthesize enough progesterone.