Cyclic Fluctuations of Plasma Cholesterol in the Female Miniature Swine and Its Relationship to Progesterone Secretion

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Abstract
Large fluctuations in plasma cholesterol concentration were noted during a study on the metabolic effects of portacaval anastomosis in the female miniature swine. The fluctuations were cyclic and related to the estrous cycle, as shown by measurements of total plasma cholesterol and progesterone on samples obtained almost daily from 6 animals over several estrous cycles. Hormone concentrations indicated a 21 day estrous cycle consisting of a 7 day follicular phase and a 14 day luteal period. Plasma cholesterol fluctuated in a cycle which was the inverse of that for progesterone: High cholesterol concentrations were observed for 3-6 days during the follicular phase with peak values as much as 80%, and on the average 50%, higher than the mean levels observed during the luteal phase. Failure to recognize these plasma cholesterol cyclic fluctuations can totally confuse the interpretation of studies on cholesterol metabolism in swine, which are increasingly popular as experimental models of atherosclerosis and lipid metabolism.