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Corpus Luteum Growth and Progesterone Synthesis during the Bovine Estrous Cycle^{1, 4,}

Endocrinology Research Laboratories, Harvard School of Dental Medicine, Boston

Abstract

Luteal growth and steroidogenesis were studied in corpora lutea from 33 heifers, five each at 2, 4, 7, 11, 18 and 20 days after estrus, and three on the day of the next anticipated ovulation (day 0). Luteal weight and total DNA growth curves leveled at day 11. Ratios of RNA/DNA was greatest during most rapid luteal growth at day 4. Free sterol concentration in fresh corpora lutea increased linearly from 1,345 µg./gm. at day 2 to 2,612 µg./gm. at day 18, but esterified sterol decreased from 618 µg./gm. at day 2 to 344 µg./gm. at day 11, and then increased to 1,081 µg./gm. on the day of the next ovulation. Corpus luteum progesterone concentration was greatest at mid-cycle (46 µg./gm.).

Incubation of homogenates of corpora lutea for 1 hr. in Krebs-Ringer bicarbonate buffer resulted in synthesis of progesterone which increased from 17 µg./gm. on day 2 to 136 µg./gm. on day 11 and 150 µg./gm. on day 20, but decreased to 46 µg./gm. on the day of the next ovulation. Total progestogen synthesis at any stage of the cvcle was no greater in the presence of NADPH than in the presence of NADP+glucose-6-phosphate. LH failed to stimulate synthesis of progesterone in these luteal homogenates. Significant quantities of esterified sterol accumulated during incubation of corpora lutea from day 18, 20 and 0, but not during incubation of younger tissues and rates of esterification of cholesterol-7-³H in the incubation medium were greater in the older than in the younger corpora lutea.

¹ This research was a part of a larger study entitled "Reproductive development of the pubertal female" (U.S.P.H.S. grant HD-01374) at the Dairy Department, Michigan State University.

⁴ The authors acknowledge the technical assistance of C. Desjardins, K. T. Kirton, A. L. Barofsky and L. V. Sanderson. This research has been supported by U.S.P.H.S. grants AM-00292 and HD-01374.

² Special Fellow, U.S.P.H.S.; On leave from the Dairy Department, Michigan State University, East Lansing.

³ Research Career Development Awardee, U.S.P.H.S.