Maintenance of Progestin Secretion from Rat Corpora Lutea

MAINTENANCE OF PROGESTIN SECRETION FROM RAT CORPORA LUTEA GORDONJ. MACDONALD and ROY O. CREEP* Introduction Earlier investigations concerning the maintenance of luteal function (progesterone secretion) were conducted with the purified prolactin preparations then available. Astwood [i] demonstrated with hypophysectomized rats that hypophyseal luteotropin maintained the ability ofthe corpus luteum to secrete progesterone, this being tested by concomitant administration ofquantities ofestrogen known to induce vaginal cornification in the absence ofprogesterone. Soon thereafter [2], it was shown that prolactin preparations maintained adequate steroidogenesis from the hypophysectomized rat ovary to support the formation ofdeciduomata. Recently, von Berswordt-Wallrabe, fantzen, Herlyn, and von BerswordtWallrabe [3] reported that it was necessary to add either PMS or HCG to prolactin in order to obtain the deciduomata response in hypophysectomized rats. It is known that deciduomata formation requires a delicate balance ofboth estrogens and progestins and that estrogens will potentiate small quantities ofprogesterone for this response or inhibit the response if the quantity is in excess [4, 5]. The present study was undertaken to determine whether progestin secretion, as determined by the inability of estrogens to induce vaginal estrus [6], is maintained by highly purified prolactin alone or requires pituitary luteinizing hormone (LH). Methods and Materials Holtzman rats 2-3 months old were housed in a temperature- and lightcontrolled room having fourteen hours of daylight and ten hours of darkness. Vaginal smears were obtained daily prior to and during the * Endocrine Research Laboratories, Harvard School of Dental Medicine, Boston, Massachusetts. Research supported by U.S. Public Health Service grant AM00292. 49? GordonJ. Macdonald and Roy O. Greep · Progestin Secretion Perspectives in Biology and Medicine · Spring 1968 experimental periods. The design ofeach experiment, the hormones used, and their dosages, vehicles, and patterns of administration will be seen under "Results," Figure i, and Tables ? and 2. All hormones were administered by injection, subcutaneously. Luteal function was tested by injecting estradiol as 50 µ?. in 0.5 ml. sesame oil daily for the last three days ofeach experiment. Ifthe estradiol was unopposed by endogenous progesterone, the vaginal smears showed cornified epithelial cells approximately seventy-two hours following the initial administration, and the uteri were filled with fluid. However, in the presence ofprogesterone, vaginal srnears remained leucocytic, and the uterus did not contain fluid. Ovarian weights and the presence or absence of uterine fluid were recorded at autopsy. Vaginae were fixed for histological examination, and completeness ofhypophysectomy was determined by examination ofthe sella turcica with a loupe. Animals suspected ofhaving pituitary remnants were excluded from consideration. Results experiment i This experiment involved four groups ofrats which were hypophysectomized in the forenoon without concern for the known stage ofthe estrous cycle. Each group was treated as shown in Figure 1. Prolactin treatment (NIH-P-S6)1 was initiated on the day depicted. It was administered twice daily by subcutaneous injection for seven days, and each dose was 500 Mg. (12.5 LU.) carried in 0.2 ml. 0.9 per cent NaCl. Group A received prolactin treatment immediately after hypophysectomy to ascertain whether it can maintain progesterone secretion. Group B was rested for three days, and prolactin treatment was then initiated to determine whether the corpus luteum retains its ability to respond to prolactin. The remaining two groups were given LH for three days prior to the initiation of prolactin treatment. Group C was treated with LH immediately after hypophysectomy, while Group D was treated following a three-day rest. NIH-LH-S8 was administered as 5 Mg. in 0.2 ml. 0.9 per cent NaCl twice daily by subcutaneous injection. The purpose was to determine if LH retains or re-establishes luteal sensitivity whereby prolactin might reinduce progesterone secretion. Every rat which did not receive prolactin 1 Prolactin NIH-P-S6 and luteinizing hormones NIH-LH-S8 and NIH-LH-B3 were generously supplied by the Endocrine Study Section, National Institutes of Health, Bethesda, Maryland. 491 aro?? TREATMENT pu PL + E B PL- PL+ E C LH PL PL + E D LH PL PL+E -I------------T6 7 IO 3 4-67IO1} DAYS AFTER HYPOPHYSECTOMY O- No treatment LW-NIHSo 5-wg/O.Eml twice daily PL - NI HS6 500^g/ 0.2ml twice daily E - Estradiol 5Qitg/0.5 rnl...