Effect of Luteinizing Hormone (LH), PGE2, 8-EPI-PGE1, 8-EPI-PGE2, Trichosanthin, and Pregnancy...

Effect of Luteinizing Hormone (LH),PGE2, 8-EPI-PGE1, 8-EPI-PGE2,Trichosanthin, and Pregnancy SpecificProtein B (PSPB) on Secretion ofProgesterone In Vitro by Corpora Lutea(CL) from Nonpregnant and PregnantCows

Y.S. Weems,1* M.A. Lammoglia,† H.R. Vera-Avila,† R.D.Randel,† C. King,‡ R.G. Sasser,‡ and C.W. Weems*

*Department of Animal Sciences, University of Hawaii, Honolulu,HI 96822

Secretion of progesterone by Day 14 bovine corpora lutea (CL) of theestrous cycle and Day 200 CL of pregnancy was evaluated in vitro todetermine what regulates secretion of progesterone by CL of preg-nancy. Weights of Day 200 CL of pregnancy (4356 6 223g) wereheavier when compared to Day 14 CL of the estrous cycle of Brahmancows (3643 6 128g; p # 0.05); however, both Day 14 and Day 200minced CL slices secreted similar basal amounts of progesterone perunit mass (p $ 0.05). Secretion of progesterone in vitro by Day 14 CLof the estrous cycle was increased at 4 and 8 h (p # 0.05) by 10 or 100ng/mL luteinizing hormone (LH) and did not differ between doses(p $ 0.05). Progesterone secretion in vitro by Day 200 CL of pregnancywas not increased (p $ 0.05) by LH at 4 or 8 h. However, progesteronesecretion in vitro by Day 14 CL of the estrous cycle or Day 200 CL ofpregnancy was increased (p # 0.05) at 4 h by 10 or 100 ng/mL PGE2,which did not differ by dose or reproductive status (p $ 0.05). At 8 h,Day 14 CL of the estrous cycle secretion of progesterone in vitro was

Address correspondence to: C.W. Weems, Department of Animal Science, Uni-versity of Hawaii, Honolulu, HI 96822; Tel: 808-956-8337; FAX: 808-956-4883.†Texas A & M University, Overton, TX 75684‡University of Idaho, Moscow, ID 83843

Prostaglandins & other Lipid Mediators 55:27–42, 1998© 1998 by Elsevier Science Inc. 0090-6980/98/$19.00655 Avenue of the Americas, New York, NY 10010 PII S0090-6980(98)00003-3

increased (p # 0.05) by both doses of PGE2 but only at 8 h by 100ng/mL from Day 200 CL of pregnancy (p # 0.05). Secretion of proges-terone in vitro was not affected (p $ 0.05) by 10 or 100 ng/mL 8-Epi-PGE1 or 8-Epi-PGE2 at 4 or 8 h from Day 14 CL of the estrous cycle orDay 200 of pregnancy. Trichosanthin increased (p # 0.05) secretion ofprogesterone in vitro by 10 ng/mL at 4 h and at 8 h by Day 14 CL ofthe estrous cycle or at 8 h by Day 200 CL of pregnancy but trichosan-thin at 100 ng/mL did not affect (p $ 0.05) secretion of progesteronein vitro by Day 14 CL of the estrous cycle or Day 200 CL of pregnancyat 4 or 8 h. Pregnancy specific protein B (PSPB) increased (p # 0.05)secretion of progesterone in vitro at 4 and 8 h by Day 14 CL of the es-trous cycle and did not differ between incubation times (p $ 0.05).PSPB increased secretion of progesterone at 4 h but not at 8 h (p $0.05) by Day 200 CL of pregnancy. These data suggest that PGE2 orPSPB but not LH, 8-Epi-PGE1 or 8-Epi-PGE2 regulates luteal secretionof progesterone by bovine CL at mid-pregnancy. In addition, it is sug-gested that weights of bovine CL of pregnancy increase to compensatefor a lack of placental secretion of progesterone.

Introduction

Conflicting results have been reported for corpora lutea (CL) regulationand function throughout pregnancy in cows. Concentrations of proges-terone in jugular venous plasma are reported to increase twofold fromDay 12 to 18 postbreeding in cows (1,2) and does not change from Day 20throughout the remainder of gestation (2). Others report that jugularvenous progesterone increases through Day 85 of pregnancy in cows anddoes not increase for the remainder of gestation, before declining atparturition (3). Progesterone in jugular blood is similar throughout Day230 before increasing on Day 240 (3,4). Weights of CL are similar through-out pregnancy in cattle (4,5). Content and concentration of progesteronein CL peak between 37 to 81 days postbreeding, decline through Day 185,increase 100% by Day 204 and decrease 10 days prior to parturition (4,5).The 20a or 20b metabolites of progesterone do not change during gesta-tion in cows (3). The placenta of cows does not secrete progesteroneunless the CL regresses (6). Since progesterone declines to 0.5 ng/mL in72 h after lutectomy of cattle after midpregnancy, cows are vulnerable toabortion (7). Two herds of cattle in Hawaii diagnosed pregnant at 100 daysof pregnancy had calving rates of 56 and 60%, respectively, possibly byloss of luteal function from exogenous or endogenous stimuli.

Secretion of progesterone in vitro by bovine luteal tissue of the estrouscycle is stimulated by luteinizing hormone (LH) (9) and luteal tissueregresses in vivo when cows are given antisera to LH (10), althoughcontrol cows never received normal horse serum. However, the in vitroLH-stimulated secretion of progesterone by bovine CL of midpregnancy is

Progesterone Secretion by Cow Corpora Lutea: Weem et al.

28 Prostaglandins 1998:55, January

reduced markedly when compared to the in vitro response by mature CLof the estrous cycle (11). In addition, circulating LH and content of LH inthe pituitary decreases throughout gestation when compared to the lutealphase of the estrous cycle of nonpregnant cows (12,13). Moreover, pulsefrequency and amplitude of LH from mid through late pregnancy arereduced in cows (14,15). These data suggest that LH is not the luteotro-pin-regulating luteal secretion of progesterone during pregnancy in thecow.

Several agonists stimulate luteal secretion of progesterone and may beluteotropins, which include PGE1 or PGE2 (16–28), pregnancy specificprotein B (PSPB) (30–35), PGI2 (36), PGF2a (36), relaxin (37), oxytocin (37),biogenic amines (38), or 8 Epi-PGE1 or 8-Epi-PGE2 (C. Weems, unpub-lished data). PGE1 and PGE2 stimulate secretion of progesterone by CL ofthe estrous cycle in vitro (17) and in vivo in cows (16). In addition, PGE1(21) or PGE2 (22) prevents a spontaneous, estradiol-17b (23,24), IUD(25,26) or PGF2a-induced luteolysis in vivo (27,28). A combination ofPGE2 and estradiol-17b may be needed to prevent luteolysis in cows (29).PSPB, which increases during gestation (30), may also be luteotropicdirectly (31–33) or indirectly (34,35). Trichosanthin, a curcubit protein, isan abortifacient (8). However, its mechanism of action is unknown. Theobjectives of this experiment were to: 1) determine whether PGE2, PSPB,8-epi-PGE1 or 8-epi-PGE2, and not LH in vitro stimulates secretion ofprogesterone by Day 200 Brahman CL of pregnancy when compared to LHor PGE2 stimulation of progesterone secretion by Day 14 CL of theestrous cycle; and 2) determine whether trichosanthin, an abortifacientcurcubit protein, inhibits luteal secretion of progesterone.

Materials and Methods

Eight nonbred Brahman cows on Day 14 of the estrous cycle and nineDay 200 pregnant Brahman cows were used. Corpora lutea were collectedduring June, 1995 by a flank laparotomy in a squeeze chute from cowsusing 2% lidocaine (The Butler Co., Columbus, Ohio) as a local anesthe-sia. Twelve slices from each CL were weighed, randomized to treatmentswithin each animal, minced and incubated at 39°C, pH 7.2 under 95%O2/5% CO2 in 3 mL of M-199 containing 25 mM Hepes buffer and Earle’ssalts (GIBCO, Grand Island, N.Y.) 0.1% bovine serum albumin (BSA)(Sigma Chemical Co., St. Louis, MO), 100 IU/mL penicillin G, 0.2 mg/mLstreptomycin sulfate (Sigma Chemical Co., St. Louis, MO), and 20 mg/mL25-hydroxy-cholesterol (Sigma Chemical Co., St. Louis, MO). Slices of CLaveraged 109 6 8 mg. Tissues were incubated for 1 h without treatmentsand for 4 and 8 h with treatments. Treatments were bovine LH (NIH-LH-B9; 10 or 100 ng/mL), PGE2-10 or 100 ng/mL (Cayman Chemical Co., AnnArbor, MI), 8-Epi-PGE1-10 or 100 ng/mL (Cayman Chemical Co., AnnArbor, MI), 8-Epi-PGE2 (Cayman Chemical Co., Ann Arbor, MI) tricho-


29Prostaglandins 1998:55, January

santhin-10 or 100 ng/mL (Academia Sinica, Beijing, China) or 4 mg/mLPSPB (R.G. Sasser). Media were collected at 4 and 8 h, acidified with 0.1mL of 0.1 N HCL per mL of medium, and medium with fresh treatmentswas replaced at 4 h. Media were stored frozen at 220°C until assay forprogesterone by RIA (39). Intraassay and interassay coeffiicients of vari-ation were 4.6 and 5.7%, respectively.

Data were anayzed for homogeneity of variance by Bartlett’s Box F test.Data for CL weights were analyzed by a completely randomized designfor a one way ANOVA. Data for progesterone were analyzed by a com-pletely randomized design for a factorial ANOVA. When differences weredetected, means were compared by a Student Newman Kuehl’s test (40).

Results

Weights of CL from Day 200 pregnant Brahman cows were heavier (p #0.05) than Day 14 CL of the estrous cycle of nonbred Brahman cows;however, secretion of progesterone in vitro by minced luteal slices be-tween the groups was similar per unit mass (p $ 0.05; Table 1).

There was a treatment 3 reproductive status 3 time interaction (p #0.05) on secretion of progesterone. Basal secretion of progesterone in vitroby Day 14 CL of the estrous cycle and Day 200 CL of pregnancy in theabsence of treatments was similar (p $ 0.05) at 4 h but lower (p # 0.05) at8 h, with Day 200 CL of pregnancy producing less progesterone (Figs. 1-6).Secretion of progesterone in vitro by Day 14 CL of the estrous cycle ofBrahman cows was increased by LH at 4 and 8 h (p # 0.05) by 10 or 100ng/mL LH and did not differ (p $ 0.05) between the doses of LH tested(Fig. 1). Progesterone secretion in vitro by Day 200 CL of pregnancy wasnot increased (p $ 0.05) by either dose of LH at 4 or 8 h and secretion ofprogesterone in vitro by Day 200 CL of pregnancy at 8 h was lower (p #0.05) than that secreted by Day 14 CL of the estrous cycle at 8 h in thecontrol nonpregnant group (Figs. 1–6).

Progesterone secretion in vitro by Day 14 CL of the estrous cycle wasincreased (p # 0.05) at 4 and 8 h by 10 or 100 ng/mL PGE2 and at 4 h by10 or 100 ng/mL PGE2 (p # 0.05) but only at 8 h by 100 ng/mL PGE2 byDay 200 CL of pregnancy (Fig. 2). Response to both doses of PGE2 by Day

TABLE 1.

ReproductiveStatus

No. ofCows

Weight of CorporaLutea1 (mg)

Progesterone1,2

(ng/ml/100 mg Tissue)

Nonpregnant-Day 14 8 3643 6 128a 438 6 80a

Pregnant-Day 200 9 4356 6 223b 433 6 74a

1Mean 6 SEM with different superscripts in columns are significant at p # 0.05.24 h incubation period.



14 CL of the estrous cycle at 4 and 8 h was similar (p $ 0.05) and similarto the response at 4 h by Day 200 CL of pregnancy (p $ 0.05; Fig. 2).Neither 8-Epi-PGE1 (Fig. 3) or 8-Epi-PGE2 (Fig. 4) affected (p $ 0.05)secretion of progesterone by Day 14 CL of the estrous cycle, or by Day 200CL of pregnancy when compared to their respective 4 or 8 h controls atthe doses tested.

Secretion of progesterone in vitro by Day 14 CL of the estrous cycle orDay 200 CL of pregnancy was increased (p # 0.05) by 10 ng/mL tricho-santhin at four h but not by 100 ng/mL at 4 h (Fig. 5). Trichosanthinincreased (p # 0.05) secretion of progesterone in vitro by Day 14 CL of theestrous cycle at 8 h by 10 ng/mL but not 100 ng/mL at 8 h and 10 or 100ng/mL trichosanthin did not affect (p . 0.05) secretion of progesterone invitro at 8 h by Day 200 CL of pregnancy (Fig. 5). Secretion of progesteronein vitro at 4 h was increased (p # 0.05) by 4mg/mL PSPB by Day 14 CL ofthe estrous cycle or Day 200 CL of pregnancy and at 8 h by Day 14 CL of

FIGURE 1. Secretion of progesterone in vitro by bovine corpora labstractutea from Day 14 of theestrous cycle or Day 200 of pregnancy treated with 0, 10, or 100 ng/mL bovine LH (NIHLH-B9).There was a reproductive status 3 treatment 3 time interaction (p # 0.05) means 6 SEM withdifferent superscripts are significant at p # 0.05.



the estrous cycle (p # 0.05), but not (p $ 0.05) by Day 200 CL of pregnancy(Fig. 6).

Discussion

Although weights of Day 200 CL of pregnancy were heavier than Day14 CL of the estrous cycle, secretion of progesterone per unit mass wassimilar. In sheep, weights and secretion of progesterone per unit mass ofDay 90 CL of pregnancy and Day 8 CL of the estrous cycle are similar (33).Progesterone in peripheral blood increases after midpregnancy in ewes(41) but not in cows (42). In sheep, the increases in peripheral progester-one after midpregnancy are from the placenta (18,19). In 90-day pregnantewes, half of the circulating progesterone is from the CL and the otherhalf is from the placenta to maintain pregnancy (39). The cow placentadoes not secrete progesterone when the CL is functional (6). In ewes, CLare not needed after Day 55 (18,19) or after Day 150 in cows to maintain

FIGURE 2. Secretion of progesterone in vitro by bovine corpora lutea from Day 14 of the estrouscycle or Day 200 of pregnancy treated with 0, 10, or 100 ng/mL PGE2. Therewas a significantreproductive status 3 treatment 3 time interaction (p # 0.05). Means 6 SEM with differentsuperscripts are significant at p # 0.05.



pregnancy (43). Embryonic or fetal wastage, which occurs throughoutgestation in ewes (44) and cows (45), is probably a result of loss of lutealprogesterone secretion first or its delivery locally from the adjacent ovaryto the uterus (46,47). This is probably more critical in cows than ewes,because the cow placenta does not secrete progesterone when the CL isfunctional (6).

Because Brahman CL are lighter than Hereford CL and are less respon-sive to LH-stimulated secretion of progesterone in vitro during the es-trous cycle (48), these data on CL weights on Day 14 of during theBrahman estrous cycle compared to Day 200 of pregnancy may suggestthat the Brahman cow CL increases in size during pregnancy to producesufficient progesterone for pregnancy maintenance. The bovine placentasecretes very little progesterone at this stage of gestation (6; Y. Weems,unpublished data). In other studies, weights of bovine CL have beenreported to be similar during the estrous cycle and pregnancy (49).

FIGURE 3. Secretion of progesterone in vitro by Day 14 bovine corpora lutea of the estrous cycleor Day 200 of regnancy treated with 0, 10, or 100 ng/mL 8-epi-PGE1. There was a treatment 3time interaction (p # 0.05) means 6 SEM with different superscripts are significant at p # 0.05.



Whether the increased weights of Day 200 Brahman CL of pregnancycompared to Day 14 Brahman CL of the estrous cycle is due to an increasein luteal cell numbers, luteal cell types, or to just hypertrophy of theluteal cells is unknown. The lighter weights of Brahman luteal tissue butnot secretion of progesterone per unit mass during the estrous cyclecompared to pregnancy of this tropically-adapted breed could be an ad-aptation to reduce heat stress because progesterone is thermogenic (50).

Because LH stimulated progesterone secretion in vitro by Day 14bovine CL of the estrous cycle but not by Day 200 bovine CL of pregnancyand PGE2 stimulated progesterone secretion in vitro by both Day 14 CLof the estrous cycle and Day 200 CL of pregnancy, these data indicate thatLH is not the luteotropin of the bovine CL of pregnancy and that PGE2 isa candidate luteotropin of pregnancy. The 10-ng dose of PGE2 used in thisexperiment is similar to the levels of PGE2 seen in ovarian venouseffluent of the luteal-bearing ovary of 90-day pregnant ewes (51). This is

FIGURE 4. Secretion of progesterone in vitro by Day 14 bovine corpora lutea of the estrous cycleor Day 200 of pregnancy treated with 0, 10, or 100 ng/mL 8-epi-PGE2. There was a reproductivestatus 3 treatment 3 time intereaction (p # 0.05) means 6 SEM with different superscripts aresignificant at p # 0.05.



supported further by data where secretion of progesterone in vitro bymidpregnant bovine CL in response to LH is reduced when compared tomature CL of the estrous cycle (11). In sheep, PGE1 or PGE2, but not LH,stimulates progesterone secretion in vitro by Day 90 CL of pregnancy(33). Further support for a switch from LH to PGE2 as a luteotropin duringpregnancy is the decrease in pituitary content of LH (12,13), the decreasein LH in jugular venous blood (13) and a decrease in pulse frequency andamplitude of LH from mid through late pregnancy compared to the lutealphase of the estrous cycle (14,15). The maternal pituitary, the source ofLH, is not necessary to maintain pregnancy after Day 50 of pregnancy insheep, while removal of the maternal pituitary before Day 50 of preg-nancy in sheep results in abortion (52). Moreover, exogenous PGF2a,which regresses Day 90 pregnant CL in vivo in sheep and which is notabortifacient, induces concomitant increases in PGF2a and PGE in uter-ine venous blood 64 h later (18,19,51).

FIGURE 5. Secretion of progesterone in vitro by Day 14 bovine corpora lutea of the estrous cycleor Day 200 of pregnancy treated with 0, 10, or 100 ng/mL trichosanthin. There was a repro-ductive status 3 treatment 3 time intereaction (p # 0.05) means 6 SEM different superscriptsare significant at p # 0.05.



PGE1 and PGE2 are luteotropic in vitro (17,33,36) and prevent luteoly-sis in vivo (18–29); however, 8-Epi-PGE1 or 8-Epi-PGE2, which are se-creted by Day 270 but not Day 200 bovine placenta in vitro along withPGE in response to PGE2 (53), did not affect secretion of progesterone byDay 14 CL of the estrous cycle or Day 200 CL of pregnancy. The reasonfor the reduced response to PGE2 at 8 h of incubation by Day 200 CL ofpregnancy but not by Day 14 CL of the estrous cycle (Y. Weems, unpub-lished data) may be related to interconversion of PGE2 to PGF2a by PGE2reductase (54). Changes in response to PGF2a by bovine luteal suspen-sions in vitro are well known (36). Secretion of progesterone in vitro bybovine luteal syspensions in response to PGF2a first increases followedlater by a decline in progesterone secretion (36), whereas PGF2a in vivo incows decreases progesterone secretion (55).

PSPB could also be a pregnancy luteotropin, because PSPB increasedsecretion of progesterone in vitro by both Day 14 bovine CL of the estrouscycle and Day 200 CL of pregnancy. PSPB is secreted by embryos at the

FIGURE 6. Secretion of progesterone in vitro by Day 14 bovine corpora lutea of the estrous cycleor Day 200 of pregnancy treated with 4mg/mL PSPB. There was a treatment 3 time interaction(p # 0.05) means 6 SEM with different superscripts are significant at p # 0.05.



time of maternal recognition of pregnancy (30,56) and increases in bloodas gestation progresses (30). Furthermore, PSPB stimulates secretion ofPGE in vitro by bovine CL of the estrous cycle (31,32) or Day 90 CL ofpregnancy in sheep (33). PSPB may also act on the endometrium orplacenta to produce PGE2 as a luteotropin for local delivery to the adja-cent luteal-bearing ovary. Concomitant increases in PSPB (57), PGF2a (51)and PGE (51) in uterine venous blood in vivo are seen 64 h after treatmentof 90–100 day pregnant ewes with PGF2a followed by increases in pla-cental secretion of progesterone (39). PGF2a causes luteolysis but doesnot abort the ewes (33). PSPB stimulates secretion of PGE in vitro bybovine endometrium from nonpregnant cows on Day 16 postestrus(34,35). PSPB may be responsible for developmental changes in the rumi-nant placenta or CL of pregnancy to produce PGE because the pituitary isno longer needed after Day 50 of pregnancy in sheep (52). Concentrationsof PGE in uterine venous blood of 90-day pregnant ewes and in ovarianvenous blood 72 h after hysterectomy of 90-day pregnant ewes are similar(51). Placental secretion of PSPB may be regulated by estradiol-17b(57,58,59) and both PSPB (30) and estradiol-17b (42) increase as gestationprogresses in cattle.

Trichosanthin, an abortifacient in rats and humans (8), did not inhibitbut enhanced luteal secretion of progesterone by Day 14 CL of the estrouscycle or Day 200 CL of pregnancy at the doses and times of incubationtested. How trichosanthin could increase progesterone secretion is un-known; however, it is suggested that trichosanthin may be affectingprostanoid secretion by luteal tissue. In vitro incubation of dispersedbovine luteal cells with PGF2a increases progesterone secretion followedby a decrease in secretion of progesterone (36). Alternatively, trichosan-thin could stimulate luteal secretion of PGE2.

In summary, PGE2 but not LH stimulated secretion of progesterone invitro by Day 200 bovine CL of pregnancy indicating a shift in luteotropicsupport for the bovine CL of pregnancy. In addition, PSPB may also be aluteotropin during pregnancy for bovine CL.

Acknowledgments

This paper is Journal Series No. 4301 of the Hawaii Institute of TropicalAgriculture and Human Resources. This research was supported in partby the USDA under CSREES Special Grant No. 95–34135-1776, to C.Weems managed by the Pacific Basin Advisory Group, USDA HatchProject 259 (C.W.W.), Hatch Project 3128 (R.D.R.) and Hatch ProjectR-876 (G.R.S.) as Hawaii’s, Texas’ and Idaho’s contribution to USDAW-112 Regional Research Project. The authors thank the NIH NationalPituitary Hormone Program for purified bovine LH used in these exper-iments; Mr. Andy Lewis, Texas A & M University for technical assis-



tance; Mr. Wayne Toma (U.H.) for assistance with statistical analysis andgraphics; and Ms. Sharleen Fujimoto (U.H.) for typing the manuscript

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Editor: Dr. P.W. Ramwell Received: 06–27-97 Accepted: 10–20-97



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Effect of Luteinizing Hormone (LH), PGE2, 8-EPI-PGE1, 8-EPI-PGE2, Trichosanthin, and Pregnancy...

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