Use of Prostaglandin F2 for Controlling the Mare's Estrous Cycle

Home , Luteolysis, Prostaglandin, Prostaglandin F2alpha

IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY

Use of Prostaglandin F2␣ for Controlling the Mare’s Estrous Cycle

Carlos R.F. Pinto, MedVet, PhD, Diplomate ACT

Author’s address: Theriogenology and Reproductive Medicine, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210; e-mail: [email protected]. © 2013 AAEP.

1. Introduction minutes; elimination half-life of 25.9 Ϯ 5.0 minutes; Prostaglandins belong to a group of modified long- and maximum plasma PGF concentration of 249.1 Ϯ 1 chain fatty acids containing 20 carbons called 36.8 ng/mL. The original studies pointed out that eicosanoids. The cyclooxygenase pathway uses mares appeared to be more sensitive to exogenous prostaglandin synthases to convert arachidonic acid PGF than cows. Indeed, an in vitro study has into prostaglandins. Arachidonic acid is available shown the affinity of equine luteal cell membrane through the hydrolysis of phospholipids present in preparations for PGF to be approximately 10 times the cell membrane. The breakdown of membrane greater than that for bovine luteal cell membrane 2 phopholipids is catalyzed by the enzyme phospho- preparations. The relatively high affinity of mare lipase A. Two isoforms of prostaglandin synthase corpus luteum (CL) to binding of PGF along with the exist: constitutive (cyclooxygenase-1) and induc- relatively slow metabolic clearance documented in ible (cyclooxygenase-2). Systemic administration mares account for the greater sensitivity of mare CL of prostaglandins (mainly prostaglandin F2␣ [PGF] to the luteolytic effect of PGF when compared with in animals) is associated with side effects affecting other domestic species. the central nervous system (incoordination, stupor, The luteal phase of the equine estrous cycle can be and ataxia) and the vascular system (contraction of reliably shortened by the administration of PGF, smooth muscle of organs such as the stomach, intes- allowing mares to return to estrus at a relatively tines, and urinary bladder). predictable time (on average 2–5 days after PGF The use of injectable preparations of PGF has administration). In horses, a single treatment with revolutionized the breeding management of horses PGF (intramuscular or subcutaneous) will induce and cattle since its identification as the main luteo- complete luteolysis if administered at least 5 to 6 lytic hormone. Pharmacokinetics of PGF after in- days after ovulation. This fact led to the prevailing travenous administration of 5 mg per mare (large assumption that the CL is not responsive to PGF mixed breeds of large ponies) has been recently de- luteolytic effects before it is at least 5 days old, scribed as follows: apparent plasma clearance, despite the fact that some initial studies reported 3.3 Ϯ 0.5 L/h/kg; distribution half-life of 1.57 Ϯ 0.26 that some mares were responsive to luteolytic effect

NOTES

AAEP PROCEEDINGS ր Vol. 59 ր 2013 337 IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY of PGF administration when treated on day 3 after pected when at least 5 days have elapsed from ovu- ovulation. In the United States, the natural ana- lation. Anecdotally, some equine practitioners logue dinoprost tromethaminea is the only Food report that whenever the day of ovulation is un- and Drug Administration–approved PGF for use in known, daily treatments of PGF are prescribed until horses, although equine practitioners commonly use treated mares show signs of behavioral estrus. the synthetic analogue cloprostenol in breeding management, mostly owing to the longer half-life 3. Luteolytic Doses of PGF Preparations than its natural analogue. A review of the effects of PGF on luteal function and characteristics of the Dinoprost Tromethamine induced estrus and ovulation is presented in the For PGF tromethamine salt (PGF tham salt) prep- subsequent sections. The use of PGF as an aborti- arations, 1.34 mg of the salt equals 1 mg of free acid facient and ecbolic for breeding management will PGF. Douglas and Ginther3 reported that doses of not be presented. 1.25, 2.5, 5.0, and 10.0 mg of PGF administered intramuscularly shortened the luteal phase of the 2. Effects of PGF Administration on the Mare’s estrous cycle. Mares in all treatment groups were Reproductive Cycle in estrus 3 to 4 days after treatment. A single bolus Natural luteolysis begins approximately 14 days af- dose of 1.25 mg of dinoprost tromethaminea per ter ovulation in mares. In the decade of the 1970s, horse mare (ϳ2.8 ␮g/kg for an average 450-kg mare) several studies investigated the effects of PGF treat- when administered between days 6 and 12 after ment on blood progesterone concentration profile ovulation has been shown to be luteolytic and induce and effects of the length of diestrus and interovula- normal ovulatory estrus periods, which in turn were tory intervals.3–5 Most of these studies were based followed by normal luteal function (diestrus).8 on examinations of serial blood samples taken before Even doses as low as 0.5 mg per mare (ϳ1.1 ␮g/kg) and after treatment with PGF or on the recording has been shown to affect luteal function; however, of the length of interovulatory intervals in treated complete luteolysis (21/21 mares) was only achieved and control mares. Studies on subsequent PGF- when mares were treated twice, 24 hours apart.9 induced estrus, follicular dynamics, and ovulation In that study, this low dose did not induce common were based mainly on findings of serial reproductive side effects (sweating, colicky behavior) generally examinations by palpation per rectum. More re- associated with PGF treatment. Most commercial cently, a significant wealth of information on the preparations of dinoprost tromethamine, however, characteristics of luteal development and regres- recommend a single intramuscular or subcutaneous ϳ sion, follicle growth, and ovulation after PGF-in- bolus administration of 5 to 10 mg per mare ( 11.1– duced luteolysis became available with the advent 22.2 ␮g/kg). of transrectal ultrasonography. The information gained with ultrasonography studies on mare repro- Cloprostenol duction contributed to the understanding of PGF In contrary to several other countries, cloprostenol actions on the mare’s reproductive cycle and tract.6,7 formulations are not Food and Drug Administra- Soon after PGF was shown to be the uterine lu- tion–approved for use in horses in the United States. teolysin in cattle, sheep, and rats, Douglas and Nevertheless, cloprostenol is widely used in the Ginther3 published convincing evidence that exoge- United States by equine practitioners because of nous (subcutaneous or intramuscular) or intrauter- the longer half-life and association with fewer side ine administration of PGF had also luteolytic effects effects than dinoprost tromethamine. Cloprostenol in mares. Since then, PGF and its synthetic ana- is available as two optically active isomers (enan- logues have been widely used for intensive brood- tiomers), combined, d-cloprostenol and l-clopros- mare management.7 In the study by Douglas and tenol. The recommended luteolytic doses of these Ginther,4 mares received PGF on day 6 after ovula- synthetic analogues are much lower than that rec- tion. Previous studies demonstrated that intra- ommended for the natural analogue dinoprost tro- uterine saline solution infusions 6 days after methamine. Luteolytic doses for d-cloprostenol are ovulation shortened the mare’s estrous cycle. The further lower than that needed for d,l-cloprostenol– shortened cycle was denoted by luteal activity inter- induced luteolysis.10 The dosage difference be- ruption that terminated diestrus.4 In that study, tween these two cloprostenol analogues is explained all mares treated with 1.25, 2.5, 5.0, or 10.0 mg of by the fact that only the d-enantiomer is pharmaco- PGF (intramuscular) had shorter diestrus and logically active (luteolytic). Most popular prepara- shorter interovulatory intervals than did control tions of cloprostenol in the United States use the mares (not treated with PGF). After that report, racemic mixtureb (d- and l-enantiomers) at a dose of several other studies confirmed that PGF treat- 250 to 500 ␮g per mare. In one study, doses as low ments not only shorten diestrus but also shorten as 25 ␮g of d,l-cloprostenol per mare successfully interovulatory intervals. Despite the fact some induced luteolysis.11 In several countries, the more mares may undergo complete luteolysis when potent preparations with only the active d-clopros- treated on day 3 after ovulation, maximal response tenol enantiomerc are also available and labeled for to one single-bolus intramuscular injection is ex- use in horses. In a recent report, the bolus dose of

338 2013 ր Vol. 59 ր AAEP PROCEEDINGS IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY 37.5 ␮g of d-cloprostenolc induced complete luteolysis, luteolysis was preceded by a transient increase in similar to that in mares receiving 250 ␮g of a d,l- progesterone, estradiol, and leuteinizing hormone at cloprostenol preparation.12 The recommended la- 10, 30, and 60 minutes after PGF treatment of di- beled doses for d-cloprostenol and d,l-cloprostenol estrual mares. In a more recent study by Ginther are 37.5 ␮g per mare (0.5-mL injection volume) and et al,18 administration of a single luteolytic intrave- 250 ␮g (1-mL injection volume), respectively, admin- nous bolus of PGF resulted in an immediate increase istered subcutaneously or intramuscularly. in circulating progesterone concentrations within 10 minutes after the bolus injection, accompanied by an 4. Luteolytic Effects of PGF and Stage of the Estrous increase in concentrations of follicle-stimulating Cycle hormone, leuteinizing hormone, and cortisol. Con- The results presented in the early studies in the versely, mares infused with PGF for 2 hours, mim- 1970s provided the basis for the assumption that icking a natural pulse of endogenous PGF action, did PGF formulations would not induce luteolysis or not show increases in the same hormones; however, affect CL function if administered before day 5 or 6 both treatments, bolus injection and infusion, re- after ovulation. Interestingly, some of these stud- sulted in similar luteolytic effects. These effects on ies reported that some mares actually responded to steroids and gonadotropin secretion associated with PGF-induced luteolysis when treated on day 3 after supraphysiologic doses of PGF may partially explain ovulation3; however, the notion that the early CL the results of one study that found that mares was not responsive to PGF administration remained treated in estrus with a synthetic PGF, fenpros- ingrained in the scientific and veterinary profes- talene, had shorter estrus-to-ovulation intervals sional community. In 1974, Thompson and With- than did control mares.19 erspoon13 briefly reported another phenomenon that has recently gained attention: the ability of PGF to 6. PGF Treatment and Antiluteogenesis induce partial luteolysis followed by resurgence in Recently, it has been reported that luteolysis or pre- CL function characterized by a transient increase vention of luteal formation may be accomplished in concentrations of blood progesterone. In that with PGF administration beginning as early as the study, two mares receiving a relatively low dose of a day ovulation is detected. This effect is dependent synthetic PGF analogue 9 days after ovulation be- on the dose and frequency of PGF treatments. gan to have a decrease in concentrations of plasma On the basis that the early developing CL Ͻ5 days is progesterone at 12 hours after PGF treatment, fol- actually responsive to luteolytic effects of PGF, a lowed by a resurgence in progesterone concentra- series of experiments conducted in our laboratory tions at 48 hours after treatment; progesterone produced data that support the hypothesis that the concentrations then remained at 30% to 50% of that early developing CL is indeed responsive to exoge- before PGF treatment. More recently, 32 years nous PGF as early as within the first 24 hours from from that initial report, Bergfelt et al14 (2006) com- ovulation.20,21 Because of this early luteolytic re- pared the pattern of luteolysis after PGF treatment sponsiveness to PGF administration before the CL is as a single bolus injection on day 3 after ovulation fully functional, we named this phenomenon as with that of mares treated on day 10. In the day 3 (PGF-induced) “antiluteogenesis.” Mares treated group, 75% (12/16) of mares had CL resurgence. once or twice daily for 3 days with 2.5 or 10 mg of Among those, six mares with “minor” progesterone PGF dinoprost failed to show a significant rise in resurgence had treatment-to-ovulation intervals concentrations of plasma progesterone during the similar to that in control mares. In summary, CL treatment period. Approximately 60% of mares resurgence after PGF treatment results in partial treated twice daily for 3 days with 10 mg of PGF luteolysis of the CL. Partial luteolysis is evident by had complete luteolysis; all mares receiving once- decreasing concentrations of blood progesterone and daily 2.5 mg of PGF for 3 days showed CL resur- followed by CL function resurgence. The resurgence. Therefore, the antiluteogenesis effect of gence is denoted by a moderate increase in proges- PGF is dependent on the dose and frequency of PGF terone concentrations. Partial luteolysis followed treatments. by CL resurgence may occur after administration of sub-luteolytic boluses doses of PGF during mid di- 7. Clinical Applications of PGF in Broodmare estrus,13,15,16 or after administration of single injec- Management tions at day 3 after ovulation.14 Use of PGF to Induce Luteolysis and Return to 5. Effects of Exogenous PGF on Steroid and Estrus Gonadotropin Secretion Termination of the luteal phase (“short-cycling”) Administration of PGF in mares with a functional with exogenous PGF may be attempted for planned CL Ͼ5 days is followed by functional luteolysis (sig- breeding of a single mare or as an approach to syn- nificant decrease in progesterone) 24 hours after chronize estrus and ovulation in a group of mares. treatment that is, however, preceded by an immedi- If reproductive examinations with palpation per ate, transient rise in progesterone shortly after PGF rectum and transrectal ultrasonography are avail- treatment. Noden et al17 reported that functional able, the predictability of onset of estrus and ovula-

AAEP PROCEEDINGS ր Vol. 59 ր 2013 339 IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY tion increases. Prediction of the next ovulation in express their endogenous luteolytic mechanism the PGF-induced estrus is not predictable as it is the (rare), or, more commonly, in mares that have early return to estrus. For example, it has been shown embryonic loss after maternal recognition takes that the diameter of follicles present in the ovaries place. In general, prolonged diestrus is often asso- at the time of PGF treatment may influence when ciated with another unique phenomenon of the the mare would ovulate.22 When a relatively large mare’s estrous cycle, the diestrus ovulation. Pro- follicle (Ն35 mm) is present at the time of PGF longed diestrus is diagnosed as a diestrus period administration, the onset of estrus and ovulation lasting more than 16 days after ovulation. A single will depend on the follicular status (growing phase luteolytic dose of PGF (5–10 mg dinoprost) should versus undergoing atresia). Accordingly, mares induce mares to return to estrus. with follicles approaching the diameter of preovula- tory follicles may come in estrus and ovulate within Use of PGF in Estrus Synchronization 2 to 5 days after PGF treatment, whereas the mean One of the most basic methods to attempt estrus interval from treatment to ovulation in mares dur- synchronization is to treat mares with PGF and ing mid diestrus and with follicles Ͻ25 mm may repeat the treatment approximately 2 weeks from vary from 7 to 12 days from treatment.22 For ex- the first injection. If teasing is available, mares ample, in some extreme instances, mares will ovu- can then be teased every other day beginning 2 days late in 2 to 3 days; mares ovulating within 48 hours after PGF treatment. The efficacy of the use of from PGF treatment often show no signs of behav- PGF in estrus synchronization programs is greatly ioral estrus. Conversely, large follicles present at enhanced with the concomitant use of progestagens the time of PGF treatment may be already undergo- and estrogens. ing atresia and will slowly regress, and the mare may not ovulate until 10 to 14 days after the treat- 8. Non-Reproductive Effects Associated With PGF ment. In most cases, however, mares will come Administration into estrus and the large follicles at the time of PGF In general, prostaglandins have significant effects treatment will continue to grow and ovulate within on vascular and non-vascular smooth muscle, the 4 to 6 days after PGF treatment. central nervous system, and carbohydrate and lipid Obviously, the prediction of PGF-induced estrual metabolism.23 The administration of exogenous events requires that treated mares have an active PGF is relatively safe, and doses 20 to 40 times corpus luteum at the time of administration. If greater than the therapeutic dose (typically 5–10 mg reproductive examination is not available, horse of dinoprost) do not elicit toxic effects.24 Even owners may be instructed to administer a single doses up to 800 mg were not fatal to mares despite dose of PGF 5 days after the mare ceases behavioral being associated with intense side effects such as signs of estrus, or, alternatively, if teasing is not recumbency; in that study, severe side effects sub- feasible, daily administration of a single PGF treat- sided by 4 to 5 hours after PGF overdose treatment. ment may be prescribed until the mare shows signs This increased sensitivity is also reflected by the of estrus or a reproductive examination by a veteri- appearance of side effects after administration of narian becomes available. Another alternative if a conventional luteolytic dose in mares in 20% to veterinary assistance, or teasing information were 40% of mares treated with PGF. Sweating, restless not available, would be to recommend administra- behavior, diarrhea, or even colic-like signs are tion of a single dose of PGF at any given day and to commonly observed in mares but not in cattle. repeat it in 5 days if the mare is not observed to be One of the most common side effects is a pronounced in estrus. sweating seen within minutes after PGF administration. The results of most research studies indi- Use of PGF in Postpartum Mares cate that equine sweating occurs by stimulation of Several factors associated with complications during adrenoreceptors on the sweat gland cells.25 Adren- foaling could compromise the fertility of the mare’s aline-induced sweating is primarily mediated by ␤2 foal heat. For most mares with dystocia or reten- adrenoreceptors. Horses given PGF intramuscu- tion of the fetal membranes, it may be prudent to not larly sweat but do not shiver, although shivering breed on the first estrus after parturition (foal heat). occurs in horses treated with adrenaline. This may In this scenario, instead of having horse owners explain why rectal temperature significantly waiting for mares to come into their second postpar- decreased in horses after PGF administration.24 tum estrus (“30-day heat”), one strategy would be to Because concentrations of plasma adrenaline and treat mares with PGF approximately 5 to 7 days noradrenaline become elevated after administration after ovulation in the foal heat. of PGF, it has been accepted that PGF-related sweating is associated with release of adrenaline Use of PGF in Mares With Prolonged Luteal from the adrenal medulla. Some mares may also Phases have abdominal discomfort resembling colic-like Occasionally, mares may have prolonged diestrus symptoms. Abdominal discomfort is a result of periods because of the presence of a persistent CL. hypergastromotility. Occasionally, some mares Persistent CLs may occur in mares that failed to also show locomotor incoordination and ataxia.

340 2013 ր Vol. 59 ր AAEP PROCEEDINGS IN-DEPTH: REPRODUCTIVE ENDOCRINOLOGY These side effects typically subside within 20 to 30 ing luteolysis without adverse side effects in mares. Equine minutes after PGF treatment. The appearance and Vet J 2002;34:191–194. 10. Beretta C, Cavalli M. A sheer pharmacologic approach to duration of these aforementioned side effects appear compare the contractile effects of PGF2alpha, DL-clopros- to vary among mares. It is important to note that tenol and D-cloprostenol on isolated uterine, tracheal, ileal these side effects are dose-dependent and typically and arterial smooth muscle preparations. Theriogenology subside within the first hour after PGF treatment. 2004;62:837–846. Irvine et al9 reported that the administration of two 11. Nie GJ, Goodin AN, Braden TD, et al. Luteal and clinical response following administration of dinoprost tromethamine low doses of PGF 24 hours apart did not elicit any or cloprostenol at standard intramuscular sites or at the appreciable side effects, including elevation in heart lumbosacral acupuncture point in mares. Am J Vet Res rate. 2001;62:1285–1289. 12. Cuervo-Arango J, Newcombe JR. Relationship between 9. Conclusions dose of cloprostenol and age of corpus luteum on the luteolytic response of early dioestrous mares: a field study. Reprod Manipulation of the mare’s estrous cycle with PGF Domest Anim 2012;47:660–665. is an important strategy in the breeding of mares. 13. Thompson FN, Witherspoon DM. Induction of luteolysis in the mare with a prostaglandin analogue. Theriogenology The CL is sensitive to PGF treatment throughout 1974;2:115–119. the whole estrous cycle. A single bolus injection of 14. Bergfelt DR, Pierson RA, Ginther OJ. Regression and re- PGF can reliably induce luteolysis when adminis- surgence of the CL following PGF2alpha treatment 3 days tered in mares with a CL Ͼ5 days. Serial injections after ovulation in mares. Theriogenology 2006;65:1605– of PGF for several days beginning (q 12 h or q 24 h) 1619. 15. Witherspoon DM, Lamond DR, Thompson FN, et al. Effi- as early as within 24 hours from ovulation will pre- cacy of a prostaglandin analogue in reproduction in the cy- vent CL formation (antiluteogenesis), as evidenced cling mare. Theriogenology 1975;3:21–30. by the absence of a rise in progesterone. Not only 16. Kiefer BL, Roser JF, Evans JW, et al. Progesterone pat- diestrus is shortened in mares treated with PGF but terns observed with multiple injections of a PGF-2 alpha analogue in the cyclic mare. J Reprod Fertil Suppl 1979;27: interovulatory intervals are also reduced in relation 237–244. to normal, untreated cycles. Estrus and ovulation 17. Noden PA, Oxender WD, Hafs HD. Early changes in serum occurring after PGF treatments are normal and the progesterone, estradiol and LH during prostaglandin inherent fertility of mares treated is not affected. F2alpha-induced luteolysis in mares. J Anim Sci 1978;47: 666–671. 18. Ginther OJ, Siddiqui MA, Beg MA. Physiologic and non- References and Footnotes physiologic effects of exogenous prostaglandin F2alpha on 1. Shrestha HK, Beg MA, Burnette RR, et al. Plasma clearance reproductive hormones in mares. Theriogenology 2009;72: and half-life of prostaglandin F2alpha: a comparison be- 417–424. tween mares and heifers. Biol Reprod 2012;87:18,1–6. 19. Savage NC, Liptrap RM. Induction of ovulation in cyclic 2. Kimball FA, Wyngarden LJ. Prostaglandin F2alpha specific mares by administration of a synthetic prostaglandin, fen- binding in equine corpora lutea. Prostaglandins 1977;13: prostalene, during oestrus. J Reprod Fertil Suppl 1987;35: 553–564. 239–243. 3. Douglas RH, Ginther OJ. Effect of prostaglandin F2alpha 20. Rubio C, Pinto CR, Holland BE, et al. Anti-luteogenic and on length of diestrus in mares. Prostaglandins 1972;2:265– luteolytic effects of PGF2a during the post-ovulatory period in 268. mares. Theriogenology 2008;70:58. 4. Oxender WD, Noden PA, Louis TM, et al. A review of pros- 21. Holland BE, Pinto CRF. Luteal function and ovulation in taglandin F2alpha for ovulation control in cows and mares. mares treated with PGF2␣ during early and mid-di- Am J Vet Res 1974;35:997–1001. estrus. Reprod Domest Anim 2008;43:111. 5. Oxender WD, Noden PA, Hafs HD. Oestrus, ovulation 22. Samper JC. Induction of estrus and ovulation: why some and plasma hormones after prostaglandin F2alpha in mares. mares respond and others do not. Theriogenology 2008;70: J Reprod Fertil Suppl 1975;23:251–255. 445–447. 6. Gastal EL, Bergfelt DR, Nogueira GP, et al. Role of lutein- 23. Smith ER, Mason MM. Toxicology of the prostaglandins. izing hormone in follicle deviation based on manipulating Prostaglandins 1974;7:247–268. progesterone concentrations in mares. Biol Reprod 1999;61: 24. Goyings LS, Lauderdale JW, McConnell RF. Pharmacologic 1492–1498. and toxicologic study of prostaglandin F2alpha in mares. 7. Goretti RG, Arau´ jo RR, Filho AN, et al. Effects of timing of Am J Vet Res 1977;38:1445–1452. induced luteolysis in embryo donor mares on reproductive 25. Jenkinson DM, Elder HY, Bovell DL. Equine sweating and performance and pregnancy rate in recipient mares. Ther- anhidrosis, part 1: equine sweating. Vet Dermatol 2006;17: iogenology 2011;75:1170–1174. 361–392. 8. Barker C, Echeverria, Davis M, et al. Effects of different a doses of PGF2␣ on luteal function and on the subsequent Lutalyse, Pfizer Animal Health, Kalamazoo, MI 49001. estrous cycle. Anim Reprod Sci 2006;94:207–209. bEstrumate, Merck Animal Health, Summit, NJ 07901. 9. Irvine CH, McKeough VL, Turner JE, et al. Effectiveness of cGenestran, FORTE Healthcare Limited; Naul, Dublin, Repub- a two-dose regimen of prostaglandin administration in induc- lic of Ireland.

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