Initiierung und endokrine Kontrolle der Geburt bei Haussäugetieren – Teil 2

Zusammenfassung

Der endokrinen Kontrolle der Geburt liegt ein intensiver Signalaustausch zwischen Fetus, Plazenta und Mutter zugrunde. Abgesehen vom Schaf ist unser Wissen über die dabei zugrunde liegenden Prozesse immer noch sehr lückenhaft. Bisherige Beobachtungen lassen jedoch erhebliche Speziesunterschiede erkennen. Von entscheidender Bedeutung für den Eintritt der finalen, zur Austreibungsphase führenden Schritte der Signalkaskade ist der „präpartale Progesteronentzug“, der in Anhängigkeit von der relevanten Gestagenquelle in der Spätgravidität auf einer Luteolyse (z. B. Rind, Ziege, Büffel, Kameliden, Schwein) oder einem Zusammenbruch der plazentaren Gestagenproduktion (Schaf, Pferd) beruht. Das Wissen über die geburtsassoziierten Regelvorgänge ermöglicht es, für eine medikamentöse Geburtseinleitung speziesspezifische Regelmechanismen zu imitieren. Darüber hinaus stehen speziesunabhängige Wirkprinzipien wie die Blockade von Progesteronrezeptoren zur Verfügung. Neben der Wirksamkeit müssen unter Praxisbedingungen bei der Auswahl von Wirkstoffen weitere Aspekte wie die Verträglichkeit für Muttertier und Nachkommen sowie arzneimittelrechtliche Vorschriften berücksichtigt werden.

Abstract

The endocrine regulation of birth is based on an intensive exchange of signals between fetus, placenta and mother. Apart from sheep, our knowledge of the underlying processes is still very incomplete. However, current observations suggest substantial species differences. Of critical importance for the onset of the final steps of the signaling cascade leading to active labor is "prepartum progesterone withdrawal," which is based on luteolysis (e. g., cattle, goat, buffalo, camelids, pig) or a breakdown in placental progestogen production (sheep, horse), depending on the relevant progestogen source in late pregnancy. Knowledge of birth-associated regulatory processes allows species-specific regulatory mechanisms to be mimicked for drug-based induction of labor. Furthermore, species-independent mechanisms such as the inhibition of progesterone receptors are available. In addition to efficacy, other aspects such as tolerability for dams and offspring as well as drug regulations must be taken into account when selecting active ingredients under practical conditions.

Schlüsselwörter

Geburtsinduktion - Wiederkäuer - Pferd - Schwein - Kameliden - Hund

Key words

Induction of parturition - ruminants - horse - pig - camelids - dog

Publication History

Received: 13 April 2023

Accepted: 21 June 2023

Article published online:
30 October 2023

• Literatur

• 1 Whittle WL, Patel FA, Alfaidy N. et al. Glucocorticoid regulation of human and ovine parturition: the relationship between fetal hypothalamic-pituitary-adrenal axis activation and intrauterine prostaglandin production. Biol Reprod 2001; 64: 1019-1032 doi: 10.1095/biolreprod64.4.1019
• 2 Schuler G. Initiierung und endokrine Kontrolle der Geburt bei Haussäugetieren – Teil 1: Vergleichende Übersicht über Regelmechanismen und beteiligte Faktoren. Tierärztliche Praxis 2023; 51: 228-236
• 3 Kirkden RD, Broom DM, Andersen IL. Piglet mortality: the impact of induction of farrowing using prostaglandins and oxytocin. Anim Reprod Sci 2013; 138: 14-24 doi: 10.1016/j.anireprosci.2013.02.009
• 4 Monteiro MS, Muro BBD, Poor AP. et al. Effects of farrowing induction with prostaglandins on farrowing traits and piglet performance: A systematic review and meta-analysis. Theriogenology 2022; 180: 1-16 10.1016/j.theriogenology.2021.12.010
• 5 Veterinary Council of New Zealand: Statement: Induction of Calving in Cattle. Im Internet: https://vetcouncil.org.nz/common/Uploaded files/Web/Publications/Cattle induction.pdf Stand: 09.05.2023.
• 6 Aurich JE, Aurich C. Geburtseinleitung bei Haustieren. Prakt Tierarzt 75: 742-750
• 7 Fowden AL, Silver M. Effects of inhibiting 3 beta-hydroxysteroid dehydrogenase on plasma progesterone and other steroids in the pregnant mare near term. J Reprod Fertil Suppl 1987; 35: 539-545
• 8 Keister DM, Gutheil RF, Kaiser LD. et al. Efficacy of oral epostane administration to terminate pregnancy in mated laboratory bitches. J Reprod Fertil Suppl 1989; 39: 241-249
• 9 Jenkin G, Thorburn GD. Inhibition of progesterone secretion by a 3β-hydroxysteroid dehydrogenase inhibitor in late pregnant sheep. Can J Physiol Pharmacol 2011; 63: 136-142 10.1139/y85-024
• 10 Gogny A, Fiéni F. Aglepristone: A review on its clinical use in animals. Theriogenology 2016; 85: 555-566 10.1016/j.theriogenology.2015.10.010
• 11 Kowalewski MP, Pereira MT, Papa P. et al. Progesterone receptor blockers: historical perspective, mode of function and insights into clinical and scientific applications. Tierarztl Prax Ausg K Kleintiere Heimtiere 2020; 48: 433-440 doi: 10.1055/a-1274-9290
• 12 Liggins GC. Premature delivery of foetal lambs infused with glucocorticoids. J Endocrinol 1969; 45: 515-523 10.1677/joe.0.0450515
• 13 Bayard F, Louvet JP, Ruckebusch Y. et al. Transplacental passage of dexamethasone in sheep. J Endocrinol 1972; 54: 349-350 doi: 10.1677/joe.0.0540349
• 14 van Runnard Heimel PJ, Franx A, Schobben AF. et al. Corticosteroids, pregnancy, and HELLP syndrome: a review. Obstet Gynecol Surv 2005; 60: 57-70 doi: 10.1097/01.ogx.0000150346.42901.07. PMID: 15618920
• 15 Rigby S, Love C, Carpenter K. et al. Use of prostaglandin E2 to ripen the cervix of the mare prior to induction of parturition. Theriogenology 1998; 50: 897-904 doi: 10.1016/s0093-691x(98)00194-0
• 16 Rudloff PR, Bostedt H. Einfluss des Betablockers Carazolol (Suacron) auf die Sauengeburt. Tierärztl Prax 1984; 12: 443-449
• 17 Liggins GC. The role of the hypothalamic-pituitary-adrenal axis in preparing the fetus for birth. Am J Obstet Gynecol 2000; 182: 475-477 doi: 10.1016/s0002-9378(00)70241-9
• 18 Challis JR, Dilley SR, Robinson JS. et al. Prostaglandins in the circulation of the fetal lamb. Prostaglandins 1976; 11: 1041-1152 doi: 10.1016/0090-6980(76)90011-3
• 19 Gyomorey S, Gupta S, Lye SJ. et al. Temporal expression of prostaglandin H synthase type 2 (PGHS-2) and P450(C17) in ovine placentomes with the natural onset of labour. Placenta 2000; 21: 478-486 doi: 10.1053/plac.1999.0503. PMID: 10940197
• 20 Whittle WL, Holloway AC, Lye SJ. et al. Prostaglandin production at the onset of ovine parturition is regulated by both estrogen-independent and estrogen-dependent pathways. Endocrinology 2000; 141: 3783-3791 doi: 10.1210/endo.141.10.7703
• 21 Mason JI, France JT, Magness RR. et al. Ovine placental steroid 17 alpha-hydroxylase/C-17,20-lyase, aromatase and sulphatase in dexamethasone-induced and natural parturition. J Endocrinol 1989; 122: 351-359 doi: 10.1677/joe.0.1220351
• 22 Schuler G, Fürbass R, Klisch K. Placental contribution to the endocrinology of gestation and parturition. Anim Reprod 2018; 15: 822-842 doi: 10.21451/1984-3143-AR2018-0015
• 23 Shenavai S, Preissing S, Hoffmann B. et al. Investigations into the mechanisms controlling parturition in cattle. Reproduction 2012; 144: 279-292 doi: 10.1530/REP-11-0471
• 24 Schuler G, Teichmann U, Kowalewski MP. et al. Expression of cyclooxygenase-II (COX-II) and 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD)/prostaglandin F-synthase (PGFS) in bovine placentomes: implications for the initiation of parturition in cattle. Placenta 2006; 27: 1022-1029 doi: 10.1016/j.placenta.2005.11.001
• 25 Schuler G, Özalp GR, Hoffmann B. et al. Reciprocal expression of 17alpha-hydroxylase-C17,20-lyase and aromatase cytochrome P450 during bovine trophoblast differentiation: a two-cell system drives placental oestrogen synthesis. Reproduction 2006; 131: 669-679 doi: 10.1530/rep.1.01033
• 26 Hoffmann B, Wagner WC, Hixon JE. et al. Observations concerning the functional status of the corpus luteum and the placenta around parturition in the cow. Anim Reprod Sci 1979; 2: 253-266 doi: 10.1016/0378-4320(79)90051-4
• 27 Currie WB, Thorburn GD. Parturition in goats: studies on the interactions between the foetus, placenta, prostaglandin F and progesterone before parturition, at term or at parturition induced prematurely by corticotrophin infusion of the foetus. J Endocrinol 1977; 73: 263-278 doi: 10.1677/joe.0.0730263
• 28 Hoffmann B, Höveler R, Nohr B. et al. Investigations on hormonal changes around parturition in the dog and the occurrence of pregnancy-specific non conjugated oestrogens. Exp Clin Endocrinol 1994; 102: 185-189 doi: 10.1055/s-0029-1211280
• 29 Nishiyama T, Tsumagari S, Ito M. et al. Immunohistochemical study of steroidogenic enzymes in the ovary and placenta during pregnancy in the dog. Anat Histol Embryol 1999; 28: 125-129 doi: 10.1046/j.1439-0264.1999.00170.x
• 30 Raeside JI. A brief account of the discovery of the fetal/placental unit for estrogen production in equine and human pregnancies: relation to human medicine. Yale J Biol Med 2017; 90: 449-461
• 31 Königsson K, Gustafsson H, Kindahl H. 15-Ketodihydro-PGF(2 alpha), progesterone and uterine involution in primiparous cows with induced retained placenta and post-partal endometritis treated with oxytetracycline and flunixin. Reprod Domest Anim 2002; 37: 43-51 doi: 10.1046/j.1439-0531.2002.00325.x
• 32 Mansell PD, Cameron AR, Taylor DP. et al. Induction of parturition in dairy cattle and its effects on health and subsequent lactation and reproductive performance. Aust Vet J 2006; 84: 312-316 doi: 10.1111/j.1751-0813.2006.00031.x
• 33 Day AM. Cloprostenol for termination of pregnancy in cattle. B) The induction of abortion. N Z Vet J 1977; 25: 139-144 doi: 10.1080/00480169.1977
• 34 Chew BP, Erb RE, Fessler JF. etal Effects of ovariectomy during pregnancy and of prematurely induced parturition on progesterone, estrogens, and calving traits. J Dairy Sci 1979; 62: 5575-5566 doi: 10.3168/jds.s0022-0302(79)83290-7
• 35 Johnson WH, Manns JG, Adams WM. et al. Termination of pregnancy with cloprostenol and dexamethasone in intact or ovariectomized cows. Can Vet J 1981; 22: 288-290
• 36 Prakash BS, Madan ML. Induction of parturition in water buffaloes (. Bubalus bubalis). Theriogenology 1985; 23: 325-331 doi: 10.1016/0093-691x(85)90034-2
• 37 Al-Hamedawi TM, Al-Yasiri EA, Alshaty ER. et al Induction of parturition in Iraqi buffaloes. Al-Anbar J Vet Sci 2012; 5: 32-35 Im Internet: https://www.iasj.net/iasj/article/61757 Stand: 05.04.2023
• 38 Purohit G, Shekher C, Kumar P. et al. Induced termination of pregnancy in domestic farm animals. Iran J Appl. Anim Sci 2012; 2: 1-12
• 39 Holtan DW, Squires EL, Lapin DR. et al. Effect of ovariectomy on pregnancy in mares. J Reprod Fertil Suppl 1979; 27: 457-463
• 40 Holtan DW, Houghton E, Silver M. et al. Plasma progestagens in the mare, fetus and newborn foal. J Reprod Fertil Suppl 1991; 44: 517-528
• 41 Legacki EL, Scholtz EL, Ball BA. et al. The dynamic steroid landscape of equine pregnancy mapped by mass spectrometry. Reproduction 2016; 151: 421-430 doi: 10.1530/REP-15-0547
• 42 Legacki EL, Corbin CJ, Ball BA. et al. Progestin withdrawal at parturition in the mare. Reproduction 2016; 152: 323-331 doi: 10.1530/REP-16-0227
• 43 Scholtz EL, Krishnan S, Ball BA. et al. Pregnancy without progesterone in horses defines a second endogenous biopotent progesterone receptor agonist, 5α-dihydroprogesterone. Proc Natl Acad Sci U S A 2014; 111: 3365-3370 doi: 10.1073/pnas.1318163111
• 44 Legacki EL, Corbin CJ, Ball BA. et al. Steroidogenic enzyme activities in the pre- and post-parturient equine placenta. Reproduction 2018; 155: 51-59 doi: 10.1530/REP-17-0472
• 45 Fowden AL, Forhead AJ, Ousey JC. The endocrinology of equine parturition. Exp Clin Endocrinol Diabetes 2008; 116: 393-403 doi: 10.1055/s-2008-1042409
• 46 Legacki EL, Ball BA, Corbin CJ. et al. Equine fetal adrenal, gonadal and placental steroidogenesis. Reproduction 2017; 154: 445-454 doi: 10.1530/REP-17-0239
• 47 Thorburn GD. A speculative review of parturition in the mare. Equine Vet J Suppl 1993; 14: 41-49 doi: 10.1111/j.2042-3306.1993.tb04808.x
• 48 Conley AJ. Review of the reproductive endocrinology of the pregnant and parturient mare. Theriogenology 2016; 86: 355-365 doi: 10.1016/j.theriogenology.2016.04.049
• 49 Fowden AL, Silver M. Comparative development of the pituitary-adrenal axis in the fetal foal and lamb. Reprod Dom Anim 1995; 30: 170-177
• 50 Ousey JC, Kölling M, Kindahl H. et al. Maternal dexamethasone treatment in late gestation induces precocious fetal maturation and delivery in healthy Thoroughbred mares. Equine Vet J 2011; 43: 424-429 doi: 10.1111/j.2042-3306.2010.00306.x
• 51 Nagel C, Aurich C. Induction of parturition in horses - from physiological pathways to clinical applications. Domest Anim Endocrinol 2022; 78: 106670 doi: 10.1016/j.domaniend.2021.106670
• 52 Du Mesnil du Buisson F, Dauzier L. Influence de l'ovariectomie chez la truie pendant la gestation. C R Seances Soc Biol Fil 1957; 151: 311-313
• 53 Robertson HA, King GJ. Plasma concentrations of progesterone, oestrone, oestradiol-17beta and of oestrone sulphate in the pig at implantation, during pregnancy and at parturition. J Reprod Fertil 1974; 40: 133-141 doi: 10.1530/jrf.0.0400133
• 54 Knight JW, Kukoly CA. In vitro release of progesterone and estrone by the porcine placenta throughout gestation. Domest Anim Endocrinol 1990; 7: 497-508 doi: 10.1016/0739-7240(90)90007-m
• 55 Loisel F, Farmer C, van Hees H. et al. Relative prolactin-to-progesterone concentrations around farrowing influence colostrum yield in primiparous sows. Domest Anim Endocrinol 2015; 53: 35-41 doi: 10.1016/j.domaniend.2015.04.005
• 56 Foisnet A, Farmer C, David C. et al. Relationships between colostrum production by primiparous sows and sow physiology around parturition. J Anim Sci 2010; 88: 1672-1683 doi: 10.2527/jas.2009-2562
• 57 Wynn MAA, Esteller-Vico A, Legacki EL. et al. A comparison of progesterone assays for determination of peripheral pregnane concentrations in the late pregnant mare. Theriogenology 2018; 106: 127-133 doi: 10.1016/j.theriogenology.2017.10.002
• 58 First NL, Lohse JK, Nara BS. The endocrine control of parturition. In: Cole DJA, Foxcroft GR, eds. Control of pig reproduction. London: Butterworths; 1982: 311-342
• 59 Randall GC. Changes in the concentrations of corticosteroids in the blood of fetal pigs and their dams during late gestation and labor. Biol Reprod 1983; 29: 1077-1084 doi: 10.1095/biolreprod29.5.1077
• 60 Silver M, Fowden AL. Pituitary-adrenocortical activity in the fetal pig in the last third of gestation. Q J Exp Physiol 1989; 74: 197-206 doi: 10.1113/expphysiol.1989.sp003255
• 61 Nara BS, First NL. Effect of indomethacin on dexamethasone-induced parturition in swine. J Anim Sci 1981; 52: 788-793 doi: 10.2527/jas1981.524788x
• 62 Leon JB, Smith BB, Timm KI. et al. Endocrine changes during pregnancy, parturition and the early post-partum period in the llama (Lama glama). J Reprod Fertil 1990; 88: 503-511 doi: 10.1530/jrf.0.0880503
• 63 Aba MA, Sumar J, Kindahl H. et al. Plasma concentrations of 15-ketodihydro-PGF2 alpha, progesterone, oestrone sulphate, oestradiol-17 beta and cortisol during late gestation, parturition and the early post partum period in llamas and alpacas. Anim Reprod Sci 1998; 50: 111-121 doi: 10.1016/s0378-4320(97)00084-5
• 64 Riveros JL, Urquieta B, Bonacic C. et al. Endocrine changes during pregnancy, parturition and post-partum in guanacos (Lama guanicoe). Anim Reprod Sci 2009; 116: 318-325 doi: 10.1016/j.anireprosci.2009.02.005
• 65 Skidmore JA, Billah M, Allen WR. Patterns of hormone secretion throughout pregnancy in the one-humped camel (Camelus dromedarius). Reprod Fertil Dev 1996; 8: 863-869 doi: 10.1071/rd9960863
• 66 Wooding FB, Ozturk M, Skidmore JA. et al. Developmental changes in localization of steroid synthesis enzymes in camelid placenta. Reproduction 2003; 126: 239-247 doi: 10.1530/rep.0.1260239
• 67 Smith BB, Timm KI, Reed PJ. et al. Use of cloprostenol as an abortifacient in the llama (Lama glama). Theriogenology 2000; 54: 497-505 doi: 10.1016/S0093-691X(00)00365-4
• 68 Al-Eknah MM, Homeida AM, Ramadan RO. et al. Pregnancy dependence on ovarian progesterone in the camel (Camelus dromedarius). Emir. J Agric Sci 2001; 13: 27-32 doi: doi.org/10.9755/ejfa.v13i1.5226
• 69 Elias E, Bedrak E, Yagil R. Peripheral blood levels of progesterone in female camels during various reproductive stages. Gen Comp Endocrinol 1984; 53: 235-240 doi: 10.1016/0016-6480(84)90248-x
• 70 Tibary A, Rodriguez JS, Anouassi A. et al. Management of dystocia in camelids. Proceedings of 41st Annual Conference of American Association of Bovine Practitioners, Charlotte, 25-27 2008; 166-176 doi: 10.21423/aabppro20084387
• 71 Bravo PW, Bazan PJ, Troedsson MH. et al. Induction of parturition in alpacas and subsequent survival of neonates. J Am Vet Med Assoc 1996; 209: 1760-1762
• 72 Kowalewski MP, Gram A, Kautz E. et al. The dog: nonconformist, not only in maternal recognition signaling. Adv Anat Embryol Cell Biol 2015; 216: 215-237 doi: 10.1007/978-3-319-15856-3_11
• 73 Kowalewski MP, Tavares Pereira M, Kazemian A. Canine conceptus-maternal communication during maintenance and termination of pregnancy, including the role of species-specific decidualization. Theriogenology 2020; 150: 329-338 doi: 10.1016/j.theriogenology.2020.01.082
• 74 Mir F, Billault C, Fontaine E. et al. Estimated pregnancy length from ovulation to parturition in the bitch and its influencing factors: a retrospective study in 162 pregnancies. Reprod Domest Anim 2011; 46: 994-998 doi: 10.1111/j.1439-0531.2011.01773.x
• 75 De Cramer KGM, Nöthling JO. The precision of peri-oestrous predictors of the date of onset of parturition in the bitch. Theriogenology 2017; 96: 153-157 doi: 10.1016/j.theriogenology.2017.04.018
• 76 Sonnack M. Untersuchungen zur Bildung, Regression und Funktionalität des Corpus luteum der nicht graviden Hündin: morphologische und biochemische Aspekte. [Dissertation]. Gießen: Justus-Liebig-Universität, Fachbereich Veterinärmedizin. 2009 doi: 10.22029/jlupub-12314
• 77 Kowalewski MP. Luteal regression vs. prepartum luteolysis: regulatory mechanisms governing canine corpus luteum function. Reprod Biol 2014; 14: 89-102 doi: 10.1016/j.repbio.2013.11.004
• 78 Hoffmann B, Höveler R, Nohr B. et al. Investigations on hormonal changes around parturition in the dog and the occurrence of pregnancy-specific non conjugated oestrogens. Exp Clin Endocrinol 1994; 102: 185-189 doi: 10.1055/s-0029-1211280
• 79 De Cramer KGM, Nöthling JO. The precision of predicting the time of onset of parturition in the bitch using the level of progesterone in plasma during the preparturient period. Theriogenology 2018; 107: 211-218 doi: 10.1016/j.theriogenology.2017.11.018
• 80 Concannon PW, Isaman L, Frank DA. et al. Elevated concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha in maternal plasma during prepartum luteolysis and parturition in dogs (Canis familiaris). J Reprod Fertil 1988; 84: 71-77 doi: 10.1530/jrf.0.0840071
• 81 Nohr B, Hoffmann B, Steinetz BE. Investigation of the endocrine control of parturition in the dog by application of an antigestagen. J Reprod Fertil Supp 1993; 47: 542-543
• 82 Veronesi MC, Battocchio M, Marinelli L. et al. Correlations among body temperature, plasma progesterone, cortisol and prostaglandin F2alpha of the periparturient bitch. J Vet Med A Physiol Pathol Clin Med 2002; 49: 264-268 doi: 10.1046/j.1439-0442.2002.00410.x
• 83 Kowalewski MP, Beceriklisoy HB, Pfarrer C. et al. Canine placenta: a source of prepartal prostaglandins during normal and antiprogestin-induced parturition. Reproduction 2010; 139: 655-664 doi: 10.1530/REP-09-0140
• 84 Thuróczy J. Foetal development of endocrine organs in dog. Reprod Domest Anim 2020; 55: 10-16 doi: 10.1111/rda.13681
• 85 Gram A, Trachsel A, Boos A. et al. Elevated utero/placental GR/NR3C1 is not required for the induction of parturition in the dog. Reproduction 2016; 152: 303-311 doi: 10.1530/REP-16-0213
• 86 Pereira MT, Schuler G, Aslan S. et al. Utero-placental expression and functional implications of HSD11B1 and HSD11B2 in canine pregnancy. Biol Reprod 2023; ioac214 doi: 10.1093/biolre/ioac214
• 87 Zone M, Wanke M, Rebuelto M. et al. Termination of pregnancy in dogs by oral administration of dexamethasone. Theriogenology 1995; 43: 487-494 doi: 10.1016/0093-691x(94)00041-r
• 88 Corrada Y, Rodríguez R, Tortora M. et al. A combination of oral cabergoline and double cloprostenol injections to produce third-quarter gestation termination in the bitch. J Am Anim Hosp Assoc 2006; 42: 366-370 doi: 10.5326/0420366
• 89 Wiebe VJ, Howard JP. Pharmacologic advances in canine and feline reproduction. Top Companion Anim Med 2009; 24: 71-99 doi: 10.1053/j.tcam.2008.12.004
• 90 Riesenbeck A, Klein R, Hoffmann B. et al Geburtsinduktion infolge verlängerter Gravidität bei einer Hündin unter Verwendung eines Antigestagens. Tierärztl Prax 1999; 27 (K) 186-188
• 91 Verhage HG, Beamer NB, Brenner RM. Plasma levels of estradiol and progesterone in the cat during polyestrus, pregnancy and pseudopregnancy. Biol Reprod 1976; 14: 579-585 doi: 10.1095/biolreprod14.5.579
• 92 García Mitacek MC, Stornelli MC, Praderio RG. et al. Ultrasonographic and progesterone changes during Days 21 to 63 of pregnancy in queens. Theriogenology 2015; 84: 1131-1141 doi: 10.1016/j.theriogenology.2015.06.014
• 93 Banks DR, Paape SR, Stabenfeldt GH. Prolactin in the cat: I. Pseudopregnancy, pregnancy and lactation. Biol Reprod 1983; 28: 923-932 doi: 10.1095/biolreprod28.4.923
• 94 Stewart DR, Stabenfeldt GH. Relaxin activity in the pregnant cat. Biol Reprod 1985; 32: 848-854 doi: 10.1095/biolreprod32.4.848
• 95 Miglino MA, Ambrósio CE, dos Santos Martins D. et al. The carnivore pregnancy: the development of the embryo and fetal membranes. Theriogenology 2006; 66: 1699-1702 doi: 10.1016/j.theriogenology.2006.02.027
• 96 Little SE. Female Reproduction. In: Little SE, ed. The cat. Philadelphia: W.B. Saunders; 2012: 1195-1227 ISBN 9781437706604 doi: 10.1016/B978-1-4377-0660-4.00040-5
• 97 Malassiné A, Ferré F. Delta 5,3 beta Hydroxysteroid dehydrogenase activity in cat placental labyrinth: evolution during pregnancy, subcellular distribution. Biol Reprod 1979; 21: 965-971 doi: 10.1095/biolreprod21.4.965
• 98 Ito J, Kiso Y, Yamauchi S. Distribution and chronological changes of hydroxysteroid dehydrogenase (HSD) in the cat placenta. Nihon Juigaku Zasshi 1987; 49: 225-233 doi: 10.1292/jvms1939.49.225
• 99 Dreker C. Untersuchungen zum Verlauf von Progesteron, freien und konjugierten Östrogenen sowie von Relaxin im peripheren Blut von Norwegischen Waldkatzen im Verlauf der Trächtigkeit und der Pseudogravidität [Dissertation]. Gießen: Lustus-Liebig-Universität, Fachbereich Veterinärmedizin. 2003 Im Internet: http://geb.uni-giessen.de/geb/volltexte/2004/1603/ Stand: 05.04.2023
• 100 Braun BC, Zschockelt L, Dehnhard M. et al. Progesterone and estradiol in cat placenta - biosynthesis and tissue concentration. J Steroid Biochem Mol Biol 2012; 132: 295-302 doi: 10.1016/j.jsbmb.2012.07.005
• 101 Siemieniuch MJ, Jursza E, Szostek AZ. et al. Steroidogenic capacity of the placenta as a supplemental source of progesterone during pregnancy in domestic cats. Reprod Biol Endocrinol 2012; 10: 89 doi: 10.1186/1477-7827-10-89
• 102 Tsutsui T, Suzuki Y, Toyonaga M. et al. The role of the ovary for the maintenance of pregnancy in cats. Reprod Domest Anim 2009; 44: 120-124 doi: 10.1111/j.1439-0531.2009.01452.x
• 103 Goericke-Pesch S. Termination of pregnancy. In: Johnson AK, Kutzler MA, eds. Feline Reproduction. Wallingford: CABI Books. CABI Internationa; 2022. doi: 10.1079/9781789247107.0012