The effect of pregnancy or corpus luteum activity

The effect of pregnancy or corpus luteum activity

ii Abstracts 3 PREDICTION OF OVULATION O.T. BAIRD, Department of Obstetrics & Gynaecology, University of Edinburgh, Centre for Reproductive Biology, ...

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Abstracts 3 PREDICTION OF OVULATION O.T. BAIRD, Department of Obstetrics & Gynaecology, University of Edinburgh, Centre for Reproductive Biology, 37 Chalmers Street, Edinburgh, EH3 9EW. Scotland. The factors determining the selection of the dominant Graafian follicle in monovular species are complex and incompletely understood. The development of a simple and accurate method of predicting the exact tidng of ovulation would have enormous implications for the treabnt of infertility, e.g. AID, oocyte recovery and in vitro fertilization, etc., in.addition to 'natural methods' of family planning. The current mathods of predictfng ovulation can be listed as follows: 8y the mid-follicular phase of the cycle (ovulation -7) there is a 1) erence in the concentration of oestradiol in ovarian venous blood draining the ovary containing the largest non-atretic follicle (Baird 6 Fraser, 1975) indicating that the measurement of oestrogen in blood or urine reflects accurately follicular development (Brown. 1971). Recent advances in the measurement of oestrone+glucumnide by RIA in aliquots of urine have simplified this technique but they are not yet adequate for self use by patients. 2) LH. Serlal measurements at 3-hourly intervals by a rapid RIA have indicated that me LH surge (as defined by a doubllng in baseline) starts some 28 ? 2 hours before ovulation. Within 6 hours of the start of the LH surge luteinization of the 3) mgrant osa ce 1s in the pre-ovulatory follicle is reflected by an increase in progesterone secretion which can be monitored by measurement in serum or saliva. 4) Ultrasound. With high resolution ultrasound it is now possible to identify 7 lllcles at least 5 days before ovulation when their diameter exceeds 6 mn Numerous studies have now conflnntd that the mean (:ackeloer et al, 1977). maximm follicular diameter of the pre-ovulatory follicle is 21.2 IIIII (range 1725 INII).8y making serlal dally measurements of follicle diameter it is possible to predict that when follfcular diameter of the dominant follicle exceeds 20 m ovulation will occur within 24 hours (Kerln et al, 1981). While this technique can only be used as yet for a limited selection of patients, the ability to monitor follicle developnant by ultrasonic means has added another important parameter with which to correlate any less direct measurements.

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4 TRBEFFBOTOFPREGI?ARCY

OHCORPUS LUTEUMACTIVITY I. Rothchild,Departmentof Reproductive Biology,Case WesternReserveUniversity, Schoolof Medicine,Cleveland,Ohio 44106, U.S.A.

Among eutherlanmsamala,pregnancya??ectscorpusluteum (CL) progesterone(P) secretiondifferentlyamong the polyestrousand monestrousspecies. The long-lived CL (P secretedfor 5 weeks or more) of the latterare, in general,unaffectedby pregnancy,but in polyestrousspecies,which have only short-lived CL (P secreted for 2 weeks or less),pregnancyalways increasesat least the durationof P secretion. The marsupials'CL are sFmilarto short-livedCL, but pregnancydoes not a??ectthem; however,no marsupialpregnancylarts longerthan 2 weeks after implantation. The much longer eutherlanpregnancydependedon P, the prolongedsecretion o? which became ppsrible throughCL responsiveness to extrinsiccontrolsof two main types. Amongmnestrous breederspituitaryhormonesalone prolongedP secretion enoughto allow a long pre@ancy to evolve. Among @yestrous breeders,the conceptus, in most (or allS) cases through trophoblasthormones,convertedthe short-lived to a long-livedCL; in stme groups,the trophoblastitselfevolveda high capacity smong: (1) trophoblast for P secretion. The conceptuseffectdependson interactions hormones(e.g. chorlonicgonadotrophin8 snd placentallactogens);(2) the stage of the CL's life cycle when these hormonesreach the CL (e.g.beginningor end of the plateauphase); (3) the site of actionof these hormones(e.g. CL, uterus,pituitary);and (4) the agent that startsthe CL's regressionphase (e.g.uterinePGs, LII, intrinsicPGs). The relativeimportanceof LR, prolactln,estrogenand autonomyin regulatingthe CL duringthe ovulationcycle may also affectthese interactions. From the analysisof such interactions. as for example,in pigs, in which the conceptus prolongsthe CL's plateauphase,or in humans,in which it temporarilyincreases P secretionrate, or in rabbits,in which it increasesboth rate and durationof P secretion,it seems that the primaryand imediate effectof the conceptusis to block the initiationof the CL's regressionphase. A secondaryeffect,which may dependon how P secretionis regulated- Is to raise the rate of P secretion. Although combinations of both effectsoccur in each species,some tend to show a predominanceof the primary (e.g.pig), or the secondaryeffect (e.g.human). The precisemechanismsthroughwhich eithereffectoccursare largelyunknown.