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Summary. A prospective study of the menstrual pattern and weight changes was made in the first year of training of 29 new female entrants to a professional ballet school. Seventy‐nine per cent of the student girls had menstrual disturbances at entry: primary amenorrhoea, four; secondary amenorrhoea, 11; irregular menses, eight. The incidence of secondary amenorrhoea increase substantially by the end of the year (20), but was not associated with any significant change in body weight. Only three students menstruated regularly during the year. Menstrual regularity improved during periods of injury and long vacation and it appears that deterioration of the menstrual pattern during dancing periods was related to strenuous physical exercise rather than to any change in body weight.

Measurements of Po2, Pco2 and pH have been carried out in human ovarian venous, peripheral venous and arterial blood, and in ovarian follicular fluid. The Po2 in ovarian venous blood is higher than in peripheral venous blood. Mean oxygen consumption by the human ovary has been calculated to be 1\m=.\4ml oxygen/100 g ovarian tissue/min. Taken in conjunction with a mean ovarian blood flow of 20\m=.\3ml/min, these findings are compatible with the presence of arterio-venous shunts within the human ovary. Oxygen tension in follicular fluid may be substantially lower than oxygen tension in peripheral and ovarian venous blood.

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Prostaglandin F2\g=a\(PGF2\g=a\) secreted from the uterus exerts a luteolytic effect on the corpus luteum in a number of species of non-pregnant mammals (see review of Labhsetwar, 1974). This luteolytic mechanism has not been demonstrated in non-pregnant women . Nor were Leader, Bygdeman, Cekan, Diczfalusy, Guerrero, Martin & Wiqvist (1975) able to demonstrate an accelerative effect of intra-uterine 15 (S) 15-methyl PGF2\g=a\ or an inhibitory effect of oral indomethacin on post-abortion luteolysis in women in early pregnancy. The presence of PGF2\g=a\receptors however, in human corpora lutea (Powell, Hammarstr\l=o"\m, Samuelsson & Sj\l=o"\berg,1974) suggested the possibility of a local production of PGF2\g=a\ within the ovary being responsible for luteolysis in women, and Korda, Shutt, Smith, Shearman & Lyneham (1975) were able to obtain a transient luteolysis when 0\ m=. \ 5\ p=n-\ 1\ m=. \ 0 mg PGF2\g=a\ was injected directly into the corpus luteum of non-pregnant women. , 1976) and human corpora lutea have the capacity to synthesize PGF and PGE (Challis et al. 1976). The present study was undertaken to examine the concentrations of PGF and steroids in corpus luteal tissue in relation to the growth of the corpus luteum and luteolysis.Corpora lutea were obtained from women admitted to the hospital for elective abdominal gynaecological surgery, providing the surgery was not for infertility or malignancy of the genital tract. Full and informed consent was obtained from all patients. The mean age of the patients was 37 years with a range of 27-48 years. Excised corpora lutea were placed directly into liquid air and stored frozen until used. Extraction, chromatography and radioimmunoassay procedures for PGF and the steroids progesterone, 17-hydroxyprogesterone and oestradiol-17j3 in corpus luteal tissue were as previously described . The presence of the PGF metabolite 13,14-dihydro-15-oxo PGF was undetected (<5ng/g) following chroma¬ tography on silica gel and selective radioimmunoassay of six corpus luteal extracts in which the PGF concentration ranged from 1 to 10ng/g. On the basis of endometrial dating of the menstrual cycle, corpora lutea were divided into three groups of eight referred to as early luteal (days 17-19 of a normal 28 day cycle), midluteal (days 20-22) and late luteal (days 23-26). A further group of twelve corpora lutea were obtained from women admitted for the termination of pregnancy and tubai ligation between weeks 7 and 12 of gestation. The mean concentrations of PGF, progesterone, 17-hydroxy¬ progesterone and oestradiol-17/3 (± S.E.M.) in corpora lutea of the early luteal phase (EL), midluteal phase (ML) and late luteal phase (LL) and of early pregnancy are shown in Fig. 1. The EL concentrations represent those present during the main growth period of the luteal cells and the LL concentrations those present during the regression of the luteal cells (see Corner, 1956). There was a significant increase (P<0-05) in mean PGF concentrations from 4 ± 1 ng/g in corpora lutea of the ML phase to 13 +...