Production of inhibin A not B in rams: changes in plasma inhibin A during testis growth, and expression of inhibin/activin subunit mRNA and protein in adult testis.

Previous studies have shown that changes in the plasma concentrations of immunoreactive inhibin measured by radioimmunoassay occur in parallel with growth and regression of the testes during a reproductive cycle in adult Soay rams induced by exposure to an artificial lighting regimen of alternating 16 week periods of long days and short days. With the development of new two-site ELISAs for sheep inhibin A and inhibin B, we have re-examined the relationship between FSH and dimeric, biologically active inhibin in the reproductive cycle in adult Soay rams. No signal was generated by sheep testicular extract, ram or ewe plasma, or sheep ovarian follicular fluid in the inhibin B ELISA. In contrast, ram plasma contained significant activity in the inhibin A ELISA, which diluted in parallel to the inhibin A standard, and was abolished by preincubation of ram plasma with monoclonal antibodies specific for the betaA, but not the betaB, subunit. These results indicate that the ram is the first adult male mammalian species identified to date in which the testes produce and secrete dimeric inhibin A and not inhibin B. Northern blot analysis and immunocytochemistry confirmed the presence of alpha, betaA and betaB inhibin/activin subunit mRNA and protein in the testes of adult rams. Changes in plasma inhibin A concentrations occurred in parallel with the growth and regression of the testes during the long day: short day: long day lighting regimen in adult Soay rams, confirming our previous observations with immunoreactive inhibin. During the growth phase of the testes in the first 8 weeks of exposure to short days there was a positive correlation between plasma FSH and inhibin A concentrations, indicating that during this phase the secretion of inhibin A is stimulated by FSH and that inhibin A did not act as a negative feedback hormone on FSH secretion. From week 8.5 to week 16.0 of exposure to short days, there was a negative correlation between FSH and testosterone concentrations, but not inhibin, indicating that when inhibin concentrations are high, testosterone acts as the negative regulator of FSH secretion. Thus, in intact adult rams, when the testes are fully active it appears that inhibin A may sensitize the pituitary to the negative feedback effects of testosterone, at which time they act synergistically to maintain plasma concentrations of FSH.

Dimeric inhibin A as a marker for Down's syndrome in early pregnancy.

BACKGROUND: In screening for Down's syndrome in the second trimester of pregnancy, the concentrations of alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, and intact human chorionic gonadotropin in material serum are widely used markers. We investigated a new marker, dimeric inhibin A, and compared its predictive value with that of the established markers. METHODS: Serum samples were obtained at 7 to 18 weeks of gestation from 58 women whose fetuses were known to be affected by Down's syndrome, 32 whose fetuses were affected by trisomy 18, and 438 whose fetuses were normal, and the samples were analyzed for each marker. Individual serum concentrations of each marker were converted to multiples of the median value at the appropriate length of gestation in the women with normal pregnancies, and rates of detection of Down's syndrome by screening for inhibin A in various combinations with the other markers were estimated by multivariate analysis. RESULTS: In the women with fetuses affected by Down's syndrome, the serum inhibin A concentrations were 2.06 times the median value in the women with normal pregnancies (P < 0.001). This compared with 2.00 times the median for the beta subunit of human chorionic gonadotropin, 1.82 times the median for intact human chorionic gonadotropin, and 0.72 for alpha-fetoprotein. The serum concentrations of inhibin A in the women with fetuses affected by Down's syndrome did not appear to be significantly elevated above normal until the end of the first trimester and were not significantly different from normal in the women with fetuses affected by trisomy 18 (P = 0.17). The rate of detection of Down's syndrome was 53 percent and the false positive rate was 5 percent when alpha-fetoprotein, the beta subunit of human chorionic gonadotropin, the maternal age were used together as predictors. The detection rate increased to 75 percent when inhibin A was added (P = 0.002). CONCLUSIONS: In the second trimester of pregnancy, measuring inhibin A in maternal serum, in combination with measurements of alpha-fetoprotein and beta subunit of human chorionic gonadotropin, significantly improved the rate of detection of Down's syndrome.

Second trimester screening for Down's syndrome using maternal serum dimeric inhibin A.

BACKGROUND AND OBJECTIVE: Prenatal maternal serum screening for Down's syndrome has become an important and established part of modern antenatal care. Previously it has been reported that non-specific immunoreactive inhibin may be useful in this context. Using a novel assay we have evaluated dimeric inhibin A as a possible second trimester marker of Down's syndrome. METHODS: From 1992-1993 records, stored sera from women with Down's affected pregnancies and chromosomally normal control pregnancies were identified and retrieved for analysis. These sera had been prospectively collected at 15, 16 and 17 weeks gestation. SUBJECTS: Records revealed 21 women who had had a Down's syndrome pregnancy and who also had serum available for analysis. Sera from 150 chromosomally normal controls, matched for gestation and duration of storage, were also retrieved. MEASUREMENTS: Dimeric inhibin A was measured using a recently developed two-site enzyme-linked immunoassay. This employs a capture anti inhibin beta A-subunit monoclonal antibody, covalently bound to a microtitre plate and a second anti inhibin alpha-subunit antibody conjugated to alkaline phosphatase, allowing detection. RESULTS: The mean (95% CI) maternal serum dimeric inhibin A in the samples from control pregnancies was 237 (201.5-273.4) ng/l, 266.9 (235.4-298.5) ng/l and 207.2 (178.5-235.9) ng/l at 15, 16 and 17 weeks gestation respectively. Expressing the results from the Down's samples as multiples of the normal median (MoM), the median (95% CI) MoM was 2.6 (2.25-3.57), significantly higher than the controls (P < 0.0001, Mann-Whitney U-test). In the sample set tested, for a given false positive rate of 5.3% inhibin A alone afforded a detection rate of 62%, detecting cases previously undetected by routine screening. CONCLUSIONS: Dimeric inhibin A appears to be a promising new marker for the prenatal detection of Down's syndrome. Further prospective evaluation and assessment with other established markers would now be merited.

Evaluation of maternal serum dimeric inhibin A as a first-trimester marker of Down's syndrome.

While second-trimester prenatal screening programmes for Down's syndrome have become established in prenatal care, it would be advantageous to be able to offer screening in earlier pregnancy. To this end, we have evaluated a new potential maternal serum marker, dimeric inhibin A, as a possible first-trimester marker. Dimeric inhibin A was measured in prospectively collected maternal serum from 23 cases of Down's syndrome and matched chromosomally normal controls, at 11-13 weeks' gestation. Levels of this protein were significantly elevated in the Down's pregnancies compared with the control pregnancies. The median multiple of the normal median (MOM) for the Down's samples was 2.46 (95 per cent confidence interval: 2.11-3.26, P < 0.0001 vs. controls). These results suggest that dimeric inhibin A is a useful discriminator of Down's-affected pregnancies from normal pregnancies in the first trimester and that sensitive screening in combination with maternal age and other possible markers may be practicable in the first trimester.

Control of inhibin production by primate granulosa cells.

In-vitro data from experiments on rats implicate granulosa cells as primary sites of hormone-dependent ovarian inhibin biosynthesis, but no equivalent data exist for primates. We have used the common marmoset (Callithrix jacchus) to investigate inhibin biosynthesis in primate granulosa cells in vitro and to determine its relationship to preovulatory follicular development. To relate the production of immunoactive inhibin to follicular maturity, we studied primary granulosa cell cultures from follicles at progressive stages of preovulatory development. Granulosa cells from 'large' (greater than or equal to 2.0 mm diameter) follicles expressed high rates of inhibin production and steroidogenesis (progesterone), and were positively regulated by human (h)LH in vitro. Less mature granulosa cells from 'medium' (1.1-1.9 mm) and 'small' (less than or equal to 1.0 mm) follicles expressed proportionately lower rates of inhibin production and steroidogenesis, but each parameter was stimulated in a dose- and time-dependent manner by hFSH in vitro. The stimulatory action of hFSH on immunoreactive inhibin was augmented by the presence of testosterone or oestradiol; testosterone (but not oestradiol) also augmented the steroidogenic response to hFSH. Marmoset luteal tissue also produced inhibin in vitro and expressed an approximately 1.5 kb inhibin alpha-subunit mRNA, confirming the corpus luteum as a source of ovarian inhibin in primates. These results provide direct experimental evidence that primate granulosa cells produce inhibin. They suggest that production of inhibin by immature granulosa cells is initially induced by FSH and subject to modulation by follicular steroids.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the plasma concentrations of inhibin throughout the normal sheep oestrous cycle and after the infusion of FSH.

A radioimmunoassay for inhibin was developed using a peptide containing the 1-26 amino acid sequence of the N-terminus of the alpha-chain of 32 kDa porcine inhibin as immunogen, and 125I-labelled tracer. Evaluation of this assay using Sephadex column chromatography, chromatoelectrophoresis and immunoblotting confirmed that it measured all forms of inhibin present in sheep follicular fluid and was suitable for measurement of inhibin in sheep plasma. There was no evidence of the presence of free alpha-subunit in either sheep follicular fluid or ovarian vein plasma. The concentration of inhibin in jugular plasma throughout the follicular and luteal phases of four ewes with ovarian autotransplants was measured. The ovarian secretion of inhibin and oestradiol were also measured simultaneously throughout the follicular phase in a spontaneous cycle and after infusion of NIH-oFSH-S14 at 10 micrograms/h for 48 h following premature luteal regression induced by prostaglandin. The results showed: (1) no change in the peripheral concentration of inhibin throughout the cycle except an increase related to the periovulatory increase in FSH and LH. (2) Following luteal regression, the concentration of FSH fell as the secretion rate of oestradiol increased. During this time there was no significant change in the peripheral concentration of inhibin or ovarian inhibin secretion rate. (3) Following the infusion of FSH there was a marked increase in the concentration of inhibin in both ovarian and peripheral plasma and an increase in ovarian inhibin secretion rate. (4) The calculated metabolic clearance rate of inhibin, 20.3 ml/min, is similar to that of FSH. We conclude that in the ewe the ovarian inhibin secretion rate is stimulated by FSH and, although inhibin may modulate the basal secretion of FSH, a change in its secretion does not account for the fall in FSH which occurs during the follicular phase of the sheep oestrous cycle.

Factors affecting the secretion of immunoactive inhibin into testicular interstitial fluid in rats.

Immunoreactive inhibin was measured in testicular interstitial fluid (IF) from rats during sexual maturation or after impairment of spermatogenesis induced by ethane dimethanesulphonate (EDS), unilateral cryptorchidism or local heating (43 degrees C, 30 min) of the testes, to ascertain its usefulness as a marker of changing Sertoli cell function. Cultures of isolated seminiferous tubules were also studied. Inhibin was measured by a radioimmunoassay directed towards the first 26 amino acids of the N-terminus of the alpha-subunit, and the results confirmed for selected pools of IF by in-vitro bioassay using dispersed ovine pituitary cells. During puberty, IF levels of immunoactive inhibin fell by more than 90% (P less than 0.001) between 30 and 60 days of age, a decrease paralleled by the levels of androgen-binding protein (ABP), another Sertoli cell product secreted into IF. These changes also paralleled, but preceded, the fall (60%; P less than 0.001) in serum levels of FSH between 40 and 70 days, while the serum and IF levels of testosterone increased more than two-fold over this period. When adult rats were injected with EDS to destroy the Leydig cells, testosterone levels in IF and serum were undetectable at 3 and 7 days after treatment, were just detectable at 14 days and thereafter returned slowly towards normal by 42 days. The initial androgen withdrawal following EDS treatment caused a progressive reduction in testicular weight up to 21 days and this was accompanied by a significant increase in the serum levels of FSH and a two- to threefold increase in the IF levels of immunoactive inhibin (and also of ABP). Serum FSH and IF levels of immunoactive inhibin returned to within the normal range by 42 days when testosterone levels had normalized. In contrast, in two other experimental situations in which a marked decrease in testicular weight coupled with an increase in IF levels of ABP occurs, different results for the IF levels of immunoactive inhibin were obtained. Thus, in rats exposed to local heating of the testes, IF levels of immunoactive inhibin remained unchanged from control values at 21-40 days after treatment, a finding confirmed by bioassay results. In rats made unilaterally cryptorchid for 10 months, levels of immunoactive inhibin in IF were reduced by 60% (P less than 0.01) in the abdominal compared with the contralateral scrotal testis.(ABSTRACT TRUNCATED AT 400 WORDS)

Specific binding sites for LH/chorionic gonadotrophin, low-density lipoprotein, prolactin and FSH in homogenates of human corpus luteum. I: Validation of methods.

The specific binding of 125I-labelled human chorionic gonadotrophin (hCG), human low-density lipoprotein (hLDL), human FSH (hFSH) and human prolactin (hPRL) to homogenates of human corpus luteum tissue was measured. Specific binding of 125I-labelled hCG was dependent on the temperature and duration of incubation, was inhibited by divalent metal ions or chelating agents, and increased linearly with homogenate concentration. Recovery of bound hormone was more effective using Millipore filtration or polyethylene glycol precipitation compared with centrifugation alone. Binding of 125I-labelled hCG was inhibited specifically by low levels of hCG and human LH (hLH) but not by ovine LH or bovine LH. Incubation of human luteal tissue with ice-cold citrate buffer (pH 3) released more than 90% of specifically bound 125I-labelled hCG within 5 min. This treatment inactivated LH receptors, but did not affect the immunoactivity of hLH released, enabling the measurement of released hormone by radioimmunoassay. Scatchard plots of binding of 125I-labelled LDL to human corpus luteum demonstrated a single class of binding sites. Binding was saturable, increased linearly with increasing concentration of homogenate, and was displaceable by low concentrations of unlabelled LDL. Binding of 125I-labelled hPRL to human luteal homogenates was increased by Mg2+ and was specific for lactogenic hormones (human prolactin, human growth hormone and ovine prolactin). Binding of 125I-labelled hFSH was not dependent on divalent metal ion concentration (in marked contrast to hFSH binding to immature pig granulosa cell receptors) and was displaced by hFSH preparations but not by hPRL, ovine LH or hCG at 1 microgram/ml. These results establish optimal conditions and hormone specificities for the measurement of human luteal gonadotrophin and LDL receptors, and methods for the estimation of hLH/hCG endogenously bound to human corpus luteum tissue.

Specific binding sites for gonadotrophin-releasing hormone, LH/chorionic gonadotrophin, low-density lipoprotein, prolactin and FSH in homogenates of human corpus luteum. II: Concentrations throughout the luteal phase of the menstrual cycle and early pregnancy.

Corpora lutea were obtained from 52 women undergoing laparotomy during the luteal phase of the menstrual cycle. In addition, stromal, thecal and granulosa cell preparations were obtained from seven women undergoing ovariectomy during the late follicular-preovulatory phase of the cycle. The specific binding of a 125I-labelled gonadotrophin-releasing hormone (GnRH) agonist [D-Ser(But)6] GnRH(1-9)-ethylamide (buserelin) and of human chorionic gonadotrophin (hCG), human FSH (hFSH), human prolactin (hPRL) and human low-density lipoprotein (hLDL) to tissue homogenates was measured under optimal conditions. Bound LH/hCG was estimated by elution with acid-citrate buffer, followed by radioimmunoassay of released hormone. Binding of GnRH agonist, though variable, was highest in mid-luteal corpus luteum and high binding was also present in three out of four corpora lutea of pregnancy. Binding of LH/hCG increased significantly with luteinization, reaching maximal levels in the mid-luteal phase before falling significantly. Occupancy of LH receptors by bound LH was relatively constant throughout the luteal phase (10.7-35.3%), but occupancy increased to greater than 90% in corpora lutea from early pregnancy. Binding of hFSH was variable, with only five out of 50 corpora lutea having binding greater than 10 pg/micrograms DNA. Similarly, hPRL binding varied markedly with only six out of 44 having binding greater than 50 pg/micrograms DNA. Binding of LDL was highest in the early- to mid-luteal phases of the cycle. In corpora lutea from all stages of the menstrual cycle (excluding corpora albicantia), GnRH agonist binding was highly correlated with the levels of unoccupied and occupied LH receptors (P less than 0.001; n = 49 and n = 48 respectively) and with LDL receptors (P less than 0.002; n = 49). Binding of GnRH agonist was also correlated with PRL binding (P less than 0.05; n = 21) but not with FSH receptors (P greater than 0.4; n = 25). In addition, LDL binding was associated with PRL (P less than 0.005; n = 21) and FSH receptors (P less than 0.05; n = 25) and with endogenously bound LH (P less than 0.03; n = 48), but not with unoccupied LH receptors (P = 0.8; n = 49). Moreover, in corpora lutea from the mid-luteal phase, there was a strong association between GnRH agonist binding and LDL receptors (P less than 0.02; n = 23). The correlations between GnRH agonist binding and a number of important indices of luteal function suggest a physiological role for GnRH-like factors in the human corpus luteum.

Changes in the concentration of prostaglandins in preovulatory human follicles after administration of hCG.

The concentrations of prostaglandins F-2 alpha, E, D-2 and 13,14-dihydro-15-keto PGE were measured in follicular fluid collected from women undergoing routine laparoscopy following induction of follicular development with clomiphene and hCG. Laparoscopy was performed before, or at 12, 24 or 36 h after administration of hCG. Prostaglandins were measured as the methyloxime derivative by radioimmunoassay. Peaks in PGE and PGF-2 alpha concentration occurred at 12 and 36 h with a significant nadir at 24 h, whereas PGD-2 production was very low at 36 h. The concentration of PGF-2 alpha rose significantly between 0 and 36 h and was greatest in follicles yielding oocytes, suggesting a possible role for this prostaglandin in the mechanism of follicle rupture.

Meiosis-inducing substances in human preovulatory follicular fluid related to time of follicle aspiration and to the potential of the oocyte to fertilize and cleave in vitro.

Meiosis-inducing substance (MIS) and steroid and gonadotropic hormones were investigated in 41 preovulatory follicular fluids (FFs) aspirated at either 0, 12, or 36 hours after human chorionic gonadotropin (hCG) administration in 25 women with clomiphene citrate-stimulated cycles. Twenty-one oocytes were recovered from these FFs and subjected to in vitro fertilization. MIS activity was present in 25 (61%) of the FFs. The frequency of MIS-active FFs increased from 11% (1 of 9) at 0 hours and 40% (2 of 5) at 12 hours to 81% (22 of 27) at 36 hours after hCG administration (P less than 0.001). The concentration of hormones in MIS-active FFs was not significantly different from that of MIS-inactive FFs. Twelve (86%) of 14 oocytes that fertilized and cleaved in vitro were recovered from MIS-active FFs. By contrast, all seven oocytes that remained unfertilized in vitro were recovered from MIS-inactive FFs. These findings support the notion that resumption of meiosis in the preovulatory oocyte is triggered by MIS in FF and suggest that follicular MIS production may be one of the factors that determines the success of in vitro fertilization and early embryonic development.

Changes in plasma levels of prolactin, in relation to those of FSH, oestradiol, androstenedione and progesterone around the preovulatory surge of LH in women.

Plasma samples were obtained at 8 hourly intervals around the preovulatory surge of LH in three groups of women with spontaneously ovulatory menstrual cycles, in order to clarify the hormonal events around the time of ovulation. In 21 of 25 women in whom samples were collected every 8 hours the start of the LH surge occurred between midnight and 0800. In 16 of these women the concentration of LH, FSH and progesterone was measured every 8 hours around the pre-ovulatory surge of LH. A progressive increase in progesterone started with the onset of the LH surge, with a transient fall after 32-40 h at a time coincident with that of ovulation. In 10 women oestradiol, androstenedione and prolactin were measured 8 hourly around the pre-ovulatory surge of LH beginning at 0800 h. Prolactin showed a sustained increase in levels beginning at the start of and lasting for the duration of the pre-ovulatory LH surge; oestradiol levels did not rise around this time, and declined by 24 h after the onset of the LH surge. These results suggest that (1) the pre-ovulatory LH surge begins between midnight and 0800 h in the majority of women, (2) luteinization of the granulosa cells within the pre-ovulatory follicle occurs in response to the LH surge, (3) the increase in prolactin at the time of the LH surge is not directly related to increasing levels of oestradiol but may be due to a decrease in hypothalamic inhibition of prolactin secretion which occurs coincident with the release of LHRH associated with the preovulatory LH surge.

Gonadotrophin and steroid concentrations in bovine follicular fluid and their relationship to follicle size.

The concentrations of LH, FSH and prolactin, and oestradiol-17 beta, androstenedione, testosterone and progesterone were measured in follicular fluid from small, medium and large bovine follicles. As follicle size increased, there was a significant increase in median fluid concentrations of prolactin (2-fold) and oestradiol-17 beta (14-fold) and a significant decrease in concentrations of LH (to 73%), androstenedione (to 30%) and testosterone (to 10%). There was no relationship between follicle size and fluid concentrations of FSH or progesterone, or between fluid concentrations of FSH and the relative concentrations of androgen and oestradiol-17 beta. As follicle size increased there was a significant increase in the proportion of follicles in which follicular fluid concentrations of oestradiol-17 beta exceeded those of androgen. There was a significant relationship between follicular fluid concentrations of prolactin and progesterone; as fluid prolactin concentrations increased, the maximum concentration of progesterone observed decreased.

Human testis does not secrete oestrone sulphate.

The concentrations of five steroids in samples of spermatic venous blood collected from 17 men undergoing ligation of varicocoeles were compared with those in samples from the antecubital vein. There was evidence of testicular secretion of testosterone, androstenedione, oestradiol-17 beta and oestrone, since the ratios of the mean concentrations in spermatic venous plasma to those in peripheral venous plasma were 77.2, 9.1, 28.7 and 1.6 respectively. The testicular secretion of oestrone sulphate was minimal; the ratio of the mean concentrations in spermatic and peripheral plasma was 1.07. These results support the view derived from isotope dilution studies that almost all oestrone and oestrone sulphate in the circulation is derived from peripheral conversion of other precursor steroids.

Raised plasma oestrogens in infertile men with elevated levels of FSH.

In twenty oligospermic or azoospermic patients with elevated plasma FSH, the mean concentrations of plasma oestrone sulphate (843 +/- 233 pg/ml), oestrone (54 +/- 10.4 pg/ml) and oestradiol (46.6 +/- 12.6 pg/ml) were found to be significantly higher than in twenty-one normal fertile men of comparable age (593 +/- 220 pg/ml, 40.6 +/- 8.8 pg/ml and 33.1 +/- 10.9 pg/ml respectively). SHBG binding capacity was elevated in the infertile group (infertile 3.35 +/- 0.82 x 10(-8) M/l v. normal 2.76 +/- 0.89 x 10(-8) M/l) but the total plasma testosterone concentrations were comparable (infertile 5435 +/- 1578 pg/ml v. normal 5046 +/- 1102 pg/ml). Evidence was cited to support the view that Sertoli cells, in response to an unphysiological FSH stimulation, are a likely source of excessive oestrogen production. The possible significance of increased intra-testicular and circulating oestrogen in the altered state of testicular steroidogenic function in men with primary seminiferous tubular defects was discussed.

Changes in the binding of human chorionic gonadotrophin/luteinizing hormone, follicle-stimulating hormone and prolactin to human corpora lutea during the menstrual cycle and pregnancy.

The changes in the binding of human chorionic gonadotrophin/luteinizing hormone (HCG/LH), follicle-stimulating hormone (FSH) and prolactin to 44 corpora lutea have been assessed during the luteal phase of the human menstrual cycle and early pregnancy. All corpora lutea bound HCG but out of 32 only ten bound FSH and only seven bound prolactin specifically. While binding of HCG increased to maximal levels in the mid-luteal phase, binding of FSH and prolactin was most often found in the early luteal phase. Maximum binding of HCG was associated with maximum serum levels of progesterone. Luteal regression was associated with a decrease in the binding of HCG but a causal relationship could not be established. Very low binding of HCG was found to corpora lutea of pregnancy. These results show that (1) the changes in binding of HCG during the luteal phase of the human menstrual cycle are similar to those in other species and (2) there are specific binding sites for prolactin and FSH in the human corpus luteum.

Alterations in steroidogenesis and human chorionic gonadotropin binding in the cryptorchid rat testis.

One month after the induction of cryptorchidism in adult rats, serum levels of LH and FSH were significantly elevated in comparison with sham-operated controls, whereas serum levels of testosterone remained low to normal. Testis weight in cryptorchid rats was reduced by over 66%, and once the extratubular fluid was removed by decapsulation, the reduction in weight was 78%. The basal production of testosterone, pregnenolone, and estradiol in vitro by testes from cryptorchid rats was similar to controls, whereas significantly less androstenedione was produced. Testicular stimulation in vitro with a high dose of hCG (360 pM) resulted in significantly greater production of testosterone, pregnenolone, and estradiol by cryptorchid than by control rat tissue. The in vitro binding of [125I]hCG per testis was decreased in the cryptorchid state to 40% of control values, probably as a result of down-regulation of LH receptors due to the 4-fold elevation of serum LH levels in the cryptorchid rats.

Androgen aromatization by luteinized bovine granulosa cells in tissue culture.

Luteinized bovine granulosa cells in tissue culture contained an active 19-hydroxylase aromatase enzyme system which converted exogenous androstenedione and testosterone to oestradiol-17beta; no oestrone was detected. In the absence of exogenous androgens, the cells failed to synthesize oestrogens due to a limited capacity to synthesize androgen precursor. Theca-lutein cells, present in those CL which synthesize oestrogens, may provide androgen precursor for aromatization by the granulosa-lutein cells.

Concentration of prostaglandin F2alpha and steroids in the human corpus luteum.

The concentration of prostaglandin F2alpha (PGF2alpha), progesterone, pregnenolone, oestradiol-17beta, oestrone, androstenedione and testosterone was measured in corpora lutea obtained from 40 women at various stages of the menstrual cycle. The concentration of PGF2alpha was significantly higher in corpora lutea immediately after ovulation (26-7 +/- 3-9 (S.E.M.) ng/g, P less than 0-005) and in corpora albicantia (16-3 +/- 3-3 ng/g, P less than 0-005) than at any other time during the luteal phase. There was no correlation between the concentration of PGF2alpha, and that of any steroid. The progesterone concentration was highest in corpora lutea just after ovulation (24-9 +/-6-7 microng/g) and in early luteal groups (25-7 +/- 6-8 microng/g) but declined significantly (P less than 0-05) to its lowest level in corpora albicantia (1-82 +/- 0-66 microng/g). The concentration of oestradiol-17beta in the corpus luteum and luteal weight were significantly greater during the mid-luteal phase than at any other stage (concentration 282 +/- 43 ng/g), P less than 0-05; weight 1-86 +/- 0-18 g, P less than 0-005). The results indicate that regression of the human corpus luteum is not caused by a rise in the ovarian concentration of PGF2alpha in the late luteal phase of the cycle.