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Glucosinolates (GSLs) are plant secondary metabolites consisting of sulfur and nitrogen, commonly found in Brassicaceae crops, such as Arabidopsis thaliana. These compounds are known for their roles in plant defense mechanisms against pests and pathogens. 'Guilt-by-association' (GBA) approach predicts genes encoding proteins with similar function tend to share gene expression pattern generated from high throughput sequencing data. Recent studies have successfully identified GSL genes using GBA approach, followed by targeted verification of gene expression and metabolite data. Therefore, a GSL co-expression network was constructed using known GSL genes obtained from our in-house database, SuCComBase. DPClusO was used to identify subnetworks of the GSL co-expression network followed by Fisher's exact test leading to the discovery of a potential gene that encodes the ARIA-interacting double AP2-domain protein (ADAP) transcription factor (TF). Further functional analysis was performed using an effective gene silencing system known as CRES-T. By applying CRES-T, ADAP TF gene was fused to a plant-specific EAR-motif repressor domain (SRDX), which suppresses the expression of ADAP target genes. In this study, ADAP was proposed as a negative regulator in aliphatic GSL biosynthesis due to the over-expression of downstream aliphatic GSL genes (UGT74C1 and IPMI1) in ADAP-SRDX line. The significant over-expression of ADAP gene in the ADAP-SRDX line also suggests the behavior of the TF that negatively affects the expression of UGT74C1 and IPMI1 via a feedback mechanism in A. thaliana.

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Recently, increasing research efforts have been made to exploit the enormous potential of nanotechnology and nanomaterial in the application of arsenic removal from water. As a result, there are myriad of types of nanomaterials being developed and studied for their arsenic removal capabilities. Nevertheless, challenges such as having a complete understanding of the material properties and removal mechanism make it difficult for researchers to engineer nanomaterials that are best suited for specific water treatment applications. In this review paper, a comprehensive review will be conducted on several selected categories of nanomaterials that possess promising prospects in arsenic removal application. The synthesis process, material properties, as well as arsenic removal performance and removal mechanisms of each of these nanomaterials will be discussed in detail. Fe-based nanomaterials, particularly iron oxide nanoparticles, have displayed advantages in arsenic removal due to their super-paramagnetic property. On the other hand, TiO2-based nanomaterials are the best candidates as photocatalytic arsenic removal agents, having been reported to have more than 200-fold increase in adsorption capacity under UV light irradiation. Zr-based nanomaterials have among the largest BET active area for adsorption-up to 630 m2 g-1-and it has been reported that amorphous ZrO2 performs better than crystalline ZrO2 nanoparticles, having about 1.77 times higher As(III) adsorption capacity. Although Cu-based nanomaterials are relatively uncommon as nano-adsorbents for arsenic in water, recent studies have demonstrated their potential in arsenic removal. CuO nanoparticles synthesized by Martinson et al were reported to have adsorption capacities up to 22.6 mg g-1 and 26.9 mg g-1 for As(V) and As(III) respectively. Among the nanomaterials that have been reviewed in this study, Mg-based nanomaterials were reported to have the highest maximum adsorption capacities for As(V) and As(III), at 378.79 mg g-1 and 643.84 mg g-1 respectively. By combining desired properties of different nanomaterials, composite nanomaterials can be made that have superior potential as efficient arsenic removal agents. Particularly, magnetic composite nanomaterials are interesting because the super-paramagnetic property, which allows efficient separation of nano-adsorbents in water, and high adsorption capacities, could be achieved simultaneously. For instance, Fe-Mn binary oxide nanowires have shown promising As(III) adsorption capacity at 171 mg g-1. Generally, nanomaterials used for arsenic removal face severe degradation in performance in the presence of competing ions in water, especially phosphate ions. This study will contribute to future research in developing nanomaterials used for arsenic removal that are highly efficient, environmentally friendly and cost-effective by providing a thorough, structured and detailed review on various nanomaterial candidates that have promising potential.

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Temperature is one of the key factors in limiting the distribution of plants and controlling major metabolic processes. A series of simulated reciprocal transplant experiments were performed to investigate the effect of temperature on plant chemical composition. Polygonum minus of different lowland and highland origin were grown under a controlled environment with different temperature regimes to study the effects on secondary metabolites. We applied gas chromatography-mass spectrometry and liquid chromatography time-of-flight mass spectrometry to identify the chemical compounds. A total of 37 volatile organic compounds and 85 flavonoids were detected, with the largest response observed in the compositional changes of aldehydes and terpenes in highland plants under higher temperature treatment. Significantly less anthocyanidin compounds and larger amounts of flavonols were detected under higher temperature treatment. We also studied natural variation in the different plant populations growing under the same environment and identified compounds unique to each population through metabolite fingerprinting. This study shows that the origin of different plant populations influences the effects of temperature on chemical composition.

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BACKGROUND: Accumulation of plaque on tooth surfaces that have fixed orthodontic appliances is increased. Effective removal is essential to maintain oral health but it is unclear whether the use of interdental or interspace brushes is useful. OBJECTIVES: To compare the effectiveness of standard toothbrushes with combined standard toothbrushes and interdental/interspace brushes used by patients during fixed orthodontic appliances therapy in relation to plaque removal, the health of dental and supporting tissues, dependability, cost and adverse effects. SEARCH STRATEGY: We searched the Cochrane Oral Health Group's Trials Register, CENTRAL, MEDLINE, EMBASE and CINAHL. Schools of dental hygiene were contacted for additional data. No language restrictions were applied. Handsearching of the relevant journals was carried out. Most recent search: January 2006. SELECTION CRITERIA: Randomised controlled trials (RCTs) including the following criteria: participants - patients with fixed orthodontic appliances and uncompromised manual dexterity; intervention - unsupervised toothbrushing with standard toothbrush alone versus standard toothbrush and interdental/interspace brush. Primary outcomes were differences in plaque control, gingival health and decalcification. DATA COLLECTION AND ANALYSIS: Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were to be conducted in duplicate and independently. Trials were to be grouped in terms of their interventions and outcome measures. Results were to be expressed as random-effects models using standardised mean differences for continuous outcomes and risk ratios for dichotomous outcomes with 95% confidence intervals. Heterogeneity was to be investigated. MAIN RESULTS: No studies were identified to support or contest the null hypothesis. AUTHORS' CONCLUSIONS: The present practice of recommending the use of interdental/interspace brushes in addition to standard toothbrushes is not supported by clinical investigations. Interdental brushes and normal toothbrushes wear is increased during orthodontic treatment and brushes need to be replaced more frequently. This increases the economic burden of oral hygiene products for the patient. Well designed RCTs are required to provide evidence for determining clinical practice in this area.

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Luteinizing hormone (LH) plays an important role in the gametogenesis in both sexes by promoting the production of sex steroid hormones in the testes and ovaries. We previously described a genetic variant (V) of LH resulted from a mutation (G1502A) in the LH beta-subunit gene, causing the glycine102serine change in the protein hormone. This variant was subsequently found to be associated with both male and female infertility. In this study, we determined the functional aspect of this LH variant in vitro. Site-directed mutagenesis was employed to construct the V-LH beta-subunit gene. Bioactivities of V-LH expressed in Chinese hamster ovary (CHO) cells cotransfected with the V-beta-subunit and native alpha-subunit genes were compared to those of wild-type (WT) LH. The amino acid replacement did not result in the change of efficacy of alpha- and beta-subunit dimerization of the hormone. However, V-LH had significantly lower receptor-binding activity (P<0.001) and lower biopotency for progesterone production (P<0.001) than WT-LH at the higher concentrations of LH. Considering the latter and its known association with both male and female infertility, it is suggested that the V-LH may be a contributing factor to the pathogenesis of infertility in the carriers of this variant.

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The present study examined the dose-response effects of eCG treatment alone and in combination with various doses of hCG on early embryonic development in vivo and viable pregnancy rate in rats. Mated female Wistar rats were treated with eCG alone (0, 10, 20 or 40 iu), or with 20 iu eCG in combination with various doses of hCG (10, 20, 40 or 80 iu) administered 48 h later. The animals were killed on days 2, 3, 4, 5 or 14 of pregnancy and the numbers of embryos and fetuses recovered were scored. All rats treated with 0 or 10 iu eCG were pregnant. The pregnancy rate was reduced from 62.5% on day 2 to 25% on day 14 and from 31% on day 2 to 10% on day 14 in the groups treated with 20 and 40 iu eCG, respectively. The reduction in pregnancy rate induced by 20 iu eCG was negated by the increasing doses of hCG used. A 100% pregnancy rate was noted on days 2 and 3 in the groups treated with doses of hCG between 10 and 80 iu and from day 2 to day 4 in the groups treated with doses of hCG between 20 and 80 iu. However, a higher viable pregnancy rate was observed only in the group treated with 10 iu hCG compared with the group treated with 20 iu eCG and 0 iu hCG. These results imply that hyperstimulation of rats with high doses of eCG compromises pregnancy rate and markedly reduces litter size and that the addition of hCG is required for complete ovulation, which results in higher embryo yield and a delay in early embryo demise.

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OBJECTIVE: Luteinizing hormone (LH) promotes ovulation and luteinization of the ovarian follicle, and stimulates steroidogenesis in the ovaries. It is known to be present in different molecular forms, and secretion of abnormal LH has been implicated in menstrual disorders and infertility. The purpose of this study was to determine any association of two recently described LH variants with menstrual disorders in Singapore Chinese women. One of these variants had Trp8 to Arg8 and Ile15 to Thr15 replacements in the LH beta-subunit, while the second variant possessed Ser102 substitution for Gly102. PATIENTS: One hundred and seventy six patients with menstrual disorders and two hundred normal ovulatory women were recruited and screened for the presence of these two LH variants. METHODS: The polymerase chain reaction (PCR) products of patients were analysed by restriction fragment length polymorphism (RFLP) and the results were compared with those of normal ovulatory women and confirmed by DNA sequencing. RESULTS: Twenty one (11.9%) patients with menstrual disorders and twenty (10%) normal ovulatory women were found to carry the first variant, but its occurrence did not show any significant statistical difference between the patient and control groups (P = 0.679). However, the second variant was only detected in seven (4%) patients with menstrual disorders, and none of the normal ovulatory subjects (P = 0.005). CONCLUSIONS: the study showed that the first variant was not associated with menstrual disorders, whereas the second variant might be implicated in menstrual disorders in some Singapore Chinese women.

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A total of 79 healthy female transsexuals, divided into four groups, were involved in this study. Group 1 comprised 15 pre-operated normal cycling females; Group 2, five pre-operated females who were on regular androgen therapy for 1-3 years; Group 3, 27 post-operated females who were on regular androgen therapy for 2-12 years; and Group 4, 32 post-operated females who either had stopped or were on irregular androgen therapy. A bone scan of the lumber spine, at positions L2-L4, was carried out for each subject. A blood sample was taken for measurement of plasma testosterone concentrations. Ten subjects from Group 3 had a repeat bone scan following 10-39 months of calcium supplement (625 mg daily as calcium carbonate); another 10 post-operated females of Group 3 had a repeat bone scan 6-59 months later; and five subjects from Group 4 had a repeat scan following resumption of regular androgen therapy for 17-27 months. The mean +/- SE concentrations of testosterone of Groups 1-4 were, respectively, 0.58 +/- 0.05, 10.1 +/- 2.48, 7.7 +/- 0.98 and 0.99 +/- 0.14 ng/ml. Pre-operated females (Group 2) following 1-3 years of regular androgen therapy had significantly higher BMD and age-matched BMD than corresponding levels in pre-operated normal cycling females in Group 1. While the age-matched BMDs of post-operated females, who were on regular androgen therapy, were not significantly different, the mean BMD was significantly lower than corresponding values in the controls of Group 1. Post-operated females in Group 4 had significantly lower BMDs and age-matched BMDs as compared to corresponding values in controls of Group 1. The BMDs and age-matched BMDs of post-operated females, who were on regular androgen therapy, were significantly raised following daily calcium supplementation for durations ranging from 10-39 months. A repeat bone scan carried out following a lapse of 6-59 months did not reveal any significant change in the BMDs and age-matched BMDs of 10 post-operated females on regular androgen therapy. On the other hand, the BMDs and age-matched BMDs of post-operated females in Group 4 were significantly raised following the resumption of regular androgen therapy for 17-27 months. Results of the present study showed that ovariectomy and remaining in the hormone-deficient state for a sufficiently long duration was associated with a definite loss of bone mass. However, it was shown in this study that the resumption of regular androgen therapy for a sufficient duration could arrest this loss and, additionally, substantially increase the bone mass. Androgen appears to have a potentially greater impact on bone mass than oestrogen. Furthermore, calcium supplementation in a Singaporean population, which is accustomed to a low dietary calcium intake, can assist in the accretion of a higher bone mass in an adult population.

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We reported the results of a randomized cross-over study comparing SH D 461 M (Climen) and Prempak-C in 38 postmenopausal women who were established users of hormone replacement therapy (HRT). Climen contains 11 tablets of 2 mg estradiol valerate (EV), and 10 tablets with 2 mg EV plus 1 mg of cyproterone acetate. Prempak-C, on the other hand, is a regimen consisting of 28 tablets of 0.625 mg conjugated equine estrogens (CEE); the last 12 tablets are taken together with 0.15 mg of norgestrel (NG) tablets. Patients in Sequence I started with Climen for 6 months and then crossed-over to Prempak-C, for the next 6 months. Patients in Sequence II followed the reverse order. Following Climen treatment, significantly higher levels (P < 0.05, t-test) of sex hormone binding globulin (SHBG) and estradiol, when compared to Prempak-C treated subjects, were noted. No significant differences in follicle stimulating hormone (FSH), corticosteroid binding globulin (CBG), renin angiotensinogen, angiotensin-I and aldosterone levels between the two treatment regimens were noted. While both regimens were effective in reducing menopausal symptoms, none of the regimens could eliminate all symptoms completely. Treatment with Climen appeared to result in less frequent occurrences of some symptoms. During periods of no estrogen (only true for Climen) as well as periods of maximum P and E, subjects on Climen had significantly lower incidence of some of the symptoms (backache, lack of concentration, lethargy and swelling) when compared to those on Prempak-C.(ABSTRACT TRUNCATED AT 250 WORDS)

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The lipid and lipoprotein profiles of 39 female transsexuals, exposed to testosterone esters (250 mg monthly) for an average duration of 33 months after their sex reassignment operation (group 2), were compared to those of 29 normal menstruating female transsexuals prior to starting androgen therapy (group 1). A third group, comprising 17 post-operative female transsexuals were studied while on, and after stopping their androgen therapy for 6-12 months (group 3). The average concentration of testosterone in androgenized women was comparable to those found in normal males and levels of SHBG were significantly lower than those in the control group. No significant difference was noted between all levels of lipids and lipoproteins in pre-operative subjects of group 1 and corresponding levels in subjects of group 3 after they had stopped their androgen therapy for 6-12 months. Significantly higher levels of triglyceride (Trig), total cholesterol (TC), low-density lipoprotein (LDL-C) and apolipoprotein-B (Apo B) and a significantly lower level of high-density lipoprotein-cholesterol (HDL-C) were noted in androgenized women (group 2) when compared to controls (group 1). The two atherogenic indices, LDL-C/HDL-C and Apo-AI/Apo-B were significantly raised and lowered, respectively. Similar results were noted when comparing lipid and lipoprotein profiles in subjects of group 3 while they were on and after stopping their androgen therapy. Results from this study indicate that testosterone, per se, at supraphysiological doses may promote atherogenicity in women. Furthermore, the male predilection for coronary vascular diseases (CVD) may be due to the adverse effects of higher androgen levels on lipid and lipoprotein profiles.

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We reported the results of a randomized cross-over study comparing SH D 461 M (Climen) and Prempak-C in 38 postmenopausal women who were established users of hormone replacement therapy (HRT). Climen contains 11 tablets of 2 mg estradiol valerate (EV), and 10 tablets with 2 mg EV plus 1 mg of cyproterone acetate. Prempak-C, on the other hand, is a regime consisting of 28 tablets of 0.625 mg conjugated equine estrogens (CEE); the last 12 tablets are taken together with 0.15 mg of norgestrel (NG) tablets. Patients in Sequence I started with Climen for 6 months and then crossed-over to Prempak-C, for the next 6 months; patients in Sequence II, followed the reverse order. Following Climen treatment, significantly higher levels (P < 0.05, t-test) of sex hormone binding globulin (SHBG) and estradiol, when compared to Prempak-C treated subjects, were noted. No significant differences in follicle stimulating hormone (FSH), corticosteroid binding globulin (CBG), renin, angiotensinogen, angiotensin-I and aldosterone levels between the two treatment regimes were noted. While both regimes were effective in reducing menopausal symptoms, none of the regimes could eliminate all symptoms completely. Treatment with Climen appeared to result in less frequent occurrences of some symptoms. During periods of no estrogen (only true for Climen) as well as periods of maximum progestagen and estrogen (P and E), subjects on Climen had significantly lower incidence of some of the symptoms (backache, lack of concentration, lethargy and swelling) when compared to those on Prempak-C.(ABSTRACT TRUNCATED AT 250 WORDS)

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Prolactin (PRL) producing capacity was studied in explants of decidua compacta and decidua spongiosa obtained from 41 patients undergoing termination of pregnancy at gestation 6 to 12 weeks. In vitro PRL producing capacity, expressed as mIU/g protein, of the decidua compacta was significantly higher (P < 0.05) than those of decidua spongiosa. Production of PRL increased with gestation from 6 to 12 weeks with a more rapid rate at the later gestation. The pattern of increase fitted significantly (P < 0.0001) to the exponential model for both decidua compacta and decidua spongiosa. The exponential regression equations for decidua compacta and decidua spongiosa were (ln y = 4.25 + 0.19x) and (ln y = 2.80 + 0.31x) respectively. Hence, although both decidua compacta and decidua spongiosa had a similar pattern of increase in PRL production, the rate of increment was significantly greater in decidua spongiosa than in decidua compacta. These findings suggest that separating decidua compacta and decidua spongiosa of the first trimester would reduce the heterogeneity of decidual tissue and offer a new approach to the studies of the synthesis, release and regulation of PRL production by human decidua.

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Ovarian stimulation is critical to the success of patients in Assisted Reproductive Technology (ART) programmes. We compared two stimulation regimes retrospectively for ART in the NUH programme. These were the 2:1 and the GnRHa-FSH/hMG regimes. The former was our first-line regime while the latter was used for cycles where there was a prior endogenous LH surge, previous poor response, or an elevated LH level between days three to five of the cycle. All cycles in our ART programme in 1991 were studied, except those for special research procedures, e.g. micro-insemination sperm transfer (MIST) cycles, a total of 241 cycles. Cancellation rates were 14.4% (21 of 146 cycles) and 37.3% (19 of 51 cycles) for the 2:1 and GnRHa-FSH/hMG regimes respectively (p > 0.001). For the 2:1 regime, the majority of cancellations were due to ovulation prior to the oocyte recovery (42.9%; nine of 21 cycles). However, for the GnRHa-FSH/hMG regime, almost all the cancellations were due to poor response (84.2%; 16 of 19 cycles). Fertilisation rates were lower for the 2:1 regime (for both IVF-ER and IVF-TET, where sperm quality was poorer) compared to the GnRHa-FSH/hMG (55.0 and 66.6% respectively; p < 0.001). Pregnancy rates were higher for the 2:1 regime when IVF-ER and IVF-TET were used (16.4% and 23.3% respectively per oocyte recovery, versus 9.8% and 18.8% respectively for the GnRHa-FSH/hMG regime).

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The response of prolonged oestrogen priming (by silastic implants) of the male rat hypothalamic-pituitary axis (HPA) to an oestrogen challenge test was investigated. Basal LH levels were suppressed to a maximum at two months and remained unchanged by four months. In contrast to response in human, oestrogen priming had failed to stimulate a positive feedback response to an oestrogen challenge test in the male rats. Instead, oestrogen priming might have attenuated the negative LH feedback response. Increasing the dose of oestrogen priming by increasing the duration was not effective in inducing positive feedback in the male rats. The failure of these priming regimes to stimulate positive feedback in male rats may reaffirm our earlier suggestion that oestrogen does not play an important role in activating the cyclic centre in rats. This would also contradict the suggestion that testicular secretions may have acted through conversion to oestradiol in the suppression of the cyclic system in males during the critical period of differentiation of the HPA.

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Five hundred and eight mature female Wistar rats divided into 35 different groups were stimulated with pregnant mare serum gonadotrophins (PMSG) (0, 5, 10, 20 & 40 IU) at the late diestrus stage to induce multiple follicular development. No chorionic gonadotrophin (CG) was used for ovulation induction. The quality of oocytes and their in vitro fertilisability, quality of Day 2-embryos, viability of pregnancy and status of fetuses on Day 14 of gestation and status of embryos retrieved on Day 2, 3, 4 and 5 of pregnancy in different subgroups of rats were examined. Results showed that more oocytes and embryos fertilised in in vivo were retrieved from rats supraphysiologically stimulated with 20 IU of PMSG. However, concurrent with the larger number, higher proportions of abnormal oocytes and embryos were found. High doses of PMSG caused lower in vitro fertilisability of oocytes and greater degrees of embryonic degeneration. Although, the number of oocytes and Day 2-embryos were higher in the 20PMGS dose group, the pregnancy rate was significantly reduced to 27%. In the 40PMSG group no viable pregnancy was noted. Most embryo demise occurred by day 3-5 of pregnancy, probably within the oviducts and before the implantation stage. In rats supraphysiologically stimulated with 20 and 40 IU of PMSG, the number of morphologically normal looking embryos was greatly reduced by Day 3-5 of pregnancy. In the 40PMSG group, there were no embryos retrieved by Day 4 and 5.(ABSTRACT TRUNCATED AT 250 WORDS)

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A total of 950 female Wistar rats in 81 groups were involved in this study. Different groups of rats were stimulated with PMSG (0, 10 & 20 IU) at diestrus followed, 48-52 hr later, by different doses of HCG (0, 10, 20, 30 & 40) for ovulation induction. The dose-dependent effects of HCG, either with or without the use of PMSG for stimulation of multiple follicular development, on the quality of oocytes and their in vitro fertilisability, quality of Day 2-embryos, viability of pregnancy and status of embryos retrieved on Day 2, 3, 4 or 5 of pregnancy in different subgroups of rats were examined. Results showed that more oocytes and embryos fertilised in vivo were retrieved from rats supraphysiologically stimulated with 20 IU of PMSG. The addition of HCG did not increase the number of ovulated oocytes or Day-2 embryos. In other words, the number of oocytes or embryos produced is dependent on the dose of PMSG administered during diestrus rather than on the dose of HCG given for ovulation induction. Hence, no increase in the amount of HCG is required to effectively ovulate bigger cohort of preovulatory follicles in supraphysiologically stimulated rats. As was shown earlier, in vitro and in vivo fertilisation rates were reduced when higher doses of PMSG were used. Similarly, these rates were reduced when increasing doses of HCG were used in rats not previously stimulated with PMSG. When higher doses of HCG were used in rats stimulated earlier with PMSG (10 and 20 IU), the in vitro but not the in vivo fertilisation rates were further reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

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It is well known that peripheral prolactin levels are significantly higher in menarcheal women than in men. Higher levels of prolactin in menarcheal women are related to exposure to higher levels of estrogen in women than in men. Increased exposure to androgens in men has also been proposed as a possible reason to account for lower prolactin levels in men; however, this suggestion has not been conclusively proven. The current study sought to evaluate the cross-gender effects of male and female hormones on basal levels and the pituitary store of prolactin in humans. Four groups of individuals were involved: normal men and women, male and female transsexuals primed with female hormones and testosterone, respectively for at least 6 months. A metoclopramide challenge test was carried out on each subject of each group. Subjects were rested for 1 h, with an indwelling catheter in the antecubital vein, before a blood sample was collected for estimation of basal hormone levels. Following an oral ingestion of 10 mg of metoclopramide, blood samples were collected at 15, 30, 60, 90, 120, 150 and 180 min. Prolactin, estradiol and testosterone concentrations were measured by radioimmunoassay. Basal levels as well as metoclopramide-induced releases of prolactin (as measured by area under the curve) in normal women were significantly higher (p less than 0.05) than corresponding levels in normal men. Following long-term priming with female hormones, the pattern of response to metoclopramide in male transsexuals was dramatically changed.(ABSTRACT TRUNCATED AT 250 WORDS)

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The effects of androgens alone and in combination with oestrogens on luteinizing hormone secretion in adult female rats were studied after 1, 2 and 4 months of priming. Each adult female rat was implanted with a Silastic capsule filled with testosterone or dihydrotestosterone alone or together with another similar capsule of oestradiol. An oestrogen challenge test was carried out in each rat after priming. Blood samples were collected before androgen priming. During the oestrogen challenge test, blood samples were collected before (0 h or day 0) and at 12, 24, 36 and 48 h after the intramuscular injection of 50 µg oestradiol vaierate for rats primed for 1 month, or daily for 5 days (days 1 to 5) for other rats. An oestrogen challenge test was also performed in two groups of untreated male and female rats which served as controls. The results indicated that long-term androgen priming had resulted in the attenuation or total blockade of the luteinizing hormone surge which normally occurs during an oestrogen challenge test in adult female rats. This suggests that androgens may be important modulators of the luteinizing hormone surge mechanism in rats. Furthermore, the fact that the luteinizing hormone surge can be blocked by androgen priming in adult female rats suggests that the sexual dimorphic response to oestrogen feedback is not immutably imprinted in the hypothalamic-pituitary axis as was originally proposed.