Patients with essential thrombocythaemia have an increased prevalence of antiphospholipid antibodies which may be associated with thrombosis.

A significant proportion of patients with Essential Thrombocythaemia (ET) have thrombotic complications which have an important impact upon the quality, and duration of their life. We performed a retrospective cross sectional study of the prevalence of antiphospholipid antibodies (APA) in 68 ET patients. Compared to 200 "elderly" controls (>50 years) there was a significant increase in anticardiolipin IgM (p < 0.0001) and anti beta2 glycoprotein I (anti-beta2GPI) IgM (p < 0.0001) antibodies in ET. Thrombosis occurred in 10/20 with APA and 12/48 without, p = 0.04, relative risk 2.0 (95% confidence intervals 1.03-3.86): these patients did not differ in terms of other clinical features. The prevalence of thrombosis in patients with dual APA (6/7) was significant when compared to those with single APA (p = 0.02) and the remaining patients (p < 0.0002). Also anti-beta2GP1 IgM antibodies either alone, or in combination with another APA, were associated with thrombosis (p = 0.02). These results suggest that the prevalence of APA in ET and their influence upon thrombotic risk merit investigation in a larger study.

Fluctuations in levels of antiphospholipid antibodies and increased coagulation activation markers in normal and heparin-treated antiphospholipid syndrome pregnancies.

Antiphospholipid antibodies (aPL) are associated with an increased risk of thrombosis and recurrent miscarriage. We assessed levels of coagulation activation markers and aPL during normal pregnancy and in women with the antiphospholipid syndrome (aPS). Fluctuations in aPL levels were observed in all patients with aPS. No particular pattern of antibody positivity, or fluctuation in aPL level, was associated with poor pregnancy outcome. A significant increase was observed in levels of factor Xlla (FXIIa; P < 0.001), factor VIIa (FVIIa, P < 0.001), thrombin antithrombin complexes (TAT; P < 0.001), prothrombin fragment F1.2 (F1.2; P < 0.001) and D-dimer (DD; P < 0.05) during normal pregnancy. Factor VIIa, TAT, F1.2 and DD increased significantly before 20 weeks gestation, while a statistically significant increase in FXIIa levels was first detected between weeks 20 and 30 of gestation. In pregnant women with aPS, increases in FXIIa were similar to those in normal pregnancy, but increased FVIIa levels were not observed until after 30 weeks gestation. Similar to normal pregnancy, increased levels of TAT and F1.2 were detected in aPS pregnancies before 20 weeks gestation, but increased DD were not observed until after week 20. Surprisingly, women with aPS receiving low molecular weight heparin prophylaxis had significantly higher (P = 0.02) levels of TAT (median 8.6; interquartile range (IQR) 6.5-20.8) between weeks 20 and 30 of gestation compared to the normal pregnant population (median 5.9; IQR 4.7-7.9), thus indicating increased thrombin generation in women with aPS in mid-pregnancy.

Antibodies to factor XII are distinct from antibodies to prothrombin in patients with the anti-phospholipid syndrome.

Patients with the anti-phospholipid syndrome (APS) have antiphospholipid antibodies (aPA) which are often targeted towards phospholipid binding proteins such as beta2-glycoprotein I and prothrombin. Antibodies to factor XII (FXIIabs) have also been identified in some patients with APS. Factor XII (FXII) is a member of the kringle family of proteins which include plasminogen and prothrombin. Antibodies to prothrombin have been associated with myocardial infarction and have been shown to cross react with plasminogen. Sixteen patients with APS and FXIIabs were investigated for the presence of antibodies to prothrombin, by enzyme linked immunosorbent assay in a calcium (Ca++) independent assay. All sixteen showed different antibody binding patterns than those observed for antibodies to FXII. Eight patients were further investigated using surface plasmon resonance (SPR) for antibody binding to covalently bound FXII and to covalently bound prothrombin in both Ca++ dependent and independent systems. Of three patients demonstrating antibody binding to FXII by SPR, none demonstrated antibody binding to prothrombin in a Ca++ independent system with one demonstrating antibody binding to prothrombin that was Ca++ dependent. Of five patients who did not bind FXII by SPR, one demonstrated antibody binding to prothrombin in a Ca++ independent system while two demonstrated antibody binding to prothrombin in a Ca++ dependent system. Antibodies to FXII in patients with APS appear to be distinct from antibodies to prothrombin.

Mass spectrometric characterization of proteins extracted from Jurkat T cell detergent-resistant membrane domains.

Plasma membranes of most cell types are thought to contain microdomains commonly referred to as lipid rafts, biochemically distinct from bulk plasma membrane, apparently enriched for proteins involved in signal transduction. In T cells, it is believed that lipid rafts aggregate at the site of T cell receptor engagement and act as foci for initiation of the signaling process. In order to gain insight into the possible functioning of lipid rafts, we applied microcapillary liquid chromatography electrospray ionization tandem mass spectrometry (microLC-ESI-MS/MS) methodologies to the identification of proteins which copurified with lipid rafts. Following isolation of lipid rafts as Triton-insoluble, low-density membrane fractions from Jurkat T cells, tryptic digests were generated of individual protein bands resolved electrophoretically. Alternatively, cysteine-containing peptides were isolated from total tryptic digests of unseparated lipid raft proteins following labeling with a cysteine-specific biotinylation reagent and avidin affinity purification. In both cases, protein identifications were made by comparison of tandem MS spectra generated by microLC-ESI-MS/MS to both protein and DNA sequence databases using Sequest software. Proteins identified essentially fell into two groups: cytoskeletal proteins, and proteins involved in signal transduction. These findings are discussed in the light of the current understanding of both lipid raft biology and signal transduction.

Anti-tissue factor pathway inhibitor activity in patients with primary antiphospholipid syndrome.

The association between antiphospholipid antibodies and an increased risk of thrombosis in antiphospholipid syndrome (aPS) patients is probably caused by numerous mechanisms, including the effects of antibodies to phospholipid-binding proteins such as beta(2)-glycoprotein I and prothrombin. In this study, we investigated the inhibition of tissue factor pathway inhibitor (TFPI) in 33 patients with primary antiphospholipid syndrome (PAPS). TFPI was measured in PAPS patients using an amidolytic assay, dependent on the generation of activated factor X (Fxa), and this was compared with 55 healthy subjects. Functional levels of TFPI (mean +/- SD) were significantly lower in PAPS patients (0.89 +/- 0.37 U/ml) than the control group (1.05 +/- 0.15 U/ml) (P = 0.02). The difference was caused by a subset of five patients who had TFPI levels below the lower 99% confidence interval of the normal reference range, representing increased FXa generation in the assay system. IgG fractions were isolated from these five patients and five control subjects, then incorporated into normal plasma to measure FXa generation in the TFPI assay system. FXa generation was increased when polyclonal rabbit anti-human TFPI IgG (P < 0.0001) or PAPS IgG (P = 0.0001) were added to normal plasma, demonstrating inhibition of TFPI. The apparent anti-TFPI activity demonstrated in the five subjects with PAPS in this study may represent a significant new mechanism for thrombosis in patients with aPS, as it implies that increased tissue factor FVIIa-mediated thrombin generation might occur.

Anti-prothrombin antibodies: assay conditions and clinical associations in the anti-phospholipid syndrome.

Anti-phospholipid antibodies (aPL) are associated with an increased risk of thrombosis and recurrent fetal loss. Antibodies to prothrombin (aPT) have been associated with the anti-phospholipid syndrome (aPS). We assessed variations in aPT assay methodology to optimize an aPT method that was used to screen patients with aPS (n = 66). Detection of aPT using enzyme-linked immunosorbent assay was influenced by the concentration of the capture antigen, the microtitre plate type and the buffer system. The combination of gamma-irradiated plates, a phosphate-buffered saline buffer and coating antigen of 10 microg/ml prothrombin was the most sensitive. Both serum and citrate samples are suitable for the detection of aPT. Under these conditions aPT IgM but not IgG were found to be associated with thrombosis and/or fetal loss.

Ontogeny of beta 2 glycoprotein I and annexin V in villous placenta of normal and antiphospholipid syndrome pregnancies.

beta2-glycoprotein I (beta2GPI) and annexin V (AV) have been implicated in the pathophysiology of the antiphospholipid syndrome (APS). We investigated their placental expression in normal villous tissues throughout gestation; first trimester n = 10, early second trimester; n = 4, preterm; n = 5) and term; n = 7 and in APS (2 first trimester, 1 preterm and 8 term deliveries). beta2GPI and AV were both expressed by the placenta from as early as seven weeks gestation and were colocalised to the syncytiotrophoblast. beta2GPI staining was also observed in stromal cells, being present in phagocytic Hofbauer cells and surrounding newly formed fetal vessels in a perivascular pattern, from seven to seventeen weeks gestation. An abnormal morphological distribution of AV was noted in one first trimester APS placenta, and for beta2GPI in a further first trimester placenta. When placental proteins were extracted from villous tissue, the concentration of AV/mg protein in term APS placentas (median, interquartile range) (aPS; 8.16, 7.879.72 microg/mg) was significantly higher (p <0.005) than normal term levels (normal; 2.47, 2.28-2.54 microg/mg). beta2GPI increased with advancing gestation (first trimester; 0.93, 0.64-1.26 microg/mg, term; 3.67, 2.58-4.48 microg/mg) in normal pregnancy. Term APS placentas had a reduced beta2GPI content (2.31, 1.87-2.49 microg/mg), p <0.05. The placental role of these proteins remains to be identified.

Cimetidine and a delayed hypersensitivity reaction.

Oral cimetidine for the treatment of verruca continues to be a topic of discussion and controversy. Although its usage has gained popularity because it offers an alternative to conventional topical and surgical verruca therapy, its reported efficacy in managing warts lacks consistency in outcomes. Using high doses of oral cimetidine, therefore, raises concern about possible untoward effects. Cimetidine relies on effecting a change in the immune system to eradicate the verruca, but such a change in the immune system may cause patients to develop responses detrimental to their well being. The authors present an unusual case of severe delayed hypersensitivity with the use of oral cimetidine.

Human monoclonal anti-phospholipid antibodies selectively bind to membrane phospholipid and beta2-glycoprotein I (beta2-GPI) on apoptotic cells.

The ability of an anti-phospholipid (LJ1) and an anti-beta2-GPI (RSP-57) human MoAb to bind to apoptotic but not viable cells was demonstrated in this study. Both MoAbs were derived from patients with systemic lupus erythematosus and anti-phospholipid antibody syndrome. The parallel analysis of the specificity and affinity of four anti-phospholipid human MoAbs suggests that the binding of LJ1 MoAb to apoptotic cells is a specific property of this MoAb. RSP-57 MoAb recognizes apoptotic cells through beta2-GPI which becomes available for binding after the interaction with negatively charged phospholipids. This observation provides evidence that the binding of human anti-phospholipid antibodies to apoptotic cells occurs in both a beta2-GPI-dependent and independent way and involves a restricted group of epitopes. The finding that LJ1 and RSP-57 MoAbs bind apoptotic cells underlines the property of these MoAbs to act as cell membrane markers of apoptosis. Major pathological implications derive from the observation that LJ1 and RSP-57 MoAbs recognize epitopes expressed on 'early' apoptotic cells. The interference with the in vivo clearance and processing of apoptotic cells is a potential pathogenic mechanism of these antibodies.

Affinity purified human antiphospholipid antibodies bind normal term placenta.

Antiphospholipid antibodies (aPL) are associated with an increased incidence of fetal loss, but the pathophysiology remains unclear. One mechanism may involve the binding of aPL directly to the placenta where they may initiate placental thrombosis and infarction. We have developed an immunofluorescent technique to detect human aPL binding to human placenta. Endogenous immunoglobulins were eluted by extensive washing and residual staining was prevented by incorporating multiple blocking steps. APL were affinity purified on both cardiolipin and phosphatidylserine liposomes from the sera of six patients with aPL (five antiphospholipid syndrome (APS) patients and one post bone marrow transplant patient). Heterogeneous binding to normal term placenta, involving either the trophoblast microvillous surface, stromal and peri-vascular regions was demonstrated by affinity purified aPL from five of six patients. Preliminary sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting studies have demonstrated that aPL bind a number of placental proteins. beta2GPI was not the predominant protein bound by aPL using this technique. This study provides further evidence for the involvement of aPL in mediating placental damage.

Maternal cardiolipin, beta 2-glycoprotein-I and prothrombin antibody expression in high-risk pregnancies with bilateral abnormal uterine artery Doppler waveforms.

OBJECTIVE: To compare the frequency of maternal serum antiphospholipid antibodies (to cardiolipin, beta 2-glycoprotein I and prothrombin) in pregnancies presenting with bilateral abnormal uterine artery Doppler waveforms. DESIGN: Retrospective analysis of stored serum. SUBJECTS: Cases comprised 47 singleton pregnancies with bilateral abnormal uterine artery Doppler waveforms at 24 weeks of gestation, followed from 20 weeks, and controls were 100 healthy pregnancies with normal uterine artery Doppler waveforms. METHODS: Ultrasound examination utilized a 5-MHz curvilinear transabdominal transducer with pulsed and color Doppler facilities. Antiphospholipid antibodies were analyzed by ELISA methodology, and reference ranges were established using the geometric mean +/- 2 SD of healthy non-pregnant adults. Human chorionic gonadotropin (hCG) levels were obtained from patient notes. RESULTS: Anticardiolipin antibodies were detected in 11 (23%) of the cases (IgG, n = 7; IgM, n = 6) compared with ten (10%) of the controls (p < 0.05). Low titer anticardiolipin IgG (range, 5.5-35.3; median, 6.3 GPL units) and anticardiolipin IgM (range, 3.4-14.7; median, 5.3 MPL units) were detected in cases. Amongst the cases, adverse perinatal outcomes were more common in the presence of raised levels of anticardiolipin antibodies. Anti-beta 2-glycoprotein I IgG was not detected in any of the cases. Antiprothrombin IgG was not detected, but antiprothrombin IgM occurred in 10.6% of cases compared with 2% of controls. CONCLUSIONS: Women with persistent bilateral abnormal uterine artery. Doppler waveforms in mid-gestation were more likely to express raised levels of anticardiolipin antibodies than healthy controls with normal uteroplacental perfusion. Anticardiolipin antibodies without anti-beta 2-glycoprotein I binding may be involved in the pathogenesis of uteroplacental ischemia in a proportion of high-risk pregnancies.

Anti-beta2-glycoprotein I, anti-prothrombin and anticardiolipin antibodies in a longitudinal study of patients with systemic lupus erythematosus and the antiphospholipid syndrome.

OBJECTIVE: To determine anti-beta2 glycoprotein-I (anti-beta2GPI) and anti-prothrombin (anti-ProT) antibody levels, and the IgG subclass distribution of anti-beta2GPI antibodies, in serial samples from patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) having initial or recurrent thrombotic/neurological (T/N) events during the study period. To investigate the correlations between these antibodies and beta2GPI antigen, anticardiolipin antibody (aCL), anti-double-stranded (ds) DNA, C3 levels and disease activity. METHODS: Fifty serum samples were identified from seven patients with SLE who had had T/N events during the follow-up from a cohort under long-term follow-up. IgG anti-beta2GPI, anti-ProT, aCL, IgG subclasses of anti-beta2GPI and beta2GPI antigen levels were determined by ELISA. Corresponding disease activity [British Isles Lupus Assessment Group (BILAG)], anti-dsDNA and C3 levels were compared. RESULTS: IgG anti-beta2GPI antibody levels were elevated in six of the patients before and after the T/N events with less marked fluctuations than aCL antibody levels. The predominant subclass of anti-beta2GPI antibodies was IgG2 before and after the T/N events. IgG anti-ProT antibodies were negative in all cases. There was a significant but weak correlation between anti-beta2GPI and aCL antibodies. No correlation was found between disease activity and IgG anti-beta2GPI antibody and beta2GPI antigen levels. There were fluctuations in beta2GPI antigen levels and a trend to increase after T/N events was observed in some patients. CONCLUSION: Most of the patients with a T/N event during the study period had IgG anti-beta2GPI, but not IgG anti-ProT antibodies. Many IgG aCL-negative samples were found to have IgG anti-beta2GPI activity during the follow-up period. The predominant subclass of IgG anti-beta2GPI was IgG2, which may have importance in the pathogenesis of APS. beta2GPI antigen levels were found to be increased in some patients with SLE after T/N events. IgG anti-beta2GPI antibodies may be used as an adjunctive marker of future T/N events in patients with SLE and APS with aCL antibodies and lupus anticoagulant.

The association of factor VIIa, factor XIIa and beta2-glycoprotein-1 with triglyceride-rich lipoproteins in normolipidaemic subjects.

The activation of factors XII (FXII) and VII (FVII) has been shown to occur on the surface of lipoproteins in the presence of lipoprotein lipase and may be modulated by beta2glycoprotein-1 (beta2GP1). In the postprandial state FVII is activated without apparent activation of FXII in plasma. We investigated whether beta2GP1, FXIIa and FVIIa are associated with triglyceride-rich lipoproteins in the fasting and postprandial state. Six normal subjects were studied while fasting and 1, 2 and 4 h after ingestion of 100 g fat. We confirmed that plasma FVIIa activity, but not FXIIa antigen, was increased in the postprandial period. FXIIa, FVIIa and beta2GP1 were associated with chylomicra-rich lipoproteins, and lipase or Triton X-100 treatment caused an increase in FXIIa in plasma and chylomicra without an increase in FVIIa. This suggests that FXIIa may be formed in the postprandial period, but its antigenic determinants are masked by the association with lipoprotein particles, although it could still express proteolytic activity. Alternatively a FXII-independent mechanism or surface other than triglyceride-rich lipoproteins may be responsible for FVII activation in the postprandial state.

Platelet activation and turnover in the primary antiphospholipid syndrome.

Thromboembolism is a common occurrence in patients with the antiphospholipid syndrome (APS). The mechanism responsible for this phenomenon is unclear; there are several theories. One possibility is that a pathogenic interaction exists between antiphospholipid antibodies and platelets, leading to their activation. This study examined the expression of the platelet activation markers CD62 and CD63 by flow cytometry in 20 patients with the primary antiphospholipid syndrome (PAPS). Levels of soluble P-selectin were also assayed. Reticulated platelets were measured as an indicator of increased platelet production and/or turnover. Median CD63 expression was significantly increased in patients (14.3%) compared to a group of healthy controls (10.1%, P = 0.0008). There was no significant difference in median CD62 expression or percent reticulated platelets between the two groups. The median level of soluble P-selectin was significantly higher in PAPS patients (35.5 ng/ml) compared to controls (18.8 ng/ml, P = 0.0028). Patients receiving aspirin had lower median CD63 values (13.1%) when compared to those patients who were not (18.0%, P = 0.023). However, aspirin therapy did not prevent significant platelet activation occurring in some individual patients. Our data suggest that although not excessive, there is a degree of increased platelet activation in some PAPS patients, which is not always suppressed by antiplatelet therapy with aspirin.

Binding of anticardiolipin antibodies to protein C via beta2-glycoprotein I (beta2-GPI): a possible mechanism in the inhibitory effect of antiphospholipid antibodies on the protein C system.

It is known that antiphospholipid antibodies (aPL) hamper the anticoagulant activity of the protein C system, but the mechanism is still obscure. In this study, we demonstrate that anticardiolipin antibodies (not anti-protein C autoantibodies) can bind protein C via beta2-GPI, which bears their binding epitope, in a fashion dependent on negatively charged phospholipids. We studied the binding of IgG from aPL to protein C in the presence of beta2-GPI by ELISA (anti-'protein C' antibody ELISA), and compared their binding with those obtained in the absence of beta2-GPI. In the anti-'protein C' antibody ELISA system, 47% of 78 aPL+ patients had a positive titre in the presence of cardiolipin (CL) and beta2-GPI, but binding was not found in the absence of beta2-GPI. Highly significant correlations were found between the titre of anti-'protein C' antibody in the presence of beta2-GPI and that of anti-beta2-GPI antibody (r = 0.802, P = 0.0001). We further analysed the interaction between protein C, phospholipids, beta2-GPI and human aCL MoAbs established from patients with antiphospholipid syndrome. In a first set of experiments, the binding of beta2-GPI to protein C and its phospholipid dependency were investigated. Beta2-GPI bound to protein C in the presence of CL or phosphatidylserine, but not in the presence of phosphatidylcholine or phosphatidylethanolamine. In a second group of experiments, the binding of three human monoclonal aCL recognizing the cryptic epitope of beta2-GPI (virtually anti-beta2-GPI antibodies) was evaluated in the presence of cardiolipin and beta2-GPI. All three human monoclonal aCL bound to protein C in the presence of CL and beta2-GPI, whereas they did not in the absence of either beta2-GPI or CL. These data suggest that protein C could be a target of aCL by making a complex with CL and beta2-GPI, leading to protein C dysfunction.

Prothrombotic changes in children with sickle cell disease: relationships to cerebrovascular disease and transfusion.

Vascular occlusion has a central role in the pathophysiology of sickle cell disease (SCD) and, although there is little evidence that thrombosis alone is responsible, patients with sickle cell disease are known to have an ill-defined but increased thrombotic risk. The most serious complication of this in childhood is stroke which occurs in 7-10% of children and a further 14% have asymptomatic cerebrovascular disease (CVD) on imaging. We have performed a comprehensive profile of coagulation inhibitors and markers of thrombin generation in 96 children (83 nontransfused [NTx] and 13 transfused [Tx]) with steady-state SCD and 18 healthy sibling controls. The levels of protein S (free and total) and heparin cofactor II were reduced in both the NTx and Tx groups compared to controls and protein C and APC resistance ratios were reduced in the NTx group only. Antithrombin levels were not different from controls. Thrombin-antithrombin complexes and prothrombin fragment F1+2 were increased in both patient groups. In the NTx subgroups with or without CVD there were no differences for any of the parameters measured except for lower haemoglobin levels and higher white cell counts in those with asymptomatic CVD. We conclude that children with SCD have a reduction in levels of the majority of the coagulation inhibitors and increased thrombin generation in the steady-state and these are only partially reversed by transfusion. However, these abnormalities do not appear to play a primary role in the development of cerebrovascular disease.

The role of estrogen and progesterone in the control of preputial gland sex attractant odors in the female rat.

Sexually experienced male rats were used to test the attractiveness of body odors of female rats. The attractiveness of these odors varied with the estrous cycle. Odors from female rats in proestrus were the most attractive to male rats and those from female rats during the darkness hours of diestrus the least attractive. The preputial glands appeared to be the source of these odors for the male rats showed no preference for the odors of proestrous female rats that had been preputialectomized. Administration of 1 microgram estrdiol benzoate (EB) for 5 days increased the attractiveness of body odors of ovariectomized rats. A higher dose of EB (5 microgram) had the same effect when administered for 1 or 5 days although the increase that occurred after 3 days was not significant. A single dose of progesterone (P) (500 microgram) on the other hand, decreased the attractiveness of ovariectomized female odors although no change was seen after 3 days of treatment. A single injection of P also decreased the attractiveness of odors of ovariectomized females that had received EB for 3 days. However, P failed to decrease the attractiveness of odors in ovariectomized females after preputialectomy. We conclude that the preputial glands are an important source of sex attractant odors in the female rat and that the changes in the release of these odors that occur throughout the estrous cycle and pregnancy are controlled by ovarian steroids. While estrogen acts to stimulate the production and release of these odors P appears to inhibit their release.

Effect of alpha-melanocyte-stimulating hormone and ovarian steroids on preputial gland function in the female rat.

Sexually experienced male rats were used to test the attractiveness of preputial gland odours of female rats. The male rats showed a clear preference for the preputial gland odours of hypophysectomized females given oestradiol benzoate (OB) for 3 or 8 days to those of control rats. Progesterone treatment had no effect on the attractiveness of the preputial gland odours of OB-treated hypophysectomized female rats. Administration of alpha-MSH for either 3 or 8 days, on the other hand, increased the attractiveness to male rats of preputial gland odours of OB-treated hypophysectomized females and the presence of progesterone produced no further change. When administered alone alpha-MSH had no effect on the attractiveness of the preputial gland odours. Other pituitary hormones, such as ACTH and prolactin, had no effect on the attractiveness of preputial gland odours of OB-treated hypophysectomized rats when administered for 3 days. An increase in preputial gland size was only seen when OB, progesterone and alpha-MSH were administered together. It would appear that no relationship exists between the size of the preputial glands and their ability to attract male rats. It is concluded that, while alpha-MSH and progesterone may be important in controlling growth of the preputial glands, an interaction between alpha-MSH and oestrogen is more important for regulating the production of sex attractants by the preputial glands.

alpha-Melanocyte stimulating hormone and the release of sex attractant odors in the female rat.

Sexually experienced male rats were used to test the attractiveness of odors of hypophysectomized females the male rats showed a clear preference for 4 days failed to alter the attractiveness of odors of hypophysectomized females and male rats showed a clear preference for the odors of females that had received 10 micrograms EB. Daily administration of 50 micrograms alpha-MSH failed to increase the attractiveness of odors of hypophysectomized females the male rats showed a clear preference for the odors of females that had received 10 micrograms EB. Daily administration of 50 micrograms alpha-MSH failed to increase the attractiveness of odors from females that received 2 microgram EB but was effective in females that had received 10 micrograms EB. However, no effect was seen in female rats that had been preputialectomized. alpha-MSH also increased the attractiveness of odors of posterior hypophysectomized rats in proestrus. Moreover, the reduction in odor attractiveness found after posterior hypophysectomy in female rats in proestrus was almost restored by alpha-MSH treatment. On the other hand, when the alpha-MSH treated posterior hypophysectomized females were in diestrus their odors were less attractive to male rats than those of the untreated controls. A similar reduction in odor attractiveness occurred in alpha-MSH treated posterior hypophysectomized females in proestrus after a single injection of progesterone. These results suggest that in the female rat alpha-MSH has a physiological role in controlling sexual odors from the preputial glands and by interacting with estrogen and progesterone can either enhance or reduce the attractiveness of these odors to male rats.