Long-term success in xenotransplantation is currently hampered by acute vascular rejection. The inciting cause of acute vascular rejection is not yet known; however, a variety of observations suggest that the humoral immune response of the recipient against the donor may be involved in the pathogenesis of this process. Using a pig-to-baboon heterotopic cardiac transplant model, we examined the role of antibodies in the development of acute vascular rejection. After transplantation into baboons, hearts from transgenic pigs expressing human decay-accelerating factor and CD59 underwent acute vascular rejection leading to graft failure within 5 d; the histology was characterized by endothelial injury and fibrin thrombi. Hearts from the transgenic pigs transplanted into baboons whose circulating antibodies were depleted using antiimmunoglobulin columns (Therasorb, Unterschleisshein, Germany) did not undergo acute vascular rejection in five of six cases. Biopsies from the xenotransplants in Ig-depleted baboons revealed little or no IgM or IgG, and no histologic evidence of acute vascular rejection in the five cases. Complement activity in the baboons was within the normal range during the period of xenograft survival. In one case, acute vascular rejection of a xenotransplant occurred in a baboon in which the level of antidonor antibody rose after Ig depletion was discontinued. This study provides evidence that antibodies play a significant role in the pathogenesis of acute vascular rejection, and suggests that acute vascular rejection might be prevented or treated by therapies aimed at the humoral immune response to porcine antigens. (

An activated ras oncogene induces a program of differentiation in the human medullary thyroid cancer cell line TT. This differentiation process is accompanied by a marked increase in the transcription of the human calcitonin (CT) gene. We have localized a unique Ras-responsive transcriptional element (RRE) in the CT gene promoter. DNase I protection indicates two domains of protein-DNA interaction, and each domain separately can confer Ras-mediated transcriptional inducibility. This bipartite RRE was also found to be Raf responsive. By affinity screening, we have cloned a cDNA coding for a zinc finger transcription factor (RREB-1) that binds to the distal RRE. The consensus binding site for this factor is CCCCAAACCACCCC. RREB-1 is expressed ubiquitously in human tissues outside the adult brain. Overexpression of RREB-1 protein in TT cells confers the ability to mediate increased transactivation of the CT gene promoter-reporter construct during Ras-or Raf-induced differentiation. These data suggest that RREB-1 may play a role in Ras and Raf signal transduction in medullary thyroid cancer and other cells.

This is the first report to describe generation of transgenic pigs that express human CD46, and the first in vivo demonstration of the ability of human CD46 expressed on pig organs to regulate complement activation and overcome hyperacute rejection upon transplantation of a vascularized organ into nonhuman primates.

These results demonstrate that anti-Galalpha1-3Gal antibodies cause acute vascular rejection and suggest that depletion of these antibodies leads to accommodation of the donor cardiac xenograft and could supply an important model for additional study.

Introduction Melanocortins affect multiple physiological responses, including sexual behaviors. Bremelanotide is a synthetic peptide melanocortin analog of α-melanocyte-stimulating hormone that is an agonist at melanocortin receptors MC3R and MC4R. Aim To evaluate a single intranasal dose of bremelanotide for potential effects on physiological and subjective measurements of sexual arousal and desire in premenopausal women with sexual arousal disorder. Main Outcome Measures Change in vaginal pulse amplitude during neutral and erotic videos after treatment with bremelanotide or placebo and subjects’ perceptions of physiological and sexual response within 24 hours of treatment with bremelanotide or placebo. Methods Eighteen premenopausal women with a primary diagnosis of female sexual arousal disorder were randomly assigned to receive a single intranasal dose of 20 mg bremelanotide or matching placebo in a double-blind manner during the first in-clinic treatment session, and the alternate medication during the second in-clinic treatment session. During each session, subjects viewed a 20-minute neutral video followed by a 20-minute sexually explicit video. Vaginal photoplethysmography was used to monitor vaginal vasocongestion and questionnaires were used to evaluate perceptions of sexual response within the following 24-hour period. Results More women reported moderate or high sexual desire following bremelanotide treatment vs. placebo (P = 0.0114), and a trend toward more positive responses regarding feelings of genital arousal occurred after bremelanotide compared with placebo (P = 0.0833). Among women who attempted sexual intercourse within 24 hours after treatment, significantly more were satisfied with their level of sexual arousal following bremelanotide, compared with placebo (P = 0.0256). Vaginal vasocongestion did not change significantly while viewing erotic videos following bremelanotide administration compared with placebo. Conclusion This preliminary evaluation suggests the potential for bremelanotide to positively affect desire and arousal in women with female sexual arousal disorder and indicates that bremelanotide is a promising candidate for further evaluation in an at-home study.

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PT-141, a synthetic peptide analogue of alpha-MSH, is an agonist at melanocortin receptors including the MC3R and MC4R, which are expressed primarily in the central nervous system. Administration of PT-141 to rats and nonhuman primates results in penile erections. Systemic administration of PT-141 to rats activates neurons in the hypothalamus as shown by an increase in c-Fos immunoreactivity. Neurons in the same region of the central nervous system take up pseudorabies virus injected into the corpus cavernosum of the rat penis. Administration of PT-141 to normal men and to patients with erectile dysfunction resulted in a rapid dose-dependent increase in erectile activity. The results suggest that PT-141 holds promise as a new treatment for sexual dysfunction.

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