No expression of APJ transcript or I125[Pyr1]apelin-13 binding was observed in a number of mouse tissues including liver and pancreas. Using RT-PCR however, APJ mRNA has been identified in mouse and human liver and pancreas [30], [41] and [48]. Apelin has been identified as a novel adipokine, which is upregulated by obesity and hyperinsulinemia in both humans and mice [5] and [7]. Expression of APJ

in mouse CAL-101 in vivo islets has been reported where apelin-36 inhibited glucose-stimulated insulin secretion both in vivo and in vitro [48] suggesting a link between this adipokine and glucose homeostasis. Thus, apelin may be involved in the regulation of islet function, although its precise role remains to be established. Additionally the finding that APJ is not expressed in mouse testis is intriguing as moderate levels of apelin mRNA are found in this tissue [14]. This lack of testicular APJ confirms previous findings in the rat by us [34] and others [17] and [30] using RT-PCR, but differs from other RT-PCR studies showing expression in human and mouse testis [30]. It is possible that testicular APJ is developmentally regulated since APJ mRNA expression appears

to be higher in infant compared to adult peripheral tissues [17]. In this study we provide APO866 mouse the first detailed characterization of APJ distribution in the mouse and report a clear correlation between mouse APJ transcription and translation. The APJ expressing tissues in the mouse where potential functional correlations are identified are the brain, heart, pituitary gland and adrenal gland. Expression was also observed in kidney, lung, stomach, uterus and ovary and no expression

of APJ transcript or I125[Pyr1]apelin-13 binding could be observed in a number of tissues including liver and pancreas. We cannot discount the possibility Cytidine deaminase that low levels of (possibly rapidly turning-over) APJ mRNA are below the detection threshold of ISHH, which may be detected with more sensitive methods such as RT-PCR, however it must be stressed that the functional significance of low levels of mRNA as detected by RT-PCR in the CNS or peripheral tissue samples is unknown. There appears to be a species difference in central APJ distribution and in the pituitary gland, with a widespread central APJ distribution in the rat compared to a more restricted distribution seen in the mouse, while APJ distribution in peripheral tissues appears to be comparable between rat and mouse. The functional significance of the apparent species differences in the central expression of APJ mRNA is not known. Our study suggests however that the apelin/APJ system may have a more wide-ranging central role in the rat than the mouse, that should be considered when drawing comparisons between studies in the rat and APJ KO mice. GRP is the recipient of a BBSRC PhD studentship.