RESUMO
BACKGROUND: Medullary blood flow is via vasa recta capillaries, which possess contractile pericytes. In vitro studies using isolated descending vasa recta show that pericytes can constrict/dilate descending vasa recta when vasoactive substances are present. We describe a live kidney slice model in which pericyte-mediated vasa recta constriction/dilation can be visualized in situ. METHODS: Confocal microscopy was used to image calcein, propidium iodide and Hoechst labelling in 'live' kidney slices, to determine tubular and vascular cell viability and morphology. DIC video-imaging of live kidney slices was employed to investigate pericyte-mediated real-time changes in vasa recta diameter. RESULTS: Pericytes were identified on vasa recta and their morphology and density were characterized in the medulla. Pericyte-mediated changes in vasa recta diameter (10-30%) were evoked in response to bath application of vasoactive agents (norepinephrine, endothelin-1, angiotensin-II and prostaglandin E(2)) or by manipulating endogenous vasoactive signalling pathways (using tyramine, L-NAME, a cyclo-oxygenase (COX-1) inhibitor indomethacin, and ATP release). CONCLUSIONS: The live kidney slice model is a valid complementary technique for investigating vasa recta function in situ and the role of pericytes as regulators of vasa recta diameter. This technique may also be useful in exploring the role of tubulovascular crosstalk in regulation of medullary blood flow.
Assuntos
Capilares/fisiologia , Medula Renal/irrigação sanguínea , Pericitos/fisiologia , Vasoconstrição/fisiologia , Trifosfato de Adenosina/metabolismo , Angiotensina II/metabolismo , Angiotensina II/farmacologia , Animais , Antígenos/metabolismo , Capilares/citologia , Sobrevivência Celular/fisiologia , Endotelina-1/metabolismo , Endotelina-1/farmacologia , Inibidores Enzimáticos/farmacologia , Imuno-Histoquímica , Técnicas In Vitro , Indometacina/farmacologia , Medula Renal/inervação , Medula Renal/metabolismo , Masculino , Microscopia Confocal , NG-Nitroarginina Metil Éster/farmacologia , Norepinefrina/metabolismo , Norepinefrina/farmacologia , Pericitos/citologia , Proteoglicanas/metabolismo , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos , Sistema Nervoso Simpático/fisiologia , Vasoconstrição/efeitos dos fármacos , Vasoconstritores/metabolismo , Vasoconstritores/farmacologiaAssuntos
Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Capsaicina/farmacologia , Rim/inervação , Fibras Nervosas/ultraestrutura , Animais , Animais Recém-Nascidos , Peptídeo Relacionado com Gene de Calcitonina/análise , Córtex Renal/inervação , Medula Renal/inervação , Túbulos Renais/inervação , Fibras Nervosas/efeitos dos fármacos , RatosRESUMO
Multiple mechanisms appear to be involved in mediation of increased secretion of cortisol after hemorrhage. Signals from cardiovascular receptors are transmitted to the hypothalamus through ascending neural pathways to release ACTH. Angiotensin II stimulates release of ACTH by an action on the median eminence, but does not stimulate adrenal secretion of cortisol directly. However, secretion of cortisol can increase rapidly after hemorrhage without changes in ACTH. Common afferent pathways probably mediate all these mechanisms.