RESUMEN
The paraventricular nucleus (PVN) of the hypothalamus plays an important role in the regulation of sympathetic nerve activity, which is significantly elevated in chronic heart failure (CHF). Fractalkine (FKN) and its cognate receptor, CX3CR1, are constitutively expressed in the central nervous system, but their role and physiological significance are not well known. The aims of the present study were to determine whether FKN plays a cardiovascular role within the PVN and to investigate how the actions of FKN might be altered in CHF. We show that both FKN and CX3CR1 are expressed on neurons in the PVN of rats, suggesting that they may have a physiological function in this brain nucleus. Unilateral microinjection of FKN directly into the PVN of anaesthetized rats elicited a significant dose-related decrease in blood pressure (1.0 nmol, -5 ± 3 mmHg; 2.5 nmol, -13 ± 2 mmHg; 5.0 nmol, -22 ± 3 mmHg; and 7.5 nmol, -32 ± 3 mmHg) and a concomitant increase in heart rate (1.0 nmol, 6 ± 3 beats min(-1); 2.5 nmol, 11 ± 3 beats min(-1); 5 nmol, 18 ± 4 beats min(-1); and 7.5 nmol, 27 ± 5 beats min(-1)) compared with control saline microinjections. In order to determine whether FKN signalling is altered in rats with CHF, we first performed quantitative RT-PCR and Western blot analysis and followed these experiments with functional studies in rats with CHF and sham-operated control rats. We found a significant increase in CX3CR1 mRNA and protein expression, as determined by quantitative RT-PCR and Western blot analysis, respectively, in the PVN of rats with CHF compared with sham-operated control rats. We also found that the blood pressure effects of FKN (2.5 nmol in 50 nl) were significantly attenuated in rats with CHF (change in mean arterial pressure, -6 ± 3 mmHg) compared with sham-operated control rats (change in mean arterial pressure, -16 ± 6 mmHg). These data suggest that FKN and its receptor, CX3CR1, modulate cardiovascular function at the level of the PVN and that the actions of FKN within this nucleus are altered in heart failure.
Asunto(s)
Sistema Cardiovascular/fisiopatología , Quimiocina CX3CL1/metabolismo , Insuficiencia Cardíaca/fisiopatología , Hipotálamo/fisiopatología , Núcleo Hipotalámico Paraventricular/fisiopatología , Animales , Presión Sanguínea/genética , Presión Sanguínea/fisiología , Sistema Cardiovascular/metabolismo , Quimiocina CX3CL1/genética , Insuficiencia Cardíaca/genética , Insuficiencia Cardíaca/metabolismo , Frecuencia Cardíaca/genética , Frecuencia Cardíaca/fisiología , Hipotensión/genética , Hipotensión/metabolismo , Hipotensión/fisiopatología , Hipotálamo/metabolismo , Masculino , Microinyecciones/métodos , Núcleo Hipotalámico Paraventricular/metabolismo , Ratas , Ratas Sprague-Dawley , Taquicardia/genética , Taquicardia/metabolismo , Taquicardia/fisiopatologíaRESUMEN
The nucleus of the solitary tract (NTS), an integral vasomotor region located in the hindbrain, is important for cardiovascular homeostasis. Fractalkine (FKN) and its cognate receptor, CX3CR1, are constitutively expressed in the normal rat brain. The physiological significance of this cytokine and its receptor are not well established. In this study, we sought to identify the expression of FKN and CX3CR1 in subnuclei of the NTS and to elucidate their functional relevance. Using immunohistochemistry, we found expression of FKN and CX3CR1 throughout the entire rostro-caudal axis of the NTS in normal adult male Sprague-Dawley rats. When FKN was unilaterally microinjected directly into the commissural and sub-postremal, but not rostral, NTS, blood pressure and heart rate were significantly decreased when compared with saline controls. The FKN-induced depressor and bradycardic responses were inhibited by pretreatment with a phosphoinositide 3-kinase inhibitor, LY294002. These data suggest that the cytokine, FKN, and its receptor, CX3CR1, may modulate cardiovascular responses in the NTS of normal healthy rats via the phosphoinositide 3-kinase intracellular signaling pathway.