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Lung megakaryocytes (Mks) are largely extravascular with an immune phenotype (1). Because bone marrow (BM) Mks are short lived, it has been assumed that extravascular lung Mks are constantly 'seeded' from the BM. To investigate lung Mk origins and how origin affects their functions, we developed methods to specifically label lung Mks using CFSE dye and biotin delivered via the oropharyngeal route. Labeled lung Mks were present for up to 4 months, while BM Mks had a lifespan of less than 1 week. In a parabiosis model, lung Mks were partially replaced over 1 month from a circulating source. Unlike tissue-resident macrophages, using [MDS1.sup.-Cre-ERT2] TdTomato mice, we found that lung Mks arose from hematopoietic stem cells. However, studies with FlkSwitch mTmG mice showed that lung Mks were derived from a Flt3-independent lineage that did not go through a multipotent progenitor. CFSE labeling to track lung Mk-derived platelets showed that approximately 10% of circulating platelets were derived from lung-resident Mks at steady state, but in sterile thrombocytopenia this was doubled (~20%). Lung-derived platelets were similarly increased in a malaria infection model (Plasmodium yoelii) typified by thrombocytopenia. These studies indicate that lung Mks arise from a Flt3- BM source, are long-lived, and contribute more platelets during thrombocytopenia., Introduction Platelets serve dual roles as a critical component of clot formation and as regulators of immune responses (1, 2). Activated platelets promote inflammation, while circulating resting platelets limit inflammation [...]

Lesions of the lateral parabrachial nucleus (LPBN) impair blood pressure recovery after hypotensive blood loss (Am J Physiol Regul Integr Comp Physiol 280: R1141, 2001). This study tested the hypothesis that posthemorrhage blood pressure recovery is mediated by activation of neurons, located in the ventrolateral aspect of the LPBN (VL-LPBN), that initiates blood pressure recovery by restoring sympathetic vasomotor drive. Hemorrhage experiments (16 ml/kg over 22 min) were performed in unanesthetized male Sprague-Dawley rats prepared with bilateral ibotenate lesions or guide cannulas directed toward the external lateral subnucleus of the VL-LPBN. Hemorrhage initially decreased mean arterial pressure (MAP) from ~100 mmHg control to 40-50 mmHg, and also decreased heart rate. In animals with sham lesions, MAP returned to 84 [+ or -] 4 mmHg by 40 min posthemorrhage, and subsequent autonomic blockade with hexamethonium reduced MAP to 53 [+ or -] 2 mmHg. In contrast, animals with VL-LPBN lesions remained hypotensive at 40 min posthemorrhage (58 [+ or -] 4 mmHg) and hexamethonium had no effect on MAP, implying a deficit in sympathetic tone. VL-LPBN lesions did not alter the renin response or the effect of vasopressin V1 receptor blockade after hemorrhage. Posthemorrhage blood pressure recovery was also significantly delayed by VL-LPBN infusion of the ionotropic glutamate receptor antagonist kynurenic acid. Both VL-LPBN lesions and VL-LPBN kynurenate infusion caused posthemorrhage bradycardia to be significantly prolonged. Bradycardia was reversed by hexamethonium or atropine, but did not contribute to posthemorrhage hypotension. Taken together, these data support the hypothesis that stimulation of VL-LPBN glutamate receptors mediates spontaneous blood pressure recovery by initiating restoration of sympathetic vasomotor drive. glutamate receptors; atropine; vasopressin receptor antagonist; heart rate; sympathetic nervous system doi:10.1152/ajpregu.00049.2006

Mammalian enabled (Mena) is a key regulator of cytoskeletal actin dynamics, which has been implicated in heart failure (HF). We have previously demonstrated that cardiac Mena deletion produced cardiac dysfunction with conduction abnormalities and hypertrophy. Moreover, elevated Mena expression correlates with HF in human and animal models, yet the precise role of Mena in cardiac pathophysiology is unclear. In these studies, we evaluated mice with cardiac myocyte-specific Mena overexpression (TTA/TgTetMena) comparable to that observed in cardiac pathology. We found that the hearts of TTA/TgTetMena mice were functionally and morphologically comparable to wild-type littermates, except for mildly increased heart mass in the transgenic mice. Interestingly, TTA/TgTetMena mice were particularly susceptible to cardiac injury, as these animals experienced pronounced decreases in ejection fraction and fractional shortening as well as heart dilatation and hypertrophy after transverse aortic constriction (TAC). By "turning off" Mena overexpression in TTA/TgTetMena mice either immediately prior to or immediately after TAC surgery, we discovered that normalizing Mena levels eliminated cardiac hypertrophy in TTA/TgTetMena animals but did not preclude post-TAC cardiac functional deterioration. These findings indicate that hearts with increased levels of Mena fare worse when subjected to cardiac injury and suggest that Mena contributes to HF pathophysiology.

Systolic and diastolic dysfunction of the left ventricle (LV) is a hallmark of most cardiac diseases. In vivo assessment of heart function in animal models, particularly mice, is essential to refining our understanding of cardiovascular disease processes. Ultrasound echocardiography has emerged as a powerful, noninvasive tool to serially monitor cardiac performance and map the progression of heart dysfunction in murine injury models. This review covers current applications of small animal echocardiography, as well as emerging technologies that improve evaluation of LV function. In particular, we describe speckle-tracking imaging-based regional LV analysis, a recent advancement in murine echocardiography with proven clinical utility. This sensitive measure enables an early detection of subtle myocardial defects before global dysfunction in genetically engineered and rodent surgical injury models. Novel visualization technologies that allow in-depth phenotypic assessment of small animal models, including perfusion imaging and fetal echocardiography, are also discussed. As imaging capabilities continue to improve, murine echocardiography will remain a critical component of the investigator's armamentarium in translating animal data to enhanced clinical treatment of cardiovascular diseases.

We have previously shown that both plasma protein restitution and plasma volume restitution are significantly enhanced in female rats hemorrhaged during the proestrus phase of the estrous cycle. Estradiol and progesterone levels are markedly elevated during proestrus and also increase during pregnancy. The present studies were therefore designed to determine whether the ability to restore plasma protein and blood volume after hemorrhage is augmented during pregnancy and by chronically elevated estradiol levels. The response to moderate hemorrhage (22-23% blood loss) was evaluated in conscious pregnant rats during early and midgestation and compared with that of virgin female rats studied during metestrus. At 22 h posthemorrhage, plasma volume had increased to greater than basal levels, and blood volume was restored to 93 +/- 1% (metestrus), 91 +/- 2% (early pregnancy), and 98 +/- 2% (midgestation) of control (P > 0.05). Animals hemorrhaged during metestrus or early pregnancy restored the same amount of protein to the plasma as had been removed, whereas those hemorrhaged during midgestation restored nearly 50% more plasma protein than had been removed (P < 0.01). In ovariectomized animals with chronic steroid replacement that maintained plasma progesterone at metestrus levels (15 +/- 2 ng/ml) but raised plasma estradiol to twofold that of midgestation (22 +/- 3 pg/ml), the blood volume and plasma protein restitution responses to hemorrhage did not differ from those of ovariectomized animals with no steroid replacement. In summary, posthemorrhage restoration of plasma protein content is significantly augmented during midgestation, but not during early pregnancy. This augmented response cannot be attributed to chronic elevation of plasma estradiol levels alone.