Hemodynamic responses and c-Fos changes associated with hypotensive hemorrhage: standardizing a protocol for severe hemorrhage in conscious rats

Abstract

The central mechanisms underlying the transition from compensation to decompensation during severe hemorrhage (HEM) are poorly understood. Furthermore, a lack of consistency in HEM protocols exists in the current literature. This study assessed the cardiovascular response and Fos-like immunoreactivity (FLI) in specific brain regions following severe HEM at three rates (2, 1, or 0.5 ml.kg(-1).min(-1)) in conscious rats. Heart rate (HR) and arterial pressure were recorded during the withdrawal of 30% of total blood volume (TBV). Data from animals hemorrhaged at the fast (F-HEM, n = 6), intermediate (I-HEM, n = 7), or slow (S-HEM, n = 7) rates were compared with saline (SAL, n = 5) and hypotensive (hydrazaline-induced, HYDRAZ, n = 5) controls. All HEM rates produced similar degrees of hypotension at the time of 30% TBV withdrawal. All HEM rates also produced bradycardia, but the change in HR was only significant in the F-HEM and I-HEM groups. Associated with I-HEM and F-HEM, but not HYDRAZ treatment were significant increases in FLI in the caudal ventrolateral periaqueductal gray (PAG), the central lateral nucleus of the rostral parabrachial nucleus, and locus coeruleus compared with SAL treatment. I-HEM also induced significant increases in FLI in the dorsomedial PAG, A7 region, and the cuneiform nucleus compared with SAL. S-HEM did not induce any significant change in FLI. Our results suggest that HEM at a rate of 1 ml.kg(-1).min(-1) may be most useful for investigating the potential role of the rostral brainstem regions in mediating hemorrhagic decompensation in conscious rats.

Hemodynamic and autonomic response to acute hemorrhage in streptozotocin-induced diabetic rats

“…Porter et al demonstrated that hemorrhage at a slow rate (20 ml/kg/40 min) did not cause elevation in HR-HF [40]. Conversely, hemorrhage at an intermediate or fast rate induced a decrease in HR associated with a significant increase in HF power [41]. These results suggest that the rate of hemorrhage has an important impact on autonomic regulation.…”

Modulation of heart rate variability during severe hemorrhage at different rates in conscious rats

“…There is, however, evidence that both central and peripheral factors contribute to hemorrhagic sympatho-inhibition, including a change in afferent activity from the heart, central activation of opioid-, γ-aminobutyric acid-(GABA), and/or serotonin-containing neurons in the brainstem (16, 17, 19-22, 46). Evidence from both our lab (1, 34) and that of Troy and colleagues has demonstrated (57) that the rate of blood loss also influences the characteristics of autonomic control during hemorrhage, including indicators of brain neuronal activation, the level of bradycardia observed at the time of peak blood withdrawal, and the HR sustained 40 min following the offset of blood loss, during the recovery phase. These observations suggest that the central neural circuits modulating sympathetic and parasympathetic recruitment activated during severe hemorrhage, may be different depending on the rate of blood loss.…”

“…Based on the results of our previous study demonstrating that brain activation varied depending on the rate of blood loss between 0.5 ml/kg to 2.0 ml/kg in conscious rats, the present study was undertaken to evaluate how autonomic control varies during different rates of blood loss rate (1). We hypothesized that the change in both the HF and LF/HF ratio would increase as the rate of blood loss increased.…”

Daily voluntary exercise alters the cardiovascular response to hemorrhage in conscious male rats

“…Animals were then subjected to either a 30% TBV HEM over 15 min (n=8 per group), were allowed to sit quietly over the same time course (non-hemorrhaged controls, n=4–5/group) or underwent baroreflex testing only (n=4–5/group). In the HEM group blood loss was induced by steady withdrawal of blood at a rate of 2% TBV/min from the second arterial catheter into a heparinized syringe (Troy, Heslop et al 2003; Ahlgren, Porter et al 2007; Shafford 2007; Porter, Ahlgren et al 2009). TBV was estimated using a previously reported equation for estimation of rat blood volume: (0.06 ml/g)*(body weight in g)+(0.77) (Lee and Blaufox 1985).…”

“…Selected brain images were then imported into Adobe Photoshop and standardized masks or outlines of each nucleus/subnucleus were placed over the image (see Fig 4) and the number of FLI neurons present were counted. Following quantification the slide was decoded and assigned a treatment group (Ahlgren, Porter et al 2007). …”