A model of cellular cardiac-neural coupling that captures the sympathetic control of sinoatrial node excitability in normotensive and hypertensive rats

Hypertension is associated with sympathetic hyperactivity. To represent this neural-myocyte coupling, and to elucidate the mechanisms underlying sympathetic control of the cardiac pacemaker, we developed a new (to our knowledge) cellular mathematical model that incorporates signaling information from cell-to-cell communications between the sympathetic varicosity and sinoatrial node (SAN) in both normotensive (WKY) and hypertensive (SHR) rats. Features of the model include 1), a description of pacemaker activity with specific ion-channel functions and Ca(2+) handling elements; 2), dynamic β-adrenergic modulation of the excitation of the SAN; 3), representation of ionic activity of sympathetic varicosity with NE release dynamics; and 4), coupling of the varicosity model to the SAN model to simulate presynaptic transmitter release driving postsynaptic excitability. This framework captures neural-myocyte coupling and the modulation of pacemaking by nitric oxide and cyclic GMP. It also reproduces the chronotropic response to brief sympathetic stimulations. Finally, the SHR model quantitatively suggests that the impairment of cyclic GMP regulation at both sides of the sympathetic cleft is crucial for development of the autonomic phenotype observed in hypertension.

The role of fat emulsion therapy in a rodent model of propranolol toxicity: a preliminary study

INTRODUCTION

In animal models, lipid emulsion therapy has been shown to ameliorate toxicity from a number of lipid soluble agents. This preliminary study addresses the hypothesis that pretreatment with lipid emulsion protects against propranolol toxicity in rodents.

METHODS

Ten spontaneously ventilating Rattus norvegicus rats were pretreated with either lipid emulsion or 0.9% normal saline before undergoing a constant infusion of propranolol until death. An electrocardiogram (ECG) sampling of heart rate and a QRS duration was performed at two-minute intervals until demise.

RESULTS

There was no significant difference in lethal doses of propranolol between groups. Comparison of percent change in QRS prolongation and heart rate reduction was performed at 60% of the mean lethal dose in control animals. The percent change in QRS duration was reduced (from -0.9 to 17.3, p=0.016) in the intralipid pretreatment group. Attenuation of propranolol-induced bradycardia observed in the lipid emulsion group approached statistical significance (0% vs. 10.3%, p=0.06).

INTERPRETATION

The results suggest that lipid emulsion may be effective in ameliorating propranolol toxicity in rats. Previous work gives reason to postulate a pharmacokinetic mechanism for this effect. The results represent encouraging exploratory work, and further work is planned to evaluate the role of lipid emulsion therapy in propranolol toxicity.

Practice-based randomized controlled-comparison clinical trial of chiropractic adjustments and brief massage treatment at sites of subluxation in subjects with essential hypertension: pilot study

OBJECTIVE

To determine the feasibility of conducting a randomized clinical trial in the private practice setting examining short- and long-term effects of chiropractic adjustments for subjects with essential hypertension compared with a brief soft tissue massage, as well as a nontreatment control group.

DESIGN

Randomized controlled-comparison trial with 3 parallel groups.

SETTING

Private practice outpatient chiropractic clinic.

PATIENTS

Twenty-three subjects, aged 24 to 50 years with systolic or diastolic essential hypertension.

INTERVENTIONS

Two months of full-spine chiropractic care (ie, Gonstead) consisting primarily of specific-contact, short-lever-arm adjustments delivered at motion segments exhibiting signs of subluxation. The massage group had a brief effleurage procedure delivered at localized regions of the spine believed to be exhibiting signs of subluxation. The nontreatment control group rested alone for a period of approximately 5 minutes in an adjustment room.

MAIN OUTCOME MEASURES

Cost per enrolled subject, as well as systolic and diastolic blood pressure (BP) measured with a random-0 sphygmomanometer and patient reported health status (SF-36). Pilot study outcome measures also included an assessment of cooperation of subjects to randomization procedures and drop-out rates, recruitment effectiveness, analysis of temporal stability of BPs at the beginning of care, and the effects of inclusion/exclusion criteria on the subject pool.

RESULTS

Thirty subjects enrolled, yielding a cost of $161 per enrolled subject. One subject was later determined to be ineligible, and 6 others dropped out. In both the chiropractic and massage therapy groups, all subjects were classified as either overweight or obese; in the control group there were only 2 classified as such. SF-36 profiles for the groups were similar to that of a normal population. The mean change in diastolic BP was -4 (95% confidence interval [CI]: -8.6, 0.5) in the chiropractic care group, 0.5 (95% CI: -3.5, 4.5) in the brief massage treatment group, and -4.9 (95% CI: -9.7, -0.1) in the no treatment control group. At the end of the study period, this change was -6.3 (95% CI: 13.1, 0.4), -1.0 (95% CI: -7.5, 15.6), -7.2 (95% CI: -13.3, -1.1) in the 3 study groups. The mean improvements in the chiropractic care and no treatment control groups remained consistent over the follow-up period.

CONCLUSIONS

This pilot study elucidated several procedural issues that should be addressed before undertaking a full-scale clinical trial on the effects of chiropractic adjustments in patients with essential hypertension. A multidisciplinary approach to recruitment may need to be used in any future efforts because of the limited subject pool of patients who have hypertensive disease but are not taking medications for its control. Measures need to be used to assure comparable groups regarding prognostic variables such as weight. Studies such as these demonstrate the feasibility of conducting a full-scale 3-group randomized clinical trial in the private practice setting.

One-to-one synchronization between the cardiac sympathetic nerve stimuli and heart beats in rats

One-to-one synchronization of heart rate to the cardiac sympathetic nerve stimuli was observed in Sprague-Dawley rats. Propranolol and L-propranolol, but not D-propranolol, blocked 1:1 synchronization evoked by the nerve stimulation. Thus, 1:1 synchronization is entirely ascribable to neurally released norepinephrine. When a single volley was applied to the cardiac sympathetic nerve, there was a significant abbreviation of the respective cardiac cycle at which the stimulus fell. The mean latency was 33.1 +/- 2.29 ms (mean +/- SE). The extent of the abbreviation of the cardiac cycle was linearly correlated to the interval between P wave and a nerve stimulus. These results ensure that the effect of the sympathetic nerve stimulation is phase dependent and that the sympathetic nerve can entrain the heart beat as well as the parasympathetic nerve can.