Antihypertensive monotherapy and cardiovascular responses to an acoustic startle stimulus

Anger and cardiovascular startle reactivity in normotensive young males

Anger has been implicated in the etiology of hypertensive disease. Trait anger has been linked to enhanced cardiovascular responsiveness. However, whether this association reflects differences in context appraisal or a general hyper-reactivity of the cardiovascular system remains unclear. We studied the cardiovascular response to acoustic startle probes in 76 healthy Caucasian males in different affective contices (pleasant, neutral, and unpleasant). All participants completed the State-Trait-Anger-Expression-Inventory (STAXI) by Spielberger and the results were analysed with stepwise regression analysis according to the anger scores and traditional risk factors for hypertension. Our study reveals differential modulation of the cardiovascular response to startle stimuli by affective pictures in the dimensions "valence" for heart rate and "arousal" for blood pressure. Anger-in was identified as the most important determinant for blood pressure responses in unpleasant context, while anger-out was associated with less cardiovascular activation in neutral context. This is the first study that relates trait anger to cardiovascular reactivity and affective reflex modulation in normotensive subjects. We could demonstrate an interaction of affective context and trait anger for cardiovascular (hyper-)reactivity. Increased cardiovascular reactivity for higher scores of anger-in in unpleasant context may indicate enhanced sympathetic reactivity and constitute a risk factor for the development of essential hypertension.

Modulation of the acoustic startle response by the level of arousal: comparison of clonidine and modafinil in healthy volunteers

A sudden loud sound evokes an electromyographic (EMG) response from the orbicularis oculi muscle in humans together with an auditory evoked potential (AEP) and an increase in skin conductance (SC). Startle responses are inhibited by weak prepulses (prepulse inhibition, (PPI)) and may also be modified by the level of alertness. We compared the sedative drug clonidine and the alerting drug modafinil on sound-evoked EMG, AEP, and SC responses, on the PPI of these responses and on level of arousal and autonomic functions. Sixteen healthy male volunteers participated in four weekly sessions (clonidine 0.2 mg, modafinil 400 mg, their combination, placebo) in a double-blind, cross-over, balanced design. Responses were evoked by sound pulses of 115 and 85 dB (PPI) for 40 ms and recorded conventionally. Level of alertness, autonomic functions (pupil diameter, blood pressure, heart rate, salivation, temperature) and the plasma levels of the hormones prolactin, thyroid-stimulating hormone and growth hormone were also measured. Data were analyzed with analysis of variance with multiple comparisons. Both prepulses and clonidine attenuated all three startle responses and modafinil antagonized clonidine's effects on the EMG and AEP responses. None of the drugs affected PPI. Clonidine showed sedative and sympatholytic effects, and modafinil showed alerting and sympathomimetic effects. In conclusion, startle responses were susceptible not only to PPI but also to the level of arousal.

The acoustic startle reflex in Sprague-Dawley rats is altered by permanent middle cerebral artery occlusion

The startle reflex is an unconditioned, quantifiable behavior used to study sensory modalities. We examined whether the acoustic startle reflex (ASR) was sensitive to lesions induced by focal cerebral ischemia. Sprague-Dawley rats were pre-screened for startle reflex responses 3-6 days prior to surgery and there were no differences in mean startle amplitude across groups. Animals were subjected to permanent middle cerebral artery occlusion (pMCAo) or a sham surgical procedure. Twenty-four hours later rats were evaluated for ASR prior to sacrifice. Infarct volumes were subsequently determined by quantitative image analysis of 2,3,5-triphenyltetrazolium chloride-stained brain sections. Infarct volumes of rats undergoing pMCAO ranged from 0 to 48%. Data were divided into three groups based upon percent infarction: mild (0-20%), moderate (21-35%), and severe (>35%). A within-subject analysis revealed a significant decrease in mean startle amplitude of only severely infarcted rats relative to their pre-surgery startle responses. Furthermore, the lesioned brain areas observed in these animals provide an anatomical basis for these results. Our findings demonstrate that ASR is affected in a model of stroke. Further work is needed to characterize this behavioral test and to determine whether it may have application as a surrogate endpoint for clinical stroke studies.

[Assessment of the effects of antihypertensive drugs on stress-induced cardiovascular changes]

The authors reviewed some of the most relevant studies dedicated to the assessment of the effects of the antihypertensive drugs on the stress-induced cardiovascular changes. The rises in both blood pressure and heart rate turned out not to be significantly altered by calcium channel blockers, ACE inhibitors, moxonidine, nor beta-blockers, whereas they seemed to be slightly blunted by alpha-blocking drugs. However, since baseline blood pressure was significantly lower in treated hypertensives than in placebo-given patients, all antihypertensive drugs eventually resulted in a lower blood pressure level during stress, as compared with untreated patients. Regarding white coat effect, which has to be considered as a very particular stress, it appeared to be lowered to the same extent by placebo and antihypertensive drugs; moreover, its changes were not associated with any clinical beneficial effect.