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At least 127 records · Page 7Linked to original sources
PubMed1997

Autonomic blockade amplifies cortisol-induced hypertension in man.

1. We investigated the role of the autonomic nervous system (ANS) in cortisol induced hypertension using the technique of total autonomic blockade (AB). 2. Four healthy young males were given 50 mg cortisol 6 hourly for 6 days. On the day prior to, and the last day of, cortisol treatment, AB was produced using oral prazosin 1 mg, intravenous clonidine 300 micrograms, propranolol 0.2 mg/kg and atropine 2 mg. The adequacy of blockade was assessed using the haemodynamic response to Valsalva manoeuvre. 3. Cortisol produced a significant rise in systolic blood pressure (130 +/- 2 vs 110 +/- 1 mmHg, pre vs post cortisol; P < 0.01). On the final treatment day, AB augmented the increase in diastolic blood pressure (delta DBP), mean arterial pressure (delta MAP) and heart rate (delta HR) compared to the pretreatment day, delta DBP: 43 +/- 6 vs 17 +/- 4 mmHg, post vs pre cortisol, P < 0.005, delta MAP: 39 +/- 4 vs 14 +/- 4 mmHg, P < 0.001, delta HR: 45 +/- 5 vs 26 +/- 4 b.p.m., P < 0.05. The change in systolic blood pressure (delta SBP) was not statistically significant (32 +/- 4 vs 7 +/- 3 mmHg, P = 0.065). 4. These results suggest that the ANS exerts a modulating influence on the hypertensive effect of cortisol.

Adrenergic alpha-Antagonists↗
PubMed1995

Kinetics of cycle length dependence of ventricular repolarization: effect of autonomic blockade.

INTRODUCTION: Beat-to-beat adaptation of ventricular repolarization duration to cardiac cycle length and autonomic activity has not been previously characterized in the spontaneously beating human heart. METHODS AND RESULTS: The ECG of 14 healthy subjects was recorded from the supine and upright positions. Autonomic blockade was accomplished by atropine and propranolol. RR and RT intervals were measured by a computer algorithm, and the impulse response (h) from RR to RT computed. In the supine position the maximal adjustment of the RT interval occurred in the first beat following a change in cycle length (hpeak = 17.8 +/- 1.6 msec/sec), but continued to be detectable for 3.8 seconds (2.9-4.7 sec). Propranolol attenuated the peak impulse response to 15.8 +/- 4.0 msec/sec (P = NS). In the standing position the peak impulse response was increased to 25.2 +/- 5.0 msec/sec (P = 0.004 vs supine), and the impulse response duration (hdur) shortened to 1.4 seconds (1.3-1.6). This was reversed by beta blockade (hpeak = 10.7 +/- 3.6 [P = 0.005 vs standing]; hdur = 5.5 sec [4.8-6.1]). Parasympathetic and combined autonomic blockade resulted in too little residual heart rate variability to estimate the impulse response accurately. The slope of the regression of delta RT and delta RR in the supine position was 0.0177 +/- 0.0016, which was closely correlated with the peak impulse response (r = 0.91). CONCLUSIONS: System identification techniques can assist in characterizing the cycle dependence of ventricular repolarization and may provide new insights into conditions associated with abnormal repolarization.

Adult↗
PubMed1986

Maternal heart rate and stroke volume in the pygmy goat: effects of exercise and cardiac autonomic blockade.

To determine the normal maternal heart rate and stroke volume response to exercise and the role of the autonomic nervous system in this response, pregnant and non-pregnant pygmy goats were studied at rest, during and following treadmill exercise, and after autonomic blockade. Resting heart rates, stroke volumes and cardiac outputs were 10%, 60%, and 76% higher in pregnant compared to non-pregnant animals (P less than 0.05, 0.001, and 0.001 respectively). During exercise, heart rate and stroke volume rose in both pregnant and non-pregnant animals by similar amounts. Immediately post-exercise, stroke volume in pregnant animals dropped precipitously below resting levels by 15% (P less than 0.005) but cardiac output was preserved by heart rate. This fall in stroke volume was not seen in control animals. Autonomic blockade lowered resting and exercise heart rates in both groups without changing stroke volume. The elevations in heart rate and stroke volume in pregnancy are not primarily mediated via the autonomic nervous system. Although the maternal cardiac output response to exercise appears normal, the post-exercise fall in stroke volume, presumed secondary to a reduction in preload, could potentially be harmful to both mother and fetus.

Animals↗
PubMed1990

Autonomic, hormonal, and local circulatory effects of hemorrhage in conscious rabbits.

Conscious instrumented rabbits were bled at a constant rate of congruent to 3% of the blood volume (BV) per minute. We determined the BV-response relationships for mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), mesenteric and hindlimb blood flows, and for the corresponding conductances. We studied the responses 1) under normal conditions; 2) after pretreatment with captopril, arginine vasopressin (AVP) antagonist, or both; 3) during total autonomic blockade (TAB); and 4) during neurohumoral blockade (NHB, i.e., TAB + captopril + AVP antagonist). We determined the direct local response component from the responses obtained during NHB. The local chronotropic effects congruent to 0, so that the reflex rise in HR was entirely autonomically mediated. The local vascular response consisted of vasodilatation and provided the base line for assessing the estimated constrictor component from the net response from control, with the former ranging from 2 to 16 times the conventional estimates based on the net responses. In normal rabbits, the phase of good maintenance of MAP was entirely governed by autonomic mechanisms, which minimized the fall in CO and offset the local vasodilator component. During the hypotensive phase immediately after hemorrhage, when congruent to 30-35% BV had been removed, the constrictor effects of AVP and angiotensin II (ANG II) became important, whereas the role of autonomic mechanisms diminished. During TAB, the constrictor effects of AVP and ANG II were prominent even with small BV losses.

Animals↗
PubMed1995

Autonomic and ventilatory components of heart rate and blood pressure variability in freely behaving rats.

The relative role of parasympathetic, sympathetic, and ventilatory influences in the genesis of blood pressure and R-R interval variability is controversial. In 13 freely behaving WKY rats instrumented with venous and arterial catheters and chest electrodes, mean arterial pressure (MAP, mmHg), R-R interval (ms), and respiratory fluctuations were monitored for 90 min in the control condition and after intravenous atropine (0.75 mg/kg) and/or propranolol (1 mg/kg). Spectral power (pw) in the 0.25- to 0.75-Hz (midfrequency, MF) and the 0.75- to 3.0-Hz (high-frequency, HF, respiratory-synchronous) bands was computed in sequences of 400 heartbeats by use of a combined autoregressive analysis. Atropine reduced but did not abolish HF R-R interval pw (from 1.73 +/- 0.50 to 0.39 +/- 0.27 ms2, P < 0.01) and halved HF MAP pw (from 0.41 +/- 0.30 to 0.21 +/- 0.12 mmHg2, P < 0.05), whereas propranolol did not affect HF pw of the R-R interval or MAP. Propranolol also failed to significantly modify MF R-R interval pw (from 0.48 +/- 0.44 to 0.40 +/- 0.34 ms2, P = NS) or MF MAP pw (from 0.54 +/- 0.39 to 0.42 +/- 0.20 mmHg2, P = NS), whereas atropine virtually abolished MF R-R interval pw (from 0.48 +/- 0.44 to 0.01 +/- 0.01 ms2, P < 0.01) and also significantly reduced MF MAP pw (from 0.54 +/- 0.39 to 0.33 +/- 0.24 mmHg2, P < 0.01). The effects of combined blockade were similar to those of atropine alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Power spectral analysis for autonomic influences in heart rate and blood pressure variability in fetal lambs.

Variability of R-R intervals and arterial blood pressure signals in chronically instrumented fetal lambs was analyzed by power spectral analysis based on an assumption of maximum entropy. There were four consistent components, very low (VL, 0.01-0.025 cycle/beat), low (L, 0.025-0.125 cycle/beat), middle (M, 0.125-0.2 cycle/beat), and high (H, 0.2-0.5 cycle/beat), in the normal heart rate variability and blood pressure spectra. Integrated peaks in the power spectrum were compared before and after the administration of sympathetic and parasympathetic blockades. beta-Sympathetic blockade reduced the spectral power in the VL and L frequency components. alpha-Sympathetic blockade reduced only the M frequency component in the spectrum of R-R interval variability. Parasympathetic blockade reduced the H and L frequency components in the R-R interval variability spectrum but increased these components in the systolic blood pressure variability spectrum. The results clearly demonstrate the association between fetal autonomic activity and change of power spectrum of heart rate and blood pressure variability.

Animals↗
PubMed1999

Autonomic control of skeletal muscle blood flow at the onset of exercise.

The purpose of this study was to determine whether the autonomic nervous system is involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries. Before treadmill exercise at 3 miles/h, 0% grade, hexamethonium (10 mg/kg) and atropine (0.2 mg/kg) or saline was infused intravenously. Ganglionic blockade increased resting heart rate from 87 +/- 5 to 145 +/- 8 beats/min (P < 0.01) and reduced mean arterial pressure from 100 +/- 4 to 88 +/- 5 mmHg (P < 0.01). During steady-state exercise, heart rate was unaffected by ganglionic blockade (from 145 +/- 8 to 152 +/- 5 beats/min), whereas mean arterial pressure was reduced (from 115 +/- 4 to 72 +/- 4 mmHg; P < 0.01). Immediate and rapid increases in iliac blood flow and conductance occurred with initiation of exercise with or without ganglionic blockade. Statistical analyses of hindlimb conductance at 5-s intervals over the first 30 s of exercise revealed a statistically significant difference between the control and ganglionic blockade conditions at 20, 25, and 30 s (P < 0.01) but not at 5, 10, and 15 s of exercise. Hindlimb conductance at 1 min of exercise was 9.21 +/- 0.68 and 11.82 +/- 1.32 ml. min(-1). mmHg(-1) for the control and ganglionic blockade conditions, respectively. Because ganglionic blockade did not affect the initial rise in iliac conductance, we concluded that the autonomic nervous system is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs. Autonomic control of skeletal muscle blood flow during exercise is manifested through vasoconstriction and not vasodilation.

Animals↗
PubMed1977

Autonomic control of cardiovascular functions during neonatal development and in adult sheep.

We studied the autonomic control of resting heart rate of systemic and pulmonary vascular blood pressures (BP) in chronically instrumented neonatal lambs 1-8 weeks of age. The maximum response to ganglionic blockade and sympathetic and parasympathetic antagonists was taken as an index of the magnitude of the total neural, adrenergic, and cholinergic tones. The reactivity of the circulatory parameters to adrenergic and cholinergic agonists also was investigated. All findings were compared with those in adult nonpregnant sheep studied concomitantly and with data previously obtained from term fetal lambs. The results of our studies show: (1) resting heart rate declines spontaneously throughout the 8 weeks of neonatal life approaching that of adult sheep; (2) the progressive bradycardia is not related to changes in the parasympathetic or sympathetic tone; (3) resting systemic BP is under strong neurohumoral control during the first two to three weeks of neonatal life; the control decreases progressively, becoming similar to that of adult sheep; (4) resting pulmonary artery pressure of neonatal and adult sheep has no neurohumoral control; (5) the systemic BP response of the neonate to autonomic agonists is greater than that of the term fetus and is similar to that of the adult; (6) in neonatal and adult sheep, compared to the term fetus, the pressor response to norepinephrine is accompanied by a baroreceptor-mediated bradycardia, and acetylcholine-induced systemci hypotension is accompanied by a "paradoxical" tachycardia mediated through beta-adrenergic stimulation; (7) in contrast to our finding for the fetus, the pulmonary vascular pressure of neonatal and adult sheep is unresponsive to autonomic agonists.

Acetylcholine↗
PubMed1992

The autonomic nervous system modulates dry air-induced constriction in the canine lung periphery.

To determine the modulatory role of the autonomic nervous system on dry air-induced bronchoconstriction (AIB) in the canine lung periphery, we examined the effect of cholinergic, alpha- and beta-adrenergic, and total autonomic ganglionic blockade on AIB. Pretreatment with atropine significantly attenuated AIB by approximately 30%, indicating that AIB is partially mediated via a vagal reflex. Pretreatment with either phentolamine or propranolol did not affect AIB, indicating that alpha- and beta-adrenoceptors, respectively, were not activated in response to dry air challenge. In contrast, pretreatment with hexamethonium significantly potentiated AIB. In addition, exogenous vasoactive intestinal peptide (VIP), a potential neurotransmitter for the nonadrenergic-noncholinergic (NANC) inhibitory system, significantly inhibited AIB. We conclude that (1) neither alpha- or beta-adrenergic efferents are activated during dry air challenge, (2) total autonomic blockade potentiates the response to dry air, and (3) VIP attenuates AIB. Based on these observations, we speculate that NANC inhibitory activity may be stimulated during dry air challenge and antagonizes AIB.

Animals↗
PubMed1992

Sinus node function in hyperthyroid patients.

We have studied the electrophysiology of the sinus node and the role of the autonomic nervous system on sinus node function in 8 thyrotoxic patients of both sexes, 37.5 +/- 4.3 (mean +/- SE) yr old. The resting heart rate (RHR), the sino-atrial conduction time (SACT), and the sinus node recovery time (SNRT) were measured in the untreated condition (basal), after sympathetic blockade with propranolol 0.2 mg/kg body weight (BW) i.v. infusion, and after complete autonomic blockade with the additional administration of atropine 0.04 mg/kg BW i.v. bolus. 1) In the thyrotoxic patients the RHR was higher [117 +/- 6 beats per min (bpm)] than in 20 normal subjects (73 +/- 1 bpm, P less than 0.001), whereas the SACT and SNRT values were not different. 2) After sympathetic blockade with propranolol, the RHR decrement and SACT increase were greater in the hyperthyroid patients than in normal subjects, whereas there was no difference in SNRT values between the two groups. 3) In the thyrotoxic patients the complete autonomic blockade reestablished the electrophysiological parameters to values similar to those observed in basal condition. In conclusion, in thyrotoxic patients the intrinsic activity of the sinus node is increased. It appears that this is a direct consequence of thyroid hormone excess, rather than an effect of extrinsic influences exerted by the autonomic nervous system on sinus node activity.

Adolescent↗
PubMed1993

Age-related changes of sinus node function and autonomic regulation in subjects without sinus node disease--assessment by pharmacologic autonomic blockade.

To assess the relationship between aging and autonomic regulation of sinus node function, 56 subjects of various ages (range 14-75 years, mean 43 +/- 19 years) without sinus node disease were studied. Heart rate, corrected sinus node recovery time and sinoatrial conduction time were measured before (basic) and after (intrinsic) pharmacologic autonomic blockade (propranolol + atropine i.v.). Percent chronotropies of the above parameters were calculated by a modified Jordan's method. Basic heart rate and basic corrected sinus node recovery time did not vary with age (r = -0.15, r = 0.08, respectively), while basic sinoatrial conduction time tended to increase with age (r = 0.32, p < 0.05). Intrinsic heart rate decreased (r = -0.76, p < 0.001), and intrinsic corrected sinus node recovery time and intrinsic sinoatrial conduction time both increased with age (r = 0.55, p < 0.001; r = 0.56, p < 0.001, respectively). The younger the subject, the more negative the percent chronotropies of the above parameters were, and the percent chronotropies correlated positively with age (r = 0.68, p < 0.001; r = 0.52, p < 0.001 and r = 0.34, p < 0.05, respectively). In conclusion, intrinsic sinus node functions deteriorated with age. Furthermore, parasympathetic tone on the sinus node functions decreased with age, which may compensate for age-related deterioration of intrinsic sinus node function.

Adolescent↗
PubMed2004

Characteristics of autonomic nervous function in Zucker-fatty rats: investigation by power spectral analysis of heart rate variability.

We investigated the characteristics of autonomic nervous function in Zucker-fatty and Zucker-lean rats. For this purpose, a long-term electrocardiogram (ECG) was recorded from conscious and unrestrained rats using a telemetry system, and the autonomic nervous function was investigated by power spectral analysis of heart rate variability (HRV). Although heart rate (HR) in Zucker-fatty rats was lower than that in Zucker-lean rats throughout 24 h, apparent diurnal variation in HR was observed in both strains and HR during the dark period was significantly higher than that in light period. Diurnal variation in locomotor activity (LA) in Zucker-fatty rats was also observed, but LA was lower than that in Zucker lean rats, especially during the dark period. There were no significant differences, however, in high-frequency (HF) power, low-frequency (LF) power, and the LF/HF ratio between Zucker-fatty and Zucker-lean rats. The circadian rhythm of these parameters was mostly preserved in both strains of rats. Moreover, the effect of autonomic blockades on HRV was nearly the same in Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal, from the aspect of power spectral analysis of HRV.

Animals↗
PubMed2003

Effect of acute nitric oxide synthase inhibition in the modulation of heart rate in rats.

Acute nitric oxide synthase inhibition with N G-nitro-L-arginine methyl ester (L-NAME) on chronotropic and pressor responses was studied in anesthetized intact rats and rats submitted to partial and complete autonomic blockade. Blood pressure and heart rate were monitored intra-arterially. Intravenous L-NAME injection (7.5 mg/kg) elicited the same hypertensive response in intact rats and in rats with partial (ganglionic and parasympathetic blockade) and complete autonomic blockade (38 +/- 3, 55 +/- 6, 54 +/- 5, 45 +/- 5 mmHg, respectively; N = 9, P = NS). L-NAME-induced bradycardia at the time when blood pressure reached the peak plateau was similar in intact rats and in rats with partial autonomic blockade (43 +/- 8, 38 +/- 5, 46 +/- 6 bpm, respectively; N = 9, P = NS). Rats with combined autonomic blockade showed a tachycardic response to L-NAME (10 3 bpm, P<0.05 vs intact animals, N = 9). Increasing doses of L-NAME (5.0, 7.5 and 10 mg/kg, N = 9) caused a similar increase in blood pressure (45 +/- 5, 38 +/- 3, 44 +/- 9 mmHg, respectively; P = NS) and heart rate (31 +/- 4, 34 +/- 3, 35 +/- 4 bpm, respectively; P = NS). Addition of L-NAME (500 micro M) to isolated atria from rats killed by cervical dislocation and rats previously subjected to complete autonomic blockade did not affect spontaneous beating or contractile strength (N = 9). In vivo results showed that L-NAME promoted a tachycardic response in rats with complete autonomic blockade, whereas the in vitro experiments showed no effect on intrinsic heart rate, suggesting that humoral mechanisms may be involved in the L-NAME-induced cardiac response.

Analysis of Variance↗