Infusions of adrenaline stimulate noradrenergic transmission in man, but adrenaline is not released later as a co-transmitter

Role of epinephrine in acute stress

This article presents the likely pathway of stimuli generated by the recognition of high-intensity stressors to ultimately produce a fight-or-flight response. A key element is the recognition that psychological stressors that do not directly alter the internal environment represent the most important etiology of a fight-or-flight response. Adrenomedullary secretion is a critical component of that response; impromptu stimulation of the adrenal medulla can produce plasma epinephrine concentrations greater than 10,000 pg/mL. When these plasma levels reach the hypothalamus to act on the CNS, the result is facilitation of the decision making, and decision execution processes (fight-or-flight), and perhaps further sympathetic stimulation and vasopressin release. Subjects with underlying cardiovascular and/or metabolic pathology may be particularly susceptible to potentially lethal reactions to this neuroendocrine response. Additionally, since this biological reaction may be triggered by sudden changes in the social environment, the coordinated actions of epinephrine, sympathetic stimulation and vasopressin must be directed at not only optimizing the chances for survival, but also at attaining maximal preservation of the individual environmental and social domains.

Temporary increase of plasma epinephrine affects stress responses 24 h later

The impact of temporary (24 h) implantation of epinephrine tables on catecholamine responses to handling and immobilization 24 h later was investigated in rats. Free plasma epinephrine responded with an increase to both types of stress (77% and 326%, respectively) while controls showed a weaker response to immobilization. The basal level of free plasma norepinephrine was reduced (46% vs. controls) after epinephrine pretreatment, but neither handling nor immobilization had a specific effect on this parameter. In contrast, the basal level of free plasma dopamine was increased after epinephrine pretreatment (183%); however, as with free norepinephrine, there was no specific effect of handling or immobilization. Conjugated plasma epinephrine was significantly lowered after epinephrine pretreatment (44% vs. controls). It did not respond specifically to handling or immobilization except for a stronger response after 20 min of immobilization. Conjugated norepinephrine showed no specific response, but increased nonspecifically after extended immobilization. Conjugated dopamine was lowered (30%-48%) in the E-treated group and did not respond to stress at any time. Thus, a temporary elevation of free plasma epinephrine affected, differentially, basal levels and stress responses of free and conjugated catecholamines 24 h later.

Accumulation and release of adrenaline, and the modulation by adrenaline of noradrenaline release from rabbit blood vessels in vitro

The accumulation of (-)-3H-adrenaline (3H-A) by rabbit isolated aorta was studied. In all experiments, monoamine oxidase and catechol-O-methyltransferase were inhibited by treatment with pargyline and 3',4'-dihydroxy-2-methyl-propiophenone, respectively. The relationship between the accumulation of 3H derived from 3H-A and the duration of incubation was linear. The 3H-accumulation after 3 h incubation was 22.5 ml/g. In reserpine-treated tissue, the 3H-accumulation levelled off after 30 min and was 8.5 ml/g after 3 h. The concentration of 3H-A or (-)-3H-noradrenaline (3H-NA) and the 3H-accumulation (ml/g) were inversely related. At 10(-8) M, the 1-hour accumulation of 3H derived from 3H-A and 3H-NA was 7.8 and 15.2 ml/g, respectively. With increasing concentrations the accumulation values approached each other. The accumulation of 3H derived from 3H-A by reserpine-treated tissue also showed an inverse relationship with concentration. The accumulation of 3H derived from 3H-A was dependent on the bath temperature. Storage of tissue (0-5 days in salt solution without equilibration with 95% O2/5% CO2; 4 degrees C) did not affect the accumulation of 3H derived from 3H-A. Thereafter (7-14 days), the accumulation decreased. The inhibitory potency (IC50; -log M) of desipramine, cocaine, propranolol, isoprenaline, and normetanephrine on accumulation of 3H derived from 3H-A was found to be 8.26; 6.50; 5.48; 4.88, and 4.02, respectively. The maximal degree of inhibition was almost the same for these drugs, while that of clonidine and corticosterone was 50 and 20%, respectively. In the presence of desipramine, either clonidine, corticosterone or isoprenaline reduces the accumulation of 3H derived from 3H-A. Ouabain and iodoacetic acid, but not sodium cyanide and 2,4-dinitrophenol, reduced the accumulation of 3H derived from 3H-A. Anoxia (95% N2/5% CO2; 37 degrees C; 1-24 h) did not alter the accumulation of 3H derived from 3H-A. Glucose deprivation alone or combined with anoxia markedly reduced the 3H-accumulation. The release of 3H-A from rabbit isolated aorta was studied. This release was compared with that of 3H-NA. The stimulation-evoked 3H-overflow from aorta preloaded with 3H-A decreased with repeated stimulation. In contrast, prestimulation enhanced subsequent stimulation-evoked 3H-overflows. For both 3H-amines, the 3H-overflow increased concomitantly to the same degree with the number of pulses. The time course of 3H-overflows with either 3H-A or 3H-NA was compared.(ABSTRACT TRUNCATED AT 400 WORDS)