Binding and clearance of radioactive adrenaline and noradrenaline in sheep blood.

An understanding of the conditions influencing protein binding of catecholamines (CAs) is important in studying their metabolic effects. Unfortunately, reports on plasma protein binding of CAs are scarce, conflicting and mainly performed in vitro. The aim of our in vivo and in vitro studies was to investigate binding and clearance of radioactive adrenaline (epinephrine) ((3)H-A), noradrenaline (norepinephrine) ((3)H-NA) and their metabolites in sheep blood. The time course of the radioactivity in the blood after intravenous injection of (3)H-A and (3)H-NA (3.7 MBq each) in 4 sheep (2 of each sex; total of 8 administrations) was determined. Blood samples were taken from the jugular vein. The highest radioactivity was observed in the first sample (5 min) following injection. Radioactivity showed a biphasic disappearance. An initial stage, in which radioactivity decreased rapidly (within 1 h) after the injection, was followed by a slow stage, lasting for up to 1 month, until background levels were reached. In vitro results indicated that NA and A were present not only in plasma (70%) but also in the erythrocytes (30%; mainly bound to haemoglobin). Sephadex G-25 gel filtration revealed that from the plasma fraction about 15% was strongly bound to proteins (mainly albumin). These results demonstrate that previous experiments in this field have overestimated the percentage of CAs bound to plasma proteins, because binding to haemoglobin was previously not known. In the future, efforts should be made to characterize the adduct products of CAs and establish an assay to determine them in vivo. If this could be achieved, it would yield a valuable tool for measuring the stress experienced for a longer period.

Accumulation of radioactivity after repeated infusion of 3H-adrenaline and 3H-noradrenaline in the rat as a model animal.

Besides enzymatic inactivation, catecholamines bind non-enzymatically and irreversible to proteins. The physiological impact of these catecholamine adducts is still unclear. We therefore collected basic data about the distribution of catecholamine adducts in the rat after repeated intravenous administration of (3)H-adrenaline and (3)H-noradrenaline. In all animals radioactivity in blood increased until the last injection on Day 7 and decreased then slowly close to background values (plasma) or remained higher (erythrocytes). In all sampled tissues radioactivity could be found, but only in hair high amounts remained present even after 3 weeks. Half-life of rat serum albumin loaded with (3)H-adrenaline or (3)H-noradrenaline was not altered. This study provides basic knowledge about the distribution of catecholamines or their adducts, but physiological effects could not be demonstrated. However, for the first time deposition and accumulation of catecholamines (adducts) in the hair could be proven, suggesting that hair might be used for evaluating long term stress.

Excretion of catecholamines in rats, mice and chicken.

Stress assessment favours methods, which do not interfere with an animal's endocrine status. To develop such non-invasive methods, detailed knowledge about the excretion of hormone metabolites in the faeces and urine is necessary. Our study was therefore designed to generate basic information about catecholamine excretion in rats, mice and chickens. After administration of (3)H-epinephrine or (3)H-norepinephrine to male and female rats, mice and chickens, all voided excreta were collected for 4 weeks, 3 weeks or for 10 days, respectively. Peak concentrations of radioactivity appeared in one of the first urinary samples of mice and rats and in the first droppings in chickens 0.2-7.2 h after injection. In rats, between 77.3 and 95.6% of the recovered catecholamine metabolites were found in the urine, while in mice, a mean of 76.3% were excreted in the urine. Peak concentrations in the faeces were found 7.4 h post injection in mice, and after about 16.4 h in rats (means). Our study provides valuable data about the route and the profile of catecholamine excretion in three frequently used species of laboratory animals. This represents the first step in the development of a reliable, non-invasive quantification of epinephrine and norepinephrine to monitor sympatho-adrenomedullary activity, although promising results for the development of a non-invasive method were found only for the chicken.