Methods used to quantify the stress response in animals are vital tools in many areas of biology. Here we describe a new method of measuring the stress response, which provides rapid results and can be used in the field or laboratory. After a stressful event, we measure the capacity of circulating leukocytes to produce a respiratory burst in vitro in response to challenge by phorbol myristate acetate (PMA). During the respiratory burst leukocytes produce oxygen free radicals, and the level of production can be measured directly as chemiluminescence. When in vitro PMA‐stimulated whole blood chemiluminescence is measured directly after a stressful event, we define the response as the leukocyte coping capacity (LCC). In an experiment badgers (Meles meles), which were caught as part of an on‐going population study, were either transported to a central site prior to blood sampling or blood was collected at their site of capture. Transported animals had a significantly lower LCC and showed changes in leukocyte composition that were indicative of stress. We conclude that the stress of transport reduced LCC in badgers and that LCC serves as a quantitative measure of stress. Potential applications of this method are discussed.

SUMMARY1. In experiments on anaesthetized rats, we have studied the role of adenosine in mediating responses induced in individual arterioles and venules of the spinotrapezius muscle by systemic hypoxia.2. During systemic hypoxia induced by breathing 6% 02 for 3 min, some arterioles and venules dilated while others constricted. Topical application of the adenosine receptor antagonist, 8 phenyl-theophylline (8-PT), to the spinotrapezius had no effect on the constrictor responses but greatly reduced the dilator responses. The vessels nearest to the capillary bed -terminal arterioles and collecting venules -were most affected; their mean changes in diameter were reduced from 39 and 8% to 11 and -16 % respectively.3. In accord with these results, topical application of adenosine (2 x 10-7-2 x 10-3 M) produced graded dilation of all sections of the arterial and venous trees; the terminal arterioles and collecting venules were most responsive, being dilated at maximum by 31 and 15% respectively. The dilator responses induced in those vessels that constricted during hypoxia were fully comparable with those that dilated during hypoxia.4. Histochemical analysis of the spinotrapezius revealed that oxidative fibres that most readily release adenosine, glycolytic and mixed fibres were all evenly distributed throughout the muscle. There is no reason to suppose that some vessels are preferentially influenced by oxidative fibres.5. These results indicate that adenosine plays a major role in dilating both arterioles and venules of muscle during systemic hypoxia. But, they are consistent with the idea that the adenosine that is important is not released from muscle fibres, but synthesized by 5'-nucleotidase localized to the blood vessels; its activity may decrease proximally along the vascular tree and may vary from one vessel to another depending on the local 02 tension.

SUMMARY1. In rats anaesthetized with Saffan, responses induced in individual arterial and venous vessels of the spinotrapezius muscle by systemic hypoxia (breathing 12 or 6 % 02 for 3 min) were directly observed by in vivo microscopy.2. Both 12 and 6 % 02 induced gradual tachycardia and a fall in arterial pressure. Concommitantly, in each section of the vascular tree, some vessels showed a gradual increase in diameter, others, a gradual decrease.3. During 12% 02, mean diameter changes were graded from mean increases of -2 % in main arteries (resting diameter 40-90 ,tm) to -20 % in terminal arterioles (7-13 ,tm), and ranged from mean increases of 5-8% in collecting and secondary venules (9-18 ,tm, 18-30 ,tm), to a decrease of -2% in main veins (65-130 ,um).4. During 6% 02, constrictor responses were more common in arterial vessels.Thus, mean changes amounted to diameter decreases of < 5 % in main arteries and secondary arterioles (13-18,tm), and increases of -5% in primary arterioles (22-50 ,tm) and terminal arterioles. By contrast, diameter increases predominated in venous vessels being graded from ' 20 % in collecting venules to -2 % in main veins.5. In seventeen rats, 6 % 0 was administered for eight 3 min periods separated by 30 min control periods. The changes evoked in arterial pressure and heart rate were consistent throughout. Diameter changes evoked in individual arterial and venous vessels were consistent in the first two hypoxic periods. However, diameter changes in the third and successive periods were significantly different from those recorded in the first period: increases in diameter became more common and pronounced.6. These changes in vessel diameter, especially their variability, are considered in relation to recordings made previously of changes in gross blood flow and vascular conductance of limb muscle during systemic hypoxia.

1. In rats housed in a hypoxic chamber at 12% 02 for 3-5 weeks (CH) and in normal rats housed in air (N), we directly observed responses of arterial and venous vessels of the spinotrapezius muscle to changes in 02 concentration in the inspirate. Both CH and N rats were anaesthetized with Saffan. They had haematocrits of 550 + 0 9% (mean + S.E.M.) and 41P9 + 05%, respectively.2. In CH rats breathing 12% 02 and N rats breathing air, arterial and venous vessels from comparable anatomical positions in the vascular tree were of similar internal diameter.They also showed similar maximum dilator responses to topical adenosine (10-3 M); 14-1 + 1 1 and 16-3 + 1-7% in all arterioles, 15.5 + 1P2 and 11.5 + 06% in all venules in CH and N rats, respectively. 3. In CH rats, the change from 12% 02 to air for 3 min induced constriction in all arterioles and venules (-12 9 + 1 0 and -14 3 + 1 7%, respectively), whereas in N rats, the change from air to 12% 02 for 3 min induced net dilatation (3 9 + 1 8 % in arterioles and 4-7 + 0O8% in venules). Topical application of the adenosine receptor antagonist 8-sulphophenyltheophylline (8-SPT, 10-3 M) had no effect on control diameters in CH or N rats, nor on constrictor responses to air in CH, but reversed or reduced dilator responses to 12% 02 in N rats (to -2f4 + 1f3% in arterioles and 2f0 + 0 9% in venules). 4. In CH rats, the change from 12 to 8 02 produced net dilatation as great as that induced in N rats by the larger change from air to 8% 02: 8-5 + 2-6 and 5 0 + 3 7% in arterioles and 103 + 1-8 and 6-4 + 1-9% in venules, respectively. These responses were similarly reduced by 8-SPT to -4-3 + 1-9 and -5-2 + 2-7% in arterioles and to -6-9 + 2-0 and -1*5 + 2 0% in venules, respectively.5. These results indicate that CH rats were acclimated to 12 % 02 such that the resting tone of arterial and venous vessels of muscle was comparable to that of N rats breathing air. They also suggest that adenosine had little tonic dilator influence in CH rats breathing 12% 02 despite its contribution to the dilatation induced in N rats by acute exposure to 12% 02. This may reflect the greater haematocrit in CH rats which normalized the 02 supply to muscle. However, CH rats were more sensitive than N rats to the dilator influence of acute systemic hypoxia and this was largely mediated by adenosine.

Re-introductions of captive-bred animals are increasingly common in wildlife conservation and it is important that they fulfil their potential. To foster this goal we examined variations in stress levels in a captive-bred population of water voles Arvicola terrestris in response to housing conditions and radio-collaring, using weight loss and leukocyte coping capacity (LCC) as measures of relative stress, to investigate the impacts of housing conditions, handling and radio-collaring on this species. Thirty-eight water voles (22 males and 16 females) were used in the investigation, 25 housed in outdoor enclosures and 13 in laboratory cages. During the 6-week study, LCC, body weight and urine refractive index (URI, an indicator of hydration levels) were recorded once a week for each individual in weeks 1, 2, 4 and 6. After the first sample, radio-collars were attached to 20 individuals (10 males and 10 females) taken from both housing types. Throughout the experiment laboratory-cage housed voles weighed less, had lower LCC scoresindicating a reduced ability to combat infection -and had higher URIs than outdoor-enclosure voles. This suggests that the laboratory-cage voles were more stressed and dehydrated than the outdoor-enclosure voles. Weights and LCC scores of both housing groups decreased as the study progressed, suggesting that elements of the study, such as repeated handling, may have caused stress to both groups. Evidence suggested a short-term effect of radio-collaring on immunocompetence. We conclude that captive housing conditions, repeated manipulation and radio-collaring had demonstrable physiological effects on the water voles studied. We recommend that the effects of husbandry and tagging practices upon captive-bred mammals be closely studied as part of the quest to improve the success of the re-introductions to which they contribute.