Basal, diurnal, and stress‐induced levels of glucose and glucocorticoids in captive bats

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Abstract
Plasma levels of glucocorticoids and glucose were measured in three species of fruit bats (Chiroptera) sampled from captive populations. Three species of Old World bats (Pteropus vampyrus, P. Hypomelanus, and Rousettus aegyptiacus) had plasma levels of glucose that were within the normal mammalian range (80–100 mg/dl), with no difference between males and females. All animals had detectable levels of one or both of the major glucocorticoids (cortisol and corticosterone) found in mammals. Steroid levels were highest in P. hypomelanus (cortisol: 1,269 ± 207 ng/ml; corticosterone; 590 ± 154 ng/ml) and lowest in R. aegyptiacus (corticosterone: 36 ± 4 ng/ml; cortisol not determined). Diurnal changes in these steroids and the effects of handling and restraint stress were further investigated in P. hypomelanus. Experimental animals were captured in their roost quarters, bled once by venupuncture within 3 min, placed singly into a small holding chamber for 50–60 min, and bled again. This procedure was performed at four different times over the course of 24 h with different groups of animals. Glucose was at a minimum just before and a maximum just after the period of food presentation. Cortisol levels remained relatively constant throughout the day‐roosting period and significantly declined to their lowest level in the period following food presentation. As expected, the effects of handling and isolation caused a significant increase in both plasma cortisol and glucose levels. When individual P. hypomelanus were subjected to 3 h restraint stress in small plastic wire‐mesh restraining devices, cortisol levels rose approximately 800% by 2 h, with the first significant increase at 20 min. Thus, effects of sampling time (time of day) on plasma levels of cortisol and glucose should be considered when designing field and laboratory studies in which hormones and other blood borne parameters are being measured. Handling and bleeding times that exceeded 3 min were associated with elevated plasma levels of cortisol and glucose above resting (unstressed) levels, suggesting that field and laboratory protocols should be designed to reduce or eliminate this problem. Finally, the exceptionally high levels of plasma corticoids in P. hypomelanus, and to a lesser extent in P. vampyrus, place these bats among the highest known circulating adrenal steroid levels of all mammals.