Physiological responses of the monocled cobra (Naja kaouthia Lesson, 1831) including venom production, to high ambient temperature exposure.

Background: Temperature regulation is essentially important for survival of poikilotherms such as snakes. Body temperature is regulated by snakes through behavioral and physiological responses. The global-warming crisis, combined with the need to house large population of snakes in limited spaces, increases the likelihood of exposing snakes to high ambient temperature (HTa), requiring it reliance on physiological responses. This study aimed to study the effect of HTa exposure on physiological responses and venom production, which have rarely been studied.

Methods: Eleven adult monocled cobras (Naja kaouthia Lesson, 1831) were divided into two groups. The concurrent control group was housed in a temperature-controlled room, and the heat exposed group was housed in the same room with gradually increasing temperatures (25°C-35°C) for 4 h on four consecutive days. Data were collected 3 days before the experiment as the baseline and then compared with day 1 and day 4 after HTa exposure data representing immediate and prolonged effects. Body temperature, body weight, water intake, heart rate, hematology, plasma biochemistry, body-fluid compartments, hormonal response, heat shock protein expression and venom production were measured.

Results: In response to HTa exposure, body temperature and heart rate increased, plasma volume significantly decreased, but water intake increased. Hematocrit and plasma protein progressively decreased in the latter stages of experimentation, but HTa diminished this effect. HTa only increased plasma corticosterone on day 1. Exposure to HTa increased venom protein concentration on day 4 and diminished the decreased proportion effect of frequent venom collection on phospholipase A₂ component.

Conclusion: Increased heart rate and fluid shift from the intravascular compartment appeared to be the underlying mechanism for heat dissipation during HTa exposure. Under the study condition, HTa caused heat stress, but the snake could adapt after continued exposure. Additionally, HTa increased venom protein concentration in N. kaouthia, particularly phospholipase A₂ component.