Within 4 days following entry into estivation, heat dissipation and oxygen consumption by the land snail Oreohelix spp. decreased by 83% compared to standard non-estivating rates. During both non-estivating and estivating conditions, the quantity of heat dissipated per mole of O2 consumed was indicative of a completely aerobic metabolism. This calorimetric-respirometric (C/R) ratio was −461±12 kJ mol−1O2 (S.E.M., N=5) under standard non-estivating conditions and −464±26 kJ mol−1O2 (N=4) during estivation. Respiratory exchange ratios reflected a primary dependence upon carbohydrate as a metabolic substrate during both states. Carbon dioxide retention occurred during the first 36h of estivation, resulting in an increase in hemolymph PCOCO2 and a decrease in pH. The respiratory acidosis during short-term estivation was not compensated by elevation of hemolymph [HCO3] above levels predicted from the in vitro nonbicarbonate buffer value of hemolymph. A brief period of rapid CO2 release, which caused hemolymph PCOCO2 and pH to return to pre-estivation values, preceded the increase in O2 consumption during arousal. Exposure of nonestivating snails to 4.67 kPa PCOCO2 (1 kPa=7.5 mmHg) caused a rapid and fully reversible 50% suppression of respiration rate. The temporal nature of CO2 retention and release during entry into and arousal from estivation, and the suppression of O2 consumption by artificial hypercapnia, support the hypothesis that elevated PCOCO2. or the resultant acidosis may contribute to metabolic suppression during estivation by land snails.

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