Incidence de la cinetique de decroissance de la temperature apres le choc thermique sur les modifications d'activite des esterases et les possibilites de survie de Scolelepis (malacoceros) fuliginosa (annelide polychete)

Scolelepis fuliginosa reared in the laboratory at 13°C were put through 10-min thermal shocks at 16°C and 18°C and were then submitted to either a slow or a rapid temperature reduction. After the thermal shock, a posterior fragment of each specimen was cut off at intervals, until six days. Samples were submitted to electrophoresis on polyacrylamide gel, esterase activity being determined with α-naphthyl acetate.Enzymograms show that thermal shocks act on esterases in decreasing the activity of the main fractions. Immediate effects result in a very precocious enzymic response; more long-term effects depend on the maximum temperature, the animal's sex and the kinetics of the post-shock thermal reduction.Females are more sensitive than males. For a given Δt, esterase changes are greater and more long-lasting. After a 16°C Δt, a rapid decrease in temperature prevents the loss of activity of the middle and fast fractions in males and delays, by about 10 h, the alteration of female esterases. After 18°C ΔT, loss of activity of the middle and fast fractions occurs in less than 1 h, independently of the thermal kinetics, but survival is only possible—solely for males—with a rapid decrease in temperature which also delays females' deaths by between 24 and 48 h.In conclusion, a rapid decrease in temperature gives organisms a better resistance to thermal shock, as determined by esterase activity and controls the lethality of a high Δt.