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The crustacean hyperglycemic hormone (CHH) is involved in the regulation of endogenous blood glucose metabolism. In this paper we describe the daily rhythmicity in the blood glucose and the blood CHH content of the crayfish Orconectes limosus. Both blood CHH and blood glucose levels increase during the first hours after the beginning of darkness. The bioactivity of released CHH is far higher than that of CHH stored in the sinus gland. Moreover, the released hyperglycemic material shows an affinity for high molecular weight proteins in the hemolymph. Preliminary results suggest that subunits of hemocyanin may act as potential carrier-proteins for bioactive CHH.

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We investigated the effects of several experimental conditions, such as constant darkness, light/dark phase-shift, covered eyes, eyestalks and rostral regions, and optic tract sectioning, on the entrainment of daily blood glucose rhythmicity in the crayfish. Hemolymph glucose determination over a 24 h period and a morphometrical study on the secretory activity of the Crustacean Hyperglycemic Hormone (CHH)-producing cells in the eyestalk using immunocytochemistry were carried out.Our results indicate that Astacus leptodactylus exhibits an endogenous circadian blood glucose rhythm entrained by the light/dark schedule.The light stimuli that control the rhythm are not detected by the compound eyes nor by the caudal photoreceptor but most probably by a photoreceptor located elsewhere in the eyestalk. After disruption of the neural connection between the optic lobes and the cerebral ganglion, blood glucose rhythmicity persists, which indicates that the biological clock of the blood glucose rhythm is located within the optic lobes.

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