Non-enzymatic antioxidant defences
Changes in the concentration of uric acid, its oxidized form (allantoin) and GSH are shown in Fig.1B–D.
The three studied organs showed a significant increase of uric acid concentration during estivation, but a significant decrease after arousal was only observed in the kidney (Fig.1B). Uric acid levels in the midgut gland of active controls were higher than those in other organs, which may be correlated with the occurrence of urate tissue in the midgut gland. However, a strikingly large increase in uric acid concentration occurred in the kidney during estivation, so that the kidney levels became not statistically different from the midgut gland (Fig.1B). This was surprising, since the kidney is devoid of specialized urate tissues.
The large increase in renal uric acid concentrations during estivation was further studied by histological examination of the kidney. The epithelium lining the renal chamber in active animals (Fig.2A) shows small basophilic or brown urinary concretions within large apical vesicles of renal epithelial cells. Estivating animals showed a marked increase in epithelial cell size, while the number, size and density of the urinary concretions, and of the concretion-containing vesicles, also increased. These urinary concretions were mostly basophilic structures within the apical vesicles, often with dark brown cores (Fig.2B). In some estivating animals, cryptal enlargement and disorganization occurred and large and dark brown concretions were contained within vesicles of many cells (Fig.2C). Also, hemocyte islets were interspersed between the epithelial crypts (Cueto, 2011); they appeared reduced in size and occasionally disorganized during estivation.
A large and statistically significant increase of allantoin concentration (indicative of uric acid oxidation) also occurred in kidney and foot after 24h of arousal (compared with active control and estivating animals; Fig.1C). Also, the allantoin concentration was higher in the kidney than in the midgut gland and foot, in both active control animals and those 24h after arousal. In addition, midgut gland concentrations were higher than those in the foot during the activity–estivation cycle (Fig.1C).
GSH concentrations in the kidney drop significantly in estivating versus active control animals, and they rose significantly at 20min after arousal (Fig.1D). Furthermore, GSH levels in kidney and midgut gland decreased significantly between active control and aroused 24h snails. No significant differences between experimental groups occurred in the foot (Fig.1D).
The midgut gland showed GSH levels higher than those of the foot, at all times during the activity–estivation cycle. Likewise, levels of GSH in the midgut gland were higher than those found in the kidney during estivation (Fig.1D).