The effect of diet, age, sex and state of hydration on the relationship between Na+, K+ and urate in the fat body tissue of the cockroach Periplaneta americana has been investigated. There is a significant correlation between K+ and urate concentrations in the fat bodies of both males and females in late nymphal and adult stages. Animals fed on a dextrin/casein diet, which had a K+ content of about one-third that of the rat pellets normally used for food, had a lower than normal K+/urate ratio. In both the normally fed and dextrin/casein-fed groups of animals, dehydration caused a decrease in the K+/urate ratio. Dehydration (and starvation) caused an increase in the amount of urate per unit weight of fat body. Some of the urate in the fat body is present in small spherical cellular inclusions. There is also a correlation between the K+ concentration and the number of spherules. The ratio of spherules/urate is significantly higher in hydrated animals than in dehydrated ones.

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