Abstract
AbstractA daily rhythm was demonstrated in levels of specific activity for the Na, K‐ATPase and glucose‐6‐phosphatase enzymes in adrenal and renal subcellular fractions in the rat. A bimodal daily rhythm was observed for 5′‐nucleotidase in a renal subcellular fraction. The rats were maintained on a 12:12 light‐dark (LD) regimen. Animals were killed at approximately 4‐hour intervals.The daily rhythm in Na, K‐ATPase and glucose‐6‐phosphatase activities persisted in animals maintained under continuous illumination (LL) and continuous darkness (DD). The 5′nucleotidase activity persisted under LL, and under DD.The data from the enzyme assays were analyzed by fitting to a cosinor regression model designed to assess the rhythmic nature of the findings. A linear transformation method was applied to assess the closeness of fit to the cosinor regression model.The Na, K‐ATPase and glucose‐6‐phosphatase activities appeared to be endogenous circadian rhythms. Glucose‐6‐phosphatase activity in renal fractions appeared to be influenced by the feeding cycle. The 5′‐nucleotidase enzyme appeared to have an ultradian rhythm. The ultimate derivation and significance of these observed rhythms remains to be determined; however, they appear to be independent of the light‐dark cycle.
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