Gen Comp Endocrinol 1994 Jun 01;943:357-65. doi: 10.1006/gcen.1994.1091.

Ontogeny of ocular serotonin N-acetyltransferase activity daily rhythm in four anuran species.

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The profile of daily ocular serotonin N-acetyltransferase (NAT) rhythm has been examined during the development of four anuran amphibians in different environments and of varying phylogenetic origins: Xenopus laevis, Discoglossus pictus, Rana perezi, and Bufo calamita. A significant day/night rhythm of ocular NAT with the acrophase at midnight was first detected at stages 43/44 and 25 in X. laevis and R. perezi, respectively. Total enzymatic activity increased with body weight throughout development, although both mean levels and amplitudes of NAT activity per milligram of protein significantly decreased; this attentuation of rhythm was more significant in postmetamorphic froglets, and the acrophase was delayed about 1 hr. There were no significant differences in daily NAT profiles before and after metamorphosis in D. pictus and B. calamita. The amplitude of the NAT rhythm was maximal (> 10-fold nocturnal values) in Xenopus compared with other species (2- to 3-fold).

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