Daily rhythms of liver cAMP, total liver lipids, prolactin-like hormone and growth hormone cell activities in Sarotherodon mossambicus acclimated to different photoperiod regimes

Liver cAMP, total liver lipids, and pituitary prolactin-like (PRL) hormone and growth hormone (STH) cell activities were determined eight times over a 24-hr period in Sarotherodon mossambicus maintained under long and short photoperiod regimes. Diurnal variations were observed in all parameters monitored. The data illustrate that the photoperiod and the time of sacrifice are important considerations in the study of metabolic hormonal parameters in fishes. A significant correspondence between the PRL cell cycle and the total liver lipid levels cycle, and between the STH cell cycle and the liver cAMP level cycle, was also observed. Possible explanations of these facts are discussed.The authors gratefully acknowledge the critical review of the manuscript by Dr. M. Olivereau and Professor W. S. Hoar. We are also grateful for the continued interest, cooperation, and facilities extended to us by the staff of the Oceanic Institute of Hawaii and by Dr. S. Ramanathan of the University of Hawaii Medical School. Part of the work was supported by a grant from the Noyes Foundation and part by a fellowship of the Program of Cultural Cooperation between Spain and the United States of America.Peer reviewe