CIRCADIAN RHYTHM IN PLASMA INORGANIC PHOSPHORUS AND SULFUR OF THE RAT: ALSO IN SUSCEPTIBILITY TO STRYCHNINE

In the first phase of this investigation adult, male Sprague-Dawley rats were maintained under rigidly standardized environmental conditions which included an artificial light-dark cycle (light from 0600 to 1800). During two separate 24-hr periods subgroups of rats were removed from the colony room every hour or. the hour and a cardiac tap was performed on each rat subsequent to sodium pentobarbital anesthesia, Inorganic sulfur and phosphorus determinations were made on the plasma obtained from these rats. The pattern of fluctuation in both compounds over the 24-hr period indicated that both had a circadian component with essentially the same phasing. The crest in the level of both compounds occurred between 1300 and 1600, the trough values for inorganic phosphorus occurred between 0300 and 0600, for the inorganic sulfur it occurred at about 2200.Similar studies were made on starved, blinded, and also on rats subjected to prolonged periods of continuous illumination. The inorganic phosphorus rhythms persisted in starved animals, inorganic sulfur was not determined on starved animals.The rhythms of both compounds persisted with altered phasing in blinded animals. The rhythms seen in blinded animals were somewhat flattened and had a tendency to be irregular when compared to animals kept in a light-dark cycle. Both the inorganic sulfur and phosphorus levels were significantly lower in blinded animals when compared to animals subjected to a light-dark cycle or to continuous illumination.In those rats subjected to continuous illumination the general tendency was for the inorganic sulfur rhythm to flatten out. The inorganic phosphorus rhythm persisted under this environmental condition but the profile was radically altered.Evidence is presented to indicate that the ability of the organism to respond to a potentially lethal dose of a drug depends on the time of day the drug is administered. When an identical dose, based on body weight, of strychnine was given to subgroups of rats at different time points along a single 24-hr time scale as many as 85% died at one time of day whereas only 35% died at another time of day.Evidence also is presented to indicate that the ability of the rat to survive a cardiac tap while under a therapeutic dose of sodium pentobarbital may depend on the time of day the cardiac tap is performed. The importance of recognizing the time structure of the living organisms is discussed.