Daily rhythmic variations in blood coagulation times in rats.

Abstract

AbstractWith all other environmental factors rigidly standardized, normal Sprague‐Dawley rats were maintained under the following schedules: (1) 12 hours of artificial light 0600 to 1800 alternating with 12 hours of darkness‐LD; (2) reversal of the first‐DL; (3) constant darkness‐DD, and (4) constant illumination‐LL.After the animals had been under a specific lighting regimen for at least three weeks, blood coagulation times were determined on separate groups of 8 to 16 animals at bi‐hourly intervals during a 24‐hour period. Significant daily fluctuations or rhythms in coagulation times under all lighting conditions were found by plotting each of the bi‐hourly mean values as a function of time. The temporal phasing of all rhythms in LD, DL, LL and DD were similar. The major changes found in the different lighting schedules involved overall magnitude, e.g., the overall 24‐hour mean coagulation time for rats maintained in LL was 21% greater than for rats maintained in DD. Although total adrenalectomy or adrenal medullectomy did not abolish the characteristic LD rhythm, there was about a 100% decrease in the mean 24‐hour coagulation time of LD adrenalectomized animals when compared to normal LD animals. No significant decrease was seen in adrenal demedullectomized animals when similarly compared with normal LD animals.