Effect of Cold Acclimation on Vascularization of Ears, Heart, Liver and Muscles of White Rats

¹ From the Division of Applied Biology, National Research Laboratories, Ottawa, Canada

The degree of vascularization of different tissues of rats killed with ether after a 4-week acclimation period to 30°C or 6°C was estimated by counting on benzidine stained cross-sections, capillaries in heart and leg muscles (soleus, gastrocnemius, plantaris), sinusoids in liver and all blood vessels in ears. Short exposure to cold (2 hr.) of the 30°C acclimated rats had no effect on the vascularization of any of the organs studied. Cold acclimation had no effect on number of capillaries in the heart and sinusoids in the liver, but in the ears it produced a 12-fold increase in number of blood vessels. In the plantaris and the red fiber regions of the gastrocnemius but not in the white fiber region of the latter, there was an absolute increase in the number of capillaries/mm². In the soleus and the two heads of gastrocnemius, there were densely vascularized subregions which were on the average approximately 50% larger after cold acclimation. The increases in the number of opened capillaries observed in the ears and the leg muscles are interpreted as indicating a higher metabolism, and possibly an increased chemical thermogenesis in the red fiber muscles.