Transparent-Chamber Studies of Vessels, Circulation, and Follicles in Thyroid Grafts in Unanesthetized Mice

Summary

This investigation was made to obtain quantitative measurements of follicles and microcirculation in thyroid tissue in vivo. Grafts of mouse thyroid tissue placed in dorsal skin folds were observed with a microscope through glass windows. During periods of observations lasting several weeks, we detected no changes in the grafts in vascular patterns or in size or shape of the follicles. The average follicle diameter was 59 µ, with a standard deviation of 30 µ. Most follicles were supplied by several capillaries. The blood flow in these capillaries was intermittent and in many was asynchronous because capillaries arose from different arterioles with different vasomotor cycles. The capillary pathway for any one corpuscle from arteriole to venule averaged 155 µ in length, with a standard deviation of 44 µ. Most pathways anastomosed with others or had one or two branches. A typical pathway went by two to four follicles, that is, one or two follicles on each side of the capillary. Blood flow in capillaries in which the red cells passed in single file was recorded by the use of cinemi-crography. The velocity of flow, based on the frequency distribution of velocities during vasomotor cycles, averaged 109 µ per second, with a standard deviation of 47 µ per second. The average transit time for a red cell in a capillary was 1.4 seconds. Analysis of transit times indicates that most radioiodide in the red cell is not available during its passage through the thyroid tissue.

Author notes

2

We wish to express our appreciation to Mr. Roy Moore for technical assistance.

3

National Institutes of Health, Public Health Service, U.S. Department of Health, Education, and Welfare.