Abstract
A total of 249 primiparous mice were used for histological studies of the thyroid gland of mice in relation to lactation, weaning and the sexual cycle. The animals were divided into two groups of lactation and weaning. The lactation group consisted of mother mice who nursed 4 sucklings up to 25 days after parturition and weaned at the 26th day. The weaning group consisted of mother mice who were forced to wean immediately after parturition.In both groups, the vaginal smear test was made on mice who weaned their sucklings.
In the lactation group-Immediately after parturition, the thyroid gland shows a microfollicular trend, feeble staining and much vacuolation of colloid and swelling of follicle epithelium with increased formation of secretory droplets. Subsequently, the gland indicates almost the same state until weaning. Immediately after weaning, the gland shows for awhile a transient increase in size of follicles (macrofollicular trend), and swelling of follicle epithelium with newly increased formation of secretory droplets.
In the weaning groupThe thyroid gland s hows a finding similar to that found in the early period of the lactation group. The formation of secretory droplets in the follicle epithelium, however, is less frequent. From 17 days after parturition, the gland shows for a while a transient increase in size of follicles and swelling of the follicle epithelium with increased formation of secretory droplets.
The thyroid gland shows histologically no significant changes in relation to the sexual cycle. The gland, however, shows on the average a slight decrease in size of follicles in diestrus, and a slight decrease in staining of colloid in estrus and metestrus.
