Progressive Recruitment of Follicular Cells with Graded Secretory Responsiveness during Stimulation of the Thyroid Gland by Thyrotropin*

Abstract

One of the earliest responses of the thyroid cells to TSH is macropinocytosis with formation of intracellular colloid droplets. We demonstrate here that increasing stimulation with TSH not only elicits a highly individual macropinocytotic response among different follicular cells but that the fraction of TSH-responsive cells is also a function of the TSH dose. After pretreatment with T4, mice and rats were injected ip with bovine TSH and killed 2 h later. The macropinocytotic response to TSH was evaluated on periodic acid-Schiff-stained 3-microns sections of the thyroids in terms of droplet number per 25 follicles and, in addition, by assessing recruitment, i.e. percentage of droplet-containing cells. Both variables increased with increasing TSH stimulation until they reached a plateau at about 9 mU TSH in mice and at about 300 mU TSH in rats: the percentage of droplet-containing cells gradually increased in mice from 2% (no TSH) to 67% (9 mU TSH) and in rats from 11% (no TSH) to 54% (300 mU TSH). Overall pinocytotic response as well as thyrocyte recruitment could be modified by extra- and intrathyroidal factors: for example, pretreatment of the mice with an iodine-deficient diet increased the maximal percentage of droplet containing cells to nearly 90%. Obviously, two separate components of the macropinocytotic response of the thyroid gland to TSH can be distinguished: the first is the gradually increasing fraction of droplet-containing cells, the second is the well known increase of the number of colloid droplets in each TSH-responsive cell with progressive TSH stimulation. Recruitment of thyrocytes with a gradually increasing natural threshold to a hormonal stimulus appears to be a fundamental mechanism in the thyroid gland and possibly in other organs.

Renin release and gene expression in intact rat kidney microvessels and single cells.

“…Further studies are necessary to determine whether a similar response is obtained with other well-known stimuli for renin release. Taken together, these findings suggest that cell recruitment may be a general biological phenomenon shared by many different endocrine cells (35)(36)(37)(38), which in turn may be important in the control of peptide hormone availability.…”

“…The results of the present study indicate that the population of renin-secreting cells is heterogeneous, with a wide range of renin secretory rates between individual cells. Although peptide-secreting pancreatic beta (35,36), thyroid (37), and hepatic cells (38) possess heterogeneous peptide synthetic and secretory capabilities, this heterogeneity had not been previously described for the renin-secreting cell. Stimulation of newborn kidney microvascular cells with forskolin resulted in a significant increase in the number of renin-releasing cells (hemolytic plaques) without a change in plaque size.…”

Light and electron microscopic study of the thyroid gland in rats exposed to power-frequency electromagnetic fields

“…Thyroid cells incubated with TSH were characterized by apical pseudopods and intracytoplasmic colloid droplets (Kawada and Naito, 1978;Rocmans et al, 1978). In mice and rats injected with TSH after pretreatment with thyroxin, the percentage of follicular cells containing colloid droplets and the number of droplets in cells gradually increased with increase of the TSH dose (Gerber et al, 1987).…”

Thyrocyte-specific Gq/G11 deficiency impairs thyroid function and prevents goiter development

“…For the evaluation of thyroid histology, thyroids were fixed in 4% paraformaldehyde and stained with hematoxylin and eosin. For the counting of droplets, fixed and sectioned thyroids were treated with periodic acid-Schiff stain as previously described by Gerber et al (53). Histological morphometry was performed using NIH ImageJ software (http://rsb.…”