Influence of cell density on desensitization of the thyroid cell cyclic adenosine 3',5'-monophosphate response to thyrotropin stimulation.

Abstract

Stimulation of cultured thyroid cells with TSH produces an acute increase in cAMP content (15–30 min maximum) followed by a decrease over 24 h representing refractoriness to further TSH stimulation. With continued exposure of thyroid cell subcultures to TSH for greater than 4 days, escape from desensitization occurred in that cAMP levels returned to the initial maximum (15–30 min) values. This increase in cAMP levels was unrelated to an increase in cell number. In addition, subculture of thyroid cells for between 1 and 6 days in the absence of TSH followed by acute (30 min) TSH stimulation revealed a progressive decrease in the maximum cAMP levels attained (50% of day 1 values after 4 and 6 days of subculture). The cAMP response to a 24-h period of TSH stimulation was examined in groups of cells after different durations of subculture without TSH. With TSH stimulation on the first day of subculture, as expected, cAMP levels increased markedly after 30 min, declined by 6 h, and remained suppressed for up t...