TSH is a glycoprotein hormone composed of two nonidentical, noncovalently associated subunits, alpha and beta. We have previously shown in vivo that intrapituitary free alpha-subunit and intact TSH have divergent responses to hypothyroidism and thyroxine treatment, suggesting fundamental differences in their regulation. To explore this further, we exposed anterior pituitary cell cultures from rats previously rendered hypothyroid to thyrotropin releasing hormone (TRH), dopamine (DA), or TRH and DA and determined TSH, free alpha-subunit and TSH-beta responses. While positive or negative trends were noted at four hours, the most significant changes were observed at 24 and 48 hours. TRH increased media TSH at 24 hours to 180% of its basal value (P less than 0.01), with a comparable response at 48 hours. TRH also increased free alpha-subunit to 155% of the basal value (P less than 0.01) and TSH-beta to 145% of the basal value (P less than 0.01) at 24 hours. In contrast, DA produced concordant inhibition of TSH to 85% (P less than 0.05), free a-subunit to 42% (P less than 0.01), and TSH-beta to 53% (P less than 0.01) of the basal values at 24 hours. However, coincubation with both TRH and DA produced discordant responses: TSH was stimulated to 126% of the basal value at 24 hours (P less than 0.01), while both free alpha-subunit and TSH-beta fell significantly below the basal values (81% and 65% respectively, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)