EFFECTS OF SUBSTANCE-P ON THE GROWTH-PROCESSES IN RAT-THYROID LOBES IN-VITRO

The effects of substance P (SP) on (1) H-3-thymidine incorporation into the DNA of rat thyroid lobes during a 4-hour incubation, and (2) thymidine kinase (TK, EC 2.7.1.21) activity in homogenates of rat thyroid lobes were investigated. We also examined the influence of the joint action of SP and thyrotropin (TSH) on these processes. It was shown that the effects of SP on these processes were dependent on the concentration of theneuropeptideapplied.Atthelowestconcentration(10(-12) M), SP significantly (p < 0.0025) decreased and at the highest one (10(-6) M) it slightly increased (p < 0.09) the values of the examined growth indices. The activity of TK rose in parallel with the increase in SP concentration. SP and TSH, when used together, exerted similar decreasing effects, both on H-3-thymidine incorporation into DNA and on TK activity.