Effects of vasoactive intestinal polypeptide on the growth processes in rat thyroid lobes: studies ex vivo in vitro.

The effects of intravenous (i.v.) injections of vasoactive intestinal polypeptide (VIP) and intraperitoneal (i.p.) injections of thyroid-stimulating hormone (TSH, thyrotropin) on 3H-thymidine incorporation into the DNA of rat thyroid lobes incubated, after collecting, in vitro, were investigated. The animals of groups 1-6 were injected with the following substances: group 1, 0.9% NaCl; group 2, 2 IU TSH (i.p.); group 3, 10(-12) mol VIP; group 4, 10(-10) mol VIP; group 5, 10(-8) mol VIP; and group 6, 10(-8) mol VIP + 2 IU TSH (i.p.). The rats of each group were divided into three subgroups, and sacrificed after 6, 12 or 24 h from the time of injection. For group 1, the additional control group zero was used, and these controls were sacrificed immediately after i.v. injections of 0.9% NaCl at zero time. After decapitation the thyroid lobes were collected and then incubated for 4 h in RPMI 1640 medium in the presence of 3H-thymidine, 15% FCS and Hepes buffer. In all groups and at all times an increase of 3H-thymidine incorporation occurred; the stimulatory effect of VIP (in all doses) was stronger than that of TSH; the rate of 3H-thymidine incorporation after injections of both VIP and TSH (group 6), was higher than the rates following injections of VIP alone (group 5) or TSH alone (group 2).