Different effects of neurotensin and neuromedin-N on the proliferative activity of rat adrenal cortex.

Evidence indicates that neurotensin (NT) and neuromedin-N (NMN) exerts an adrenocorticotropic effect in the rat. The present study aimed to investigate whether these neuropeptides are able to stimulate the proliferation of rat adrenocortical cells in vivo and to compare their mode of action. Adrenocortical proliferative activity was assessed by the metaphase-arrest technique and metaphases were counted per medulla-containing adrenal section. A bolus administration of NT (3 micrograms/rat) resulted in a significant increase in the number of metaphases in both zona fasciculata and the entire cortex, an effect observed 48 h after the injection. The administration of NMN (3 micrograms/rat) induced a notable rise in the number of metaphases in the zona fasciculata and the entire cortex within 12 h, followed by a subsequent drop after 24 h and a return to normal values at 48 h. These findings indicate that NT and NMN enhance rat adrenal growth in vivo acting via different mediators.