Neuropeptide Y modulates pituitary–adrenal axis activity in the lizard, Podarcis sicula

Abstract

The role of neuropeptide Y (NPY) in the modulation of the pituitary–adrenal axis activity in a lizard, Podarcis sicula, was investigated by in vivo NPY administration. The effects were evaluated by examination of the morphological and morphometrical features of the tissues as well as the plasma levels of ACTH, corticosterone, aldosterone, norepinephrine, and epinephrine. Intraperitoneally administered NPY (27 nmol /100 g body wt) raised ACTH plasma levels (from 5.23 ± 0.06 pg/ml in carrier injected specimens to 6.83 ± 0.01 pg/ml, 24 h after the injection). In the steroidogenic cells a strong decrease of lipid amount was found; corticosterone plasma level increased from 6.28 ± 0.02 ng/ml in carrier injected lizards to 7.96 ± 0.01 ng/ml 24 h after the injection); aldosterone levels were raised from 1.88 ± 0.02 ng/ml in carrier injected specimens to 6.38 ± 0.05 ng/ml 24 h after the experimental treatment. In the chromaffin tissue, an increase in the number of epinephrine cells and a decrease in the number of norepinephrine cells were observed, decreasing the numeric norepinephrine/epinephrine (NE/E) cell ratio, from 1.4/1 of control specimens to 0.5/1 24 h after NPY administration. Moreover, norepinephrine plasma level were elevated from 922 ± 4.30 pg/ml in carrier injected specimens to 3075 ± 11.30 pg/ml 24 h after NPY administration; epinephrine plasma level increased from 502 ± 2.40 pg/ml in carrier injected specimens to 2759 ± 8.70 pg/ml 24 h after the experimental treatment. Consistent with these findings, morphological observations showed many chromaffin cells weakly stained and with a reduced content of secretory granules. These results suggest that, in P. sicula, NPY may play a role in the modulation of the pituitary–adrenal axis activity. Previous studies localized NPY in the epinephrine cells of P. sicula adrenal gland; taken together, these results suggest that this peptide might participate in the regulation of adrenal gland activity, enhancing corticosteroid and catecholamine secretion in a paracrine/autocrine manner. The mechanism of action of NPY is discussed.