Effects of neurokinin-A on the rat hypothalamo-pituitary-adrenal axis

The effects of neurokinin-A (NKA) on the rat hypothalamo-pituitary-adrenal (HPA) axis were studied in vivo and in vitro. A subcutaneous injection of 1 or 3 nmol/100 g NKA did not alter plasma ACTH concentration. The lower dose of NKA evoked a transient rise in plasma corticosterone (B) concentration (PBC) at 30 min, and did not change plasma aldosterone (ALDO) concentration (PAC). The higher dose of NKA increased PBC at 30 and 60 min, and PAC at 30, 60 and 120 min. NKA did not affect basal ALDO secretion of dispersed zona glomerulosa (ZG) cells, but it markedly enhanced basal B production by dispersed zona fasciculata/reticularis (ZF/R) cells (minimal and maximal effective concentrations were 10(-9) M and 10(-6) M). Video-imaging analysis showed that 10(-6) M NKA increased intracellular Ca2+ concentration in dispersed ZF/R cells, but not in ZG ones. These findings indicate that NKA exerts a stimulatory action on the rat adrenal secretory activity, which is independent of any effect on the pituitary ACTH release: the B secretagogue action seems to be due to a direct effect of NKA on ZF/R cells, while the ALDO secretagogue action is not direct. but probably mediated by factor(s) other than ACTH.