EFFECTS OF NEUROKININ-A ON THE RAT HYPOTHALAMOPITUITARY-ADRENAL AXIS

The effects of neurokinin-A (NKA) on the rat hypothalamo-pituitary-adr enal (HPA) asis were studied in vivo and in vitro. A subcutaneous inje ction 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 corticostero ne (B) concentration (PBC) at 30 min, and did not change plasma aldost erone (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 b asal ALDO secretion of dispersed zona glomerulosa (ZG) cells, but it m arkedly enhanced basal B production by dispersed zona fasciculata/reti cularis (ZF/R) cells (minimal and maximal effective concentrations wer e 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 stimul atory action on the rat adrenal secretory activity, which is independe nt of any effect on the pituitary ACTH release: the B secretagogue act ion 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 fact or(s) other than ACTH.