ANTIDIURETIC ACTION OF TACHYKININ NK-3 RECEPTOR IN THE RAT PARAVENTRICULAR NUCLEUS

Studies were performed on the central antidiuretic actions via the tac hykinin NK-3 receptor in the rat hypothalamic paraventricular nucleus (PVN). Microinjections of the selective tachykinin NK-3 receptor agoni st senktide (2-200 pmol) into the PVN resulted in prolonged inhibition of urine output in water-loaded rats, its effect being dose-dependent . The antidiuretic action of senktide was blocked by pretreatment with the vasopressin V2 receptor antagonist OPC-31260 (1 mg/kg, i.v.), but not by microinjection of the angiotensin II AT-1 receptor antagonist losartan (1 nmol) into the PVN. NK-3 receptor mRNA was strongly detect ed in the magnocellular part of the PVN and the supraoptic nucleus (SO N) of the hypothalamus as detected by in situ hybridization histochemi stry. Moreover, [H-3]senktide binding sites were also detected in the PVN and the SON by receptor autoradiography. These findings suggest th at NK-3 receptors in the PVN may be involved in water regulation by st imulation of vasopressin secretion from the posterior pituitary gland, and that vasopressin caused water reabsorbtion via the kidney V2 rece ptor.