Luteinizing hormone-releasing hormone and function of the magnocellular vasopressinergic system

Mechanisms by which luteinizing hormone-releasing hormone (LHRH) affects vasopressin secretion were investigated using the isolated rat hypothalamo-neurohypophysial explants. LHRH in a concentration of 4 x 10(-7) M inhibited both the basal and K+-stimulated vasopressin release from explants isolated from euhydrated rats. When, however, the tissue was obtained from animals previously salt-loaded, the inhibitory effect of LHRH was completely abolished, thus implying a decrease in the sensitivity to LHRH. LHRH did not affect vasopressin secretion under conditions of generalized blockade of synaptic inputs by 15 mM MgSO4, suggesting the indirect action of this neurohormone on the hypothalamic magnocellular system. It is concluded that LHRH may play the role of a neuromodulator of vasopressinergic neurones in the rat.