NEUROKININ-A AFFECTS THE TUBERO-HYPOPHYSEAL GABAERGIC SYSTEM

WE have studied the in vitro effects of neurokinin A (NKA) on anterior pituitary GABA concentration and GABA release from the mediobasal hyp othalamus and the neurointermediate lobe of male and ovariectomized fe male (OVX) rats, NKA significantly decreased the anterior pituitary GA BA concentration, while the presence of a specific anti-NKA serum in t he incubation medium increased the GABA concentration in this gland. B y contrast, NKA did not modify basal or K+-evoked GABA release from th e mediobasal hypothalamus of male or OVX rats. However, NKA decreased basal and K+-evoked GABA release from the neurointermediate lobe, Sinc e GABA inhibits both prolactin (PRL) secretion from the anterior pitui tary and the release of several putative PRL-releasing factors from th e neurointermediate lobe, the decrease in anterior pituitary GABA conc entration and the reduction in tubero-hypophyseal GABAergic activity i nduced by NKA may contribute to the stimulatory effect of this peptide on PRL secretion.