Positive role of non-N-methyl-D-aspartate receptors in the control of growth hormone secretion in male rats.

The role of kainic acid (KA) (an agonist of non-NMDA receptors) in the control of GH secretion and the modulation of KA action by gonadal secretion were analysed in male rats. In the first experiment 4, 8, 12, 16, 20 and 30-day old males were sacrificed 15 min after injecting with vehicle or KA (2.5 mg/kg BW). In the second experiment, the effects of KA, 6,7-dinitroquinoxaline-2,3-dione (DNQX) and MK-801 were analysed in monolayer cultures of dispersed adenohypophyseal cells. In the third experiment, adult males were sham-operated or orchiectomized and decapitated seven days later, 15 min after injecting with vehicle or KA (2.5 or 15 mg/kg BW). In the fourth experiment, males neonatally injected with estradiol benzoate or vehicle were sacrificed on days 45, 60 or 90, 15 min after administration of vehicle or KA (2.5 or 15 mg/kg BW). We found that: (i) KA is a powerful secretagogue for GH in neonatal and postpubertal males but its releasing effectiveness decreases in adulthood; (ii) GH secretion by cultured pituitary cells remains unaffected in the presence of KA (1,10 or 100 mumol/l); (iii) the KA-stimulated GH secretion is increased after orchiectomy and abolished in males neonatally estrogenized. These results indicate that in male rats activation of non-NMDA receptors, probably those located in hypothalamus, increases GH secretion. The releasing properties of KA increases in orchiectomized males and completely disappears in males neonatally estrogenized.