EFFECT OF N-METHYL-D,L-ASPARTATE ON ISOLATED RAT SOMATOTROPHS

The effect of excitatory amino acid receptor agonists on GH secretion was tested in isolated male rat somatotrophs. N-Methyl-D,L-Aspartate (NMDA) had a dose-dependent stimulatory effect on GH secretion in perifused somatotrophs. The effect was observed already during the first minute after exposure to NMDA and was reversible after its omission. The effect of 1 muM NMDA was inhibited by the NMDA receptor antagonists 10 mum AP7 and 5 mum MK801, and by 5 mum dextromethorphan. L-Glutamate, 100 mum, and 100 Am kainic acid also stimulated GH secretion. The stimulatory effect of NMDA on GH release was paralleled by an increase in Ca-45 efflux and an increase in somatotroph intracellular calcium concentration. Efflux of 86Rb (tracer for potassium) was not affected by NMDA. It is concluded that excitatory amino acids can stimulate GH secretion in rats through a direct effect on the somatotrophs.