Summary
Although the presence of ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors
has been demonstrated in the anterior pituitary, recent reports on the direct effect
of glutamate on prolactin (PRL) secretion by anterior pituitary cells have presented
contradictory results. Hence, the aim of this study was to determine the effect of
ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptor agonists on prolactin
(PRL) release. In addition, since D-Aspartate (D-Asp) is found in the pituitary and
is involved in neuroendocrine regulation, we also studied the direct action of D-Asp
on PRL secretion. Finally, since the posterior pituitary participates in the regulation
of PRL secretion, we examined the influence of the posterior pituitary on the effects
of NMDA and D-Asp on PRL release. - Glutamate (1000 μM) increased PRL secretion from
cultured anterior pituitary cells. Both NMDA (100 μM) and kainate (100 μM) increased
PRL secretion and these effects were blocked by a specific NMDA receptor antagonist.
AMPA did not modify PRL release in these cultures. The group I and II mGluR agonist,
trans-ACPD (1000 μM), and a specific group II mGluR agonist, L-CCG-I (100-1000 μM),
inhibited whereas specific group I and III mGluR agonists, 3-HPG and L-AP4 respectively,
had no effect on PRL release. Finally, D-Asp (100-1000 μM) stimulated PRL secretion
and this effect was reduced by a NMDA receptor antagonist. When anterior pituitary
cells were cultured in the presence of posterior pituitary cells, NMDA did not modify
PRL or GABA release, while D-Asp increased PRL secretion and decreased GABA release
in these cocultures. - In conclusion, our results show that L-glutamate has a differential
direct effect on PRL release: it exerts a stimulatory action via iGluRs and an inhibitory
effect via mGluRs. D-Asp could directly stimulate PRL release through NMDA receptors.
D-Asp may also stimulate PRL release by decreasing GABA release from the posterior
pituitary.
Key words:
Pituitary - Glutamate - Ionotropic receptors - Metabotropic receptors - D-aspartate
- Prolactin
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Mercedes Lasaga
Centro de Investigaciones en Reproducción
Facultad de Medicina
Piso 10
Buenos Aires (1121)
Argentina
Phone: +54-11-5950-9612
Fax: +54-11-4807-4052
Email: mlasaga@fmed.uba.ar
