Galanin modulates pituitary hormones release

Galanin and its receptors are widely distributed within the central and peripheral nervous system, especially in hypothalamus including preoptic area, paraventricular nucleus (PVN), supraoptic nucleus (SON) and median eminence. Galanin plays an important role in the control of food intake, energy expenditure, reproduction, water balance and various neuroendocrine functions. Galanin may affect hormones release, but the exact mechanism of the peptide action remains unclear and possible direct effects of galanin on the pituitary are controversial. The aim of this study was to examine the effects of galanin on pituitary hormones release after the central and peripheral administration of the peptide.

(i) Experiment I - Intracerebroventricular (icv) administration of galanin: Galanin at a concentration of 0.5 microg in 5microl vehicle (artificial cerebrospinal fluid) or equal volume of the vehicle was slowly (1microl/min) infused into the third ventricle with an automatic pump (CMA/100; Sweden) through an inner cannula inserted into the guide cannula. After the end of the infusion the rats were transferred to their home cages with free access to food and water. At 60 min after the infusion of galanin or vehicle, animals were decapitated and trunk blood was collected in plastic tubes containing 1000 IU aprotinin (inhibitor of protease) per each ml of blood. (ii) Experiment II - Intravenous (iv) injection of galanin: Galanin in a dose of 10 microg in 300 microl of saline or 300 microl of saline alone was injected into the tail vein. After the injection the animals were transferred to individual cages with free access to food and water. At 60 min after the injection of galanin or saline, animals were decapitated, and trunk blood was collected in plastic tubes containing 1000 IU of aprotinin (Trascolan). The blood samples were centrifuged (3000 rpm for 20 min at 4 degrees C). Serum samples were frozen until hormonal analyses were performed. Serum rLH, rFSH, rPRL, rGH, rTSH concentrations were measured with RIA methods.

Galanin administered icv increased significantly rPRL and rTSH levels (p<0.01, p<0.05, respectively). Plasma rPRL and rTSH concentrations were not changed after iv injection of galanin. Galanin injected centrally inhibited significantly rGH release (p<0.01), however, galanin given iv stimulated rGH (p<0.01). Serum rLH and rFSH concentrations were not changed after icv and iv injections of galanin.

Galanin may be involved in the modulating mechanism of pituitary hormones release.