Lipopolysaccharide (LPS) is a component of the wall of gram-negative bacteria which induces an inflammatory response. During inflammation the adrenal axis is activated, and in most cases this increase is accompanied by the inhibition of the somatotropic axis. However, the mechanism by which inflammation inhibits the growth hormone and insulin-like growth factor-I (GH-IGF-I) axis is not well known. The aim of this study was to analyse the effect of low LPS doses on pituitary GH secretion and serum IGF-I levels.

Rats received two LPS injections (at 17.30 and at 08.30 h the following day) of different dosages (0, 5, 10, 50 or 100 µg kg^-1, I.P.). Four hours after the last injection rats were humanely killed. Serum GH and IGF-I concentrations were analysed by RIA and pituitary mRNA levels of GH were analysed by Northern Blot. Comparison of means was performed with Duncan’s multiple range test.

LPS administration decreased serum IGF-I levels in a dose-dependent way (P < 0.01). In contrast, serum GH concentrations increased after 5 and 10 µg kg^-1 of LPS administration (P < 0.05 and P < 0.01 respectively). In addition, pituitary GH mRNA was increased with the LPS dosages of 10 and 50 µg kg^-1 (P < 0.05). In order to elucidate if the increase in GH secretion is secondary to the IGF-I decrease or a specific LPS-effect, a second experiment was performed. Primary pituitary cell cultures (200 000 cells well^-1) were incubated with LPS (0, 0.1, 10, 100, 1000 ng well^-1) for 4 h. GH release to the culture medium was analysed by RIA. The in vitro studies showed that LPS induced an increase of GH release after the addition of 0.1 and 10 ng well^-1 of LPS in the culture media (P < 0.05). The data indicate that LPS in low doses directly stimulates pituitary GH release, whereas it decreases circulating IGF-I by a GH-independent mechanism.

This work has been supported by FIS grant 00/0949.