Stimulation and inhibition of growth hormone secretion by interleukin-1 beta: the involvement of growth hormone-releasing hormone.

The effects of intracerebroventricularly (i.c.v.) injected interleukin-1 beta (IL-1 beta: 1, 2.5, 10, and 25 ng) were studied on plasma growth hormone (GH) and prolactin (PRL) concentrations in freely moving rats chronically implanted with i.c.v. cannulas and intracardial catheters. Significant changes in PRL secretion were not found. Small i.c.v. doses of IL-1 stimulated GH secretion 15 min postinjection (significant after 2.5 ng IL-1) whereas high doses of IL-1 suppressed plasma GH concentrations. The stimulation of GH secretion by 2.5 ng IL-1 was abolished when endogenous growth hormone-releasing hormone (GHRH) was immunoneutralized by pretreating the rats with GHRH antibodies. The results indicate that IL-1 elicits GH secretion by stimulating the release of hypothalamic GHRH. The inhibition of GH secretion after high doses of IL-1 is attributed to the previously reported corticotropin-releasing-hormone-releasing activity of IL-1.