Lactate activates the somatotropic axis in rats.

Under physical activity a wide variety of cellular metabolic products and hormones are altered in the blood stream, including lactate, a metabolite of pyruvate reduction, and growth hormone (GH). Although a positive correlation between lactate and GH seems to exist during exercise, the role of lactate as a mediator of GH production has never been investigated. Thus, the aim of this study was to investigate whether lactate could activate the somatotropic axis and stimulate GH synthesis/release, contributing to the enhanced somatotropic activity described in exercise conditions. Male adult Wistar rats were acutely treated with sodium lactate [15 or 150μmols, i.p.] at the beginning of the active period (Zeitgeber time 13-14), and euthanized by decapitation 30, 60 and 120min after the injections. Serum GH concentration were determined using ELISA and Gh and Igf-1 mRNA expressions were quantified by qPCR. Serum GH concentration and Gh mRNA expression were increased 30min after lactate injections for both treatments. However, [15μmols] of lactate injection kept GH serum concentration chronically high throughout the experimental period. Igf-1 mRNA expression was increased only 60min after challenge with [15μmols] of lactate, time point which corresponded to 30min after the serum GH peak. The present results led us to conclude that lactate mediates activation of the somatotropic axis, therefore emphasizing its possible role on GH synthesis/release, and further indicating that it could play a part on the increased GH secretion observed in exercise conditions.