Previous studies have shown that pharmacologically both peripheral and central administration of lactate inhibit food intake and lower body weight, but the physiological function of lactate in feeding and body weight regulation remains unclear. Based on the evidence that physical exercise induces reductions of food intake and body weight in male rats and intensive exercise also results in increased plasma levels of lactate.
One cohort of male Sprague Dawley rats had voluntary access to running wheels for examining the effect of physical exercise on plasma levels of lactate. In the feeding study, animals received intraperitoneal (ip) administration of 0, 0.25, 0.5 or 1.0 g/kg of lactate. Blood samples were collected via tail vein bleeding for determinations of plasma levels of lactate, glucose, insulin, and glucagon at 0.5, 1, 2, 3, and 4 hours. Food intake was examined at 0.5, 1, 2 and 22 hours following the lactate injection. Body weight was measured before and after ip lactate. At sacrifice, cerebrospinal fluid (CSF) and brains were collected for determinations of lactate levels and hypothalamic gene expression.
We found that running wheel activity resulted in reductions of food intake and body weight. Plasma levels of lactate were significantly increased in rats with long-term access to running wheels, but not in short-term exercised rats. Peripheral administration of lactate resulted in increased plasma levels of lactate, glucose and glucagon. This treatment reduced food intake and body weight at a dose-dependent manner. In addition, intraperitoneal lactate elevated thermogenic activity in the brown adipose tissue. The systemic administration of lactate elevated CSF levels of lactate and altered hypothalamic signaling.
Together, our results demonstrate that running wheel activity alters lactate levels, but whether central, peripheral or both lactate contributes to the feeding and body weight effects of physical exercise remains further evaluation.