Propionate is not an important regulator of plasma leptin concentration in dairy cattle

Abstract

Propionate was recently shown to increase leptin synthesis in rodents. To determine if a similar effect occurs in ruminants, propionate was administered to lactating dairy cows. In experiment 1, 31 cows were given an intrajugular Na propionate bolus (1040 μmol/kg body weight), increasing plasma propionate from 160 to 5680 μM and plasma insulin from 6.8 to 77.8 μIU/mL. Plasma leptin concentration decreased from 2.11 ng/mL before bolus to 1.99 ng/mL after dosing ( P < 0.05) with no differences in leptin concentrations at 20, 50, and 100 min post-bolus ( P > 0.10). In experiment 2, 12 cows were used in a duplicated 6 × 6 Latin square experiment to assess the dose–response effect of ruminal propionate infusion on plasma leptin concentration. Sodium propionate was infused at rates of 0, 260, 520, 780, 1040, or 1300 mmol/h, while total short-chain fatty acid infusion rate was held constant at 1300 mmol/h by addition of Na acetate to the infusate. Coccygeal blood was sampled following 18 h of infusion. Increasing the rate of propionate infusion linearly increased plasma propionate concentration from 180 to 330 μM ( P < 0.001) and plasma insulin concentration from 6.7 to 9.1 μIU/mL ( P < 0.05). There was a quadratic response in plasma leptin concentration ( P = 0.04) with a maximum at 780 mmol/h propionate, but leptin concentrations increased by no more than 8% relative to the 0 mmol/h propionate infusion. Leptin concentrations were correlated with insulin concentrations but not with propionate concentrations in plasma. Propionate is not a physiological regulator of leptin secretion in lactating dairy cows.