Short communication: change in plasma ghrelin in dairy cows following an intravenous glucose challenge.

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor and a potent orexigenic (appetite-stimulating) agent in humans and rodents, but little is known about its effect in dairy cows. Ten multiparous dairy cows 35 d in milk were subjected to an i.v. glucose challenge (300 mg of D-glucose/kg of body weight). Before infusion and at regular intervals after infusion, plasma glucose, insulin, nonesterified fatty acids (NEFA), growth hormone, epinephrine, and ghrelin concentrations were monitored. Plasma insulin rose (27.2 mU/L at 10 min) and NEFA, epinephrine, and ghrelin declined (nadir = 0.22 mmol/L, 22.2 microg/L, and 272 microg/L at 31, 13, and 22 min, respectively) after the glucose infusion. Ghrelin declined for 22 min before returning to suprabasal levels at approximately 75 min postinfusion. Sequential changes of the hormones and metabolites suggested a glucose transporter, type 2- and glucose transporter, type 4-mediated disposal of glucose, and an insulin-mediated reduction in NEFA. Ghrelin and epinephrine declined after glucose infusion and before the insulin peak, but the effect of insulin as a controlling factor in the hyperglycemic reduction in these hormones cannot be discounted. The post-nadir surge in ghrelin may be regulated by the decline in circulating concentrations of glucose and NEFA (an energy-deficit signal). The profile of change in plasma ghrelin in lactating dairy cows after a glucose challenge was similar to that in monogastric animals.