PLASMA-CONCENTRATIONS OF PROLACTIN, GLUCOSE, INSULIN, UREA NITROGEN, AND TOTAL AMINO-ACIDS IN STALLIONS AFTER INGESTION OF FEED OR GASTRIC ADMINISTRATION OF FEED COMPONENTS

Concentrations of prolactin, glucose, insulin, urea N, and total amino acids in plasma of stallions after ingestion of pelleted feed were co mpared to those after direct gastric administration of water, NaCl, eg g albumin, or corn starch (Exp. 1) or water, egg albumin, hydrolyzed c asein (Amicase(R)), or a mixture of indispensable amino acids (Exp. 2) . Stallions were fed once daily (75% pellet and 25% hay) at 1500 for 3 0 d. On d 22, 24, 26, 28, and 30, blood samples were collected every 3 0 min from 1 h before through 4 h after treatment, which occurred at 1 100. In Exp. 1, there was a positive secretory response for prolactin (P = .013) only after the meal. Positive glucose and insulin responses were observed after the meal(P < .055) and after gastric administrati on of corn starch (P < .001). Total amino acids increased(P = .008) on ly after the meal. In Exp. 2, a positive prolactin response (P < .001) occurred after the meal and a negative response (P = .023) after admi nistration of water; administration of Amicase increased(P = .061) pro lactin concentrations after a 2.5-h delay. Positive responses were obs erved for glucose, insulin, and total amino acids after the meal ( P < .001) and after administration of Amicase or the amino acid mixture ( P < .026). Positive urea N responses were observed after administratio n of Amicase and the amino acid mixture (P < .001). We conclude that n o single nutrient type (water, salt, amino acid mixture, protein, or c arbohydrate), administered directly into the stomach, increased prolac tin concentrations in a manner identical to that observed after the in gestion of a meal, even when the responses of other hormones and metab olites indicated that normal digestion and absorption occurred.