EFFECTS OF DIFFERENTLY COMPOSED FEEDS AND PHYSICAL STRESS ON PLASMA GASTRIN-CONCENTRATION IN HORSES

Plasma gastrin concentrations were determined in 6 Standardbreds (4 ge ldings and 2 mares) after 3 different meals consisting of unlimited am ounts of hay (8-9 kg per horse), a restricted amount of hay (0.6 kg/10 0 kg bodyweight) and grain (0.2 kg/100 kg body-weight) in combination or of grain alone (0.2 kg/100 kg body-weight). In another series of ex periments the possible role of gastrin as a stress hormone was investi gated. Plasma gastrin and cortisol concentrations were determined duri ng fasting and compared with concentrations during hay feeding. In add ition, gastrin and cortisol concentrations were determined before, dur ing and after 2 kinds of physical exercise on a treadmill. Meal stimul ation significantly increased the plasma gastrin concentration, irresp ective of the meal composition. An immediate and large increase in pla sma gastrin concentration was found when voluminous meals were given, whereas a small meal evoked a later onset of gastrin release, suggesti ng that gastric distention plays an important role in inducing gastrin release during a meal. Meals consisting of grain seem to evoke a slow er onset and then a more prolonged gastrin response than a hay meal, p ossibly due to different emptying rates of the stomach. Nervous excita tion may play a minor role in the activation of gastrin release in hor ses. No experimental support was obtained for the idea that gastrin ac ts as a stress hormone in the horse.