Effects on plasma insulin of intermittent infusions of propionic acid, glucose or casein into the alimentary tract of non-lactating cows maintained on a liquid diet.

1. An experiment was conducted using three non-lactating cows completely maintained by infusions of volatile fatty acids into the rumen, and casein into the abomasum. Plasma insulin responses to propionic acid, glucose or casein were recorded. Further information was obtained using protein-free infusions. 2. When part of the propionic acid was infused into the rumen in a twice-daily 3 h dose and the remainder infused continuously with acetic and butyric acids and casein, there were large increases in the concentrations of propionic acid and insulin in the jugular blood. When glucose, corresponding in energy to that supplied by the intermittent propionic acid infusions was similarly infused, the plasma levels of glucose and insulin were increased. Glucose appeared to stimulate a greater increase in insulin than did propionic acid. Casein infused into the abomasum in intermittent doses produced a rise in plasma insulin, but smaller than that observed with propionic acid or with glucose. 3. The protein-free infusion was characterized by a lower concentration of insulin in the blood plasma, a reduction in plasma urea and free amino nitrogen and unchanged plasma glucose.

Motilin secretion and the migrating myoelectric complex in the pig.

The concentration of motilin in plasma from the abdominal aorta and the hepatic portal vein and the net portal motilin output varied with the phase of the migrating myoelectric complex (m.m.c.) in five of six pigs fasted for 17 h. Maximum concentrations and output occurred 9-12 min before phase III in the duodenum or upper jejunum. In fed pigs m.m.c.s occurred and the first phase III in the duodenum occurred within 90 min of feeding. Both portal and arterial motilin concentrations were reduced after feeding and no longer varied with the phase of the m.m.c. Altered secretion of motilin after feeding did not appear to be associated with absorption of glucose as infusion of glucose (50 g/l, 10 ml/min) into the duodenum raised arterial and portal plasma glucose concentrations to post-prandial levels yet motilin concentrations and output rates still varied with the phase of the m.m.c. Infusions of motilin (1 or 10 ng/kg X min) into the portal vein of 17 h fasted pigs did not induce an extra phase III or alter the duration of the m.m.c. Hydrochloric acid (100 mmol/l) infused into the duodenum of fasted pigs at 10-21 ml/min increased the concentration of motilin in the portal blood but was without effect at 5 ml/min. Rapid injections of 50 ml hydrochloric acid into the duodenum also increased the portal motilin concentration. Hydrochloric acid infusion or injection did not alter the interval between phase IIIs. It is concluded that motilin secretion is a consequence of the m.m.c. or shows the same periodicity as the m.m.c. but that motilin is not an important factor in the initiation and control of the m.m.c. in the pig.

Winter food restriction and summer compensation in red deer stags (Cervus elaphus).

Twelve red deer stags (Cervus elaphus) penned individually from weaning were fed on a concentrate diet. Six stags received the diet to appetite throughout the study, and the other six were restricted to 70% of the intake of the first group during winter and then fed to appetite during summer. The winter-restricted stags showed remarkable compensatory growth during summer. Compared with the unrestricted stags they showed greater food intake, greater daily live-weight gain and increased food conversion efficiency. Nonetheless, they failed to compensate fully for the previous undernutrition. The hind-foot of the restricted stags failed to grow as long as that of the unrestricted stags. Poor winter nutrition, particularly during the first year of life, and subsequent failure to compensate during the short periods of summer plenty, provides an explanation for the small mature size of wild stags in Scotland. Although the winter-restricted stags were less fat both grossly and relative to body-weight than the unrestricted stags, both groups showed the same relationship of level of fatness to empty-body-weight. In both the groups of stags, extensive fat deposition began once they had reached about half their expected mature weight, a much later stage of development and age than in sheep and cattle. The annual cycle of growth and appetite is considered to form part of a complex adaptive system to enhance survival in a harsh seasonal environment followed by a mild seasonal environment. On Scottish hills deer reach a size appropriate to their environment rather than their genetic potential size.