Factors influencing insulin yield and secretion from the ovine pancreas

The ovine pancreas was studied to determine the yield of insulin, the effect of dietary treatments on insulin yield and factors which influence the secretion of insulin from the gland. Thus, pancreas glands were collected from lines of lambs from local freezing works, the insulin extracted and assayed. Results showed that the yields of insulin from New Zealand pancreatic glands were considerably higher (295 I.U. 100 g pancreatic tissue⁻¹) than first reported for glands exported and extracted for insulin in the U.S.A. (100 - 120 I.U. 100 g pancreatic tissue⁻¹). The procedure used to collect the pancreas glands and the age of the animal are probably responsible for the increased yields of insulin. In New Zealand, lucerne or white clover and ryegrass, the forages normally grazed by lambs, had little effect on pancreatic and plasma insulin levels. The pancreatic insulin levels could, however, be significantly increased (up to 520 I.U. 100 g⁻¹) by the lambs either grazing rape or being fed a concentrate diet based on maize. A close association was also found between pancreatic and plasma insulin levels in the lambs fed maize diets. Feeding only milk to lambs also increased the levels of plasma insulin and presumably the pancreatic insulin levels. It was clearly demonstrated that whenever exogenous glucose was available in the small intestine either by feeding maize, infusing glucose directly into the duodenum or by feeding milk, blood glucose levels were increased and associated with this, plasma insulin levels also increased. The high correlation between blood glucose and plasma insulin levels, in milk fed lambs, suggests that the absorption of dietary carbohydrate in these pre-ruminant animals controls the levels of plasma insulin. This relationship probably accounts for the high correlation between the intake of dietary lactose and the turnover of plasma glucose in milk fed lambs. In the grass fed lambs, however, there was little association between the intake of digestible organic matter and the turnover of plasma glucose. Similarly, in these animals, there was a poor correlation between the levels of plasma insulin and the intake of digestible organic matter. Furthermore, gut hormones were not apparently released from the duodeneum by the presence of exogenous glucose in the ruminant animal. It was concluded that in ruminants no single factor influences insulin secretion, however, as the animal obtains a greater proportion of its glucose from the diet, the regulation of insulin secretion moves towards that observed in the monogastric