THE EFFECTS OF SOMATOSTATIN INFUSION ON THE PLASMA PROFILE OF GROWTH HORMONE, INSULIN AND CORTISOL IN SHEEP

Four castrated Corriedale sheep were used in an experiment to observe the changes in insulin, growth hormone and cortisol in blood plasma following a prolonged infusion of a high rate of somatostatin (SRIF). The animals wee infused with either saline, 25 or $50{\mu}g/kg/h$ of SRIF for 3 hours. Blood samples wee taken every 20 minutes until 1 hour following the end of the SRIF infusion. Both SRIF infusion levels suppressed the release of insulin into plasma to approximately 3.5 mU/l. The SRIF infusions reduced the concentration of growth hormone to barely detectable levels. Following the withdrawal of SRIF there was a massive release of growth hormone. The plasma concentration of growth hormone reached 60 ng/ml within 20 minutes, the length of the growth hormone discharge was in excess of 1 hour. The extent of the discharge of growth hormone following the SRIF infusions was greater than that suppressed by the infusion. The SRIF apparently caused an increase in the plasma concentration of cortisol at the end of the infusion and following is withdrawal. This is possibly associated with some change in the metabolic rate associated with the suppression of insulin or glucagons release. The present experiment demonstrates that a high rate of SRIF infusion can not completely inhibit the release of insulin into the plasma.