GLUCOSE-TOLERANCE AND PROPIONATE LOADING TESTS IN THE ASSESSMENT OF ENDOCRINE PANCREATIC FUNCTION IN HEALTHY AND KETOTIC COWS

An attempt to assess the secretory capacity of endocrine pancreas beta -cells was made in healthy and ketotic cows by determination of glucos e and insulin concentrations in the peripheral circulation during gluc ose tolerance and propionate loading tests. Each test was carried out in the second week of lactation with twenty cows, of which ten were he althy and ten were exhibiting the first clinical signs of ketosis. In both tests mean initial blood glucose concentrations were higher in th e healthy group of cows than in the ketotic group, while basal serum i nsulin concentrations did not show statistically significant differenc es between the respective groups. Following intravenous loading with g lucose the increment and rate of disappearance of glucose from the per ipheral circulation was similar in the healthy and ketotic cows indica ting similar degrees of glucose tolerance. However, the insulin respon se, while following the same dynamics, was significantly smaller in th e group of ketotic cows as demonstrated by markedly lower serum insuli n concentrations at 30 minutes (P <0.01) and 60 minutes (P <0.05) afte r glucose injection. Namely, assuming that liver insulin uptake was no t higher in the ketotic group, it may be concluded that the glucose to lerance test can be used to detect reduced pancreatic secretory capaci ty in cows in the earliest phase of lactation. After intravenous loadi ng with sodium propionate there was a similar difference in serum insu lin response between the control and ketotic groups of cows. Namely, t he insulin increment 8 minutes after injection, taken to reflect the i mmediate pancreatic response, was statistically significant only in th e group of healthy cows. Thereafter, insulin concentrations returned t o the initial values to be followed by a second later increase which r eflected the increase in glycemia. Since the glycemic response to intr avenous propionate is a measure of liver gluconeogenic capacity the la te differences in insulin concentration between the healthy and ketoti c cows reflect the differences in glucose concentration and are theref ore primarily the result of differences in liver function, although a contribution of differences in glucagon secretion (pancreatic alpha-ce ll function) cannot be excluded. Thus, the propionate loading test may provide information about both pancreatic beta-cell secretory capacit y as well as liver function in cows.