Effect of estrogens on blood sugar, serum insulin and serum free fatty acids, and pancreas cytology in female dogs.

We analyzed the changes in blood sugar (BS), serum immunoreactive insulin (IRI), circulating free fatty acids (FFA) and pancreatic cytology caused by estrogenization at low pharmacological dosage in female dogs. Vehicle-injected and untreated controls (anestrus) were studied as well. Neither mean basal BS nor basal serum IRI was modified by the treatments, while the mean basal serum FFA value was raised. Glucose tolerance was not modified by the estrogens while glucose y-mean was significantly raised. Hyperglycemia was higher for a longer time in estrogenized animals compared to both controls, while the profiles of hyperinsulinemia coincided. In the estrogen-treated bitches, the pancreatic B-cells contained scarse brown-stained granules near their vascular pole, as shown by an immunochemical method. In the peripheral part of the pancreas, near the acini, some solitary, poorly beta-granulated B-cells were present. During the IVGTT, serum FFA reached lower values for a longer time in the estrogenized bitches as compared to those found in both control groups. Insulin-induced hypoglycemia in the estrogenized animals coincided with the one evoked in the vehicle controls; in the semilog relationship of serum IRI and time, y-mean was lower than that observed in oil-injected controls, and insulin space was larger. The serum FFA levels of these estrogenized bitches, very high in the basal conditions, did not respond to insulin administration, and were above those found in untreated controls and also in vehicle-injected controls just at the beginning of the test. These results are discussed. We came to the conclusion that estrogenization causes some glucose intolerance in bitches while insulin sensitivity remains normal in the IVITT as studied measuring BS. The glucose intolerance is thought to be related to a reduction in glucose space and occurs despite the normality of the serum IRI response. The pancreas must have an intense secretory response in vivo as as to maintain normal IRI activity despite degranulation of the islets of Langerhans and poor islet hypertrophy and neoformation. The serum FFA changes are thought to contribute towards the tendency to adiposity in these animals.