Anterior Pituitary and Morphology of the Pancreatic Islets in the Rat

Abstract

In the pancreas of adult normal rats the ratio of the surface areas of islets to acinar tissue is below 1/100. The alpha/beta cell ratio is about 25/75. With colchicine treatment very few mitoses are demonstrable in the islets and these are proportionally distributed in the alpha and beta cells. GH (growth hormone) seems to increase the number of mitoses in beta cells. ACTH on the other hand diminishes the number of mitoses in both alpha and beta cells. Combined treatment with GH and ACTH, however, increases the number of mitoses in both types of cells. After hypophysectomy the body weight falls, as also the acinar tissue, while the islets cease to increase with age. However, there are no changes in the ratio of islet to body weight nor in the ratio of alpha to beta cells. Treatment with GH, after hypophysectomy, results in a rise of body weight and a partial recovery of the acinar tissue, even when the amount of food supplied is the same. The islets and the alpha/beta ratio are unaffected.In young normal rats the ratio of islets to acinar tissue is about the same as in adult animals. The islet/body weight ratio is also equal in the young and adult. The alpha/beta cell ratio, however, is about 35/65 for the first 60--70 days of life and then decreases. Injection of colchicine reveals increased mitoses in beta cells during the decrease of the ratio. GH is without effect on the normal decline in the alpha/beta ratio and does not alter the number of mitoses as revealed by colchicine. ACTH, however, diminishes the number of colchicine mitoses. Hypophysectomy diminishes the rate of body growth and causes atrophy of the acini. The islets, however, in spite of constancy of food intake, continue to increase after hypophysectomy so that the ratio of islets to body weight becomes much higher than normal. Moreover, the alpha/beta cell ratio remains at the high juvenile level with advancing age. Treatment with GH, given some weeks after hypophysectomy, also causes in young rats an increase in body weight and a partial recovery of the acini. As with adult rats neither the surface area of islet tissue nor the alpha/beta ratio is affected by this treatment. Combined injections of GH and ACTH cause a gain in body weight and a recovery of the size of the adrenals, then a large number of mitoses in beta cells of the islets is detectable, and finally the typical fall of alpha to beta cell ratio from the high juvenile to the lower adult level takes place.

Some Effects of Tolbutamide on the Pancreatic Islets of Growing Rats

“…At the end of the experiment, 9 hr. before their sacrifice, the animals received a subcutaneous injection of colchicine in a dose of 0-15 mg./100 g. body weight [Mosca, 1957]. This mitoses-enhancing drug facilitated the detection of which cells are fit for multiplication [Dustin, 1939;Cavallero, 1947;Cavallero and Mosca, 1953].…”