The effects of insulin upon the metabolism of glucose by single rat anterior pituitary glands in vitro have been compared with the effects of raising the concentration of glucose in the suspending medium. The pattern of stimulation with insulin differed from that induced by increasing glucose. Insulin enhanced glucose oxidation, glycogenesis and lipogenesis out of proportion to the increase in glucose uptake.
The anterior pituitary exhibited relative insensitivity to insulin in vitro compared to muscle and adipose tissue. Stimulation of glucose metabolism was detectable at 1,000 uU. insulin per milliliter medium, and maximum stimulation occurred between 0.1 and 1.0 U. per milliliter. Insulin sensitivity was not altered by fasting. The effect of insulin was attenuated upon substituting phosphate for bicarbonate as buffer in the incubation medium.
The incorporation of glycine C-14 into tissue protein was stimulated by insulin and this effect was undiminished in the absence of glucose in the medium. The incorporation of C-14-alpha-amino-isobutyric acid from the medium into the anterior pituitary was greater than that reported for rat diaphragm and was not affected by insulin.
The data indicate that insulin could potentially affect hormonogenesis in anterior pituitary through stimulation of protein synthesis. The cell types responsive to insulin and the physiologic consequences of insulin activity upon the anterior pituitary remain to be established.