Glucose tolerance in rats with elevated circulating prolactin levels.

The consideration of prolactin as one of the anti-insulin hormones has been based on studies describing the ability of injected prolactin to raise the serum glucose. We studied the glucose tolerance of rats made hyperprolactinemic by the implantation of extra anterior pituitary glands under the kidney capsule. Surprisingly the hyperprolactinemic rats had lower serum glucose levels after a bolus injection of dextrose. Furthermore, their serum insulin levels were no higher than sham-operated control rats. AFter a fast of 18 or 24 hours, the serum glucose was lower in the hyperprolactinemic rats, and the serum insulin concentrations were similar in implanted and control rats. These data suggest that chronic hyperprolactinemia does not decrease glucose tolerance. Whether prolactin has a direct insulin-like effect or whether it may potentiate insulin's effects will require further study.