Effect of experimentally-induced chronic hyperprolactinemia on insulin binding and antilipolytic response in adipocytes from male rats

Male Wistar rats with chronic hyperprolactinemia induced by grafting an anterior pituitary gland under the right kidney capsule were studied as experimental model. In these animals basal plasma glucose and insulin levels were unaltered. Epididymal adipocytes from hyperprolactinemic rats showed a significant increase in insulin binding at low unlabeled insulin concentrations. This increase in insulin binding can be principally attributed to an increase in the high affinity-low capacity binding sites, as demonstrated when Scatchard analysis was interpreted in terms of two types of insulin receptors. The dissociation constants (KD1 and KD2) were not different between the groups. The apparent insulin receptor affinity was also unchanged. Moreover, a decreased sensitivity to the antilipolytic effect of insulin was also obtained in adipocytes from hyperprolactinemic rats. These findings indicate that chronic hyperprolactinemia is able to increase high affinity insulin receptors in epididymal adipocytes, but tends to diminish the antilipolytic response, suggesting a lack of coupling between insulin binding and its biological activity in male adipose tissue. Several possible mechanisms involved in the process are suggested.