The interaction of insulin with its specific receptors was studied in jejunoileal epithelial cells from 14-, 20-, and 60-day-old rats. Characteristics such as potency and specificity of the insulin receptor system did not vary during development. However, insulin binding decreased with age due to a diminished concentration of insulin receptors, whereas the circulating levels of the hormone followed an inverse evolution. These results support previous suggestions on the potential role of insulin on the mechanisms of differentiation and proliferation of small intestinal mucosa.

The dual regulation of cyclic AMP accumulation was studied in rat prostatic epithelial cells incubated with somatostatin, vasoactive intestinal peptide (VIP), and the fl-adrenergic agent isoproterenol. Somatostatin noncompetitively inhibited the stimulatory effect of VIP and isoproterenol, but it did not alter basal cyclic AMP levels. In addition to the multifactorial regulation of the cyclic AMP system in rat prostatic epithelium, these results suggest that somatostatin may play a physiological role at this level.

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