Electrical stimulation of the preoptic area resulted in a significant increase in the secretion rate of immunoreactive somatostatin (IRS) and its concentration in the hypophysial portal blood of urethane-anesthetized rats. In contrast, stimulation of the ventromedial nucleus did not cause any changes in portal immunoreactive somatostatin. The flow rate of portal blood also increased significantly by electrical stimuli to the preoptic area but not to the ventromedial hypothalamus. These findings support the view that the preoptic area plays an inhibitory role in the regulation of GH secretion by increasing the release of somatostatin into hypophysial portal vessels in the rat.
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