Growth hormone increases connexin-43 expression in the cerebral cortex andhypothalamus

Several studies indicate that systemic GH influences various brain function s. Connexin-43 forms gap junctions that mediate intercellular communication and establish the astroglial syncytium. We investigated the effects of per ipheral administration of bovine GH (bGH) and recombinant human insulin-lik e growth factor I (rhIGF-I) on the expression of connexin-43 in the rat bra in. Hypophysectomized female Sprague Dawley rats were substituted with cort isol (400 mu g/kg.day) and L-T-4 (10 mu g/kg.day) and treated with either b GH (1 mg/kg .day) or rhIGF-I (0.85 mg/kg.day) for 19 days. The abundance of connexin-43 messenger RNA (mRNA) and protein in the brainstem, cerebral co rtex, hippocampus, and hypothalamus was quantified by means of ribonuclease protection assays and Western blots. Treatment with bGH increased the amou nts of connexin-43 mRNA and protein in the cerebral cortex and hypothalamus . No changes were found in the brainstem or hippocampus. Infusion of rhIGF- I did not affect connexin-43 mRNA or protein levels in any of the brain reg ions studied. These results show that administration of bGH increases the a bundance of cx43 in specific brain regions, suggesting that GH may influenc e gap junction formation and thereby intercellular communication in the bra in.