GHRH and Morphine Modulate Growth Hormone Secretagogue Action in Rat Brain

Growth hormone secretagogues (GHSs) are compounds that stimulate the release of growth hormone (GH), often by acting on the ghrelin receptor. The arcuate nucleus in the hypothalamus is a critical brain region involved in regulating GH secretion and energy balance. While GHSs are known to activate this region, the interplay between GHSs and other key neuroendocrine regulators, such as growth hormone-releasing hormone (GHRH), and neuromodulators like morphine, remains complex. This study aimed to elucidate how GHRH and morphine influence GHS-induced neuronal activation within the arcuate nucleus.

Administration of GHS alone significantly increased c-Fos expression in the arcuate nucleus by 150% compared to saline controls (p<0.001), indicating robust neuronal activation. Co-administration of GHRH with GHS markedly attenuated this activation, reducing the GHS-induced c-Fos increase to only 50% above baseline, representing a 66% reduction in GHS-mediated activation (p<0.001 vs. GHS alone). Similarly, morphine co-treatment significantly blunted the GHS effect, decreasing c-Fos expression by 45% compared to GHS alone (p<0.01). Neither GHRH nor morphine alone significantly altered basal c-Fos levels. The most significant finding was that both GHRH and morphine potently and independently suppressed the neuronal activation induced by GHS in the arcuate nucleus, suggesting a complex modulatory network.