NEUROTRANSMITTER RECEPTOR AGONISTS REGULATE GROWTH-HORMONE GENE-EXPRESSION IN CULTURED OVINE PITUITARY-CELLS

The regulation of growth hormone (GH) secretion and GH mRNA content by the dopaminergic agonist, bromocriptine (BRO); the beta-adrenergic ag onist; isoproterenol (ISO); the alpha(1)-adrenergic agonist, methoxami ne (MET); the alpha(2)-adrenergic agonist, clonidine (CLON); the serot onergic agonist, quipazine (QUIP); somatostatin (SS) and GH-releasing hormone (GHRH) were studied using cultured ovine anterior pituitary ce lls. Clonidine and BRO (10(-6) M) inhibited basal and GHRH (10(-10) M) -stimulated GH release. Bromocriptine enhanced GH mRNA content and pot entiated the GHRH (10(-8) M)-stimulated content of GH mRNA, while CLON had no effect on GH mRNA. Quipazine had little effect on GH secretion and no effect on GH mRNA content. Methoxamine and ISO (10(-6) M) incr eased basal secretion of GH and both enhanced GHRH-stimulated GH secre tion. Both MET and ISO increased GH mRNA content of cultured ovine pit uitary cells. Somatostatin (10(-7) M) inhibited GHRH-stimulated GH sec retion and GH mRNA accumulation. These results support the hypothesis that neurotransmitters may regulate or interact to further modulate pi tuitary hormone release. Moreover, the data indicate that neurotransmi tters may not only regulate secretion but also regulate GH mRNA conten t and thus affect hormone synthesis.