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A B ST R A CT Cyclic AMP and cyclic GMP were measured in rat adrenal glands after either hypophysectomy alone or after hypophysectomy and treatment with ACTH. Adrenal cyclic GMP levels rise in acutely hypophysectomized rats to a maximum at 1 h of ap- about 1 pmol per mg tissue for 7 days, adrenal cyclic GMP showed a biphasic rhythm in long-term hypophysectomized animals. After an initial peak at 1 h after hypophysectomy, adrenal cyclic GMP declined to baseline at 4-12 h but thereafter progressively rose with time, eventually reaching levels over 1 pmol per mg tissue. Fluorescent immunocytochemical staining of rat adrenal zona fasciculata showed cyclic AMP largely confined to cytoplasmic elements with little fluorescence contained in nuclei. In contrast, cyclic GMP was found discretely positioned in nuclei with prominent fluorescence in nucleoli in addition to cytoplasmic localization.It is concluded that in hypophysectomized rats ACTH, either directly or in conjunction with alteration of adrenal cyclic AMP, appears to be one factor which regulates adrenal cyclic GMP. The direction of cyclic GMP change and the different subcellular localization of the nucleotides suggest divergent roles for cyclic AMP and cyclic GMP in adrenocortical function. Furthermore, our observations suggest a role for adrenal cyclic GMP in nuclear directed events.

Cyclic GMP and cyclic AMP have been localized in rat liver, small intestine, and testis by a fluorescent immunocytochemical procedure. In liver, cyclic AMP is distributed along sinusoids predominantly, and increased fluorescence is seen in sinusoidal areas after glucagon administration. Cyclic GMP is located in nuclear elements and on the plasma membranes of hepatocytes. In jejunum, cyclic AMP is found predominantly at the basal and lateral sides of brush border cells and in the lamina propria, while cyclic GMP is located to the brush border membrane, smooth muscle, and nuclear elements. In testis, cyclic AMP is found in cytoplasm of cells at the perimeter of the seminiferrous tubules and in interstitial cells, while cyclic GMP is visualized on the plasma membrane of the cells lining the tubules. Cyclic GMP is also seen on chromosomes of premeiotic spermatocytes and in sperm. These data provide histological evidence implicating diverse roles for the nucleotides in these tissues. The nuclear localization of cyclic GMP in all of these tissues suggests a role for the nucleotide in nucleus-directed events.Accumulating evidence suggests that cyclic GMP is involved in a number of cellular events ranging from the action of acetylcholine at muscarinic receptors (1-3) to growth regulation in lymphocytes (4) and fibroblasts (5). In these studies increased tissue concentrations of cyclic GMP have been demonstrated after hormonal stimulation. Despite this evidence, the role of cyclic GMP in cell function has been difficult to determine, partly because exogenously administered cyclic GMP in most tissues acts as a weaker cyclic AMP (6).To gain insight into the relative roles of cyclic AMP and cyclic GMP in cell function, we have recently applied the technique of cyclic nucleotide immunocytochemistry to studies in canine thyroid tissue, and contrasted the localization of cyclic GMP with that of cyclic AMP. We utilized canine thyroid tissue for these studies because thyrotrophin stimulating hormone increases cyclic AMP, without affecting cyclic GMP levels, and cholinergic compounds increase cyclic GMP while cyclic AMP is unchanged. We found cyclic GMP to be located in the area of the follicular plasma membrane bordering the colloid, and showed an increase in cytoplasmic fluorescence after acetylcholine treatment. In contrast, cyclic AMP was found throughout the cytoplasm of the follicular cells, and increased cytoplasmic fluorescence was seen after administration of thyrotrophin stimulating hormone. The distinct differences in localization of cyclic AMP and cyclic GMP suggested that the specific roles and the intracellular localization of these two nucleotides may be related (7).We have continued to apply this immunocytochemical procedure for the localization of cyclic AMP and cyclic GMP in a variety of rat tissues. In general, the two nucleotides have distinctly different staining patterns in individual cells. Cyclic AMP is found mostly in cytoplasm and sometimes on plasma membranes, but cyclic GMP is usually distinctl...

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