The antidiuretic effect of pneumadin requires a functional arginine vasopressin system

Tissue distribution of pneumadin immunoreactivity in the rat

Pneumadin (PNM) is a decapeptide, originally isolated from mammalian lungs, which exerts a potent stimulating effect on arginine-vasopressin (AVP) release, thereby evoking an antidiuretic effect. We have established a specific radioimmunoassay (RIA) method for rat PNM determination, the sensitivity of which is sufficient for measuring tissue content of the peptide. Moreover, raised antibodies have been used for the immunocytochemical detection of PNM in several rat organs. As expected, high concentrations of PNM were detected by RIA in newborn and adult rat lungs and immunocytochemistry (ICC) localized PNM immunoreactivity (IR) in the bronchial and bronchiolar epithelium. Very high concentrations of PNM were measured by RIA in the prostate, and ICC showed that PNM-IR is contained in the epithelial cells. RIA and ICC demonstrated the presence of low amounts of PNM in the thymus. The highest content of radioimmunoassayable PNM was found in the kidneys and intestinal tract, but dilution test suggested the presence of some interfering substances in these tissues. Accordingly, ICC-detectable PNM-IR was absent in the kidneys and present only in the duodenal criptae and Brunner's glands of the intestinal tract. RIA did not measure sizeable PNM concentrations in the thyroid gland, but ICC showed PNM-IR in C-cells. RIA and ICC did not detected PNM in testes, seminal vesicles, ovaries, uterus, pancreas, liver, spleen, adrenal glands, and heart. Taken together, our findings suggest that PNM, in addition to its role as hypothalamo-pituitary AVP secretagogue, may be involved in the autocrine-paracrine functional regulation of other peripheral organs, like lungs and prostate and perhaps duodenum, thymus and thyroid gland.

Chromatography of guanidino compounds

Guanidino compounds involved in the urea and guanidine cycles have been found in serum of nephritic patients, and some guanidino compounds have been suspected to be uremic toxins. The simultaneous analysis of naturally occurring metabolites is important for diagnosis of diseases. In this review, liquid chromatographic analysis of natural metabolites of guanidino compounds are described. the information about arginine as a precursor of nitric oxide are included. The reports of pharmaceutical compounds having a guanidino group, peptides containing arginine and aminoglycosides are summarized in Table 1.

Pneumadin-evoked intracellular free Ca2+ responses in rat aortic smooth muscle cells: effect of dexamethasone

The direct vascular effect of pneumadin (PN) was determined by studying the changes in intracellular free calcium ([Ca2+]i) levels in cultured rat aortic smooth muscle cells maintained between the second and fifth passages. PN evoked a rapid, concentration-dependent, biphasic increase in [Ca2+]i. The [Ca2+]i level rose from a basal value of 108 nM to a maximum increase in peak value of 170 nM. Although the level of maximal [Ca2+]i response evoked by PN was less than with other vasoactive agonists, it was more potent (EC50 0.5 nM) than even endothelin-1 (EC50 3.1 nM). At concentrations > 100 nM, [Ca2+]i elevations induced by PN above basal levels were no longer observed. Pretreatment with dexamethasone (100 nM for 24 hr) resulted in a significant increase (P < 0.01) in the peak [Ca2+]i response (310 nM) to PN. However, the biphasic pattern in the peak [Ca2+]i responses encountered with increasing concentrations of PN remained unaffected. The exaggerated [Ca2+]i response to PN was abolished by preincubation of cells with either the glucocorticoid antagonist mifepristone (RU 486) or the protein synthesis inhibitor cycloheximide. Inclusion of either an AT1 antagonist (losartan), a V1 selective vasopressin antagonist (d(Ch2)5 Tyr (Me) AVP), or an alpha-adrenoceptor antagonist (phentolamine) failed to affect the increases in [Ca2+]i induced by PN. PN-evoked increases in inositol 1,4,5-trisphosphate levels paralleled the [Ca2+]i changes. These data suggest that PN increases Ca2+ mobilization in rat aortic smooth muscle cells via activation of phospholipase C coupled receptors. This effect is up-regulated by dexamethasone.