Leukocytes synthesize angiotensinogen

To determine whether leukocytes express the angiotensinogen gene, we subjected circulating rat leukocytes and murine bone marrow cells to Northern blot analysis and hybridization with homologous angiotensinogen complementary DNA. Angiotensinogen messenger RNA sequences were detected in circulating adult rat leukocytes, in murine-irradiated and nonirradiated bone marrow stromal cells, and in an adherent stromal cell line (preadipocyte). Western blot analysis of rat leukocyte homogenate showed that rat leukocytes contain two main angiotensinogen isoforms with approximate molecular weights of 46.5 and 53.9 kd. Synthesis and release of angiotensinogen protein by rat leukocytes was confirmed by immunoprecipitation of radiolabeled angiotensinogen from cell lysate and media of rat leukocytes that were metabolically labeled with 35S-L-methionine. In addition, the angiotensinogen protein present in media of rat leukocytes was enzymatically cleaved by hog renin, resulting in generation of angiotensin I (305 +/- 47 pg angiotensin I per milliliter of media per hour). We conclude that circulating rat leukocytes express the angiotensinogen gene and synthesize and release angiotensinogen with the capability to generate angiotensin. Expression of angiotensinogen by leukocytes may provide a mobile angiotensin-generating system of potential importance in the regulation of local inflammatory responses, tissue injury (i.e., myocardial infarction), and arterial hypertension.

Renin and angiotensinogen expression during the evolution of diabetes

The expression of renin and angiotensinogen genes and their proteins were studied during the progression of diabetes using adult BioBreeding spontaneously diabetic rats at 1 day and 2-12 months of diabetes. The number of renin-stained cells per juxtaglomerular apparatus was determined by immunocytochemistry. Initially, at 2 months of diabetes the number of renin-stained cells per juxtaglomerular apparatus increased significantly (p less than 0.0001, 2 months versus resistant groups) and was followed by a decrease in the number and intensity of renin-stained cells after 12 months of diabetes (p = 0.007, 2 months versus 12 months). A significant negative correlation was observed between the number of renin-containing cells and the duration of diabetes (r = 0.99, p = 0.014). Immunoreactive angiotensinogen was restricted to the proximal tubule and appeared increased after 4 and 8 months of diabetes as compared with the 2- and 12-month diabetic groups. Renin messenger RNA (mRNA) levels increased with the onset of diabetes and decreased markedly during chronic diabetes. At 1 day of diabetes, renin mRNA levels were 700% higher than at 12 months of diabetes. Angiotensinogen mRNA levels were unchanged. We conclude that diabetes results in an initial increase in renin gene expression, and as the duration of diabetes lengthens, there is a progressive decrease in renin gene expression and in the number of cells containing renin. These findings suggest that as the duration of diabetes and the age of the animal lengthens, there is a decrease in the number of cells expressing the renin gene.

Fetal expression of the angiotensinogen gene

To determine whether the angiotensinogen (Ao) gene is expressed in multiple organs of the fetal rat and the changes associated with maturation, fetal (15-20 days of gestation), newborn (1-10 days old), and adult (90 days old) rat tissues were subjected to Northern analysis and hybridization with a full length Ao complementary DNA (cDNA). Whereas Ao messenger RNA (mRNA) was undetectable in fetal livers, Ao sequences were readily detectable 1 h after birth and reached a peak at 24 h of birth. Levels remained elevated at 5 and 10 days after birth to decrease slightly at 90 days of postnatal life. Poly A+ enriched liver RNA was subjected to a similar analysis demonstrating that fetal liver Ao mRNA levels were 50-fold less than the corresponding adult levels. In contrast to the finding in the fetal liver, Ao mRNA was found in fetal brown fat, brains, and kidneys. We conclude that 1) Expression of the Ao gene is developmentally regulated in a tissue-specific manner; 2) Unlike the adult animal, the liver may not be the primary source of Ao in the fetus; 3) Alternate sources of Ao synthesis include fetal brown fat, brain, and kidneys.

Renin and angiotensinogen gene expression and intrarenal renin distribution during ACE inhibition

To define whether intrarenal renin and angiotensinogen synthesis and distribution are affected by angiotensin-converting enzyme (ACE) inhibition, a control group of adult, male Wistar-Kyoto rats (n = 7) was compared with a group of rats treated with enalapril (n = 8) for 5 days. Kidney renin and angiotensinogen mRNA levels were detected by Northern and dot blot analysis, using full-length rat renin and angiotensinogen cDNAs. Renin mRNA levels in the enalapril-treated group were 4.6-fold higher than in the control group (P less than 0.05). Angiotensinogen mRNA levels were not significantly different. The intrarenal distribution of renin assessed by immunocytochemistry was markedly different between the two groups of rats. Whereas in the control kidney renin was localized in a juxtaglomerular position, in the kidneys from enalapril-treated rats, renin immunoreactivity of the afferent arteriole extended well beyond the juxtaglomerular loci in the direction of the interlobular artery. The percent of afferent arteriolar length immunostained for renin was higher in the enalapril-treated (53 +/- 17%) than in the control (33 +/- 15) group. Similarly, the ratio of immunostained juxtaglomerular apparatuses (JGA) over total number of JGA and the ratio of immunostained arteries over total number of arteries were higher in the enalapril-treated (0.84 +/- 0.017; 0.68 +/- 0.03) than in the control (0.67 +/- 0.034; 0.43 +/- 0.045) group (P less than 0.05). We conclude that chronic ACE inhibition enhances intrarenal renin synthesis and increases renin expression upstream from the glomerulus and in new sites in blood vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin and angiotensinogen gene expression in maturing rat kidney

To determine whether angiotensinogen (Ao) and renin are synthesized by the immature kidney and to assess the changes in intrarenal renin distribution that occur with maturation, the kidneys from 24 newborn and 12 adult Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were processed for renin immunocytochemistry using a highly specific anti-rat renin antibody. Kidney renin and Ao relative mRNA levels (mRNA/total RNA) were detected by Northern and dot blot techniques, using full-length rat renin and Ao cDNAs. Renal renin concentration (RRC) was measured by radioimmunoassay of angiotensin I (ANG I) and expressed as ng ANG I.h-1.mg protein-1 in the incubation media. RRC was higher in newborn than in adult SHR (979 +/- 164 vs. 206 +/- 47) and WKY (573 +/- 69 vs. 297 +/- 74) (P less than 0.05). In the newborn kidneys of both rat strains, renin was distributed throughout the entire length of the afferent arterioles and interlobular arteries, whereas in the adult kidneys renin was confined to the classical juxtaglomerular position. With maturation, there was a decrease in the proportion of immunoreactive juxtaglomerular apparatuses and arterial segments that contained renin. Kidney renin mRNA levels were 7.9-fold higher in the newborn than in the adult animal. Ao mRNA was detected in the newborn and adult kidneys of both rat strains. This study demonstrates conclusively that both renin and Ao genes are expressed in the newborn kidney, providing evidence for a local renin-angiotensin system that is subjected to developmental changes.