Vasopressin-stimulated release of atriopeptin: endocrine antagonists in fluid homeostasis.

Administration of pharmacological doses of arginine-vasopressin, related peptides, and other pressor agents induced a profound release of atriopeptin immunoreactivity into the circulation. The stimulated release of atriopeptin apparently was related to increased arterial blood pressure. Neither the nonpressor vasopressin analog 1-deamino-D-Arg8-vasopressin nor arginine-vasopressin in the presence of a specific pressor antagonist caused atriopeptin to be released into the circulation. Urine output was correlated with the level of atriopeptin released. Physiological levels of arginine-vasopressin suppress diuresis and produced vasoconstriction. Pharmacological levels of the hormone stimulated the cardiac endocrine system to release atriopeptin, which may cause diuresis and vasodilation to physiologically antagonize the effects of vasopressin.

Bioactive cardiac substances: potent vasorelaxant activity in mammalian atria.

Mammalian atrial extracts possess natriuretic and diuretic activity. In experiments reported here it was found that atrial, but not ventricular, extract also causes relaxation of isolated vascular and nonvascular smooth muscle preparations. The smooth muscle relaxant activity of atrial extract was heat-stable and concentration-dependent and could be destroyed with protease. Rabbit aortic and chick rectum strips were used for the detection of atrial biological activity. The atrial activity was separated by column chromatography into two peaks having apparent molecular weights of 20,000 to 30,000 and less than 10,000. The atrial substance that copurified with the smooth muscle relaxant activity in both peaks caused natriuresis when injected into conscious rats. It appears that atria possess at least two peptides that elicit smooth muscle relaxation and natriuresis, suggesting an endogenous system of fluid volume regulation.

Enzyme replacement therapy for murine mucopolysaccharidosis type VII leads to improvements in behavior and auditory function.

Mucopolysaccharidosis type VII (MPS VII; Sly syndrome) is one of a group of lysosomal storage diseases that share many clinical features, including mental retardation and hearing loss. Lysosomal storage in neurons of the brain and the associated behavioral abnormalities characteristic of a murine model of MPS VII have not been shown to be corrected by either bone marrow transplantation or gene therapy. However, intravenous injections of recombinant beta-glucuronidase initiated at birth reduce the pathological evidence of disease in MPS VII mice. In this study we present evidence that enzyme replacement initiated at birth improved the behavioral performance and reduced hearing loss in MPS VII mice. Enzyme-treated MPS VII mice performed similarly to normal mice and significantly better than mock- treated MPS VII mice in every phase of the Morris Water Maze test. In addition, the auditory function of treated MPS VII mice was dramatically improved, and was indistinguishable from normal mice. These data indicate that some of the learning, memory, and hearing deficits can be prevented in MPS VII mice if enzyme replacement therapy is initiated early in life. These data also provide functional correlates to the biochemical and histopathological improvements observed after enzyme replacement therapy.

Heparin interferes with the biological effectiveness of atriopeptin.

The chromatographic mobility of atriopeptin-28 or of the prohormone is markedly altered by preincubation of the peptides with heparin before separation on reverse-phase high performance liquid chromatography. Protamine prevented the heparin effect and reestablished the original migration pattern of the atrial peptides. The addition of heparin to either rat or human plasma samples did not interfere with the atriopeptin immunoreactivity. The influence of heparin on the biological activity of the atriopeptin-28 in anesthetized rats was also investigated. Infusion of heparin (30 U/min) significantly reduced the dose-dependent fall of blood pressure produced by atriopeptin-28, but did not interfere with the hypotensive effect of nitroglycerin. Similarly, infusion of heparin in volume-expanded rats markedly decreased the diuresis produced by atriopeptin-28 without altering the urine volume excreted in response to furosemide. These data suggest that the highly charged molecule heparin can modify the physical and biological properties of atriopeptins, perhaps by binding to the numerous arginine residues (i.e., 5 arginine residues in atriopeptin-28) in the atriopeptin molecules.

Eicosanoid balance and perfusion redistribution of oleic acid-induced acute lung injury.

We have proposed that endogenous prostacyclin opposes the vasoconstriction responsible for redistribution of regional pulmonary blood flow (rPBF) away from areas of increased regional lung water concentration (rLWC) in canine oleic acid- (OA) induced acute lung injury (D. P. Schuster and J. Haller. J. Appl. Physiol. 69: 353-361, 1990). To test this hypothesis, we related regional lung tissue concentrations of 6-ketoprostaglandin (PG) F1 alpha and thromboxane (Tx) B2 in tissue samples obtained 2.5 h after administration of OA (0.08 ml/kg iv) to rPBF and rLWC measured by positron emission tomography. After OA only (n = 16), rLWC increased in dependent lung regions. Some animals responded to increased rLWC by redistribution of rPBF away from the most edematous regions (OA-R, n = 6), whereas others did not (OA-NR, n = 10). In another six animals, meclofenamate was administered after OA (OA-meclo). After OA, tissue concentrations of 6-keto-PGF1 alpha were greater than TxB2 in all groups, but concentrations of 6-keto-PGF1 alpha were not different between OA-R and OA-NR animals. TxB2 was increased in the dependent regions of animals in both OA-R and OA-NR groups compared with controls (no OA, n = 4, P < 0.05). The tissue TxB2/6-keto-PGF1 alpha ratio was smaller in controls and OA-NR in which no perfusion redistribution occurred than in OA-R and OA-meclo in which it did occur. This TxB2/6-keto-PGF1 alpha ratio correlated significantly with the magnitude of perfusion redistribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhaled [13N]nitric oxide: a positron emission tomography (PET) study.

Using positron emission tomography (PET) and nitric oxide radiolabeled with nitrogen-13 (half-life 9.97 min) we probed the distribution and kinetics of inhaled nitric oxide in anesthetized dogs. The washout of this gas after inhalation was much slower than that observed for [13N]nitrogen gas, demonstrating its uptake by lung tissue. The small fraction of radioactivity found in the plasma was determined to be in the form of [13N]nitrate. The administered gas contained < 1 ppm of nonradioactive nitric oxide, which is believed to be below the physiologic threshold for vasorelaxation.

Mechanisms underlying atriopeptin-induced increases in hematocrit and vascular permeation in rats.

Infusion of atriopeptin into humans and animals induces diuresis, natriuresis, hemodynamic changes, and an increase in arterial hematocrit. The objective of the present study was to elucidate the mechanism(s) responsible for the increase in hematocrit in rats given atriopeptin-24 (AP-24). Infusion of AP-24 for 30 minutes increased large vessel and total vascular hematocrits by 10-15% while decreasing microvascular hematocrits by 9-26% in numerous tissues. Regional vascular permeation by [131I] bovine serum albumin was markedly increased (2-5.6-fold) in many tissues, consistent with a 16% decrease in plasma volume. AP-24 infusion had no effect on extracellular fluid volume or the volume of circulating red cells. Vascular resistance was decreased and was associated with a significant increase in blood flow in many, but not all, tissues. In the atrium and in the small and large intestine the percentage decrease in microvascular hematocrit exceeded the increase in blood flow. These observations indicate that the increase in large vessel hematocrit induced by AP-24 infusion 1) is accompanied by a decrease in (microvascular) hematocrit in many tissues, 2) reflects an increase in overall (i.e., total vascular hematocrit), and 3) is the consequence of a decrease in plasma volume resulting from a marked increase in the rate of vascular permeation by plasma constituents in multiple tissues.

Comparative vascular pharmacology of the atriopeptins.

The atriopeptins are potent relaxants of norepinephrine-constricted aortic strips or are dilators of renal blood vessels in isolated perfused rat kidneys that are constricted by norepinephrine. This vasorelaxant property of the atriopeptins requires the presence of phenylalanine arginine (i.e., atriopeptin II, III, or ser-leu-arg-arg atriopeptin III) residues in the carboxy terminus which are considerably more effective than atriopeptin I (the 21 amino acid peptide which lacks the phe-arg C-terminus) or the core peptide (residues 3-19). However, these artificially in vitro precontracted preparations do not accurately predict the vascular effectiveness of the atriopeptins in intact rats. Intravenous administration of the atriopeptins (including atriopeptin I) to anesthetized rats produces concentration-dependent hypotension, a selective decrease in renal resistance in low doses (determined with microspheres), and pronounced diuresis. At higher doses, atriopeptins increase blood flow in other vascular beds. On the other hand, in the anesthetized dog, injection (intraarterially) of the phe-arg-containing peptides produces a concentration-dependent increase in both renal blood flow and sodium excretion, whereas atriopeptin I is inactive. Although there is a species difference in responsiveness to atriopeptin I, these data demonstrate a direct correlation between the renal vasodilation and diuresis produced by this novel family of atrial peptides.