Howard Lippton

Diuretic and antinatriuretic responses produced by the endogenous opioid-like peptide, nociceptin (orphanin FQ)

Nociceptin (orphanin FQ) is a novel peptide isolated from brain tissue that has an amino acid sequence most similar to that of the endogenous opioid peptide dynorphin A. Aside from this similarity, the association of nociceptin to the endogenous opioid peptide systems and the functional importance of this new peptide in vivo are not completely known. Here we report that nociceptin is physiologically active in vivo and produces marked changes in the renal excretion of water and sodium. In conscious Sprague-Dawley rats, intravenous infusion of nociceptin produced a profound increase in urine flow rate and decrease in urinary sodium excretion. In further studies, intracerebroventricular (i.c.v.) injection of nociceptin into conscious rats produced a concurrent diuresis (dose-dependent) and antinatriuresis. The magnitude and pattern of the central nociceptin-induced water diuresis was similar to that produced by i.c.v. dynorphin A. Whereas i.c.v. pretreatment with the selective kappa-opioid receptor antagonist, nor-binaltorphimine, completely prevented the renal responses produced by dynorphin A, this antagonist did not alter the diuresis or antinatriuresis produced by central nociceptin. Thus, these results indicate that in conscious rats, nociceptin produces a selective water diuresis via a central nervous system mechanism independent of kappa-opioid receptors. Together, these observations suggest that endogenous nociceptin may be a novel peptide involved in the central control of water balance and ultimately in the regulation of arterial blood pressure. In the future, analogues of nociceptin may prove to be the first clinically useful water diuretics for patients with water-retaining diseases.

Effects of endothelin in the systemic and renal vascular beds in vivo

The effects of intravenous (i.v.) and intrarenal (i.a.) injections of endothelin on systemic and renal vascular resistances were investigated. I.v. bolus injection of endothelin, 300 ng, decreased systemic arterial pressure and renal perfusion pressure. This systemic vasodilator response to endothelin i.v. was dose-related at the 100, 300 and 1000 ng doses. I.a. injection of endothelin, 10 and 30 ng, decreased renal perfusion pressure. In contrast, endothelin, 100 ng into the renal arteries, produced a biphasic response and higher doses, 300 and 1000 ng, increased renal perfusion pressure. Although endothelin was initially reported as an endothelial-derived peptide with vasoconstrictor properties, the present data suggest that the physiologic effect of this peptide may be vasodilation

Pentoxifylline inhibits lipopolysaccharide-induced serum tumor necrosis factor and mortality

Tumor necrosis factor, a mononuclear phagocyte-derived peptide produced in response to lipopolysaccharide, has been shown to mediate certain aspects of septic shock and multiple organ failure resulting from gram-negative septicemia. In the present investigation, pretreatment of animals with pentoxifylline inhibited lipopolysaccharide-induced serum tumor necrosis factor in a dose-dependent fashion. Pentoxifylline prevented the sequestration of neutrophils seen in animals given intravenous lipopolysaccharide. Furthermore, pentoxifylline protected animals from the lethal effects of an intravenous challenge with lipopolysaccharide. These data indicate that pentoxifylline inhibits lipopolysaccharide-induced tumor necrosis factor and may be an effective agent in mitigating the lethal consequences of sepsis and other disease processes mediated by this cytokine.

THE PHARMACOLOGICAL EFFECTS OF ALLICIN, A CONSTITUENT OF GARLIC OIL

Garlic has been used in herbal medicine for thousands of years. While garlic oil contains many components and has been widely studied, the pharmacology of pure allicin, a constituent of garlic oil, is not well understood. We report that allicin inhibits human platelet aggregationin vitro without affecting cyclooxygenase or thromboxane synthase activity or cyclic adenosine monophosphate (AMP) levels. Allicin does not alter the activity of vascular prostacyclin synthase. However, it inhibits ionophore A23187-stimulated human neutrophil lysosomal enzyme release.In vivo allicin dilates the mesenteric circulation of the cat independent of prostaglandin release or a beta adrenergic mechanism.

Endothelin - a new family of endothelium-derived peptides with widespread biological properties

Endothelin (ET) is a novel family of three isopeptides (ET-1, ET-2, ET-3) each containing twenty-one amino acids and two disulfide bonds. Initially isolated from the supernatant of cultured porcine aortic endothelial cells, ET is stored as a preproform and released through an unusual proteolytic cleavage. In general, ET-1, ET-2, ET-3 differ quantitatively but not qualitatively in their biologic activity. ET have potent contractile activity in a variety of isolated tissues including arteries veins, trachea, duodenum urinary bladder and uterus. In vivo, ET possesses potent vasodilator and vasoconstrictor properties. Although the mechanisms mediating the hemodynamic effects of ET are not entirely clarified, recent evidence indicates a role for endothelium-derived relaxant factor (EDRF), protein kinase C and extracellular calcium. Moreover, ET appears to produce inflammation and bronchoconstriction through the formation of arachidonic acid metabolites via the cyclooxygenase pathway. The presence of ET binding sites in blood vessels and in several organ systems suggests ET may have important regulatory functions, which remain to be determined.

NOCICEPTIN : AN ENDOGENOUS AGONIST FOR CENTRAL OPIOID LIKE1 (ORL1) RECEPTORS POSSESSES SYSTEMIC VASORELAXANT PROPERTIES

The purpose of the present study was to investigate the effects of nociceptin on peripheral arterial rings from the cat. When feline renal, mesenteric, carotid and femoral rings with intact endothelium were precontracted with phenylephrine (100 nanomolar), nociceptin (3 x 10(-11)-3 x 10(-6) M) decreased tension in a concentration-dependent manner. The present data suggest nociceptin possesses biologic activity outside the CNS and may contribute to the regulation of systemic blood pressure and regional blood flow.

Interaction of human adrenomedullin 13–52 with calcitonin gene‐related peptide receptors in the microvasculature of the rat and hamster

1 Adrenomedullin (ADM), a recently discovered circulating hypotensive peptide, shares limited sequence homology with the sensory nerve‐derived vasodilator, calcitonin gene‐related peptide (CGRP). This study compared the vasodilator effect of sequence 13–52 of human adrenomedullin (ADM13–52) with that of human α CGRP (CGRP), in the microvasculature of the hamster cheek pouch and rat skin in vivo. 2 Single arterioles (20–40 μm diameter) in the hamster cheek pouch were visualised by intravital microscopy and video recording, and measured by image analysis. Both ADM13–52 (1 pmol–0.4 nmol) and CGRP (0.1 pmol–1 nmol) evoked dose‐related increases in the diameter of preconstricted arterioles (n = 6). ADM13–52 (ED50 14 pmol) was 20 fold less active than CGRP (ED50 0.71 pmol). The kinetics of onset and decline of vasodilator responses to both peptides were similar, with vasodilator responses to both peptides reaching a maximum at ca. 2 min, and reversing after 10–15 min (n = 5–7). The submaximal increase in blood flow evoked by ADM13–52 was significantly inhibited (P < 0.05; n = 6) by the CGRP1 receptor antagonist, CGRP8–37, at a dose (300 nmol kg−1, i.v.) that we have previously shown to inhibit significantly equivalent vasodilator responses to CGRP in this preparation. 3 In experiments measuring changes in local blood flow in rat skin by a 133xenon clearance technique, intradermal injection of both ADM13–52 (3–300 pmol) and CGRP (0.1–30 pmol) evoked dose‐related increases in local blood flow. ADM13–52 (ED50 27 pmol) was 17 fold less potent than CGRP (ED50 1.6 pmol) (n = 6). The submaximal increase in blood flow evoked by both peptides was significantly inhibited (P < 0.02; n = 5) by CGRP837 (100 nmol kg−1, i.v.). 4 We conclude that ADM13–52 is a potent vasodilator in the microvasculature of the hamster and rat in vivo. It mediates its vasodilator effect by arteriolar dilatation and this effect is due, at least in part, to the stimulation of CGRP1 receptors.

Pharmacological regulation of the circulation of bone

A study was undertaken to investigate the reactivity of the circulation of bone and to pharmacologically characterize the receptor populations that may be present in this poorly described vascular bed. The nutrient artery of the tibia in skeletally mature mongrel dogs was cannulated, under direct vision, through a posterolateral operative approach. An extracorporeal circuit was established so that the nutrient artery of the tibia could be perfused in vivo under conditions of constant blood flow. Diverse vasoactive substances were injected into the perfusion circuit in small volumes as a bolus close to the nutrient artery of the tibia. A range of doses of nitroglycerin, acetylcholine, isoproterenol, methoxamine, U46619 (a thromboxane A2 mimic), dibutyryl cyclic AMP, 8-bromo-cyclic GMP, and endothelin-1 were injected in a randomized sequence for each experiment. The antagonists that were used were atropine (a non-selective muscarinic receptor antagonist), ICI 118551 (a selective beta 2-adrenoceptor antagonist), ONO 3708 (a prostaglandin H2/thromboxane A2 receptor antagonist), and prazosin (an alpha 1-adrenoceptor antagonist). The results of changes in bone-perfusion pressure under conditions of constant blood flow indicated that the vascular bed of bone actively responds to various vasoconstrictor mechanisms, whereas vasodilator mechanisms appear to be considerably less active. Intra-arterial injections of nitroglycerin, acetylcholine, and 8-bromo-cyclic GMP resulted in dose-related decreases in bone-perfusion pressure that were weak relative to concomitant changes in systemic arterial pressure. Intra-arterial administration of methoxamine, U46619, and endothelin-1 resulted in a potent dose-related increase in bone-perfusion pressure. The results of intra-arterial injections of isoproterenol and dibutyryl cyclic AMP were surprising; both substances caused a substantial rise in bone-perfusion pressure. The responses to acetylcholine, methoxamine, and U46619 were blocked in a competitive manner after administration of atropine, prazosin, and ONO 3708, respectively.

Cardiovascular effects of prorenin blockade in genetically spontaneously hypertensive rats on normal and high-salt diet

Recent reports have demonstrated a potential role of tissue prorenin in the pathogenesis of cardiovascular and renal damage. This study was designed to examine the role of prorenin in the pathogenesis of target organ damage in spontaneously hypertensive rats (SHRs), the best naturally occurring experimental model of essential hypertension. To this end, we studied 20-wk-old male SHRs receiving a normal diet and 8-wk-old male SHRs given food with 8% NaCl. One-half the rats in each group were given prorenin inhibitor (PRAM-1, 0.1 mg.kg(-1).day(-1)) via osmotic minipumps; the other half served as controls. Arterial pressure, left ventricular function, cardiovascular mass indexes, cardiac fibrosis, and renal function were examined at the end of the experiment. Arterial pressure was unaffected by PRAM-1 in rats on either regular or salt-excess diets. In those rats receiving a normal diet, the blockade of prorenin activation consistently reduced left ventricular mass but affected no other variable. Salt-loaded rats given PRAM-1 for 8 wk demonstrated (1) reduced serum creatinine level, (2) decreased left ventricular mass, (3) improved left ventricular function, and (4) reduced left ventricular fibrosis. These data demonstrated that the blockade of nonproteolytic activation of prorenin exerted significant cardiovascular and renal benefit in SHRs with cardiovascular damage produced by salt excess and suggested that the activation of cardiovascular or renal prorenin may be a major mechanism that mediates cardiac and renal damage in this form of accelerated hypertension.

Adrenomedullin dilates rat pulmonary artery rings during hypoxia: role of nitric oxide and vasodilator prostaglandins.

Hypoxia decreases vasorelaxation and leads to pulmonary arterial hypertension. A newly identified 52 amino-acid peptide adrenomedullin (ADM) exerts vasodilator effect in intact animals under normoxic condition. We studied the effect of human ADM on rat pulmonary arterial and aortic rings under normoxic and hypoxic conditions. During normoxia, ADM caused a concentration-dependent relaxation of precontracted aortic and pulmonary arterial rings; the relaxation was much more pronounced in pulmonary arterial rings and was abolished by the nitric oxide (NO) synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) and by deendothelialization. A fragment of ADM, ADM13-52, caused a degree of relaxation similar to that induced by ADM in pulmonary arterial rings, but not in the aortic rings, and the relaxation of pulmonary artery caused by ADM13-52 was not affected by the cyclooxygenase inhibitor indomethacin but was abolished by L-NAME and by deendothelialization. During hypoxia, ADM13-52 failed to relax pulmonary arterial rings, whereas ADM caused modest relaxation of pulmonary arterial rings (one third of the relaxation during normoxia), which was abolished by pretreatment with indomethacin. Our results indicate that the vasorelaxant effect of ADM is more pronounced in pulmonary artery than in the aorta; ADM has more potent vasodilator effect than ADM13-52 during hypoxia; ADM relaxes hypoxic pulmonary artery through an indomethacin-sensitive pathway; amino acids 1-12 in ADM must be present for relaxation of chronic hypoxic pulmonary arterial rings; and last, the presence of endothelium is necessary for the expression of ADM-mediated relaxation.