Albert L. Hyman

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

Gene Transfer of Endothelial Nitric Oxide Synthase to the Lung of the Mouse In Vivo Effect on Agonist-Induced and Flow-Mediated Vascular Responses

The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice. After intratracheal administration of AdCMVbetagal, expression of the beta-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMVbetagal peaked 1 day after administration and decayed over a 7- to 14-day period, whereas gene expression after AdRSVbetagal transfection peaked on day 5 and was sustained over a 21- to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders.

In Vivo Gene Transfer of Prepro-Calcitonin Gene–Related Peptide to the Lung Attenuates Chronic Hypoxia-Induced Pulmonary Hypertension in the Mouse

BACKGROUND Calcitonin gene-related peptide (CGRP) is believed to play an important role in maintaining low pulmonary vascular resistance (PVR) and in modulating pulmonary vascular responses to chronic hypoxia; however, the effects of adenovirally mediated gene transfer of CGRP on the response to hypoxia are unknown. METHODS AND RESULTS In the present study, an adenoviral vector encoding prepro-CGRP (AdRSVCGRP) was used to examine the effects of in vivo gene transfer of CGRP on increases in PVR, right ventricular mass (RVM), and pulmonary vascular remodeling that occur in chronic hypoxia in the mouse. Intratracheal administration of AdRSVCGRP, followed by 16 days of chronic hypoxia (FIO(2) 0.10), increased lung CGRP and cAMP levels. The increase in pulmonary arterial pressure (PAP), PVR, RVM, and pulmonary vascular remodeling in response to chronic hypoxia was attenuated in animals overexpressing prepro-CGRP, whereas systemic pressure was not altered while in chronically hypoxic mice, angiotensin II and endothelin-1-induced increases in PAP were reduced, whereas decreases in PAP in response to CGRP and adrenomedullin were not changed and decreases in PAP in response to a cAMP phosphodiesterase inhibitor were enhanced by AdRSVCGRP. CONCLUSIONS In vivo CGRP lung gene transfer attenuates the increase in PVR and RVM, pulmonary vascular remodeling, and pressor responses in chronically hypoxic mice, suggesting that CGRP gene transfer alone and with a cAMP phosphodiesterase inhibitor may be useful for the treatment of pulmonary hypertensive disorders.

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.

Adenoviral gene transfer of endothelial nitric-oxide synthase (eNOS) partially restores normal pulmonary arterial pressure in eNOS-deficient mice

It has been shown that mice deficient in the gene coding for endothelial nitric-oxide synthase (eNOS) have increased pulmonary arterial pressure and pulmonary vascular resistance. In the present study, the effect of transfer to the lung of an adenoviral vector encoding the eNOS gene (AdCMVeNOS) on pulmonary arterial pressure and pulmonary vascular resistance was investigated in eNOS-deficient mice. One day after intratracheal administration of AdCMVeNOS to eNOS−/− mice, there was an increase in eNOS protein, cGMP levels, and calcium-dependent conversion of l-arginine to l-citrulline in the lung. The increase in eNOS protein and activity in eNOS−/− mice was associated with a reduction in mean pulmonary arterial pressure and pulmonary vascular resistance when compared with values in eNOS-deficient mice treated with vehicle or a control adenoviral vector coding for β-galactosidase, AdCMVβgal. These data suggest that in vivo gene transfer of eNOS to the lung in eNOS−/− mice can increase eNOS staining, eNOS protein, calcium-dependent NOS activity, and cGMP levels and partially restore pulmonary arterial pressure and pulmonary vascular resistance to near levels measured in eNOS+/+ mice. Thus, the major finding in this study is that in vivo gene transfer of eNOS to the lung in large part corrects a genetic deficiency resulting from eNOS deletion and may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders in which eNOS activity is reduced.

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.

Pulmonary Vasodilator Activity of Prostacyclin (PGI2) in the Cat

We studied the pulmonary vascular effects of prostacyclin, PGI2, in the cat with intact chest under conditions of controlled blood flow. Intralobar injections of PGI2, 0.03-1 fig, decreased arterial pressure in the perfused lobe in a dose-dependent manner. Inasmuch as lobar blood flow was held constant and left atrial pressure was unchanged, the fall in lobar arterial pressure reflects a decrease in lobar vascular resistance. Prostaglandin Et (PGE1) and nitroglycerin also decreased lobar arterial pressure; however, PGI2had greater vasodilator activity than did these substances. Vasodilator responses to PGI2, PGE1, and nitroglycerin in absolute terms were dependent on the baseline level of tone in the pulmonary vascular bed. Prostacyclin reversed the hypertensive and platelet aggregating effects of ADP in the lobar vascular bed. These data indicate that PGIi has significant vasodilator activity in the feline pulmonary lobar vascular bed. Circ Res 45: 404-409, 1979

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.