Showing papers by "Suzanne Oparil published in 1986"

Mechanism of the pressor action of LY171555, a specific dopamine D2 receptor agonist, in the conscious rat.

Abstract: Administration of LY171555, a specific dopamine D2 receptor agonist, (10-1000 micrograms/kg i.v.) produced dose-related increases in mean arterial pressure in conscious Sprague-Dawley rats. Pretreatment with metoclopramide (5 mg/kg i.v.) abolished the pressor action of LY171555, whereas pretreatment with domperidone (2.5 mg/kg i.v.) and propranolol (10 mg/kg i.p.) did not affect the pressor action of LY171555. The vasopressor antagonist of arginine vasopressin (AVP), d(CH2)5Tyr(Me)AVP (10 micrograms/kg i.v.) and phenoxybenzamine (1 mg/kg i.v.) partly blocked and hexamethonium (25 mg/kg i.v.) enhanced the pressor action of LY171555. After combined treatment with both d(CH2)5Tyr(Me)AVP and phenoxybenzamine, LY171555 induced a depressor response which was completely blocked by pretreatment with domperidone. LY171555 administration induced a rapid, short-acting depressor response followed by a pressor response in conscious adrenomedullectomized Sprague-Dawley rats which was smaller in magnitude than that seen in intact Sprague-Dawley rats. LY171555 administration increased plasma norepinephrine, epinephrine and AVP in conscious Sprague-Dawley rats. These results suggest that the pressor action of LY171555 in conscious rats is dependent on activation of sympathetic outflow and AVP release through the central D2 dopaminergic system and that the central pressor effects of LY171555 could mask a depressor effect of LY171555 at the peripheral D2 dopamine receptor.

Effects of locally formed angiotensin II on renal hemodynamics

Abstract: The kidney produces angiotensin II (AngII) by conversion of both locally formed and systemically delivered angiotensin I (AngI). The latter may be physiologically significant because the kidney can convert 20-25% of systemically delivered AngI. To determine possible differences between the effects of circulating and locally converted AngII, we compared the renal responses to renal arterial infusions of AngI and AngII in equiconstrictor doses. Both reduced the renal blood flow and increased the filtration fraction; it is important that the AngI infusions consistently reduced glomerular filtration rates (GFR), which indicates effects proximal to or at the glomerulus. Micropuncture experiments revealed that AngI infusions reduced proximal tubular and peritubular capillary pressures and the single-nephron GFR; glomerular capillary pressure was not altered significantly. AngI infusions increased both pre- and postglomerular resistances and reduced the glomerular filtration coefficient. In other studies designed to estimate net intrarenal AngII generation, it was determined that the kidney degrades about 90% of arterially delivered AngII. Thus, most of the AngII in renal venous blood was formed intrarenally. Local production of AngII was enhanced, in association with increased renin release, after reductions in renal arterial pressure. Such increases in intrarenal AngII production may contribute to the AngII-dependent changes in renal vascular resistance that occur in conditions where the renin-angiotensin system is stimulated.

Impaired pulmonary conversion of angiotensin I to angiotensin II in rats exposed to chronic hypoxia.

Abstract: The effects of exposing rats to hypoxia at normal atmospheric pressure for periods of 21–24 days on intrapulmonary conversion of angiotensin I (ANG I) to angiotensin II (ANG II) were examined using an isolated rat lung preparation perfused at constant flow. 125I-ANG I (160 fmol) was injected alone and with graded doses (0.1, 1.0, and 100 nmol) of unlabeled ANG I into the pulmonary artery, and the effluent was collected for measurement of ANG I, ANG II, and metabolites. At low doses of injected ANG I (125I-ANG I alone or with 0.1 or 1.0 nmol unlabeled ANG I), the percent conversion of ANG I to ANG II was 67.5 +/- 2.1 (SE), 65.1 +/- 2.0, and 62.5 +/- 1.6 in 21-day hypoxia-exposed animals and 83.8 +/- 2.7, 81.4 +/- 3.9, and 79.6 +/- 2.3 (P less than 0.01) in control rats maintained under normoxic conditions. At the highest dose (100 nmol) of injected ANG I, percent conversion was reduced in both hypoxic and control groups to 46.8 +/- 5.0 and 64.0 +/- 6.0, respectively (P less than 0.05). Mean transit times of labeled material through the pulmonary circulation were not significantly different in hypoxic vs. normoxic lungs at any ANG I load, suggesting that the decreased conversion seen in hypoxic lungs was not related to altered kinetics of substrate exposure. Thus chronic hypoxia is associated with significant inhibition of transpulmonary ANG I conversion that is independent of perfusate flow. We postulate that this phenomenon is due to alterations at the endothelial membrane level.

Proteoglycans and hypertension. I. A biochemical and ultrastructural study of aorta glycosaminoglycans in spontaneously hypertensive rats.

Abstract: The extracellular matrix of blood vessel walls contains elastin, collagen, and proteoglycans, all of which can affect vascular resistance and, hence, blood pressure by virtue of their biomechanical properties.In the present study, we have begun to explore the possibility that proteoglycans may play a role in the pathophysiology of hypertension by analyzing, qualitatively and quantitatively, the polysaccharide components of proteoglycans from aorta of two normotensive rat strains, Wistar Kyoto (WKY) and Wistar rats, and from spontaneously hypertensive (SH) rats of the Okamoto strain.The total concentration of aorta glycosaminoglycans in the SH rat was 33% higher than in the WKY rat, due to a 164% increase in chondroitin 4- and 6-sulfate.The content of dermatan sulfate (DS), hyaluronic acid (HA), and heparan sulfate (HS) was similar in the two strains.The 4-wk-old SH rat also had an increase in chondroitin sulfate (CS) compared to the 4-wk-old WKY rat, without any change in DS, HA, or HS.The Wistar rat had approximately the same concentration of CS and DS in the aorta as the WKY rat, but HS and HA were reduced by 62 and 37%, respectively.The galactosaminoglycans (CS and DS) were heterogeneous on cellulose acetate electrophoresis and exhibited a different pattern for each of the three strains.Undersulfated CS accounted for 15 % of the total CS in WKY aorta but was present in only trace amounts in the SH aorta; 2% of the CS from the Wistar aorta was undersulfated.In all three strains, DS was exclusively 4-sulfated, and the CS contained approximately equal amounts of 4- and 6-sulfated galactosamine residues.Ultrastructural studies demonstrated that the HS was localized in the subendothelial matrix and the pericellular region surrounding the medial smooth muscle cells.CS and DS were primarily associated with collagen in the media.In the SH rat aorta the subendothelial matrix was thicker, and there was a relative increase in the CS/DS in the smooth muscle cell pericellular matrix.We suggest that, if similar alterations in CS proteoglycans are present in the resistance vessels, these changes may contribute to the increased peripheral vascular resistance in the hypertensive animal.

Mechanism of the depressor action of LY171555, a selective dopamine D2 receptor agonist, in the anesthetized rat.

Abstract: Administration of LY171555 (1 mg/kg i.v.) decreased mean arterial pressure (MAP) and heart rate in both pentobarbital- and urethane-anesthesized Sprague-Dawley rats. The depressor response to LY171555 in pentobarbital-anesthetized rats was sustained for at least 30 min, but in urethane-anesthetized rats lasted only approximately 3 min after LY171555 injection. In pentobarbital-anesthetized rats, pretreatment with domperidone (0.5 mg/kg) or metoclopramide (5 mg/kg) attenuated the depressor action of LY171555, whereas pretreatment with d(CH2)5Tyr(Me)arginine vasopressin (AVP) (10 micrograms/kg) only delayed the recovery phase of the depressor response to LY171555. In contrast, LY171555 administered to urethane-anesthetized rats after domperidone pretreatment induced a pressor response which was blocked completely by d(CH2)5Tyr(Me)AVP. Metoclopramide pretreatment in urethane-anesthetized rats prevented the decreases in MAP and heart rate induced by LY171555, whereas pretreatment with d(CH2)5Tyr(Me)AVP delayed the recovery phase of the depressor response. Pretreatment with d(CH2)5Tyr(Me)AVP per se decreased basal MAP in the urethane-anesthetized group, but not in pentobarbital-anesthetized rats. Basal plasma norepinephrine, epinephrine and AVP levels were higher in urethane-anesthetized rats than in the pentobarbital-anesthetized group. LY171555 administration decreased plasma norepinephrine without altering plasma epinephrine in both groups and induced a significant increase in plasma AVP which was greater in the urethane-anesthetized rats than in pentobarbital-anesthetized animals. These results suggest that LY171555 decreases MAP and heart rate in anesthetized rats by inhibiting norepinephrine release from nerve endings through the peripheral dopamine D2 receptor and that the time course of the depressor response may be altered by LY171555-induced AVP release, the magnitude of which appears to be dependent on the anesthetic agent.

Angiotensin extraction by trout tissues in vivo and metabolism by the perfused gill

Abstract: Plasma clearance and tissue accumulation of 125I-angiotensin I, [Asp1, Ile5]ANG I, and [14C]sucrose, an inert volume reference, were measured after a bolus injection into the dorsal aorta of rainbow trout, Salmo gairdneri. Retention and metabolism of ANG I to angiotensin II (ANG II) and their constituent 1-4 peptide by the gill were examined using an isolated perfused arch preparation in which outflow from the respiratory and central filamental (venous) pathways was separated. Clearance of ANG I from plasma is multiexponential, reflecting dilution and tissue extraction. Liver, bile, gonads, corpuscles of Stannius, and white skeletal muscle accumulate more 125I than 14C; gill tissue accumulates less 125I than 14C. ANG I and II are retained by the perfused gill longer than the inert vascular marker sucrose, even though the distribution volumes of the former are less. The gill respiratory pathway converts ANG I to ANG II whereas the venous pathway metabolizes either ANG I or II to the 1-4 peptide and other metabolites. The gill respiratory pathway is in series with the systemic vasculature, has a large blood-cell contact area, and, like the mammalian lung, is ideally suited to activate ANG I. The gill venous pathway is in parallel with the systemic vasculature and removes ANG II from the circulation. During stress, elevated plasma catecholamines may reduce venous perfusion and thereby help maintain elevated circulating ANG II levels through reduced venous metabolism.

Genetic and salt-related alterations in monoamine neurotransmitters in Dahl salt-sensitive and salt-resistant rats.

Abstract: Monoamine and metabolite levels were determined in brain regions and in the kidney, heart and adrenals taken from Dahl salt-sensitive (DS) and salt-resistant (DR) rats on either normal (NS) or high (HS) (8.5% NaCl) salt diets. The HS diet significantly (p