Earl W Dunham

High-speed liquid chromatographic analysis of prostaglandins in rat kidney.

Abstract Conditions for the measurement of prostaglandin B by high-speed liquid chromatography with ultra violet detection are described. The method is simple, rapid and can detect as little as 5 ng of prostaglandin B2. Prostaglandins E and A were analyzed in lipid extracts of incubated rat renal papilla homogenates as prostaglandin B following treatment with base. The values for prostaglandin synthesis obtained with the high-speed liquid chromatographic method compared favorably with results obtained by bioassay.

Effects of essential fatty acid deficiency on prostaglandin synthesis and fatty acid composition in rat renal medulla.

Studies are reported on the capacity of isolated rat renal papilla (inner medulla) to synthesize and release prostaglandin (PG) E from endogenous and exogenous precursor(s) during development of an essential fatty acid (EFA) deficiency in the rat. Weanling (21-day-old) male Sprague-Dawley rats were fed a fat-free diet supplemented with either 5% hydrogenated coconut oil (HCO) or 5% safflower oil (SO). At approximately 3, 6 and 7 weeks (6, 9 and 10 weeks of age), groups of animals fed each diet were killed for studies of PGE synthesis in the renal papillae. Differences in the fatty acid composition of the papillae lipids of the animals of each group were also determined. The in vitro production of PGE from endogenous precursor(s) was significantly reduced in the papillae from the 6-week-old rats fed the HCO diet compared to the control (SO) rats, and appeared to be near maximally depressed in the 10-week-old animals compared to that of animals fed an EFA deficient diet for over a year in an accessory experiment. Analyses of the fatty acids of the papillae lipids of the HCO groups showed that the levels of 18∶2 and 20∶4 were markedly reduced, and those of 16∶1, 18∶1 and 20∶3 were elevated compared to the controls even in the 6-week-old animals, typical of an EFA deficiency. The papillae lipids of the animals fed the HCO diet were also depleted of their stores of 22∶4ω6. A fatty acid believed to be derived by chain elongation of 20∶3ω9, 22∶3, was found in large concentrations in the papillae triglycerides of the EFA deficient rats. Incubations of exogenous arachidonic acid (20∶4) in homogenates and tissue slices of the papillae of the HCO dietary groups showed that the PG synthetase was not impaired by an EFA deficiency. The rate of PGE synthesis in the papillae of the EFA deficient animals was generally enhanced when exogenous 20∶4 was added, indicating that the concentration of available precursor(s) is a primary factor in the control of PGE synthesis in the papilla of the rat.

Kinin-Mediated Antihypertensive Effect of Captopril in Deoxycorticosterone Acetate–Salt Hypertension

On the basis of evidence suggesting the activation of the kallikrein-kinin system in steroid-induced hypertension, we considered the possibility that the angiotensin-converting enzyme inhibitor captopril would lower the arterial blood pressure in deoxycorticosterone acetate (DOCA)-salt hypertensive rats through kininase II inhibition. In conscious DOCA-salt hypertensive rats with intact kidneys (n = 6) or uninephrectomized rats (n = 5), the short-term administration of captopril (8 mg/kg IV) decreased mean blood pressure from 141 +/- 3 to 118 +/- 3 mm Hg (P < .05) and from 176 +/- 12 to 158 +/- 15 mm Hg (P < .05), respectively. The maximal effect of captopril was manifested between 40 and 50 minutes after its administration, and blood pressure remained depressed for at least 2 hours. The bradykinin B2 receptor antagonist Hoe 140 (500 micrograms/kg IV) abolished the antihypertensive effect of captopril in the DOCA-salt hypertensive rats, indicating kinin involvement. Losartan, an angiotensin type 1 receptor antagonist, had no effect on blood pressure in another group of DOCA-salt hypertensive rats (n = 9) and did not significantly change the response to captopril. No effect of the angiotensin-converting enzyme inhibitor was seen in normotensive control rats (n = 5), indicating the absence of a nonspecific hypotensive action of the drug. Plasma renin activity was lower in the DOCA-salt hypertensive rats (0.7 +/- 0.2 ng angiotensin I/mL per hour, n = 4) than in normotensive control rats (8.8 +/- 1.7, n = 4). The involvement of kinins in the antihypertensive effect of captopril in DOCA-salt hypertension supports the contention that the kallikrein-kinin system contributes to blood pressure regulation in this hypertension model.

9,11-AZO-13-OXA-15-hydroxyprostanoic acid: A potent thromboxane synthetase inhibitor and a pgh2/txa2 receptor antagonist

9,11-Azo-13-oxa-15-hydroxyprostanoic acid (AOHP) is shown to be a potent inhibitor of thromboxane synthetase with an IC50 at about 10(-6)M. It also blocked the agonist actions of 9,11-epoxymethano-PGH2 (IC50 9 x 10(-7) M) and TxA2 (IC50 2.4 x 10(-6) M) on human platelet-rich plasma indicating that it also is a PGH2/TxA2 receptor blocker.

Identification of 15-keto-9, 11-peroxidoprosta-5, 13- dienoic acid as a hematin-catalyzed decomposition product of 15-hydroperoxy-9, 11-peroxidoprosta-5, 13-dienoic acid.

A labile prostaglandin was isolated as one of the products generated from [1-14C] eicosatetraenoic acid incubated with sheep vesicular gland microsomes. The eicosatetraenoic acid metabolite amounted to ca. 16% of the total radiolabeled products. Formation of this new prostaglandin was prevented when heat-denatured microsomes were employed or when incubation mixtures were supplemented with indomethacin or phenol. However, incubation of prostaglandin G2 (PGG2) with hematin in the presence or absence of catalytically active or heat-inactivated microsomes led to production of approximately the same quantity of the new prostaglandin. These results indicated that the new prostaglandin can be formed nonenzymically. The new prostaglandin was conclusively identified by gas liquid chromatography-mass spectrometry analysis as 15-keto-9,11-peroxidoprosta-5,13-dienoic acid (15-keto-PGG2) after chemical conversion to known prostaglandins. The effects of 15-keto-PGG2 and PGG2 were similar on canine lateral saphenous vein; both promoted contraction followed by prolonged relaxation, but 15-keto-PGG2 appeared to be 1/50 as potent as PGG2.

Threshold sodium excretory and renal blood flow effects of angiotensin converting enzyme inhibition

Objective To probe the potential influence of a high renal tubular level of angiotensin II on sodium reabsorption using angiotensin converting enzyme inhibitors and a non-peptide angiotensin antagonist. Methods Systemic arterial blood pressure, renal blood flow (RBF) and electrolyte and urinary excretion were measured in anesthetized uninephrectomized Wistar rats. Captopril (n = 12), ramiprilat (n = 10) or EXP 3174 (n = 9) was infused into the renal artery in graded doses to examine whether the threshold dose that increased RBF was lower than that which increased sodium excretion rate (Na+ excretion rate). Results: Whereas ramiprilat (0.5–4 μg/kg/min intra-arterially) and EXP 3174 (0.5–4 μg/kg/min intra-arterially) decreased blood pressure in all but the lowest dose of 0.5 μg/kg/min, captopril (1–8 μg/kg/min intra–arterially) did not change blood pressure except for a slight effect with the two higher doses. These three agents increased RBF to about the same degree, between 6% and 18%, which was relatively large compared with the maximal vasodilator response achievable in the kidney with acetylcholine (30–37%). Captopril given intra–arterially had a more consistent effect on Na+ excretion rate than either ramiprilat or EXP 3174. An increase in Na+ excretion rate occurred with captopril ranging from 44% to 78%, whereas no significant change was obtained with the other drugs. The dose of captopril that increased RBF was the same as that which increased Na+ excretion rate. In those experiments in which ramiprilat resulted in an increase in Na+ excretion rate (five of 10 experiments), the effective dose was the same as that which increased RBF. Conclusion When administered by the intra-arterial route, captopril was more effective in increasing Na+ excretion rate than either ramiprilat EXP 3174. Although the threshold dose of captopril and ramiprilat required to increase Na+ excretion rate and RBF was similar, suggesting blockade of a common angiotensin II pool, there was not a good correlation between these two effects.

Rat renal papillary release of hypotensive substances in vitro.

Platelet activating factor (PAF) is produced by the rat renal papilla from a neutral lipid, alkylacetylglycerol. Renal release of another neutral lipid, antihypertensive neutral renomedullary lipid, and PAF might account for normalization of blood pressure after unclipping in Goldblatt hypertensive rats. We studied the potential storage and release of hypotensive substances by the rat renal papilla in vitro. Rat kidneys were snap-frozen in liquid N2-cooled freon immediately after removal and the total lipids were extracted from pooled dissected papillae and partially separated by thin layer chromatography on silica gel with a hexane: ether: acetic acid (40:60:1) solvent system. Lipids eluted from four, contiguous silica gel zones were assayed in anesthetized spontaneously hypertensive rats. No hypotensive activity was found in the thin layer chromatography lipid fraction co-migrating with palmitylacetylglycerol or in any other neutral lipid fraction. In contrast, the Krebs medium obtained after 30-min incubation of freshly minced papillary tissue induced dose-related hypotension and bradycardia. The hypotensive activity was equivalent to 48 +/- 9 ng prostaglandin E2 (PGE2)/mg wet papilla. Bradycardia induced by the incubation medium was correlated with decrements in blood pressure. In the same assays, nitroprusside caused tachycardia which was correlated with hypotension, and the bradycardia associated with PGE2-induced hypotension was significantly less than that induced by the incubation medium. The dose-related effects of the incubation medium were dramatically attenuated by indomethacin treatment of the papilla, suggesting that the hypotensive activity is dependent upon papillary cyclooxygenase activity. However, PGI2 elicited hypotension concomitant with tachycardia rather than bradycardia and PGE2 did not mimic the incubation medium-induced bradycardia. Therefore, the effects of the papillary incubation medium may be mediated by other cyclooxygenase metabolites. Production/release of hypotensive material by indomethacin-treated papillary tissue was potentiated by co-incubation with non-hypotensive quantities of PGE2, suggesting a potential role for PGE2 in the renal antihypertensive function. Increasing pressure on the papilla from 6 to 20 mmHg during incubation did not increase release of non-prostanoid hypotensive substance(s). These results suggest that the formation and release of cyclooxygenase metabolites accounts primarily for the hypotensive activity released from rat renal papillae in vitro, and that prostaglandins might play a permissive role in the release of other renomedullary hypotensive substances.

Antagonism of the vasodilator effects of a platelet activating factor precursor in anesthetized spontaneously hypertensive rats

The hemodynamic effects of platelet activating factor (PAF), PAF antagonists and a precursor of PAF, 1-palmityl-2-acetyl-glycerol (PAG), were examined in pentobarbital-anesthetized spontaneously hypertensive rats to determine whether functionally significant amounts of PAF are produced via the cholinephosphotransferase pathway of PAF synthesis in vivo. Intravenous bolus doses of PAF, PAG and nitroprusside elicited hypotension and active mesenteric vasodilatation. Responses to PAG were slower in onset and longer in duration than those of PAF and nitroprusside. The specific PAF antagonists, CV-3988 and SRI 63-675, attenuated PAG- and PAF-, but not nitroprusside-induced changes in blood pressure and mesenteric flow/resistance. In contrast, captopril, which blocked the effects of angiotensin I, did not influence the hypotension caused by PAG, PAF and nitroprusside. The results suggest that the vasodilator effects of PAG are attributable to PAF produced from this alkylacetylglycerol, and the renin-angiotensin system does not appear to influence the biotransformation of PAG to PAF or the hypotensive action of PAF.

Reduced prostaglandin synthesis by renal and aortic tissues from adult rats fed essential fatty acid-deficient diet after food deprivation

Studies were conducted to determine the efficacy of a dietary technique for reducing prostaglandin (PG) synthesis in adult rats. Rats weighing 280-318 g were fed either essential fatty acid (EFA)-deficient or EFA-adequate diets for 10-17 days after a period of food deprivation. Synthesis of renal papillary PGE2 and aortic PGI2 from endogenous precursor in vitro were estimated by liquid chromatographic and bioassay/radioimmunoassay techniques, respectively, as indices of the capacity of the technique to induce EFA deficiency. PGE synthesis and PGI2 synthesis by isolated tissues from rats fed the EFA-deficient diet were significantly decreased (ca. 50%) relative to control rats fed an EFA-adequate diet. Body and renal papillary weights were not significantly altered by the EFA-deficient diet.