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Biomedical subjects

J G Gerber

Publications and source records attributed to J G Gerber.

124 records · Page 7Linked to original sources
PubMed1979

Prostaglandins and renin release: the effect of PGI2, PGE2, and 13,14-dihydro PGE2 on the baroreceptor mechanism of renin release in the dog.

We compared the ability of the vasodilator prostaglandins PGI2, PGE2, and 13,14-dihydro PGE2 to release renin when infused into the denervated, nonfiltering canine kidney in vivo. Papaverine was used as a nonprostaglandin vasodilator. All the prostaglandins tested were capable of stimulating renin secretion, with the scale of potency being 13,14-dihydro PGE2 greater than PGI2 greater than PGE2; papaverine had no effect on renin secretion. These results indicate that both PGE2 and PGI2 can stimulate renin secretion but that vasodilation per se is not a stimulus. 13,14-Dihydro PGE2 was included because it is a poorer substrate than PGE2, both for transport into cells and catabolism to inactive products, but has comparable potency to PGE2 when tested in systems with limited ability to catabolize PGE2. The fact that 13,14-dihydro PGE2 was the most potent prostaglandin tested suggests that the effects of PGE2 in our system are reduced by the kidneys' recognized ability to extract and catabolize PGE2. Since PGI2 is less avidly metabolized than PGE2 by the kidney, the differences in observed potency between PGE2 and PGI2 could be largely the result of differences in renal catabolism of the two prostaglandins rather than differences in intrinsic potency. Therefore, both PGE2 and PGI2 are candidates for the endogenous prostaglandin responsible for stimulating renin secretion.

Animals↗
PubMed1979

Measurement of arachidonic acid in the plasma by gas-liquid chromatography-flame ionization using dihomo-gamma-linolenic acid as an internal standard.

A gas-liquid chromatography-flame ionization method is described for measuring arachidonic acid in plasma using dihomo-gamma-linolenic acid as an internal standard. We found this technique to -e reproducible, and quicker and superior to previously described techniques because of the similar physico-chemical properties of the unsaturated fatty acid internal standard and arachidonic acid. In addition, we observed that the use of the saturated fatty acid, n-tricosanoic acid, was unsatisfactory as an internal standard because of its poor extractability from plasma as compared to arachidonic acid.

8,11,14-Eicosatrienoic Acid↗
PubMed1978

The lack of an effect of furosemide on uterine prostaglandin metabolism in vivo.

We determined the effect of 2 mg/kg intravenous furosemide on the production and metabolism of prostaglandin E2 in the utero-placental unit of pregnant dogs. Uterine venous prostaglandins E2 and 15-keto-13,14-dihydro E2 were measured by gas chromatography-mass spectrometry. Even though the dose of furosemide was adequate to effect a good diuresis, neither the production nor the metabolism of prostaglandin E2 by the uterus was altered by that dose of the drug. Using radioactive microspheres to measure hemodynamic parameters, we observed no change in uterine vascular resistance while renal vascular resistance decreased. Although the renal concentration of furosemide may be higher than the uteroplacental concentration, there is so far no evidence in vivo that usual doses of furosemide enhance the production or inhibit the metabolism of prostaglandin E2.

Animals↗
PubMed1978

The effect of PGI2 on canine renal function and hemodynamics.

The effect of prostaglandin I2 (prostacyclin) on renal and intrarenal hemodynamics and function was studied in mongrel dogs to elucidate the role of this novel prostaglandin in renal physiology. Starting at a dose of 10(-8) g/kg/min, PGI2 decreased renal vascular resistance and redistributed the blood flow away from the outer cortex (zone 1) and towards the juxtamedullary cortex (zone 4). At 3 X 10(-8) g/kg/min, the renal vascular resistance decreased even further, but at this dose the mean arterial blood pressure also declined 13% indicating recirculation of this prostaglandin. PGI2 infusion at a vasodilatory dose resulted in natriuresis and kaliuresis. With a decline in filtration fraction, these changes were most likely secondary to the hemodynamic effects of this prostaglandin. Unlike PGE2, PGI2 had no direct effect on free water clearance indicating lack of activity at the collecting duct. PGI2 may be the important renal prostaglandin involved in modulating renal vascular resistance and intrarenal hemodynamics as well as influencing systemic blood pressure.

Animals↗
PubMed1978

Redistribution of intrarenal blood flow following ADH administration: lack of inhibition by blockade of prostaglandin in cyclooxygenase.

The effect of prostaglandin synthesis inhibition on the redistribution of renal cortical blood flow in response to antidiuretic hormone (ADH) was examined using radioactive microspheres in water loaded, thiopental-anesthetized dogs. Microsphere injections were made during a control and an ADH infusion period (0.35 mU/kg/min following a 20 mU/kg bolus) both before and after indomethacin pretreatment (8 mg/kg intravenously). Urinary prostaglandin E2 (PGE2) excretion in each period was measured by gas chromatography-mass spectrometry. ADH caused a marked redistribution of flow toward inner cortical zones from 19 +/- 1 to 25 +/- 2 ml/min (mean +/- SE, p less than 0.01). Fractional flow to inner zones was also significantly increased. Indomethacin pretreatment had no effect on the ADH-induced redistribution (17 +/- 2 vs. 24 +/- 2 ml/min, p less than 0.01), although urinary PGE2 excretion was suppressed by indomethacin by 60%. It is concluded that prostaglandins do not mediate the redistribution of intrarenal blood flow accompanying ADH administration.

Animals↗
PubMed1978

Prostaglandins and renin release: II. Assessment of renin secretion following infusion of PGI2,E2 and D2 into the renal artery of anesthetized dogs.

The influence of intra-renal infusions of prostaglandin (PG) I2, PGE2 and PGD2 on renin secretion and renal blood flow was investigated in renally denervated, beta-adrenergic blocked, indomethacin treated dogs with unilateral nephrectomy. All three prostaglandins when infused at doses of 10(-8) g/kg/min and 10(-7) g/kg/min resulted in marked renal vasodilation. Renin secretory rates increased significantly with both PGI2 and PGE2 at the 10(-8) g/kg/min and 10(-7) g/kg/min infusion rates in a dose dependent manner. However, PGD2 was inactive. At 10(-7) g/kg/min, PGI2 infusions resulted in systemic hypotension indicated recirculation of this prostaglandin. These findings suggest that PGI2 should be included among the cyclooxygenase derived metabolites of arachidonic acid to be considered as possible mediators of renin release.

Animals↗
PubMed1978

Enhanced renal prostaglandin production in the dog. The effect of sodium arachidonate in nonfiltering kidney.

Sodium arachidonate, 10(-5) g/kg per minute, was infused into the renal artery of a nonfiltering canine kidney in situ in order to determine the effects of enhanced prostaglandin synthesis on renal blood flow and its distribution in circumstances where prostaglandins produced in the medulla could not gain access to the cortex via tubular fluid. The contralateral normal kidney was also infused with sodium arachidonate and served as control. Radioactive microspheres were used to calculate the hemodynamic effects. In the nonfiltering kidney, the total renal blood flow increased after sodium arachidonate from a mean of 105 ml/min per 100 g to 146 ml/min per 100 g (P less than 0.01). This increase was completely abolished by prior treatment with indomethacin, 8 mg/kg, intravenously. The normal kidney responded qualitatively the same as the nonfiltering side. In both kidneys, blood flow increased significantly to all cortical zones except the outermost (zone 1), but the fractional distribution of renal blood flow was significantly increased only in the innermost cortex (zone 4). Since the kidneys were nonfiltering, the increase of renal blood flow during infusion of arachidonic acid cannot be explained by prostaglandins being transported from renal medulla to the cortex through renal tubules. Most likely prostaglandins are produced locally in the cortex and have only local effects.

Animals↗
PubMed1978

Indomethacin is a placental vasodilator in the dog. The effect of prostaglandin inhibition.

The effect of 8 mg/kg of indomethacin on uterine blood flow, prostaglandin production, and intraamniotic fluid pressure was examined in late pregnant dogs. Uterine blood flow was measured with 15 mum radiolabeled microspheres. Because we found that a significant percentage of the microspheres shunted through the placental circulation into the lungs, we calculated placental blood flow by adding the shunted microspheres through the placenta to the nonshunted microspheres in the placenta. Total uterine blood flow significantly increased from 271+/-69 ml/min during control period to 371+/-72 ml/min (P < 0.01) 30 min after indomethacin. This increase was attributable to the change in blood flow to the placental circulation (222+/-58 to 325+/-63 ml/min; P < 0.01). Associated with these hemodynamic changes we found an almost complete suppression of uterine prostaglandin E(2) production (1,654+/-305 to 51+/-25 pg/ml; P < 0.01) as measured by gas chromatography-mass spectrometry. In addition, we found that indomethacin treatment resulted in uterine relaxation as measured by intraamniotic fluid pressure changes (11.2+/-1.3 mm Hg to 8.5+/-1.2 mm Hg; P < 0.001). We conclude that indomethacin causes an increase in placental blood flow without any change in flow to the rest of the uterus, and that this dose of the drug inhibits greater than 95% of uterine prostaglandin production. In addition, indomethacin is responsible for uterine relaxation. The increase in placental blood flow after indomethacin is probably a result of uterine relaxation, which is secondary to prostaglandin synthesis inhibition.

Amniotic Fluid↗
PubMed1975

Insulinoma with low circulating insulin levels: the diagnostic value of proinsulin measurements.

Hypoglycemia coexisting with very low plasma immunoreactive insulin concentrations was found in a 78-year-old woman with an insulinoma. However, the absolute proinsulin levels during hypoglycemia were elevated (0.9 to 1.4 ng/ml), accounting for 66.5% of the total circulating immunoreactive insulinlike material. The raised serum proinsulin concentrations together with an abnormal proinsulin:insulin ratio proved to be of critical importance in establishing the diagnosis of an islet-cell tumor in this patient.

Adenoma, Islet Cell↗
PubMedDate not supplied

Neither dapsone hydroxylation nor cortisol 6beta-hydroxylation detects the inhibition of CYP3A4 by HIV-1 protease inhibitors.

OBJECTIVE: This study examined the use of dapsone N-hydroxylation and cortisol 6beta-hydroxylation, well accepted in vivo probes of cytochrome P4503A4 (CYP3A4) activity, on defining the effect of three HIV protease inhibitors on CYP3A4 activity. METHODS: Subjects from University Hospital Infectious Disease Clinic about to be started on indinavir, and subjects from two clinical studies, one using ritonavir and the other using amprenavir, were recruited to participate in the study. Subjects received dapsone 100 mg p.o. followed by an 8-h urine collection for dapsone, dapsone N-hydroxylamine, cortisol, and 6beta-hydroxycortisol concentrations before HIV protease inhibitor administration, and 3 4 weeks into receiving HIV protease inhibitors. RESULTS: None of the HIV protease inhibitors demonstrated statistically significant alterations in dapsone recovery ratio and 6beta-hydroxycortisol/cortisol ratio. In fact, with ritonavir, the dapsone recovery ratio tended to increase rather than decrease, suggesting induction. These negative results were found despite evidence of CYP3A4 inhibition by these three HIV protease inhibitors via published drug-drug interactions with drugs that are substrates for CYP3A4. CONCLUSIONS: These in vivo assays used to probe CYP3A4 activity are suboptimal, most likely because of the presence of extrahepatic sites of metabolism for both dapsone and cortisol, and multiple CYP isozymes involved in dapsone N-hydroxylation.

Adult↗
PubMedDate not supplied

Combination therapy with indinavir, ritonavir, and delavirdine and nucleoside reverse transcriptase inhibitors in patients with HIV/AIDS who have failed multiple antiretroviral combinations.

PURPOSE: Ritonavir (RTV) and delavirdine (DLV) are inhibitors of cytochrome P450 (CYP) 3A4, the specific CYP that metabolizes indinavir (IDV). We hypothesized that patients who have failed multiple therapies containing protease inhibitors would still respond to IDV if high plasma concentrations were achieved. We retrospectively examined the antiviral efficacy of the combination of RTV, DLV, and IDV in heavily antiretroviral-experienced patients. METHOD: A chart review of patients treated with IDV/RTV/DLV and two nucleoside reverse transcriptase inhibitor (NRTI) drugs was performed. Only patients who failed at least three highly active antiretroviral therapy (HAART) regimens and remained on IDV/RTV/DLV therapy for at least 2 months were included. Plasma concentrations for IDV and RTV were obtained if patients were still on therapy. RESULTS: Ten participants were identified who qualified for this study. The median plasma HIV RNA prior to initiating IDV/RTV/DLV was 359,300 copies/mL. Nine of the 10 patients had failed nonnucleoside reverse transcriptase inhibitor (NNRTI)-containing regimens in the past. Eight out of 10 patients had at reduction in HIV RNA. Four of eight patients maintained the 1 log(10) reduction in HIV RNA past 6 months. Mean CD4 cell count increased from 142+/-99 to 273+/-126 cells/mm(3). Genotypic data available on six patients showed multiple protease gene mutations. Plasma concentration of IDV in three patients (two troughs and one 7 hours postdose) were >1,000 ng/mL. CONCLUSION: Our data suggests that in heavily antiretroviral drug-treated patients, partial antiretroviral response to RTV/IDV/DLV can still be achieved. The use of IDV/RTV/DLV and two NRTIs as salvage therapy has merit in patients who have no viable treatment options. A prospective trial utilizing this drug combination is warranted.

Adult↗