Plasma beta-endorphin during clinical and experimental ischaemic pain

An improved radio-immunoassay using an antiserum directed towards the N-terminal part of the endogenous opioid peptide beta-endorphin 1-31 (beta-EP) was validated and applied to a study of beta-EP in plasma during ischaemic pain. Experimental ischaemic pain induced in seven healthy volunteers by the submaximal effort tourniquet test did not change plasma beta-EP or adrenocorticotrophin. Plasma beta-EP was determined in 21 patients with acute myocardial infarction (AMI) and in seven patients with unstable angina pectoris. Plasma beta-EP was 4.9 fmol/ml with 95% confidence limits, 3.2-7.8 fmol/ml in AMI patients at admittance, and 2.9 (2.0-3.4) fmol/ml one week later in stable and pain-free condition (p less than 0.05). The level in 49 healthy persons was 2.8 (2.4-2.9) fmol/ml. Elevated beta-EP levels were found in five AMI patients with cardiogenic shock and in four AMI patients dying within 24 h after admittance compared to the rest of AMI patients (p less than 0.02). beta-EP was not elevated during unstable angina pectoris, although pain scores were similar to AMI. The AMI group revealed a significant, although weak, positive correlation between plasma beta-EP and pain score (Spearman r = 0.49, p less than 0.05), while there was no correlation during unstable angina pectoris. beta-EP was not correlated to the amount of morphine required within the 48 h after admittance of AMI patients. We conclude that the increase of beta-EP in plasma during AMI may be due to stressful factors other than ischaemic pain and that it is questionable whether beta-EP in plasma is related to antinociception.     

Referees

An improved radio-immunoassay using an antiserum directed towards the N-terminal part of the endogenous opioid peptide β-endorphin 1–31 (β-EP) was validated and applied to a study of β-EP in plasma during ischaemic pain. Experimental ischaemic pain induced in seven healthy volunteers by the submaximal effort tourniquet test did not change plasma β-EP or adrenocorticotrophin. Plasma β-EP was determined in 21 patients with acute myocardial infarction (AMI) and in seven patients with unstable angina pectoris. Plasma β-EP was 4.9 fmol/ml with 95% confidence limits, 3.2–7.8 fmol/ml in AMI patients at admittance, and 2.9 (2.0–3.4) fmol/ml one week later in stable and pain-free condition (p<0.05). The level in 49 healthy persons was 2.8 (2.4–2.9) fmol/ml. Elevated β-EP levels were found in five AMI patients with cardiogenic shock and in four AMI patients dying within 24 h after admittance compared to the rest of AMI patients (p<0.02). β-EP was not elevated during unstable angina pectoris, although pain scores were similar to AMI. The AMI group revealed a significant, although weak, positive correlation between plasma β-EP and pain score (Spearman r = 0.49, p<0.05), while there was no correlation during unstable angina pectoris. β-EP was not correlated to the amount of morphine required within the 48 h after admittance of AMI patients. We conclude that the increase of β-EP in plasma during AMI may be due to stressful factors other than ischaemic pain and that it is questionable whether β-EP in plasma is related to antinociception.     

Plasticity of 5-HT serotonin receptor in patients with analgesic-induced transformed migraine

Chronic drug exposure can induce a significant change in neurotransmitter receptor systems and is possibly involved in the pathogenesis of drug-induced neurological disorders. Abuse of analgesics is known to induce deterioration in headache status in patients with primary headaches, especially migraine. To assess the possibility of 5-HT2A serotonin receptor plasticity in this condition, we investigated receptor binding on the platelet membrane in patients with analgesic-induced transformed migraine, patients with migraine, and nonheadache controls. Various concentrations of [3H]-spiperone (0.4 to 12 nmol) was used as a radioligand, and ketanserin was used to determine nonspecific binding. A lower maximal number of receptors (Bmax) was observed in patients with migraine as compared to patients with transformed migraine, and controls (467 +/- 58, 708 +/- 36, and 786 +/- 64 fmol/mg protein, respectively, P<0.01); whereas the value of the dissociation equilibrium constant (Kd) remained unchanged (1.72 +/- 0.16, 1.41 +/- 0.13, and 1.25 +/- 0.21 nmol for patients with migraine, patients with transformed migraine, and nonheadache controls, respectively). A significant decrease in Bmax value was observed in patients with transformed migraine after 4 weeks of analgesic withdrawal (770 +/- 25 and 345 +/- 31 fmol/mg protein, P<0.001), whilst no significant change in Kd value was observed (1.95 +/- 0.12 and 2.47 +/- 0.30 nmol, respectively). These findings indicate that 5-HT2A serotonin receptor system is altered in patients with transformed migraine with analgesic overuse. Such receptor plasticity may be an important step in the pathogenic mechanism of transformed migraine.     

Association between increased atrial natriuretic peptide and reduced cisplatin nephrotoxicity in rats.

Plasma atrial natriuretic peptide (ANP) concentrations were monitored in two experimental models of protection from cisplatin nephrotoxicity. Sprague-Dawley rats made diabetic with streptozotocin (65 mg/kg) were protected from cisplatin-induced nephrotoxicity when compared to control rats as indicated by reduced plasma creatinine (0.49 +/- 0.02 vs. 0.9 +/- 0.06 mg/dl; P less than .001) and blood urea nitrogen concentrations (18.51 +/- 1.4 vs. 43.08 +/- 2.1 mg/dl; P less than .001). Plasma ANP was also increased with experimental diabetes (76.5 +/- 8.98 fmol/ml) vs. normoglycemic controls (43.8 +/- 8.9 fmol/ml; P less than .02). When diabetic rats were treated with insulin, the renal protection observed with the diabetic state was reversed (creatinine, 0.70 +/- .05 mg/dl); plasma ANP concentrations were also reduced (52.2 +/- 15.2 fmol/ml). Renal platinum concentrations were significantly lower in the diabetic group and the reversal of diabetic-induced renal protection with insulin was associated with increased renal platinum concentrations. In rats given a single i.p. dose of cisplatin (5 mg/kg), a reduction in cisplatin-induced nephrotoxicity was observed when 5% NaCl was the vehicle of choice compared to that seen in rats given the same dose of drug in 0.9% saline (creatinine, 0.43 +/- 0.07 with 5% NaCl vs. 0.63 +/- 0.03 with 0.09% NaCl). NaCl (5%) administration also resulted in increased plasma ANP concentrations when compared to rats receiving equivalent volumes of 0.9% NaCl (88.4 +/- 6.2 vs. 50.5 +/- 5.6 fmol/ml, respectively). These data suggest that increased endogenous ANP may be a mechanism of renal protection common to both experimental diabetes and hypertonic saline administration. Chronically increased ANP may prevent renal accumulation of platinum in the kidney.     

Different behaviour of the N-terminal and C-terminal fragment of proatrial natriuretic factor in plasma of healthy subjects as well as of patients with cirrhosis

N-terminal (atrial natriuretic factor (ANF) 1-98) and C-terminal (ANF 99-126) fragments of proatrial natriuretic factor (NTA and CTA, respectively) were determined in plasma of healthy subjects adopting different postures and in patients with cirrhosis. Seven healthy subjects were investigated while seated and 30 min after assuming a horizontal position. NTA plasma concentrations increased in subjects in the horizontal position (from 734 +/- 250 (SE) fmol/ml to 902 +/- 227 fmol/ml; p less than 0.05). In contrast, CTA plasma concentrations remained unchanged (9.2 +/- 1.3 fmol/ml vs 8.9 +/- 1.6 fmol/ml). In 10 patients with cirrhosis of the liver, NTA concentrations were markedly (p less than 0.001) elevated compared to 11 healthy subjects (2334 +/- 291 fmol/ml vs 743 +/- 155 fmol/ml). However, there was no difference of CTA plasma levels between cirrhotic patients and healthy subjects (8.7 +/- 1.3 fmol/ml vs 8.2 +/- 0.9 fmol/ml). These data demonstrate changes of the plasma concentration of the N-terminal fragment of proatrial natriuretic factor by posture and in liver disease, in contrast to unchanged levels of the C-terminal fragment.     

Platelet membrane glycoproteins in thrombasthenia, Bernard-Soulier syndrome, and storage pool disease.

Quantitative polyacrylamide gel electrophoresis has been carried out on patients with Bernard-Soulier syndrome, Glanzmann's thrombasthenia, and storage pool defect in order to clarify the abnormalities in their platelet membrane glycoproteins. Normal individuals had values (expressed as PAS staining units/mg of membrane protein) of 5.11 +/- 0.63 for glycoprotein 1 (Mr 150,000), 2.35 +/- 0.35 for glycoprotein II (Mr 120,000), 0.89 +/- 0.22 for glycoprotein III (Mr 100,000), and 1.34 +/- 0.64 for glycoprotein IV (Mr 85,000). Total PAS staining of these four major bands was 9.70 +/- 1.26 PAS units/mg of membane protein. Patients with Bernard-Soulier syndrome completely lacked glycocalicin and had about one half (1.90 PAS units/mg) of the glycoprotein I of normal controls. These was no significant reduction in glycoproteins II, III, and IV, but total PASstaining was reduced to 4.40 units/mg, reflecting the importance of the contribution of glycoprotein I to this parameter. Thrombasthenic platelets gave values for glycoprotein II of 0.66, which were about 25% of controls, and the values for glycoprotein III (0.34) were about 40% of controls. Patients with storage pool disease gave values within the normal range with the exception of one family which showed, in addition, small platelets and an associated lipid defect. In thic case of glycoprotein (2.71) was significantly elevated.     

Isosorbide-5-mononitrate in angina pectoris: plasma concentrations and duration of effects after acute therapy

In a double-blind, randomized, crossover study, the duration of effects of single oral doses of 20 and 40 mg isosorbide-5-mononitrate (IS-5MN) and matching placebo were studied in 12 male patients with angina pectoris. Plasma IS-5MN concentrations (mean +/- SD) 2 and 6 hours after administration were 300 +/- 60 and 144 +/- 43 ng/ml after 20 mg IS-5MN and 551 +/- 191 and 376 +/- 129 ng/ml after 40 mg IS-5MN. Exercise time to the onset of angina 2 and 6 hours after administration increased after 20 mg IS-5MN (5.88 +/- 1.85; P less than 0.001 and 5.08 +/- 1.97 minutes; P less than 0.002) and 40 mg IS-5MN (6.17 +/- 1.88; P less than 0.001 and 5.78 +/- 1.72 minutes; P less than 0.001) in comparison to placebo (4.57 +/- 1.22 and 4.15 +/- 1.22 minutes). Similarly, total exercise duration increased at 2 (P less than 0.001) and 6 hours (P less than 0.002) after both doses of IS-5MN. Compared with placebo, ECG ST segment depression during exercise was less (P less than 0.05) 2 hours after both doses of IS-5MN. Thus single oral doses of 20 and 40 mg IS-5MN exert antianginal and anti-ischemic effects for at least up to 6 hours.     

Pharmacokinetics of Ceftriaxone in Pediatric Patients With Meningitis

Pharmacokinetics of ceftriaxone after a single dose of 50 or 75 mg/kg were determined in 30 pediatric patients with bacterial meningitis. Data for doses of 50 and 75 mg/kg, respectively, were as follows (mean +/- standard deviation): maximum plasma concentrations, 230 +/- 64 and 295 +/- 76 mug/ml; elimination rate constant, 0.14 +/- 0.06 and 0.14 +/- 0.04 h(-1); harmonic elimination half-life, 5.8 +/- 2.8 and 5.4 +/- 2.1 h; plasma clearance, 51 +/- 24 and 55 +/- 18 ml/h per kg; volume of distribution, 382 +/- 129 and 387 +/- 56 ml/kg; mean concentration in cerebrospinal fluid 1 to 6 h after infusion, 5.4 and 6.4 mug/ml. A dosage schedule of 50 mg/kg every 12 h for bacterial meningitis caused by susceptible organisms is suggested for pediatric patients over 7 days of age.     

Disposition of phosphomycin in patients with pleural effusion

The pharmacokinetics of phosphomycin were studied in seven patients with pleural effusion of varied etiologies. All patients received a single intravenous bolus of 30 mg of antibiotic per kg. Phosphomycin levels in plasma and pleural fluid were determined simultaneously. Antibiotic levels in plasma followed a two-compartment open kinetic model. In the pleural fluid, maximum concentrations of phosphomycin, 42.63 +/- 16.03 micrograms/ml (mean +/- standard deviation), were reached at 3.69 +/- 1.08 h after administration of the antibiotic. The disappearance constant of the antibiotic from the pleural fluid was significantly smaller (0.16 +/- 0.06 h-1) than the elimination constant determined from the levels of drug in plasma (0.73 +/- 0.26 h-1). Phosphomycin persisted in antibacterial concentrations in the pleural fluid for a considerable period of time. The low accessibility of phosphomycin observed in one of the patients in the study, with a maximum concentration value of 2.16 micrograms of phosphomycin per ml of pleural fluid, could be due to the existence of pachypleuritis in that patient; this was later confirmed in clinical and histological studies done after the research described here.     

Plasma immunoreactive gamma melanotropin in patients with idiopathic hyperaldosteronism, aldosterone-producing adenomas, and essential hypertension.

A non-ACTH aldosterone-stimulating factor(s) has been implicated in the pathogenesis of idiopathic hyperaldosteronism (IHA). Although this factor has not been fully characterized, some evidence suggests that it may be related to a pro-gamma-melanotropin (pro-gamma-MSH), derived from the NH2-terminal region of pro-opiomelanocortin. In the present study, plasma immunoreactive (IR-) gamma-MSH levels at 0800 h in patients with IHA were evaluated (90 +/- 17 fmol/ml; range: 13-173 fmol/ml) and found to be significantly higher (P less than 0.05) than those in subjects with aldosterone-producing adenomas (33 +/- 8 fmol/ml), essential hypertension (33 +/- 6 fmol/ml), and normotensive controls (19 +/- 2 fmol/ml). Seven of nine IHA subjects had circulating IR-gamma-MSH levels above the normal range (greater than 35 fmol/ml). In plasmas sampled at 1200 h, IR-gamma-MSH was significantly higher in patients with IHA (95 +/- 26 fmol/ml) and adenomas (63 +/- 23 fmol/ml), as compared with essential hypertensives (31 +/- 6 fmol/ml) and normotensives (19 +/- 3 fmol/ml). Mean plasma IR-ACTH, plasma cortisol, and urinary cortisol levels did not differ significantly between any of these groups. In order to evaluate the effect of a pro-gamma-MSH in vitro, adrenal adenoma tissue was obtained from two patients, one with elevated IR-gamma-MSH (61 fmol/ml) and a second with low IR-gamma-MSH (12 fmol/ml). Aldosterone secretion by dispersed adenoma cells from the former, but not the latter, underwent a fourfold dose-dependent (10(-14)-10(-9) M) increase in response to human Lys-gamma 3-MSH. These data suggest that a pro-gamma-MSH may be implicated as a pathogenic factor in a subset of patients with primary aldosteronism, particularly among those differentially diagnosed as having IHA.     

Enhanced cardiac production of matrix metalloproteinase-2 and -9 and its attenuation associated with pravastatin treatment in patients with acute myocardial infarction

Previous experimental studies have demonstrated that MMPs (matrix metalloproteinases) contribute to LV (left ventricular) remodelling. We hypothesized that cardiac MMPs are activated in patients with AMI (acute myocardial infarction) and, if so, MMP production may be attenuated by statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) through their cardiovascular protective actions. We studied 30 patients, ten control patients with stable angina pectoris and 20 patients with AMI, in whom LV catheterization at the chronic stage was performed 22+/-12 days (value is mean+/-S.D.) after the onset of AMI. Blood samples were collected from the CS (coronary sinus) and a peripheral artery. In patients with AMI, the levels of MMP-2 and MMP-9 were significantly (P<0.05) higher in the CS than the peripheral artery (MMP-2, 853+/-199 compared with 716+/-127 ng/ml; MMP-9, 165+/-129 compared with 98+/-82 ng/ml), whereas no significant differences were observed in the patients with angina pectoris. The CS-arterial concentration gradients of MMP-2 and MMP-9 correlated positively with BNP (brain natriuretic peptide) levels (MMP-2, R=0.68, P<0.01; MMP-9, R=0.59, P<0.05) and LV end-diastolic volume index (MMP-2, R=0.70, P<0.01; MMP-9, R=0.70, P<0.01). When patients with AMI treated with 10 mg of pravastatin or without (n=10 in each group) were compared, this statin therapy significantly (P<0.05) decreased the CS-arterial concentration gradients of MMP-2 (69+/-43 compared with 213+/-185 ng/ml) and MMP-9 (14+/-27 compared with 119+/-84 ng/ml). In conclusion, the enhanced production of cardiac MMP-2 and MMP-9 is associated with LV enlargement and elevated BNP levels in patients with AMI. A pleiotropic effect of statins appears to be associated with the modulation of cardiac MMP activation, which may be potentially beneficial in the attenuation of post-infarction LV remodelling.     

Elevated CSF levels of substance P and high incidence of Raynaud phenomenon in patients with fibromyalgia: new features for diagnosis

In 30 patients with diagnosed fibromyalgia, the CSF level of immunoreactive substance P (SP) was investigated. Compared to normal values (9.6 +/- 3.2 fmol/ml), all the patients had elevated CSF levels of SP (36.1 +/- 2.7 fmol/ml, range 16.5-79.1 fmol/ml). Anamnestic information from the patients revealed that 53.3% had Raynaud/Raynaud-like phenomenon localized in the fingers, the toes or both. Although SP levels did not differ significantly in patients with or without the Raynaud phenomenon, elevated activity may be present in the peripheral branches of SP neurons which could be responsible for the last (rubor) phase of the triphasic Raynaud's phenomenon. SP levels were significantly higher in patients who were smokers (40.1 +/- 2.7 fmol/ml, range 25.3-64.1 fmol/ml), compared to patients who were non-smokers (29.2 +/- 5.0 fmol/ml, range 16.5-79.1 fmol/ml). We propose elevated CSF levels of SP and the Raynaud phenomenon as characteristic features for fibromyalgia with potential as diagnostic markers of the disease and further that smoking might be an aggravating factor for its pathogenesis or development.     

Pharmacokinetics and cerebrospinal fluid concentration of nafcillin in pediatric patients undergoing cerebrospinal fluid shunt placement

Postoperative infection is among the most common complications in patients with cerebrospinal fluid shunt placement. Nafcillin is often used for prophylaxis but not pharmacokinetic data are available perioperatively in pediatric patients. The objectives of this study were to characterize the pharmacokinetics and determine the cerebrospinal concentrations of nafcillin. Ten patients (mean age 8.0 +/- 5.6 years) received three doses of intravenous nafcillin, 50 mg/kg every 6 h; the first dose was administered 1 h prior to surgery. Multiple blood samples were collected during and after surgery and the cerebrospinal fluid sample was obtained at the time of shunt insertion. Urine samples were collected for 24 h after initiation of nafcillin. Nafcillin was analyzed with an HLPC method. The peak serum concentrations ranged from 22 to 107 micrograms/ml; cerebrospinal fluid concentrations ranged from 0.02 to 0.30 (mean 0.16 +/- 0.11) micrograms/ml. The mean total clearance, renal clearance, apparent volume of distribution, and elimination half-life were 0.90 +/- 0.55 l/kg/h, 0.12 +/- 0.04 l/kg/h, 0.70 +/- 0.52 l/kg, and 0.5 +/- 0.1 h, respectively. 16% of total nafcillin dose was excreted in the urine. A 4-fold variability in total clearance and a 10-fold variation in cerebrospinal fluid concentrations of nafcillin was observed in these patients. Further, the concentrations of nafcillin attained in the cerebrospinal do not appear to be adequate, based on its minimum inhibitory concentration of 0.5 micrograms/ml against very susceptible staphylococci. These data, in addition to the fact that an increasing number of staphylococci are becoming resistant to nafcillin, question the usefulness of prophylactic nafcillin in pediatric patients undergoing shunt procedures.     

Streptodecase-2 in the treatment of acute myocardial infarct, unstable stenocardia, thromboembolism and thrombosis

Eleven patients underwent thrombolytic therapy with streptodekase-1 and 19 with streptodekase-2. Of these, 11 patients suffered acute myocardial infarction, 10 had unstable angina pectoris, 6 thromboembolism of the pulmonary artery, 2 thromboembolism of the peripheral arteries and 1 thrombosis of the femoral vein. Administration of streptodekase-2 brought about an increase of the total blood fibrinolytic activity (the fibrinolysis time dropped from 248.8 +/- 82.1 to 137.5 +/- 42.5 min after 12 h), plasmin activation (from 0.00 +/- 0.00 to 23.5 +/- 7.5 mg after 24 h), reduction of the plasminogen content (from 94.0 +/- 2.5 to 46.8 +/- 5.3% after 12 h). The parameters of the coagulation hemostasis did not undergo any appreciable changes. Fibrinolysis activation following streptodekase-2 administration was unchanged within the first 48 hours. No material differences were identified in fibrinolysis activation in patients given streptodekase-2 and streptodekase-1. Administration of streptodekase-2 was found to exert a marked beneficial clinical effect on acute myocardial infarction, unstable angina pectoris, thromboembolism of the pulmonary and peripheral arteries.     

Effects of fenigidin treatment regimen on the state of peripheral hemodynamics of patients with stable effort angina pectoris and postinfarction cardiosclerosis

AIM: To examine the impact of fenigidin treatment regimen on peripheral hemodynamics in patients with stable angina pectoris of effort and postinfarction cardiosclerosis without signs of heart failure. MATERIALS AND METHODS: Thirty two patients with functional classes II and III stable angina of effort and 32 with postinfarction cardiosclerosis without signs of heart failure were examined. RESULTS: Monotherapy with fenigidin, 30-40 mg/day in patients with stable angina pectoris of effort and in those with postinfarction cardiosclerosis lowered systolic and mean blood pressures, total and specific peripheral vascular resistance, venous tone and increased additional venous volume and maximum vein emptying rate in the upper and lower extremities. Fenigidin therapy caused no side effects. CONCLUSION: Fenigidin monotherapy improves hemodynamic parameters in stable angina pectoris of effort and postinfarction cardiosclerosis without obvious signs of heart failure and causes no side effects when the drug is used in a dose of 30-40 mg/day for 3 weeks.     

Human serum Zn-alpha2-glycoprotein in amniotic fluid

Human serum Zn-alpha2-glycoprotein (Zn-alpha2-GP) was found to be present in the amniotic fluid in the mean concentration of 0.98 +/- 0.40 mg/100 ml, which represents about one-tenth of its concentration in the maternal serum (9.65 +/- 1.18 mg/100 ml). Its concentration in the amniotic fluid was proportional to the amniotic fluid total protein and very approximately to the maternal serum Zn-alpha2-GP. The relationship between the maternal serum Zn-alpha2GP and the maternal serum total protein as well as between the amniotic fluid total protein and the maternal serum total protein was found to be not significant. The amniotic fluid Zn-alpha2-GP as well as the amniotic fluid total protein showed some increase during gestation to reach the highest values at the end of the second trimester. At present both the origin and significance of the amniotic fluid Zn-alpha2-GP are not known.     

Ketoconazole kinetics in chronic peritoneal dialysis

The kinetics of oral ketoconazole in serum and peritoneal fluid were studied in six patients with renal failure receiving peritoneal dialysis. A dose of 400 mg ketoconazole resulted in a maximum blood concentration of 2.3 +/- 1.7 microgram/ml (mean +/- SD), which occurred 3.3 +/- 1.6 hours after dosing. The serum t1/2 was 2.4 +/- 0.8 hours. Peritoneal clearance values were less than 1 ml/min, and peritoneal penetration reached 3.4% of the serum concentration by 5 hours. Protein binding studies were also performed. Compared with healthy controls, patients receiving peritoneal dialysis have significantly less ketoconazole serum protein binding. Fifty to eighty percent of the drug is protein bound in the peritoneal fluid, and the unbound concentration is in the same range as that in the serum of healthy individuals with "therapeutic" total ketoconazole levels of 1 to 2 micrograms/ml.     

Pharmacokinetics and dynamics of furosemide in the newborn piglet

Furosemide was administered as either an i.v. bolus (6 mg/kg) or primed continuous infusion (4 mg/kg/hr) with quantitative fluid replacement to 10 3-day-old and 9 18-day old piglets. Total and unbound plasma as well as urinary furosemide concentrations were measured for up to 6 hr and drug disposition and renal sodium excretory dynamics were compared at the two ages. The plasma clearance of furosemide was concentration-independent over the range studied (0.1-10 mg/l). Steady-state volume of distribution and unbound fraction of furosemide in plasma were both considerably higher in the younger piglets (618 +/- 320 vs. 201 +/- 71 ml/kg, p less than .01 and 0.22 +/- 0.08 vs. 0.06 +/- 0.02 ml/kg, p less than .001, respectively) while unbound secretory clearance was several-fold lower in this age group (49.2 +/- 23 vs. 107 +/- 55 ml/min/kg, P less than .01). A log-logistic equation was fitted to sigmoidal plots of sodium excretion rate vs. log furosemide excretion rate. While basal response and slope parameters did not differ significantly, maximal response and stimulus required for half-maximal response were both reduced in the younger piglets (0.70 +/- 0.24 vs. 1.18 +/- 0.30 mmol/min and 0.06 +/- 0.04 vs. 0.14 +/- 0.06 mumol/min, respectively, P less than 0.05). Thus, younger piglets were more sensitive to the natriuretic effects of the drug. While term piglets were useful for studying the maturation of protein binding and renal drug excretory processes for furosemide, drug disposition was not comparable to that in human premature infants because of the higher secretory capability of the piglet.     

Biosynthesis and release of thyrotropin-releasing hormone immunoreactivity in rat pancreatic islets in organ culture. Effects of age, glucose, and streptozotocin

Thyrotropin-releasing hormone immunoreactivity (TRH-IR) was measured in isolated islets and in medium from rat pancreatic islets maintained in organ culture. TRH-IR in methanol extracts of both islets and culture medium was eluted in the same position as synthetic TRH by ion-exchange and gel chromatography and exhibited dilution curves parallel with synthetic TRH in radioimmunoassay. [3H]Histidine was incorporated into a component that reacted with TRH antiserum and had the same retention time as synthetic TRH on reversed-phase high-performance liquid chromatography. A continuous release of TRH-IR into the culture medium was observed from islets of both 5-d-old (newborn) and 30-d-old (adult) rats with a maximum on the second day of culture (28.7 +/- 7.0 and 13.3 +/- 3.6 fmol/islet per d, respectively). The content of TRH-IR was higher in freshly isolated islets from newborn rats (22.4 +/- 2.3 fmol/islet) than in adult rat islets, which, however, increased their content from 1.3 +/- 0.5 to 7.0 +/- 0.5 fmol/islet during the first 3 d of culture. Adult rat islets maintained in medium with 20 mM glucose released significantly more TRH-IR than islets in 3.3 mM glucose medium (13.0 +/- 0.7 vs. 4.3 +/- 0.3 fmol/islet per d). In contrast, the content of TRH-IR in the islets was reversed (1.4 +/- 0.3 vs. 4.7 +/- 1.6 fmol/islet). By exposing islets from newborn rats to streptozotocin 0.7 mg/ml for 30 min, a 50% reduction of TRH-IR content in the islets compared with the non-treated islets was seen after subsequent culture for 7 d. The insulin content was reduced by 80%, while glucagon was slightly elevated. In conclusion, these results indicate that TRH is synthesized in rat pancreatic islets, and that the release is stimulated by glucose.