A new method of measuring renal function in conscious rats without the use of radioisotopes.

The purpose of the current experiment was to develop fast and accurate assays for measuring glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). An enzymatic method was developed for the determination of inulin, and a colorimetric method was developed for determination of p-aminohippurate (PAH) in the plasma and urine of rats. These assays are easily automated and do not require the use of radioisotopes or corrosive chemicals. Glomerular filtration rate was measured by the clearance of inulin, and effective renal plasma flow was measured by the clearance of PAH. Blood pressure, heart rate, and renal function (urine volume, electrolytes, GFR, and ERPF) were measured in conscious rats for 1.5 h prior to drug treatment and for 3 h after treatment. Baseline renal function was compared to historical data. Acute changes in GFR and ERPF following administration of the vasoconstrictor peptide endothelin-1 (ET-1) were accurately measured with results similar to those obtained with older methodologies. These new methods offer many advantages over previously described methods by eliminating the use of radioisotopes and harsh chemicals. In addition, these methods can be used with an automated instrument with high accuracy and precision. Therefore, these new methods can be used to accurately determine GFR and ERPF and are sensitive enough to detect acute changes in GFR and ERPF in conscious animals.

Pharmacology of L-754,142, a highly potent, orally active, nonpeptidyl endothelin antagonist.

L-754,142, (-)-N-(4-iso-propylbenzenesulfonyl)-alpha-(4-carboxyl-2-n-propy lphenoxy)-3,4- methylenedioxyphenylacetamide, is a potent nonpeptidyl endothelin antagonist (e.g., Ki: cloned human ETA = 0.062 nM: cloned human ETB = 2.25 nM), with high specificity for endothelin receptors. In vitro, L-754,142 is a potent antagonist of ET-1-induced phosphatidyl inositol hydrolysis in Chinese hamster ovary cells expressing cloned human endothelin receptors (IC50: hETA = 0.35 nM; hETB = 26 nM) and of ET-1 induced contractions in rabbit iliac artery rings (pA2 = 7.74) and rat aortic rings (pA2 = 8.7). In vivo, L-754,142 is a potent and specific antagonist of exogenously administered ET-1 or big ET-1, L-754,142 fully protects against ET-1-induced lethality in mice (AD50 = 0.26 mg/kg i.v.). The pressor response to big ET-1 in the anesthetized ferret is blocked by this compound with an ED50 value of 0.019 mg/kg i.v. L-754,142 also blocks the pressor response to big ET-1 in the conscious rat with ED50 values of 0.30 mg/kg i.v. and 0.56 mg/kg p.o. The duration of action of L-754,142 in this rat model is more than 12 hr after an oral dose of 3 mg/kg. In summary, L-754,142 is a potent, orally active ET antagonist with a long duration of action in several in vivo models.

In vivo pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for AT2 receptors.

L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[[2'-(N-(3-methyl-1-butoxy) carbonylaminosulfonyl)[1,1']-biphenyl-4-yl]methyl]-3H-imidazo[4,5- b]pyridine) is a potent, orally active, nonpeptide angiotensin II receptor antagonist. Conscious rats and dogs were dosed p.o. and i.v.; in both species the plasma bioequivalents are similar at the angiotensin AT1 and AT2 receptor sites indicating balanced activity is maintained in vivo. L-163,017 prevents the pressor response to intravenous (i.v.) angiotensin II in the conscious rat, dog, and rhesus monkey. L-163,017 also significantly reduces blood pressure in a renin-dependent model of hypertension, similar to an angiotensin converting enzyme inhibitor (Enalapril) and an angiotensin AT1 receptor-selective antagonist (L-159,282). These studies indicate that neither the angiotensin AT2 receptor nor bradykinin is important in the acute antihypertensive activity of angiotensin converting enzyme inhibitors or angiotensin II receptor antagonists.

In vivo pharmacology of L-159,913, a new highly potent and selective nonpeptide angiotensin II receptor antagonist.

The present study was designed to characterize the in vivo pharmacology of L-159,913 (4-[[2'-(N-benzoylsulfamoyl)biphenyl-4-yl]-5butyl-2,4-dihydr o-2- [2-(trifluoromethyl)phenyl]-3H-1,2,4-triazol-3-one); a potent All receptor antagonist. In normotensive rats, dogs, rhesus monkeys, and chimpanzees, L-159,913 inhibited All-induced elevations in blood pressure. In conscious rats, the relative potencies (ED50) were 0.51 mg/kg i.v. and 0.72 mg/kg p.o. Duration of action with single i.v. or p.o. doses exceeded 6 hr in rats. L-159,913 was 3 times less potent than losartan in rats and equipotent to losartan in monkeys. All induced elevation of plasma aldosterone in rats was also inhibited by L-159,913. L-159,913 was antihypertensive in high renin hypertensive rats (aortic coarctation). The maximum hypotensive response to an acute dose of L-159,913 (10 mg/kg, po) was equal to that of enalaprilat (0.3 mg/kg, iv) in this renin dependent animal model. In conscious normotensive dogs, L-159,913 had a moderate diuretic, natriuretic and kaliuretic response with no effect on glomerular filtration rate, effective renal plasma flow or filtration fraction, suggesting a tubular site of action. L-159,913 is a selective and potent All receptor antagonist with good oral activity, long duration of action and antihypertensive efficacy.

In vivo pharmacology of a novel AT1 selective angiotensin II receptor antagonist, MK-996.

MK-996, N-(4'-(5,7-dimethyl-2-ethyl-3H-imidazo[4,5-b]pyridin-3-yl- methyl)1,1'-biphenyl-2-yl)-sulfonylbenzamide, is a potent, orally active, highly selective, nonpeptide angiotensin II (AII) receptor antagonist. MK-996 prevents the pressor response to intravenous AII in the conscious rat, dog, and rhesus monkey (ED50, mg/kg; oral/intravenous = 0.067/0.014, 0.035/0.017, and 0.1/0.036, respectively). In the anesthetized chimpanzee, MK-996 (1 mg/kg, iv) produces 100% (peak) inhibition of the AII pressor response and is still active (52%) at 24 h. To our knowledge this pharmacologic profile in the rat, dog, rhesus monkey, and chimpanzee presents the least species variability of any AII receptor antagonist yet described. Responses to methoxamine and arginine vasopressin are not affected by MK-996. In aortic coarcted (high renin) rats, MK-996 (3 mg/kg, by mouth) reduces blood pressure to normotensive (< 120 mm Hg) levels without reflex tachycardia. This dose of MK-996 reduces blood pressure to approximately the same level as both losartan (3 mg/kg, by mouth) and enalapril (3 mg/kg, by mouth) in this model. The duration of antihypertensive activity of MK-996 is similar to enalapril and shorter than losartan at the doses tested. Additionally, in the rat MK-996 does not potentiate the vasodepressor response to bradykinin and completely prevents the ability of AII to stimulate an increase in plasma levels of aldosterone. Therefore, MK-996 is a potent, orally active, nonpeptide AII receptor antagonist with a long duration of action, little species variability, and anti-hypertensive activity.

Effects of BQ-123 on renal function and acute cyclosporine-induced renal dysfunction.

Cyclosporin A (CsA) is widely used to suppress graft rejection following transplantation and in the treatment of a variety of autoimmune diseases. Therapy with CsA is often accompanied by adverse effects which include hepatotoxicity, hypertension, and nephrotoxicity. The role of endothelin (Et) in CsA-induced nephrotoxicity has been the subject of recent investigations. BQ-123 is a recently discovered Et receptor antagonist which is selective for the EtA receptor. In the present study, BQ-123 was used to further characterize the role of Et in CsA-induced nephrotoxicity. All experiments were performed in Inactin (100 mg/kg, i.p.) anesthetized male Munich-Wistar rats (250 to 350 g). Animals were prepared for the recording of blood pressure (MAP) and heart rate (HR) as well as the measurement of urine volume (UV), UNaV, UKV, GFR and effective renal plasma flow (ERPF). GFR and ERPF were estimated from the clearance of 14C-inulin and 3H-PAH, respectively. On the day of the experiment, animals were randomly assigned to one of three groups and treated according to the following protocols: Group 1, pretreatment with BQ-123 (1 mg/kg, i.v. bolus with 0.1 mg/kg/hr i.v. infusion) followed by treatment with vehicle (cremophor; 0.15 ml, i.v.); Group 2, pretreatment with normal saline (1.0 ml/kg; plus 25 microliters/min infusion) followed by treatment with CsA (20 mg/kg, i.v.); and Group 3, pretreatment with BQ-123 (same as group 1) followed by CsA (20 mg/kg, i.v.). BQ-123 administration alone produced transient changes in several of the measured parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Quality assurance/peer review for recredentialing/relicensure in New York State.

In consultation with the State Health Department, the New York State Society of Anesthesiologists has developed a Model Program of Quality Assurance/Peer Review for Recredentialing/Relicensure. The Model Program was developed to provide a standardized peer review process through which anesthesiologists practicing in New York State can be recredentialed and relicensed when recredentialing becomes a requirement for relicensure of New York State physicians. The program of recredentialing and relicensure is part of the agenda of the Governor's office, the State Health Department, and the State Education Department to improve the quality of healthcare in New York State through (1) identifying physicians whose quality of care is below reasonable thresholds, (2) assuring that these physicians receive appropriate remedial education or training, and (3) generally raising the quality of healthcare provided by all physicians practicing in New York State.

Heart failure augments the cardiovascular and renal effects of neutral endopeptidase inhibition in rats.

We compared the cardiovascular and renal actions of the neutral endopeptidase (NEP) inhibitor, SQ 28,603, in normal rats and in rats with healed myocardial infarcts. The infarcted rats were studied in the conscious state 8 weeks after ligation of the left main coronary artery and 4 h after placement of cardiovascular and renal catheters. Infarct size was 39 +/- 1.2% of left ventricle circumference; right ventricle and lung weight to body weight ratios were twice those of normal rats. These postmortem values were shown to be associated with elevated left ventricular end diastolic pressure and high plasma atrial natriuretic peptide (ANP) concentration in separate groups of rats. SQ 28,603 at 100 mumol/kg intravenously (i.v.) caused urine volume and sodium excretion to increase by 79 +/- 11 microliters/min and 8.2 +/- 1.4 microEq/min, respectively, 20 min after injection in infarcted rats; these changes were significantly greater than those in normal rats (12 +/- 5 microliters/min and 1.6 microEq/min, respectively). Thoracic venous pressure decreased by 1.9 +/- 0.4 mm Hg 80 min after SQ 28,603 in infarcted rats and by only 0.1 +/- 0.1 mm Hg in normal rats (p less than 0.05 vs. infarcted rats). SQ 28,603 had no effects on mean arterial pressure (MAP), cardiac output (CO), or glomerular filtration rate (GFR). The observation that NEP inhibition has more pronounced effects in animals with high ambient ANP level than in those with normal ANP is consistent with previous studies in a variety of animal models and supports the concept that NEP inhibition potentiates endogenous ANP.

Hypotension induced by growth-hormone-releasing peptide is mediated by mast cell serotonin release in the rat.

Growth-hormone-releasing peptide (GH-RP-6) is a synthetic hexapeptide that selectively releases growth hormone (GH) when administered to a number of animals species. In the rat, maximal GH release occurs after intravenous administration of 100 micrograms/kg GH-RP-6. Intravenous administration of 5 mg/kg GH-RP-6 produced 100% lethality within 2-5 min of drug administration. Further investigative studies demonstrated that the lethal effect of GH-RP-6 was preceded by an initial hypertensive episode, followed by a rapid, profound hypotension and bradycardia. The rise and fall in blood pressure also were observed in pithed rats treated with GH-RP-6, suggesting that the central nervous system was not responsible for the changes in blood pressure. However, the GH-RP-6-induced bradycardia was not observed in pithed rats, indicating the fall in heart rate was mediated through a central reflex mechanism. No direct effects of GH-RP-6 were seen in the isolated rat aorta or canine saphenous vein. Pretreatment of conscious rats with naloxone (10 mg/kg, iv), an opiate receptor antagonist, did not prevent the hypertensive response to GH-RP-6, but the hypotension and lethality were attenuated. Pretreatment with cyproheptadine (2.5 mg/kg, iv), a dual serotonin/histamine antagonist, or ketanserin (3 mg/kg, iv), a selective serotonin antagonist, prevented the GH-RP-6-induced hypotension and lethality. Cyproheptadine unmasked a 40 mm Hg rise in mean arterial pressure which persisted for over 10 min. In addition, degranulation of mast cells with compound 48/80 inhibited the toxicity of GH-RP-6, suggesting that mast cell degranulation and the subsequent release of autocoids is responsible for the cardiovascular effects of GH-RP-6. In vitro, GH-RP-6 (10(-5) - 10(-3) M) produced a concentration-related release of histamine from rat peritoneal mast cells. However, the histamine release by GH-RP-6 (10(-4) M) was not inhibited by naloxone (10(-4) M) in isolated mast cells, suggesting either that peritoneal mast cells are not responsible or that the mast cell degranulation in vitro is not opiate mediated. In conclusion, it appears that GH-RP-6 degranulates mast cells releasing serotonin, which produces hypotension, bradycardia, and death. This degranulation of mast cells is apparently inhibited by naloxone in vivo, suggesting that opiate receptors are involved in the hypotension and lethality associated with the administration of GH-RP-6.

Hypotension induced by vasopressin antagonists in rats: role of mast cell degranulation.

SK&F 101926, a synthetic peptide, is a potent antagonist of vasopressin at both the V2 and the V1 receptors. Following intravenous administration of SK&F 101926 (5 mg/kg), mean arterial pressure (MAP) immediately fell 75 mm Hg. Heart rate increased approximately 50 beats/min. Cutaneous flushing and cyanosis appeared approximately 2 to 5 min after the SK&F 101926 administration. Three of the five rats died within 40 min with no improvement in either color or MAP. The two surviving animals slowly recovered from these symptoms. The hypotension and flushing recorded in these studies resembled the effects during hypotensive shock. SK&F 101926 degranulated rat peritoneal mast cells in vitro as measured by the liberation of histamine. Analogs of SK&F 101926 were identified having reduced activity to release histamine from mast cells in vitro. The activity of these analogs to release histamine in vivo was also tested, as reflected by rat paw edema. A positive correlation was found between the potency to produce edema in vivo and the potency to release mast cell histamine in vitro (r = 0.94, p less than 0.05). In addition, compounds that released mast cell histamine and induced rat paw edema also produced hypotension and death when administered intravenously, while analogs which produced minimal histamine release in vitro produced minimal or no cardiovascular changes or lethality in vivo at the same dosages (5 mg/kg). Finally, cyproheptadine (10 mg/kg), an antagonist at both the serotonin and the histamine receptors, blunted the effects of SK&F 101926 on MAP and blocked the lethality. Pretreatment with a combination of histamine (H1 and H2) antagonists provided little protection against the SK&F 101926-induced toxicity. These data indicate that the cardiovascular toxicity of SK&F 101926 (and related peptides) is mediated via the release of autocoids from mast cells. Serotonin appears to play a major role in mediating the cardiovascular toxicity of SK&F 101926.

Endogenous opioids and ventilatory adaptation to prolonged hypoxia in goats.

To investigate whether endogenous opioid peptides mediate time-dependent changes in ventilatory control during prolonged hypoxia, we studied four adult goats at rest during 14 days at simulated high altitude in a hypobaric chamber (PB approximately 450 Torr). Arterial PCO2 fell during the first several hours of hypoxia, remained stable over the next 7 days, and then rose slightly (but without statistical significance) by day 14. Ventilatory responsiveness to CO2 increased during the first week of hypoxia. By day 14, while still greater than control, the ventilatory response to CO2 was less than that observed on day 7. Immunoactive beta-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO2 to the level observed during the first week of acclimatization. We conclude that in adult goats, time-dependent changes in ventilatory response to CO2 during acclimatization to prolonged hypoxia are not primarily attributable to alterations in endogenous opioid peptide activity.

Hemodynamics of obesity: influence of pattern of adipose tissue cellularity.

Direct quantitation of blood flow with radioactive microspheres in conscious spontaneously obese rats indicated that the development of obesity was associated with an elevated cardiac output and stroke volume, a normotensive blood pressure, and a reduced total peripheral resistance when directly comparing obese rats with their lean counterparts. Obesity was also associated with increased blood flow and decreased regional vascular resistance in a variety of vascular beds, whereas cardiac index and total peripheral resistance per unit of body weight were similar between groups. When corrected for tissue weight, unique alterations in flow and resistance were observed in the adipose tissue. When expressed as resistance per organ, the greatest relative alterations in vascular resistance with the development of obesity also occurred in the adipose tissue. Furthermore, localized adipose tissue expansion through cellular hypertrophy was consistently associated with a different pattern of blood flow and vascular resistance than adipose tissue that expanded through both cellular hypertrophy and hyperplasia, implying an association between depot cellularity and its hemodynamic profile.

Dental complications during and after tracheal intubation.

Surveyed were 133 directors of training programs in anesthesiology. The directors reported an average incidence of 1:1,000 dental injuries during or after 1,135,212 tracheal intubations in 1 year. A well-documented dental evaluation before delivery of anesthetics and appropriate precautions and protective devices during intubation will prevent most dental trauma related to the delivery of general anesthetics. Also, early use of dental and risk management services often will ensure timely resolution of such problems.

Effect of platelet activating factor (PAF) on blood flow distribution in the spontaneously hypertensive rat.

A dose-dependent decrease in mean arterial blood pressure was produced in spontaneously hypertensive rats by intravenous PAF infusion. Heart rate was monitored, while cardiac index and regional blood flow were quantitated during maintenance of the PAF-induced hypotension using the radioactive microsphere method. Our results suggest that PAF administration is associated with specific changes in vascular resistance, since estimated blood flow was decreased to certain organs or tissues, but remained unchanged in others. Therefore, the hypotension observed during PAF infusion is dose-dependent, and is contributed to by decreases in vascular resistance in specific organs.

Hemodynamic effects of weight reduction in the obese rat.

The effect of defined increments of weight loss on hemodynamics has been investigated in conscious, unrestrained, spontaneously obese rats. Obese rats were subjected to a calorically restricted diet and were used for experimentation on achieving a 10, 20, or 30% reduction in body weight. After monitoring resting blood pressure and heart rate, radioactive microspheres were infused for determination of blood flow distribution. Of 10 organs sample, only heart, liver, kidneys, and 2 adipose tissue depots exhibited significant decreases in weight associated with body weight reduction. Mean arterial blood pressure remained unchanged, while stroke volume, left ventricular work, and cardiac output decreased significantly. Blood flow decreased to kidneys, testes, and adipose tissue through a 30% reduction in body weight, but the fractional distribution of cardiac output decreased only to adipose tissue. Therefore the large decreases in renal and adipose tissue blood flow during weight reduction may contribute to the associated decrease in cardiac output. Of those vascular beds examined, however, both absolute and relative blood flow decreased only to adipose tissue, thus denoting the influence of fat mass on hemodynamics during obesity.

Respiration of chemodenervated goats in acute metabolic acidosis.

In awake goats before and after ablation of carotid bodies (CBx) we studied the effect of acute metabolic acidosis (AMA) produced by intravenous infusion of HCl on composition of arterial blood and CSF, and on ventilatory responsiveness to hyperoxic CO2 rebreathing AMA caused decrease in PaCO2 (breathing air at rest) indicating that alveolar ventilation was increased relative to CO2 production; position of CO2 response curves was shifted toward lower values of PCO2. These changes were similar before and after CBx, though the levels of PCO2 in arterial blood during air breathing at rest, and in expired gas at a given level of ventilation during CO2 rebreathing, were higher after CBx. We conclude that a respiratory adaptation to AMA does occur in goats deprived of peripheral chemoreceptors, and is probably mediated by the central chemoreceptors.

Strength and cycle time of high-altitude ventilatory patterns in unacclimatized humans.

Respiration was monitored with magnetometers in 12 healthy supine young adults at sea level and in an altitude chamber at simulated high altitudes of 8,000, 9,000, 11,000, and 14,000 ft. Periodic breathing that was strong enough to include apnea at the time of minimum ventilation was seen in all subjects at high altitude. Cycle time of periodic breathing ranged from 12 to 34 s. On average across the population the incidence of periodic breathing increased with altitude. Cycle time of the periodic pattern increased as strength of the pattern increased. After normalizing to a standard pattern strength, cycle time decreased as altitude increased. The study included two series of experiments, the second occurring 3 wk after the first and involving seven of the same subjects. The standard cycle time at 14,000 ft for each subject in the second series was the same as in the first series to within, on the average, 6%. Each subject studied at 11,000 ft in both series reproduced his cycle time to within, on the average, 9%. The variation of standard cycle time for a given subject is less than the variation across the population, indicating characteristic cycle times for some individuals (one-way analysis of variance, P less than 0.025).

Segmental levels of anaesthesia following the extradural injection of 0.75% bupivacaine at different lumbar spaces in elderly patients.

Segmental anaesthesia levels were determined in 80 elderly patients following the extradural injection of 0.75% bupivacaine 15 ml at four separate lumbar interspaces. Mean levels were T11 in the L5-S1 group, T7 in the L4-5, T5 in L3-4 and T3 in the L2-3 group (P less than 0.001). Varying the lumbar interspace at which the extradural anaesthesia is performed is recommended as a means of adjusting the levels of anaesthesia for different surgical procedures.