Effect of pediatric surgical practice on the treatment of children with appendicitis

OBJECTIVE

Acute appendicitis in children is managed by both general surgeons (GSs) and pediatric surgeons (PSs). Our objective was to investigate the economics of surgical care provided by either GSs or PSs for appendicitis.

METHODS

The outcome of children within our state who underwent operative treatment for appendicitis (January 1994 to June 1997) by board-certified GSs were compared with the results of PSs. Data were sorted according to patient age and diagnosis according to the International Classification of Diseases, Ninth Revision. Analysis of variance was performed on continuous data, and chi(2) analysis was performed on nominal data; data are depicted as mean +/- standard error of the mean.

RESULTS

GSs (n = 2178) managed older children when compared with PSs (n = 1018; 11.0 +/- 0.1 vs 9.1 +/- 0.1 years) and less frequently treated perforated appendicitis (18.8% vs 31.9%). Independent of diagnosis (simple or perforated appendicitis), younger children (0-4 years, 5-8 years, and 9-12 years) who were treated by PSs had a significantly shorter hospital stay and/or decreased hospital charge when compared with those who were treated by GSs. However, older children (13-15 years) seemed to have comparable outcomes.

CONCLUSIONS

Younger children with appendicitis have reduced hospital days and charges when they are treated by PSs.

Prenatal diagnosis of esophageal atresia using sonography and magnetic resonance imaging

BACKGROUND

The diagnosis of esophageal atresia may be suspected on prenatal ultrasound scan in fetuses with a small or absent stomach or unexplained polyhydramnios. However, these findings are thought to have a low positive predictive value and clinical decisions affecting timing or site of delivery may be made erroneously. The authors evaluated the accuracy of fetal sonography followed by magnetic resonance imaging (MRI) for the diagnosis of this lesion.

METHODS

Fetuses considered to be at risk for esophageal atresia based on detailed obstetric sonography underwent fetal MRI using a single-shot rapid-acquisition technique, and the T(2)-weighted images were evaluated prospectively. Scans were considered to be positive if the proximal esophagus was dilated, and the distal esophagus was not seen and negative if the esophagus was visualized throughout its length.

RESULTS

Ten fetuses underwent MRI scanning. All had a small or absent stomach bubble with unexplained polyhydramnios. Four scans were considered to be negative for esophageal atresia; all 4 were found to have a normal esophagus after delivery. Six scans were considered to be positive; 5 had esophageal atresia (2 with tracheoesophageal fistula and 3 without), and one had a neurologic syndrome with a normal esophagus.

CONCLUSIONS

Magnetic resonance imaging appears to be accurate for establishing or ruling out a prenatal diagnosis of esophageal atresia, and should be considered in fetuses who are at high risk based on ultrasound findings.

A prospective study of botulinum toxin for internal anal sphincter hypertonicity in children with Hirschsprung's disease

BACKGROUND

Internal anal sphincter hypertonicity with nonrelaxation can cause persistent constipation and obstructive symptoms in children after surgery for Hirschsprung's disease. Intractable symptoms traditionally have been treated with anal myectomy, which may be ineffective or complicated by long-term incontinence. The authors evaluated prospectively the use of intrasphincteric botulinum toxin for these patients.

METHODS

Eighteen children were studied (age 1 to 13; median, 4 years). Botulinum toxin was injected (total dose 15 to 60 U) into 4 quadrants of the sphincter. Resting sphincter pressure was measured in 14 patients before and after injection. Ten have had 1 to 5 additional injections (total dose, 30 to 60 U per injection).

RESULTS

Four patients had no improvement in bowel function, 2 had improvement for less than 1 month, 7 had improvement for 1 to 6 months, and 5 had improvement more than 6 months. Nine of those with symptomatic improvement longer than 1 month had pressures measured, with a documented decrease in 8. Five with no significant clinical improvement had pressure measurements, with a decrease in 3. There were no adverse effects associated with botulinum toxin injection. Four children had new encopresis postinjection, which was mild and resolved in each case.

CONCLUSIONS

Intrasphincteric botulinum toxin is a safe and less-invasive alternative to myectomy for symptomatic internal sphincter hypertonicity. Persistent symptoms, despite a fall in sphincter pressure, suggest a nonsphincteric etiology. Repeat injections often are necessary for recurrent symptoms.

Pediatric surgery on the Internet: is the truth out there?

BACKGROUND

The enormous amount of unmonitored medical information on the Internet prompted this investigation into the quality of pediatric surgery information on the Internet.

METHODS

The Internet was searched for information on diaphragmatic hernia (CDH), abdominal wall defects (AWD), pediatric inguinal hernia (IH), and pectus excavatum (PE). Websites were characterized, classified, and evaluated for completeness, accuracy and bias toward or against the medical profession.

RESULTS

A total of 141 websites were evaluated (N(CDH) = 37, N(AWD) = 49, N(IH) = 26, N(PE) = 29). A total of 59.6% targeted medical professionals, and 46.8% targeted the lay population. A total of 58.2% described symptoms and diagnosis. Etiology, pathology, surgery, postoperative course, and prognosis each were addressed by under 40%. A total of 58.2% were accountable for the information presented. A total of 93.1% were incomplete, 75.7% contained accurate information, and 97.7% were positive or neutral toward medical treatment. Among diagnoses, CDH had the highest percentage of websites owned by academic institutions. PE had the highest percentage of websites owned by lay people. PE websites also were the least accurate.

CONCLUSIONS

Internet information on pediatric surgery varies significantly in quality. Lay people own most websites targeted at the lay audience, and the information may not reflect the opinions of most pediatric surgeons. Increasing use of the Internet by parents seeking medical information warrants an organized approach to ensure complete and accurate information online.

One-stage Soave pull-through for Hirschsprung's disease: a comparison of the transanal and open approaches

PURPOSE

The authors reviewed their experience using the transanal Soave technique, to determine (1) if it offers any advantages over the standard open approach and (2) whether routine laparoscopic visualization is necessary.

METHODS

The case reports of 37 consecutive children less than 3 years old undergoing Soave pull-through were reviewed. Patients were excluded from analysis if they had total colon disease or had a previous colostomy. The patients were divided into 3 groups: open Soave (OS, n = 13), transanal Soave with routine laparoscopic visualization (LVS, n = 9), and transanal Soave with selective laparoscopy or minilaparotomy (TAS, n = 15). Cost was calculated based on hospital stay, operating room time, and use of laparoscopic equipment.

RESULTS

In the TAS group, suspicion of a longer segment led to the selective use of laparoscopy with or without biopsy in 2 children, and the use of a small umbilical incision for mobilization of the splenic flexure in 2. There were no differences among groups with respect to age, weight, gender, transition zone, operating time, blood loss, intraoperative complications, enterocolitis, or stricture or cuff narrowing. Hospital stay was significantly longer in the OS group (median, 7 days; range, 3 to 47) than the LVS (median, 1; range 1 to 6) or TAS (median, 1, range, 1 to 3) groups. Cost (in thousands of dollars) was also higher in the OS group (median, 6.9; range, 3.9-25.7) than the LVS (median, 3.9; range, 3.6 to 6.4) or TAS (median, 3.4; range, 2.2 to 9.4) groups. Repeat surgery was necessary for 4 OS patients: 2 adhesive small bowel obstructions (1 of whom died), 1 twisted pull-through, and 1 recurrent aganglionosis. Three TAS patients required repeat surgery: 1 twisted pull-through, 1 anastomotic leak, and 1 cuff narrowing.

CONCLUSIONS

These data suggest that the transanal pull-through is associated with a significantly shorter hospital stay and lower cost than the open approach, without an increased risk of complications. Because there is no intraabdominal dissection, there probably is a lower incidence of adhesive bowel obstruction. Routine laparoscopic visualization or minilaparotomy is not necessary but should be used in children who are at higher risk for long segment disease.

Routine insertion of a silastic spring-loaded silo for infants with gastroschisis

BACKGROUND/PURPOSE

Gastroschisis traditionally is managed by emergency operating room closure (EC), with a silo reserved for cases that cannot be closed primarily. The authors recently began using routine insertion of a SILASTIC (Dow Corning, Midland, MI) spring-loaded silo (SLS), followed by elective closure.

METHODS

A total of 43 consecutive neonates with gastroschisis were treated between 1993 and 1998.

RESULTS

Thirty patients underwent EC, and 13 underwent closure after insertion of a SLS (10 at bedside, 3 in the operating room). Eight infants treated by EC required staged repair. There were no differences with respect to gestational age, birth weight, gender, Apgar score, maternal age, or mode of delivery. Median length of stay was 32 days for EC and 25 days for SLS (P = .05). The SLS group required fewer days on a ventilator (4 v 6 days, P = .03) and had lower intraoperative (28 v 21, P = .02) and early postoperative peak airway pressures. The time to tolerate full feedings was 21 days for SLS and 27 days for EC (P = .07). The SLS group had fewer complications and a lower median hospital charge ($71,498 v $85,147; P = .05).

CONCLUSION

SLS followed by elective repair permits gentle, gradual reduction of the viscera. When compared with EC, SLS is associated with significantly lower airway pressures, earlier extubation, fewer complications, and decreased length of stay and hospital charges.

Laparoscopic versus open splenectomy in children

BACKGROUND

The authors have reviewed their initial experience with laparoscopic splenectomy (LS) to identify the indications, success rate, and complications associated with this procedure compared with a series of children undergoing open splenectomy (OS) during the same time period.

METHODS

The records of 51 children who underwent splenectomy from 1993 through 1998 were reviewed retrospectively.

RESULTS

Thirty-five patients aged 1 to 17 years (mean, 9.4 years) underwent LS for the following indications: ITP (n = 20), sickle cell disease or thalassemia (n = 6), hereditary spherocytosis (n = 5), other hematologic disorders (n = 4). Seventeen patients aged 2 to 17 years (mean, 11.8 years) underwent OS during the same time period for ITP (n = 4), sickle cell disease or thalassemia (n = 4), hereditary spherocytosis (n = 5), and other indications (n = 4). Concomitant cholecystectomy was performed in 4 of 35 LS and 4 of 17 OS. Accessory spleens were identified in 10 of 35 LS and 2 of 17 OS cases. Eleven spleens were enlarged in the LS group, and 8 were enlarged in the OS group. One LS required conversion to an open procedure because the spleen did not fit in the bag. No other cases were converted. Median estimated blood loss was 50 mL for both the LS and OS groups. The only intraoperative complication in the LS group was a splenic capsular tear, which had no effect on the successful laparoscopic removal of the spleen. No patient in either group required a blood transfusion. The LS patients had a shorter length of hospital stay (1.8 +/- 1 versus 4.0 +/- 1 day, P = .0001). Total hospital charges were not significantly different. Follow-up ranged from 6 to 40 months. One LS patient died 47 days postoperatively from unrelated causes. Two LS patients had recurrent ITP; accessory spleens were found in one and resected laparoscopically.

CONCLUSION

LS in children can be performed safely with a low conversion rate (2.9%) and is associated with a shorter hospital stay and comparable total hospital cost when compared with OS.

Intestinal obstruction after lung transplantation in children with cystic fibrosis

BACKGROUND/PURPOSE

Distal intestinal obstruction syndrome (DIOS) occurs in 15% of patients with cystic fibrosis (CF). The authors reviewed their experience to determine the incidence, risk factors, and natural history of adhesive intestinal obstruction and DIOS after lung transplantation.

METHODS

Eighty-three bilateral transplants were performed in 70 CF patients between January 1990 and September 1998. All were on pancreatic enzymes preoperatively, and none had preoperative bowel preparation. Fifty-six patients (80%) had prior gastrostomy (n = 54) or jejunostomy (n = 2). Eighteen patients (25.7%) had a previous laparotomy for meconium ileus (n = 8), fundoplication (n = 4), liver transplant (n = 1), jejunal atresia (n = 1), Janeway gastrostomy takedown (n = 1), pyloromyotomy (n = 1), free air (n = 1), or appendectomy (n = 1).

RESULTS

After lung transplantation, 7 patients (10%) required laparotomy for bowel obstruction (6 during the same hospitalization, and 1 during a subsequent hospitalization). The causes of obstruction were adhesions only (n = 1), DIOS only (n = 2), and a combination of DIOS and adhesions (n = 4). Adhesiolysis was performed in the 5 patients with adhesions, and a small bowel resection was also performed in 1 patient. DIOS was treated by milking secretions distally without an enterotomy (n = 3) with an enterotomy and primary closure (n = 1) or with an end ileostomy and mucus fistula (n = 2). Five had recurrent DIOS early postoperatively. One resolved with intestinal lavage, 2 were treated successfully with hypaque disimpaction, and 2 underwent reoperation; 1 required an ileostomy. The most important risk factor for posttransplant obstruction was a previous major abdominal operation. Obstruction occurred in 7 of 18 (39%) who had undergone a prior laparotomy versus 0 of 52 who had not (P < .001, chi2).

CONCLUSIONS

(1) The incidence of intestinal obstruction is high after lung transplantation in children with CF. (2) Previous laparotomy is a significant risk factor. (3) Recurrent obstruction after surgery for this condition is common. (4) Preventive measures such as pretransplant bowel preparation and early postoperative bowel lavage may be beneficial in these patients.

Transanal one-stage Soave procedure for infants with Hirschsprung's disease

PURPOSE

Many centers perform a one-stage pull-through procedure for Hirschsprung's disease (HD) diagnosed in infancy. The authors have developed a one-stage pullthrough procedure using a transanal approach that eliminates the need for intraabdominal dissection.

METHODS

Nine children aged 3 weeks to 18 months with biopsy-proven HD underwent a transanal pull-through procedure over a 13-month period. A rectal mucosectomy was performed starting 0.5 cm proximal to the dentate line, and extending proximally to the level of the intraperitoneal rectum. In the first eight children, intraperitoneal position was confirmed with a laparoscope placed through a 3- to 5-mm port in the base of the umbilicus. The muscular sleeve was divided circumferentially to allow full-thickness mobilization of the rectosigmoid junction. Manual transanal traction permitted direct visualization and division of mesenteric vessels with transanal mobilization above the transition zone. Ganglion cells were confirmed by frozen section, and the bowel was transected. The rectal muscular cuff was divided longitudinally, and the anastomosis was completed. The laparoscope confirmed orientation and adequate hemostasis. In a ninth patient, the identical procedure was performed, but with the laparoscope used only for confirmation at the end of the procedure.

RESULTS

Operative time, including frozen sections, averaged 194 minutes (range, 169 to 250 minutes), and the average length of bowel resected was 12 cm (range, 7.5 to 22 cm). Four of the nine patients were discharged on postoperative day (POD) 1, four on POD 2, and one patient with Down's syndrome was discharged on POD 6. Median follow-up was 6 months (range, 3 to 14 months). One death occurred 2.5 months postoperatively secondary to sudden infant death syndrome. Complications included postoperative apnea spells (n = 1), mild enterocolitis (n = 2), constipation (n = 1), anastomotic stricture(n = 1), and muscularcuff narrowing (n = 1); each responded to nonoperative management. Stool output has ranged from four to eight per day.

CONCLUSION

A one-stage pull-through for HD can be performed successfully using a transanal approach without intraperitoneal dissection. This procedure is associated with excellent clinical results and permits early postoperative feeding, early hospital discharge, and no visible scars.

Role of K+ATP channels and EDRF in reactive hyperemia in the hindquarters vascular bed of cats

The mechanism underlying reactive hyperemia was investigated in the feline hindquarters vascular bed under natural- and constant-flow conditions. A 30-s occlusion of the distal aorta produced a marked hyperemic increase in distal aortic blood flow that was attenuated by the ATP-sensitive K+ (K+ATP) channel blocking agent, glibenclamide. When blood flow to the hindquarters vascular bed was held constant with a pump, interruption of blood flow for 5- to 90-s periods produced reactive vasodilator responses that increased in magnitude and duration as the period of ischemia increased. The magnitude and duration of the reactive vasodilator responses were reduced by K+ATP channel antagonists and an inhibitor of nitric oxide synthase, whereas indomethacin had no significant effect. In the pulmonary vascular bed, under constant-flow, elevated tone conditions, a 30-s period of ischemia produced a small reactive vasodilator response and a larger secondary vasoconstrictor response. The present data suggest that reactive hyperemia in the hindquarters vascular bed is mediated by the opening of K+ATP channels and nitric oxide release and that the reactive hyperemic response is not pronounced in the pulmonary circulation.

Differential responses to angiotensin-(1-7) in the feline mesenteric and hindquarters vascular beds

Regional vascular responses to angiotensin (Ang)-(1-7), a heptapeptide derivative of Ang II were investigated in the feline hindquarters and mesenteric vascular beds under conditions of controlled flow. In the mesenteric vascular bed, injections of Ang-(1-7) in doses of 1, 3 and 10 micrograms produced dose-dependent decreases in mesenteric perfusion pressure whereas at doses of 30 and 100 micrograms, increases were observed. In contrast, in the hindquarters circulation, low doses produced increases while high doses produced decreases in perfusion pressure. In both vascular beds the degree of vasoconstriction was weak, being less than 1% of that elicited by Ang II. The vasoconstrictor effect of Ang-(1-7) in both the mesenteric and hindquarters vascular bed was blocked by DuP 753 (1 mg/kg i.v.), an Ang receptor subtype 1 (AT1) antagonist. The vasodilator responses in both vascular beds were partially blocked by the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (100 mg/kg i.v.) but were unaffected by the cyclooxygenase inhibitor, meclofenamate (2.5 mg/kg i.v.). The present results show that in the peripheral vascular bed of the cat, Ang-(1-7) causes vasodilation or modest vasoconstriction, depending on the dose and the regional vascular bed studied. The present data also suggest that the vasodilator effect of the peptide may be mediated in part by the release of endothelium-derived relaxing factor and the vasoconstrictor effect by activation of the AT1 receptor subtype.

Analysis of the inhibitory effects of DuP 753 and EXP 3174 on responses to angiotensin II in the feline hindquarters vascular bed

The effects of DuP 753 and EXP 3174, nonpeptide angiotensin II type 1 antagonists, on responses to angiotensin II were investigated in the hindquarters vascular bed of the cat. Under constant flow conditions, injections of angiotensin II into the hindquarters perfusion circuit elicited dose-dependent increases in perfusion pressure. Responses to the peptide were stable with respect to time, did not exhibit tachyphylaxis, and 2-n-butyl-4-chloro-5-hydroxymethyl-1-[2'-(1H-tetrazol-5-yl)biph eny l-4-yl]methyl]methyl]imidazole (DuP 753) in doses of 1 and 2.5 mg/kg decreased vasoconstrictor responses to angiotensin II in a competitive manner, with a longer duration of action at the higher dose. DuP 753 had no significant effect on vasoconstrictor responses to vasopressin, norepinephrine, neuropeptide Y or 11 alpha,6 alpha-epoxymethano-9 alpha,11 alpha-dideoxy-prostaglandin F2 alpha, on biphasic responses to endothelin-1, or on vasodilator responses to acetylcholine. 2-n-Butyl-4-chloro-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]im idazole-5-carboxylic acid (EXP 3174) also decreased responses to angiotensin II without altering responses to norepinephrine, vasopressin, U46619 or endothelin-1. The inhibitory effect of EXP 3174 was surmountable; however, large doses of angiotensin II were required, and the blockade was long in duration. The effects of DuP 753 and EXP 3174 on responses to angiotensin II and angiotensin III were similar, and when EXP 3174 was administered in doses of 0.1 and 0.05 mg/kg i.v., the blockade was overcome and the dose-response curves for angiotensin II were shifted to the right in a parallel manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Penile erections induced by vasoactive intestinal peptide and sodium nitroprusside

The use of vasoactive intestinal peptide (VIP), sodium nitroprusside (SNP), and the reference combination of papaverine, prostaglandin E1, and phentolamine was studied in 22 adult cats. The maximal erectile response (intracavernous pressure, penile length, and rigidity) was produced by intracavernous injection of a combination of 1.65 mg papaverine, 0.5 micrograms PGE1, and 25 micrograms phentolamine. This combination was considered as "control" in order to compare the effect of other agents. VIP and SNP increased the intracavernous pressure and caused erection in a dose-dependent manner with a maximal response obtained with 5 micrograms VIP or 10 micrograms SNP. The duration of peak erection and the total duration of drug effect were significantly shorter with VIP and SNP than with the reference combination (P < 0.01). Epinephrine (30 micrograms) reversed the effects of SNP and significantly shortened the duration of peak action and total effect (P < 0.05). This study supports the use of an in vivo feline model for the evaluation of vasoactive agents and demonstrates that the intracavernous injection of either VIP or SNP can induce penile erection in the adult cat.

Analysis of systemic and pulmonary vascular responses to PACAP and VIP: role of adrenal catecholamines

Systemic and pulmonary vascular responses to pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide with 68% sequence homology to vasoactive intestinal peptide (VIP), were investigated in the anesthetized cat. Intravenous injections of PACAP in doses of 0.1-3.0 nmol/kg produced decreases in arterial pressure (AP) at low doses and biphasic changes (decreases followed by increases) at higher doses, which were accompanied by increases in central venous pressure (CVP) and cardiac output (CO), and decreases and biphasic changes in systemic vascular resistance (SVR). In contrast, VIP in doses of 0.1-3.0 nmol/kg produced only dose-dependent decreases in AP and SVR and produced little change in CVP and CO. PACAP produced increased pulmonary arterial pressure (PAP), left atrial pressure (LAP), and increases in pulmonary vascular resistance (PVR). PACAP increased heart rate (HR) and right ventricular contractile force (RVCF), while VIP had no effect. Increases in AP and SVR in response to PACAP were changed to decreases following the administration of phentolamine or after adrenalectomy. Under constant flow conditions, PACAP and VIP produced dose-dependent decreases in lobar arterial pressure when tone was elevated, with PACAP being threefold more potent than VIP. Meclofenamate and nitro-L-arginine methyl ester (L-NAME) had no effect on pulmonary responses to the peptides. PACAP produced dose-dependent biphasic changes in hindquarters perfusion pressure, whereas VIP produced only decreases that were unchanged by indomethacin, L-NAME, and glibenclamide. Phentolamine and adrenalectomy eliminated the hindquarters pressor response to PACAP and D-Phe2-VIP, a VIP antagonist, reduced responses to VIP but not to PACAP. These data suggest that responses to PACAP and VIP are mediated by distinct receptors and that pressor responses to PACAP are due to the release of catecholamines from the adrenal gland.

Comparative effects of endothelin (ET-1) and U46619 on human saphenous vein and gastroepiploic artery, sources of human autologous grafts

The effects of endothelin (ET-1) on smooth muscle contractile activity were investigated and compared in human saphenous vein and gastroepiploic artery, vessels frequently used in revascularization procedures. ET-1 contracted saphenous vein and gastroepiploic artery in a concentration-dependent manner. The peptide produced a greater maximal effect in the vein than in the artery and, in both preparations, ET-1 was less efficacious than U46619, an agent which mimics the actions of thromboxane A2 at the thromboxane A2/prostaglandin H2 receptor. The contractile response to ET-1 declined spontaneously at a more rapid rate in the artery than in the vein. The present data indicate that ET-1 has significant contractile activity in both vessels which are used for coronary arterial bypass surgery and suggest that although, a weaker vasoconstrictor than U46619, the peptide could induce vasospasm in both graft vessels.

Analysis of responses to big endothelin in the hindquarters vascular bed of the cat

OBJECTIVE

To investigate vascular responses to the endothelin-1 (ET-1) precursor, human big endothelin 1-38 (big ET), in the peripheral vascular bed of the cat.

DESIGN

These studies were designed to investigate the hypothesis that bit ET is converted to an active peptide with properties similar to ET-1.

SETTING

Hindquarters vascular bed of the cat under conditions of controlled bloodflow; changes in perfusion pressure reflect changes in vascular resistance.

ANIMALS

Fifty-four adult mongrel cats.

INTERVENTIONS

Big ET, ET-1, the peptidases chymotrypsin, pepsin and cathepsin-D, and the metalloprotease inhibitor phosphoramidon.

MAIN RESULTS

Intra-arterial injections of big ET induced a slow-developing and sustained increase in hindquarters perfusion pressure which could be blocked by phosphoramidon. ET-1 (0.3 nmol), administered as a slow infusion over a 10-min period, produced a slowly developing increase in hindquarters perfusion pressure in a manner similar to that observed in response to injection of big ET. A bolus injection of ET-1 produced a biphasic response characterized by a transient decrease in pressure followed by an increase which was significantly greater in magnitude and more rapid in onset than the pressor response to big ET (0.3 nmol). After incubation of big ET with chymotrypsin, pepsin and cathepsin-D (each 5% weight/weight) for 30 mins at 37 degrees C, injection of activated big ET produced a biphasic response characteristic of the response to ET-1 with an initial transient decrease in pressure followed by a secondary increase in hindquarters perfusion pressure.

CONCLUSIONS

Big ET produces a phosphoramidon-sensitive pressor response which is similar to that produced by an infusion of ET-1. These data suggest that chymotrypsin, pepsin and cathepsin-D can convert big ET to an active peptide which elicits a biphasic response similar to that produced by ET-1.

Inhibitory effects of DuP 753 and EXP3174 on responses to angiotensin II in pulmonary vascular bed of the cat

The effects of the non-peptide antagonist DuP 753 and its metabolite EXP3174 on responses to angiotensin II were investigated in the pulmonary vascular bed of the intact-chest cat. Under conditions of controlled blood flow and constant left atrial pressure, injections of angiotensin II into the perfused lobar artery caused dose-related increases in lobar arterial pressure. Responses to angiotensin II were reproducible and were not changed by meclofenamate or prazosin, indicating that prostaglandin or norepinephrine release does not mediate or modulate pulmonary vascular responses to the peptide. DuP 753 (1-5 mg/kg iv) decreased responses to angiotensin II in a competitive manner, and the duration of the blockade was related to dose of the antagonist. DuP 753 had no significant effect on responses to U-46619, norepinephrine, serotonin, endothelin-1, vasopressin, or BAY K 8644. EXP3174 also decreased responses to angiotensin II without altering responses to agents that act by a variety of mechanisms. The inhibitory effect of EXP3174 (1 mg/kg iv) was not overcome by angiotensin II in the range of doses studied, and the shift to the right of the dose-response curve was nonparallel, suggesting that the blockade was noncompetitive. The blockade was long in duration, and, when the dose of EXP3174 was decreased to 0.1 mg/kg iv, the blockade was surmounted and the shift to the right of the dose-response relationship was parallel. DuP 753 and EXP3174 had little effect on mean baseline pressures in the cat.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of pulmonary and systemic vascular responses to platelet-activating factor in the cat

Pulmonary and systemic vascular responses to platelet-activating factor (PAF) were investigated in the anesthetized cat. Intravenous injections of PAF decreased arterial pressure, increased pulmonary arterial pressure, and caused small but significant decreases in right and left atrial pressures. A transient increase in cardiac output was followed by a secondary decrease, and heart rate was increased. Pulmonary vascular resistance (PVR) was increased, systemic vascular resistance (SVR) was reduced, and changes in PVR and SVR in response to PAF were blocked by the novel PAF receptor antagonist, BN 50730. Under constant-flow conditions PAF dilated the hindlimb vascular bed in a dose-related manner, whereas in the pulmonary lobar vascular bed, PAF caused dose-related increases in perfusion pressure. Hindlimb and lobar vascular responses to PAF were blocked by BN 50730 in a selective manner, whereas cyclooxygenase inhibitors had no effect on responses to the phospholipid mediator. Hindlimb vasodilator responses to PAF were reduced by N omega-nitro-L-arginine in a dose that blocked the response to acetylcholine but did not decrease responses to prostaglandin E1 or nitroprusside. Increases in lobar arterial pressure in response to PAF were not altered by treatment with a thromboxane receptor antagonist, when the lung was perfused with a low-molecular-weight dextran solution, or when ventilation to the lobe was interrupted. These data suggest that the release of cyclooxygenase products, activation of thromboxane A2 receptors, cellular aggregation, release of leukocyte or platelet mediators, or changes in bronchomotor tone do not contribute to the pulmonary vasoconstrictor response to PAF and that the hindlimb vasodilator response to the phospholipid mediator is dependent in part on the release of endothelium-derived relaxing factor.

Comparison of responses to sarafotoxins 6a and 6c in pulmonary and systemic vascular beds

Cardiovascular and pulmonary responses to sarafotoxin (S) 6a and S6c were investigated in the anesthetized cat. Intravenous injections of the peptides in doses of 0.1-1.0 nmol/kg caused decreases or biphasic changes in arterial pressure (AP) and increases in central venous pressure, pulmonary arterial pressure (PAP), and cardiac output (CO). Secondary decreases in CO were observed in response to higher doses, and biphasic changes in systemic (SVR) and pulmonary (PVR) vascular resistances were observed. Under constant-flow conditions, the peptides only increased pulmonary lobar arterial perfusion pressure and lobar vascular resistance. AP responses to S6a, S6c, endothelin (ET)-1, ET-2, vasoactive intestinal contractor (VIC), and Lys7-ET-1 were similar, whereas AP responses to S6b and ET-3 were similar. S6a, S6b, S6c, ET-1, ET-2, ET-3, VIC, Lys7-ET-1, and big ET-1 increased PAP. S6a and S6c increased distal aortic and superior mesenteric arterial (SMA) blood flow and caused biphasic changes at the highest doses. Under constant-flow conditions, S6a and S6c produced dose-dependent biphasic changes in hindquarters perfusion pressure. Changes in SVR and PVR in response to the peptide were not affected by hexamethonium, glyburide, or meclofenamate, indicating that responses are independent of autonomic reflexes, activation of ATP-regulated K+ channels, or release of cyclooxygenase products. In contrast, N-nitro-L-arginine methyl ester decreased hindquarters vasodilator response to S6a and S6c. The present data show that S6a and S6c produce both vasodilation and vasoconstriction in the systemic vascular bed and increase lobar vascular resistance and that hindquarters vasodilator responses are mediated, in part, by the release of endothelium-derived relaxing factor.

Differential effects of PACAP and VIP on the pulmonary and hindquarters vascular beds of the cat

Responses to pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide derived from ovine hypothalamus with 68% sequence homology with vasoactive intestinal polypeptide (VIP), were investigated in the pulmonary and hindquarters vascular beds of the anesthetized cat under conditions of controlled blood flow. Injection of the peptide into the perfused lung lobe under elevated tone conditions produced dose-dependent decreases in lobar arterial pressure that were accompanied by biphasic changes in systemic arterial pressure characterized by an initial decrease followed by a secondary increase in pressure. When compared with other vasodilator agents in the pulmonary vascular bed, the relative order of potency was isoproterenol greater than PACAP greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP. In the hindquarters vascular bed, intra-arterial injections of PACAP produced biphasic changes in hindquarters perfusion pressure characterized by initial decreases followed by secondary increases, which were accompanied by biphasic changes in systemic arterial pressure. In terms of relative vasodilator activity in the hindlimb, the order of relative potency was isoproterenol greater than acetylcholine greater than calcitonin gene-related peptide greater than VIP greater than PACAP. PACAP was the only agent that caused a secondary vasoconstrictor response in the hindlimb and produced biphasic changes in systemic arterial pressure. D-Phe2-VIP, a VIP receptor antagonist, blocked the hindquarters vasodilation in response to VIP but had no effect on responses to PACAP. The present investigation shows that PACAP produces pulmonary vasodilation, as well as dilation, and vasoconstriction in the systemic (hindlimb) vascular bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of SQ 29,548 on vasoconstrictor responses in the hindquarters vascular bed of the cat

The effects of SQ 29,548, a thromboxane (TX) receptor blocking agent, on vasoconstrictor responses were investigated under conditions of controlled blood flow in the hindquarters vascular bed of the cat. Intravenous injection of SQ 29,548 at a dose of 0.1 mg/kg had no significant effect on systemic arterial pressure but caused a significant reduction in hindquarters perfusion pressure. Injection of the TXA2 mimics, U44069 and U46619, into the perfusion circuit caused dose-dependent increases in hindquarters perfusion pressure with U46619 being approximately 3 times more potent than U44069. Following the administration of SQ 29,548, pressor responses to both U44069 and U46619 were reduced significantly, and the dose-response curves for both TXA2 mimics were shifted to the right in a parallel fashion. SQ 29,548 had no significant effect on the dose-dependent increases in hindquarters perfusion pressure in response to angiotensin II or BAY K8644, a nifedipine analog which promotes calcium entry. The TXA2 receptor blocking agent had no significant effect on increases in hindquarters perfusion pressure in response to angiotensin II or BAY K8644, a nifedipine analog which promotes calcium entry. The TXA2 receptor blocking agent had no significant effect on increases in hindquarters perfusion pressure in response to sympathetic nerve stimulation or injections of norepinephrine and tyramine. These findings suggest that SQ 29,548 blocks responses to the TXA2 mimics in a competitive manner, and that this inhibitory effect is selective.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of pulmonary and systemic vascular responses to cromakalim, an activator of K+ATP channels

Cardiovascular and pulmonary responses to cromakalim, a member of a novel class of antihypertensive agents that open ATP-sensitive K+ (K+ATP) channels, were investigated in the anesthetized cat. Intravenous injections of cromakalim in doses of 30-300 micrograms/kg decreased arterial pressure (AP), pulmonary arterial pressure (PAP), and increased cardiac output (CO), while producing small changes in right and left atrial pressures. Pulmonary and systemic vascular resistances were decreased and vasodilator responses to cromakalim were blocked by glybenclamide, a K+ATP channel-blocking agent. The low dose of cromakalim caused a reflex increase in heart rate (HR) and right ventricular contractile force (RVCF), whereas the high dose decreased HR and RVCF. Under constant-flow conditions the K+ATP channel opener caused dose-dependent decreases in hindquarters perfusion pressure, and when tone was elevated in the pulmonary vascular bed, dose-dependent decreases in pulmonary lobar arterial perfusion pressure. Hindquarters and pulmonary lobar vasodilator responses to cromakalim were inhibited in a specific manner by glybenclamide. The present data show that cromakalim has significant vasodilator activity in both the systemic and pulmonary vascular beds and suggest that responses to this agent result from activation of glybenclamide-sensitive K+ATP channels. These data show that cromakalim can cause substantial decreases in systemic and pulmonary vascular resistance in a dose that has little effect on RVCF.

N omega-nitro-L-arginine selectively inhibits vasodilator responses to acetylcholine and bradykinin in cats

The effects of N omega-nitro-L-arginine (nitroarginine), an inhibitor of endothelium-dependent relaxing factor (EDRF) production, on vascular tone and responses to vasodilator and vasoconstrictor agents were investigated in the hindquarters vascular bed of the cat. Under constant flow conditions, infusion of nitroarginine into the hindquarters vascular bed caused a significant increase in systemic arterial and hindquarters perfusion pressures. During infusion of nitroarginine, hindquarters vasodilator responses to acetylcholine and bradykinin were reduced significantly whereas vasodilator responses to isoproterenol, PGE1, nitroprusside, and 8-bromoguanosine 3',5'-cyclic monophosphate were not altered. Infusion of nitroarginine significantly enhanced vasoconstrictor responses to the thromboxane receptor agonist U 46619 and to phenylephrine. The results of these studies are consistent with the hypotheses that EDRF production may involve the formation of nitric oxide or a nitroso compound from L-arginine, and that EDRF production may play a role in the regulation of vascular tone and in the mediation of responses to the endothelium-dependent vasodilators, acetylcholine and bradykinin, in resistance vessels in the hindquarters. These data support the concept that EDRF is very likely an endogenous nitrovasodilator derived from L-arginine in the hindquarters vascular bed of the cat.

Influence of vasoactive intestinal contractor on the feline pulmonary vascular bed

Pulmonary vascular responses to vasoactive intestinal contractor (VIC) (endothelin-B) were investigated in the feline pulmonary vascular bed under constant and natural flow conditions. Injection of VIC, 0.3 nmol/kg i.v., increased pulmonary arterial and left atrial pressures and cardiac output and caused a biphasic change in pulmonary vascular resistance. VIC and endothelin-1 (ET-1) caused a similar pattern of response and under constant flow conditions, VIC increased lobar arterial pressure in a dose-related manner and was similar in potency and duration of action to ET-1. The thromboxane mimic, U46619, was far more potent than VIC, and a monocyclic ET-analog had no activity in the pulmonary vascular bed. The present data show that VIC has significant vasoconstrictor activity in the pulmonary vascular bed of the cat.

Comparative responses to endothelin-2 and sarafotoxin 6b in the pulmonary vascular bed of the cat

Pulmonary vascular responses to endothelin-2 and sarafotoxin 6b were investigated in the feline pulmonary vascular bed under natural flow and constant flow conditions. Injections of endothelin-2 and sarafotoxin 6b in a dose of 0.3 nmol/kg iv increased pulmonary arterial and left atrial pressures and cardiac output, and caused a biphasic change in calculated pulmonary vascular resistance. Endothelin-2 caused a biphasic change in systemic arterial pressure, while sarafotoxin 6b only decreased arterial pressure. Under constant flow conditions in the intact-chest cat, injections of endothelin-2 and sarafotoxin 6b in doses of 0.1-1 nmol into the perfused lobar artery increased lobar arterial pressure in a dose-related manner but were less potent than the thromboxane A2 mimic, U46619. An ET analog with only the Cys1-Cys15 disulfide bond and an amidated carboxy terminus had no significant activity in the pulmonary vascular bed. The present data show that endothelin-2 and sarafotoxin 6b have significant vasoconstrictor activity in the pulmonary vascular bed of the cat.

Hemodynamic responses to sarafotoxin 6 peptides

Hemodynamic responses to sarafotoxin (SFTX6) peptides and endothelin-1 (ET-1) were compared in the anesthetized cat. SFTX6a and ET-1 at a dose of 0.3 nmol/kg i.v. produced a biphasic change in arterial pressure characterized by an initial decrease followed by a secondary increase in pressure. In contrast, similar doses of SFTX6b and SFTX6c produced mainly decreases in arterial pressure. Each peptide produced increases in central venous pressure, pulmonary arterial pressure, left atrial pressure, and cardiac output. Secondary decreases in cardiac output could be observed in response to SFTX6a and ET-1. SFTX6a and ET-1 produced biphasic changes, whereas SFTX6b and SFTX6c produced only decreases in systemic vascular resistance. In contrast, each peptide produced biphasic changes in pulmonary vascular resistance. The initial fall in pulmonary vascular resistance may be passively related to an increase in pulmonary blood flow because it occurs at a time when cardiac output is increased and no initial fall in pulmonary arterial pressure is observed. The present data show that the SFTX6 peptides can produce different patterns of responses in the systemic vascular bed of the cat, whereas responses in the pulmonary vascular bed are similar.

Pulmonary vascular and airway responses to endothelin-1 are mediated by different mechanisms in the cat

The role of cyclooxygenase product formation and thromboxane A2 receptor activation in the response to endothelin-1 (ET-1) was investigated and compared in the airways and in the pulmonary vascular bed of the intact-chest cat. Intravenous injections of ET-1, 0.3 nmol/kg, increased lung resistance and decreased dynamic compliance. Bronchoconstrictor responses to ET-1 were decreased significantly by a cyclooxygenase inhibitor and by a thromboxane receptor blocking agent. In the pulmonary vascular bed of the cat under constant flow conditions, ET-1 increased lobar arterial pressure in a dose-related manner, and pulmonary vasconstrictor responses to the peptide were not altered by a cyclooxygenase inhibitor or thromboxane receptor blocking agent. The cyclooxygenase inhibitor blocked responses to the prostaglandin precursor, arachidonic acid; and the thromboxane receptor blocking agent reduced responses to the thromboxane mimic, U-46619. The present data suggest that bronchoconstrictor responses to ET-1 are dependent on the release of arachidonic acid, the formation of prostaglandins, and activation of thromboxane A2 receptors whereas pulmonary vasoconstrictor responses to the peptide are mediated by a different mechanism.

Influence of SK&F 95587 and BN 50730 on bronchoconstrictor responses in the cat

The effects of SK&F 95587 (4[2-(benzenesulfonamido)-ethyl] phenoxyacetic acid), a thromboxane (TX) receptor blocking agent, on bronchoconstrictor responses were investigated in paralyzed, anesthetized, mechanically ventilated cats. Intravenous injections of the TXA2 receptor mimics, U-46619 [(15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta5Z,13E-dienoic acid] and U-44069 (9,11-dideoxy-11 alpha,9 alpha-epoxymethano PGF2 alpha), produced dose-related increases in transpulmonary pressure and lung resistance and decreases in dynamic compliance. After administration of SK&F 95587, 5 mg/kg i.v., bronchoconstrictor responses to U-46619 and U-44069 were reduced markedly, whereas airway responses to prostaglandin (PG)F2 alpha, serotonin, PGD2 or the PGD2 metabolite, 11 beta-PGF2 alpha, were not altered. The duration of action of SK&F 95587 was greater than 3 hr, and the blockade was overcome when 10-fold larger doses of the TXA2 mimics were administered. Bronchoconstrictor responses to platelet-activating factor (PAF) were blocked by SK&F 95587 and by the novel PAF receptor antagonist, BN 50730. BN 50730 also blocked the fall in systemic arterial pressure in response to PAF. However, BN 50730 did not influence airway responses to U-46619, PGF2 alpha, PGD2 or serotonin and had no effect on baseline bronchomotor tone or arterial pressure. The PAF receptor antagonism with BN 50730 was overcome when 10-fold larger doses of PAF were administered and the dose-response curves for changes in lung resistance and dynamic compliance were shifted to the right in a parallel manner. The present data suggest that SK&F 95587 has selective TX receptor blocking activity, and that BN 50730 has selective PAF receptor blocking properties in the airways of the cat. The present data also provide support for the hypothesis that bronchoconstrictor responses to PAF are mediated by specific receptors, which are coupled to a phospholipase and, when activated, result in the release of TXA2 and contraction of airway smooth muscle.

Cardiovascular responses to vasoactive intestinal contractor, a novel endothelin-like peptide

Cardiovascular and pulmonary responses to vasoactive intestinal contractor (VIC), an endothelin (ET)-like peptide from the murine gastrointestinal tract, were investigated in the cat. VIC (0.1-1.0 nmol/kg iv) decreased or elicited biphasic changes in arterial pressure (AP) and increased central venous pressure, cardiac output, pulmonary arterial pressure, and left atrial pressure. VIC produced biphasic changes in systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR). VIC increased heart rate (HR) and, at the 1 nmol/kg dose, a secondary decrease was observed. Hexamethonium blocked the changes in HR in response to VIC, whereas the ganglionic blocker, meclofenamate, or glybenclamide had no effect on changes in AP, SVR, and PVR elicited by the peptide. VIC caused small changes in right ventricular contractile force and increased distal aortic and carotid artery blood flow at all doses, with secondary decreases at the higher doses. VIC decreased superior mesenteric artery flow and decreased renal blood flow at the 1 nmol/kg dose. The changes in AP in response to VIC, ET-1, and ET-2 were similar, whereas those elicited by ET-3 and sarafotoxin 6b were similar. The present data show that VIC can produce both vasodilation and vasoconstriction in the systemic vascular bed and biphasic changes in PVR in the cat. These data show that VIC can produce complex cardiovascular responses similar to those elicited by the ET peptides and that these responses are largely independent of autonomic reflexes, release of cyclooxygenase products, and activation of ATP-regulated potassium channels. We conclude that VIC may act as an ET-like peptide.

Concentration-activity profile of the modulation of cyclooxygenase product formation by reduced glutathione in microsomal fractions from the goat lung

Age-related changes in pulmonary formation of arachidonic acid (AA) metabolites are thought to play an important role in regulating cardiopulmonary function. This study addresses the potential role of reduced glutathione (GSH) in modulating cyclooxygenase product formation in the developing lung. Prostaglandin H2 (PGH2) metabolism was studied in microsomal fractions isolated from the lungs of unventilated fetal, neonatal and adult goats. GSH-dependent PGH2 to PGE2 isomerase activity in microsomal fractions from the perinatal (fetal and neonatal) goat lung was not saturable with respect to GSH and can respond to changes in GSH concentration over the range of 0.01 to 30 mM, which encompasses the full range the intracellular GSH levels reported in the literature. However, in fractions from the adult, a lower rate of PGE2 formation is observed at higher GSH concentrations. In addition, the tissue levels of GSH exhibited developmental stage-related differences with fetal being higher than neonatal or adult. The present observations may have physiologic relevance, in that decreases in pulmonary GSH levels after birth may contribute to decreases in plasma PGE2 levels by decreasing pulmonary PGE2 synthesis, thereby contributing to closure of the ductus arteriosus; conversely, increased GSH levels associated with hyperoxia may contribute to persistence of ductal patency. Formation of 6-keto-PGF1 alpha and of TXB2 (the stable metabolites of prostacyclin and TXA2) was decreased when PGE2 formation was increased by GSH activation of PGE2 isomerase in fractions isolated from all three developmental stages. A similar pattern of product formation was observed when AA was employed as substrate. These data suggest the possibility that changes in GSH concentration may modulate eicosanoid formation in cells that contain GSH-dependent PGE2 isomerase, as well as either or both prostacyclin or thromboxane synthase(s).

Analysis of cardiovascular and pulmonary responses to endothelin-1 and endothelin-3 in the anesthetized cat

Cardiovascular and pulmonary responses to endothelin (ET)-1, ET-3 and neuropeptide Y (NPY) were investigated in the anesthetized cat. ET-1, 0.1 to 1 nmol/kg i.v., decreased or elicited biphasic changes in arterial pressure (AP), whereas ET-3, in the same doses, decreased AP. Both ETs increased cardiac output (CO) and, at the highest doses, a secondary decrease in CO was observed. NPY, 0.3 to 3 nmol/kg i.v., increased AP and at the highest dose decreased CO. All three peptides had inconsistent effects on right ventricular contractile force and increased central venous pressure. ET-1 at lower doses increased heart rate (HR) and, at 1 nmol/kg, caused a biphasic change. ET-3 increased HR, whereas NPY decreased HR. Systemic vascular resistance (SVR) was increased by NPY and decreased by ET-3, whereas ET-1 elicited biphasic changes. ET-1 and ET-3 increased pulmonary arterial pressure, left atrial pressure and caused biphasic changes in pulmonary vascular resistance (PVR). NPY had no significant effect on PAP or PVR. When pulmonary blood flow was maintained constant, ET-1 and ET-3 had only pulmonary vasoconstrictor activity, whereas NPY and the ET analog had no significant effect. The increase in SVR in response to NPY, the decrease in response to ET-3 or the biphasic change in response to ET-1 were not modified by meclofenamate, hexamethonium or propranolol. Increases in HR in response to ET-1 and ET-3 were reduced by the beta receptor and ganglionic blocking agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative responses to endothelin 2 and sarafotoxin 6b in systemic vascular bed of cats

Cardiovascular responses to endothelin 2 (ET-2) and sarafotoxin 6b (S6b) were investigated in the cat. ET-2 (0.1-1 nmol/kg iv) decreased or elicited biphasic changes in arterial pressure (AP), whereas S6b (0.1-1 nmol/kg iv) only decreased AP. Central venous pressure (CVP), cardiac output (CO), and pulmonary arterial pressure (PAP) were increased. ET-2 produced biphasic changes in systemic vascular resistance (SVR), whereas S6b decreased SVR at the two lower doses and caused a biphasic change at the 1 nmol/kg dose. The effects of ET-1 and ET-2 were similar, whereas the effects of S6b were similar to ET-3. ET-2 and S6b had small effects on right ventricular contractile force and caused transient increases in heart rate. Distal aortic blood flow was increased in response to all doses of both peptides, whereas increases in carotid blood flow were observed only in response to the higher doses of ET-2 and S6b. ET-2 produced dose-dependent decreases in superior mesenteric artery (SMA) blood flow, whereas decreases in SMA flow in response to S6b were observed only at the 1 nmol/kg dose. Renal blood flow was decreased significantly only at the higher doses of ET-2 and S6b. The present data show that ET-2 and S6b can produce both vasodilation and vasoconstriction in the systemic and regional vascular beds of the cat and demonstrate previously unrecognized vasodilator activity in response to S6b. It is concluded that ET-2 and S6b produce complex cardiovascular responses in the anesthetized cat.

Influence of SQ 29,548 on vasoconstrictor responses in the mesenteric vascular bed of the cat

The effects of SQ 29,548 on vasoconstrictor responses were investigated in the feline mesenteric vascular bed. Injections of the thromboxane (TX) A2 mimics, U46619 and U44069, caused dose-related increases in mesenteric arterial perfusion pressure. After administration of SQ 29,548, 0.5 mg/kg i.v, vasoconstrictor responses to U46619 and U44069 were reduced markedly whereas responses to prostaglandin (PG) F2 alpha, angiotensin II, vasopressin and BAY K 8644, an agent which enhances calcium entry, were not altered. The duration of the TXA2 receptor blockade was greater than 2 h and SQ 29,548 had no significant effect on mesenteric vasodilator responses to PGE2, isoproterenol, nitroglycerin, acetylcholine or bradykinin. SQ 29,548, at a dose of 0.5 mg/kg i.v., significantly reduced the response to TXB2, which had modest vasoconstrictor activity in the mesenteric vascular bed. However, when the dose of SQ 29,548 was reduced to 0.05 mg/kg i.v., responses to TXB2 were not altered, whereas responses to U46619 were significantly decreased. SQ 29,548 had no significant effect on vasoconstrictor responses to norepinephrine or to sympathetic nerve stimulation. The TXA2 receptor antagonist blocked the vasoconstrictor component of the biphasic response to the PG precursor, arachidonic acid, and the endoperoxide, PGH2. The results of these studies suggest that SQ 29,548 is a specific TX receptor antagonist in the mesenteric vascular bed, that the vasoconstrictor component of the biphasic response to arachidonic acid and PGH2 is due to formation of TXA2, and that endogenously formed TXA2 does not modulate adrenergic responses in the mesenteric circulation of the cat.

Nisoldipine inhibits adrenergic responses in the hindquarters vascular bed of the cat

The effects of the calcium entry blocking agent nisoldipine on adrenergic vasoconstrictor responses were investigated in the hindquarters vascular bed of the cat under conditions of controlled blood flow. Nisoldipine dilated the hindquarters vascular bed and inhibited vasoconstrictor responses to Bay K 8644, a nifedipine analog which promotes calcium entry. During infusion of nisoldipine, vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine, and tyramine were inhibited in a reversible manner. In addition to blocking responses to nerve-released and exogenous norepinephrine, the calcium entry antagonist decreased responses to methoxamine and BHT 933, alpha 1- and alpha 2-adrenoceptor agonists. Responses to methoxamine were reduced by prazosin, an alpha 1-adrenoceptor antagonist, but not by yohimbine, an alpha 2-adrenoceptor blocking agent, whereas responses to BHT 933 were decreased by yohimbine but not by prazosin. The results of these studies suggest that vasoconstrictor responses to neuronally released and exogenous norepinephrine, as well as to selective alpha 1- and alpha 2-adrenoceptor agonists, are dependent in part on an extracellular source of calcium in resistance vessels of the feline hindquarters vascular bed. The inhibitory effect of nisoldipine on vasoconstrictor responses to neuronally released norepinephrine may be important in the antihypertensive actions of calcium entry blocking agents.

Differential effects of rat endothelin on regional blood flow in the cat

Regional vascular responses to rat endothelin were investigated in the anesthetized cat. Intravenous injection of the peptide in doses of 0.1-1 nmol/kg decreased arterial pressure and increased distal aortic blood flow with a small secondary reduction in flow at the high dose. Mesenteric blood flow was decreased, and the decreases in flow were proportionately greater than the decreases in pressure so that mesenteric resistance increased at all doses. The rat peptide increased blood flow or caused biphasic changes in flow in the renal vascular bed. At 0.1 and 0.3 nmol the peptide decreased renal resistance, whereas at 1 nmol a biphasic change occurred. The present data suggest that responses to rat endothelin are dependent on dose and the vascular bed studied and indicate that the peptide can cause both vasodilation and vasoconstriction.

Effects of porcine and rat endothelin and an analog on blood pressure in the anesthetized cat

Arterial responses to a wide range of doses of porcine and rat endothelin and a monocyclic analog were compared in the anesthetized cat. Injections of the porcine peptide in doses of 0.01-0.1 nmol/kg i.v. decreased systemic arterial pressure in a dose-related manner, whereas doses of 0.3 and 1 nmol/kg i.v. elicited biphasic responses. The rat peptide, in doses of 0.03-1 nmol/kg i.v., also decreased arterial pressure in a dose-related fashion, whereas injection at 3 nmol/kg i.v. caused a biphasic response. With both peptides the biphasic response was characterized by an initial short-lived decrease followed by a secondary sustained increase in pressure. The monocyclic porcine analog in doses of 3-30 nmol/kg i.v. had no significant effect on arterial pressure. Both peptides increased cardiac output, and changes in peripheral vascular resistance in response to both peptides were not altered by sodium meclofenamate. These data suggest that arterial depressor responses to porcine and rat endothelin are similar and dose-dependent. However, the porcine peptide has 3-fold greater pressor activity in the cat. The lack of effect with the monocyclic porcine analog suggests that the two disulfide linkages are necessary for activity.

Influence of endothelin on systemic arterial pressure and regional blood flow in the cat

Regional vascular responses to endothelin were investigated in the anesthetized cat. I.v. injection of endothelin at 0.1 nmol/kg decreased arterial pressure and renal vascular resistance but increased vascular resistance in the small intestine. At 0.3 nmol/kg i.v. the peptide caused a greater decrease in arterial pressure and increased mesenteric resistance but had no significant effect on renal resistance. In contrast, at 1 nmol/kg i.v. endothelin caused a biphasic change in arterial pressure and marked increases in mesenteric and renal resistance. Injection of the peptide in doses of 0.1-1 nmol/kg i.v. caused only increases in carotid blood flow. These data suggest that responses to endothelin are dependent on dose and vascular bed studied.

Analysis of regional responses to endothelin in hindquarters vascular bed of cats

Regional responses to endothelin, a peptide derived from endothelial cells in culture, were investigated in the hindquarters vascular bed of cats, when flow varied naturally and when flow was maintained constant with a pump. Intravenous injections of endothelin at doses of 0.03 and 0.1 nmol/kg caused dose-dependent decreases in systemic arterial pressure and increases in distal aortic blood flow. Injection of endothelin at a dose of 0.3 nmol/kg iv caused a biphasic response characterized by an initial decrease in arterial pressure and an increase in blood flow, which was followed by a secondary rise in pressure and a fall in blood flow. When blood flow to hindquarters was maintained constant with a pump, intra-arterial injection of 0.03 nmol endothelin caused a decrease in perfusion pressure, whereas 0.1-1 nmol doses elicited biphasic responses characterized by an initial decrease followed by a secondary increase in perfusion pressure. When compared with other vasoactive peptides, the pressor activity of endothelin was less than angiotensin II by an order of magnitude but was threefold greater than that of neuropeptide Y in the hindquarters vascular bed. The pressor component of the response to endothelin and the response to the calcium agonist BAY K 8644 were decreased in a reversible manner by nisoldipine, a dihydropyridine calcium entry blocking agent. The results of these studies indicate that porcine-human endothelin has both vasodilator and vasoconstrictor activity in the hindquarters vascular bed of cats. The predominant response at a low concentration is vasodilation, whereas at higher concentrations a vasoconstrictor response that was dependent in part on the influx of extracellular calcium could be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)