Search PubMed⌕ Search

Biomedical subjects

R A Morgan

Publications and source records attributed to R A Morgan.

At least 127 records · Page 7Linked to original sources
PubMed1978

Effects of microiontophoretic and intravenous application of gonadotrophic hormones on the discharge of medial-basal hypothalamic neurones in rats.

In ovariectomized rats, the responses of medial-basal hypothalamic neurones to gonadotrophic hormones have been recorded. The luteinizing and follicle stimulating hormones (LH and FSH) were applied to neurones both by microiontophoresis and by intravenous injection. Although LH was the more frequently effective, both hormones caused either excitation or inhibition of neurones, and the effects were consistently repeatable on the same neurones. Iontophoretic and intravenous application of the same hormones to the same neurone gave identical responses. Responsive neurones were found throughout the medial-basal hypothalamus and hormones were effective both on neurones which could be antidromically activated from the median eminence and on those which could not be activated. Treatment of rats with oestradiol, either during the experiment or 24 h earlier, did not significantly alter neuronal responses to the gonadotrophins. The results are discussed in terms of possible feedback by gonadotrophic hormones on the brain and it is suggested that such a feedback may not be concerned with control of gonadotrophic hormone secretion.

Action Potentials↗
PubMed1976

Hepatic pyruvate kinase. Regulation by glucagon, cyclic adenosine 3'-5'-monophosphate, and insulin in the perfused rat liver.

A reversible interconversion of two kinetically distinct forms of hepatic pyruvate kinase regulated by glucagon and insulin is demonstrated in the perfused rat liver. The regulation does not involve the total enzyme content of the liver, but rather results in a modulation of the substrate dependence. The forms of pyruvate kinase in liver homogenates are distinguished by measurements of the ratio of the enzyme activity at a subsaturating concentration of P-enolpyruvate (1.3 mM) to the activity at a saturating concentration of this substrate (6.6 mM). A low ratio form of pyruvate kinase (ratio between 0.1 and 0.2) is obtained from livers perfused with 10(-7) M glucagon or 0.1 mM adenosine 3':5'-monophosphate (cyclic AMP). A high ratio form of the enzyme is obtained from livers perfused with no hormone (ratio = 0.35 to 0.45). The regulation of pyruvate kinase by glucagon and cyclic AMP occurs within 2 min following the hormone addition to the liver. Insulin (22 milliunits/ml) counteracts the inhibition of pyruvate kinase caused by 5 X 10(-11) M glucagon, but has only a slight influence on the enzyme properties in the absence of the hyperglycemic hormone. The low ratio form of pyruvate kinase obtained from livers perfused with glucagon or cyclic AMP is unstable in liver extracts and will revert to a high ratio form within 10 min at 37 degrees or within a few hours at 0 degrees. Pyruvate kinase is quantitatively precipitated from liver supernatants with 2.5 M ammonium sulfate. This precipitation stabilizes the enzyme and preserves the kinetically distinguishable forms. The kinetic properties of the two forms of rat hepatic pyruvate kinase are examined using ammonium sulfate precipitates from the perfused rat liver. At pH 7.5 the high ratio form of the enzyme has [S]0.5 = 1.6 +/- 0.2 mM P-enolpyruvate (n = 8). The low ratio form of enzyme from livers perfused with glucagon or cyclic AMP has [S]0.5 = 2.5 +/- 0.4 mM P-enolpyruvate (n = 8). The modification of pyruvate kinase induced by glucagon does not alter the dependence of the enzyme activity on ADP (Km is approximately 0.5 mM ADP for both forms of the enzyme). Both forms are allosterically modulated by fructose 1,6-bisphosphate, L-alanine, and ATP. The changes in the kinetic properties of hepatic pyruvate kinase which follow treating the perfused rat liver with glucagon or cyclic AMP are consistent with the changes observed in the enzyme properties upon phosphorylation in vitro by a clyclic AMP-stimulated protein kinase (Ljungström, O., Hjelmquist, G. and Engström, L. (1974) Biochim. Biophys. Acta 358, 289--298). However, other factors also influence the enzyme activity in a similar manner and it remains to be demonstrated that the regulation of hepatic pyruvate kinase by glucagon and cyclic AMP in vivo involes a phosphorylation.

Adenosine Triphosphate↗
PubMedDate not supplied

Endovascular embolization of visceral artery aneurysms with ethylene-vinyl alcohol (Onyx): a case series.

We report the application of the liquid embolic agent ethylene-vinyl alcohol (Onyx; MicroTherapeutics, Irvine, CA, USA) in the management of visceral artery aneurysms. The technique and indications for using Onyx are discussed with emphasis on the management of wide-necked aneurysms and maintenance of patency of the parent vessel. None of the cases was considered suitable for stent-grafting or embolization with conventional agents. Two aneurysms of the renal artery bifurcation and one aneurysm of the inferior pancreaticoduodenal artery were treated. Following treatment there was complete exclusion of all aneurysms. There was no evidence of end-organ infarction. Follow-up with intervals up to 6 months has shown sustained aneurysm exclusion. Onyx is known to be effective in the management of intracranial aneurysms. Our experience demonstrates the efficacy and applicability of the use of Onyx in the treatment of complex visceral artery aneurysms.

Aged↗
PubMedDate not supplied

Management of ureteral strictures in renal transplants by antegrade balloon dilatation and temporary internal stenting.

PURPOSE: To evaluate the efficacy of percutaneous balloon dilatation and temporary internal stenting in the treatment of transplant ureteral strictures. METHODS: Nine patients presenting with obstructed renal transplants were treated by antegrade nephrostomy insertion, ureteroplasty, and temporary internal stenting. Following stent removal, patients were divided into two groups for analysis according to whether the obstruction occurred less than (group A) or more than (group B) 3 months following transplantation. RESULTS: All procedures were technically successful. In group A (n = 6), all patients were successfully treated by one or two dilatations with stenting. In group B (n = 3), two patients were successfully treated by one dilatation with stenting. Overall, eight patients (89%) have had their primary or secondary stent removed successfully at a mean interval of 97.5 days after insertion, and remain well at a mean follow-up interval of 22 months. CONCLUSION: Balloon dilatation and temporary internal stenting is a useful method for treating transplant ureteral strictures.

Catheterization↗
PubMedDate not supplied

Intracellular mechanisms of constriction of rat aorta by ethanol.

The intracellular mechanisms mediating vasoconstriction by ethanol are poorly understood. This investigation was designed to provide evidence on the role of protein kinase C (PKC) and calmodulin in vasoconstriction by ethanol. We studied helically cut strips of rat aorta that were exposed to ethanol before and in the presence of the PKC inhibitors calphostin C (79, 239, and 798 nM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7, 10 microM), and the calmodulin inhibitor, trifluoperazine (TFP, 10 microM). To test for the specificity of the PKC inhibitors, we measured the responses of aortas to potassium and phorbol 12-myristate 13-acetate (PMA) in the absence and presence of calphostin C and H7. To test for the specificity of TFP, we measured the responses of aortas to serotonin, potassium, PMA, and the thromboxane A2 mimic. 9,11-dideoxy-11 alpha, 9 alpha-epoxy-methanoprostaglandin F2a (U46619), in the absence and presence of TFP. We also studied the effect of the combination of calphostin C and TFP on constriction of the aorta by ethanol. We also measured the importance of intracellular and extracellular calcium in constriction of the aorta by ethanol. Force generation was measured before, and then during exposure of the strips to calcium-free buffer with EGTA, or calcium-free buffer with EGTA plus caffeine. We found that both PKC inhibitors antagonized vasoconstriction by ethanol and PMA. However, H7 antagonized contractions by potassium, but calphostin C did not. We found that TFP caused 99 +/- 1% inhibition of maximum contraction to serotonin, 90 +/- 4% inhibition of maximum contraction to potassium, 63 +/- 6% inhibition of maximum contraction to PMA, and 8 +/- 5% inhibition of maximum contraction to U46619. TFP caused a 22 +/- 8% inhibition of contraction to ethanol. The combination of TFP and calphostin C antagonized vasoconstriction by ethanol to a degree similar to that of calphostin C alone. We also found that contractions to ethanol were only 16 +/- 7% of control values in a calcium-free plus EGTA buffer. Contractions to ethanol were 0 +/- 1% of control values in calcium-free buffer with EGTA plus caffeine. We conclude that: 1-vasoconstriction by ethanol is, at least in part, mediated by PKC; 2-constriction by ethanol is mediated to a minimal extent by calmodulin, and 3-part of the constriction by ethanol of the aorta is mediated by a caffeine-sensitive pool of intracellular calcium.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

Portal venous thrombosis: percutaneous therapy and outcome.

PURPOSE: To study the efficacy of percutaneous treatment for portal vein thrombosis (PVT). MATERIALS AND METHODS: Of 20 patients who were evaluated for symptomatic portal occlusion, 14 were successfully treated with use of percutaneous techniques. In patients with noncavernomatous PVT (n = 15), the initial treatment was to increase portal output by creating a transjugular intrahepatic portosystemic shunt (TIPS), which was successful in 12 cases. Methods to decrease arterial input to the portal system (hepatosplenic arterial embolization) were used as primary therapy in two patients and in an additional two patients with continued symptoms, despite a functioning TIPS. RESULTS: All TIPS survivors had patent shunts, although patients with complete PVT required more frequent revisions compared to patients with nonocclusive PVT. Hepatosplenic arterial embolization controlled symptoms in the four patients who were treated, but both patients with patent TIPS died of liver failure after embolization. Of the 14 patients treated, eight died at a mean of 6.2 months (six from hepatoma). CONCLUSION: TIPS is effective in patients with noncavernomatous PVT, although patients with complete thrombosis experience recurrent shunt occlusions and also may develop hepatoma. If TIPS fails, or if symptoms recur, hepatosplenic arterial embolization may be an option.

Adult↗
PubMedDate not supplied

A mechanical comparison of subtrochanteric femur fracture fixation.

OBJECTIVE: To determine whether the mechanical properties of first-generation interlocking femoral nails are different from those of second-generation interlocking femoral nails in a subtrochanteric femur fracture model. DESIGN: Randomized laboratory investigation using a synthetic subtrochanteric femur fracture model. SETTING: Simulated stable and unstable fractures were created at three levels in the subtrochanteric region of synthetic femora. Instrumented specimens were tested elastically in a biomaterials testing system. INTERVENTION: Synthetic femora were instrumented with either a statically locked first-generation femoral nail or a statically locked second-generation femoral nail. MAIN OUTCOME MEASUREMENTS: Elastic stiffness for both the stable and unstable fracture groups was measured in both compression and torsion. Unstable fracture specimens were tested to failure in compression, and load to failure was measured. RESULTS: Throughout the subtrochanteric region, second-generation femoral nail constructs were consistently stiffer in compression and torsion than were statically locked first-generation femoral nail constructs. In general, second-generation constructs also withstood larger loads to failure in the unstable fracture model. CONCLUSIONS: Second-generation nails provided significantly enhanced mechanical stiffness compared with first-generation femoral nails when used to treat both stable and unstable subtrochanteric femur fractures. Although these results were obtained by using a well-controlled, mechanically consistent model, clinical validation of an increased incidence of fracture unions or of decreased time to union is required before we can recommend that second-generation nails be used routinely to treat subtrochantenic femur fractures.

Analysis of Variance↗
PubMedDate not supplied

Distal venous arterialization for lower limb salvage: angiographic appearances and interventional procedures.

Approximately 14%-20% of patients with critical lower limb ischemia are unsuited for distal arterial reconstruction and face major distal amputation. Distal venous arterialization is a unique procedure in which the venous bed is used as an alternative conduit for perfusion of peripheral tissues. Eighteen patients with stage IV Fontaine critical lower limb ischemia underwent venous arterialization. Preoperative angiographic findings confirmed the absence of any below-knee continuous arterial vessels. The most distal satisfactory artery was used for proximal bypass anastomosis, and venous valves were destroyed with Parsonnet probes, cutting balloons, Fogarty catheters, and valvulotomes under radiologic guidance. All patients underwent intra- and postoperative angiography of the venous grafts and the distal venous bed. Primary and secondary graft patencies were 66% and 72%, respectively, at a mean follow-up of 25 months. The limb salvage rate was 83% overall and 75% at 2-year follow-up. Vascular imaging is essential in selecting and following up patients and in determining the appropriate intraoperative procedure.

Aged↗