Acute hyperhomocysteinaemia affects pulse pressure but not microvascular vasodilator function

AIMS

Raised homocysteine (hcy) levels are associated with premature coronary artery disease, but the underlying vascular mechanism and the extent to which hcy affects small vessel vasodilator responses (especially non-nitric oxide mediated pathways) are unclear.

METHODS

This double-blind, placebo-controlled crossover study in 14 healthy male subjects evaluated the effects of single-dose oral methionine 15 g (to induce acute hyperhomocysteinaemia) on cutaneous microvascular vasodilator responses to incremental-dose iontophoretic administration of acetylcholine (Ach) and sodium nitroprusside (SNP) using laser Doppler fluximetry (LDF), and the effects on von Willibrand factor (vWF) levels and systemic haemodynamics.

RESULTS

Methionine administration produced a three fold rise in plasma hcy levels at 8 h, which was accompanied by a significant increase in pulse pressure (53 vs 49 mmHg, P < 0.05) but no change in heart rate. Acute hyperhomocysteinaemia had no significant effect on incremental microvascular vasodilator dose-response curves to Ach and SNP, or circulating levels of vWF.

CONCLUSIONS

The present study shows that acute hyperhomocysteinaemia increases pulse pressure (a marker of large vessel stiffness) but has no effect on endothelial-dependent (non-NO-mediated) microvascular vasodilation.

Antenatal screening for HPA-1a by flow cytometry

Pregnant women who attended antenatal clinics at King George V Hospital, the Birth Centre or were referred by obstetricians from February 19 July, 1996 were screened for the platelet antigen HPA-1a by flow cytometry. Forty out of 2,300 (1.7%) were found to be negative for this antigen. Of the 28 women followed throughout their pregnancy, none developed antibody to HPA-1a. Platelet counts performed on samples from 17 babies born to 17 of these mothers were all normal. This study proves the simplicity and rapidity of flow cytometry for platelet antigen screening. The results were comparable with the Solid Phase Red Cell Adherence (SPRCA) method and with PCR. The lack of a plentiful supply of specific antibody and the rarity of fetomaternal alloimmune thrombocytopenia (FMAIT) argue against the introduction of routine screening for maternal HPA-1a status at the present time.

A comparison of the effects of halothane and isoflurane in combination with nitrous oxide on lower oesophageal sphincter pressure and barrier pressure in anaesthetised dogs

The effects of surgery, and of halothane and isoflurane, on oesophageal pressures were examined in 30 dogs. The dogs were premedicated with a combination of acepromazine maleate (0.1 mg/kg) and pethidine hydrochloride (1 mg/kg), and anaesthesia was induced with thiopentone (10 mg/kg). Ten of the dogs underwent abdominal surgery with halothane, 10 underwent abdominal surgery with isoflurane and 10 underwent non-abdominal surgery with halothane. Gastric pressure, lower oesophageal sphincter pressure and oesophageal barrier pressures were measured at five to 10 minutes after induction, five to 10 minutes after the initial surgical incision, during the abdominal surgery and while the skin was being sutured. There were no significant differences in lower oesophageal sphincter pressure between the groups of dogs but the pressures were greater in all the dogs during the surgical manipulation than shortly after induction or while the skin was being sutured. During abdominal surgery with halothane the barrier pressure was significantly higher (P < 0.05) than during non-abdominal surgery with halothane. The barrier pressure was lower (P < 0.001) during skin suturing after abdominal surgery with isoflurane than after abdominal or non-abdominal surgery with halothane. The lower oesophageal sphincter appears to be more sensitive to isoflurane than halothane.

A review of pathological diagnoses made from 87 canine splenic biopsies

The pathological findings in 87 cases of canine splenic abnormality recognised clinically by abdominal palpation or radiography, or at exploratory laparotomy, are presented. The most common diagnosis was of splenic neoplasia (n = 38) and the most frequently recognised canine splenic neoplasm was haemangiosarcoma (17 of 38 cases). Benign splenic enlargement secondary to nodular hyperplasia (n = 6), haematoma (n = 16) or non-specific changes including congestion, haemorrhage, extramedullary haemopoiesis and haemosiderin deposition (n = 14) was also recognised. A diagnosis of non-specific pathology was more frequently recorded when portions of spleen, as opposed to the entire organ, were submitted for assessment. Splenic infarction, with (n = 3) or without (n = 7) torsion, abscessation (n = 2) and focal mast cell proliferation (n = 1) accounted for the remainder of the cases. Clinical follow-up was available for 35 cases and revealed good long-term survival in cases of splenic haematoma or haemangioma, with relatively poor survival with a diagnosis of splenic haemangiosarcoma or anaplastic sarcoma. A range of splenic disorders was recognised in dogs of the labrador breed (16 of 87 cases) and three of 17 cases of haemangiosarcoma occurred in German shepherd dogs. The possible predisposition of dogs of these breeds to splenic disorders is discussed.

Effect of body position on oesophageal and gastric pressures in the anaesthetised dog

The effect of body position on lower oesophageal sphincter pressure (LOSP), gastric pressure and barrier pressure (BrP) was investigated in 40 dogs anaesthetised for neutering procedures. The dogs were placed in lateral recumbency followed by dorsal recumbency (group 1) or vice versa (group 2). LOSP decreased significantly in the animals which were positioned initially in lateral recumbency, when they were then placed in dorsal recumbency, while those initially positioned in dorsal recumbency showed no significant change in their LOSP or BrP when their position was altered to lateral recumbency. When the data from both groups were pooled, LOSP and BrP were significantly lower when the dogs were in dorsal compared to lateral recumbency (P < 0.05).

Acidified chloroquine treatment for the removal of class I HLA antigens

With the aim of reducing the damage to platelets while effectively removing class I HLA antigens from their surfaces, we developed a new method using acidified chloroquine diphosphate. Platelets were treated with a 0.2 M solution of chloroquine diphosphate (pH 4.0). More than 90% of the platelets remained viable after treatment. While a marked reduction in reactions of acidified chloroquine-treated platelets with multispecific HLA antisera was noted in comparison with phosphate-buffered-saline-(PBS)-treated platelets, reactions with platelet-specific antibodies were preserved. This was demonstrated by immunofluorescence tests and solid-phase and monoclonal antibody immobilization of platelet antigen assays. Aggregation responses, though reduced in comparison with PBS-treated platelets, were still preserved after acidified chloroquine treatment. Ultrastructural analysis did not show any significant difference from PBS-treated platelets. We conclude that treatment of platelets with acidified chloroquine diphosphate is a simple and effective method for removing class I HLA antigens from their surfaces with minimal damage to their structure and function.

Pertussis toxin treatment increases glutamate release and dihydropyridine binding sites in cultured rat cerebellar granule neurons

This study was designed to examine the ability of pertussis toxin to block various responses due to (-)-baclofen in cultured cerebellar granule neurons of the rat. Treatment with pertussis toxin for 3 h markedly reduced the ability of (-)-baclofen to stimulate GTPase in membranes, and its ability to inhibit forskolin-stimulated adenylyl cyclase in intact cells, whereas the ability of (-)-baclofen to inhibit glutamate release was not affected at 3 h, but was abolished after 16 and 48 h treatment with pertussis toxin. The amount of ADP-ribosylation of Gi/Go due to pertussis toxin in intact cells correlated well with the former two effects, but not with the prevention of the ability of baclofen to inhibit glutamate release. Pertussis toxin treatment for up to 48 h did not significantly affect the levels of Gs, Gi and Go in membranes from granule neurons determined by immunoblotting. Pertussis toxin treatment for 16 or 48 h but not 3 h increased the total amount of stimulated release of glutamate by about 40% under normal conditions, and by 84% under depolarizing conditions. In parallel experiments it was observed that pertussis toxin treatment for 16 h increased the number of dihydropyridine binding sites by about 90% on intact granule neurons. Whole-cell calcium channel currents, recorded under several conditions in the cells, were not increased in amplitude by pertussis toxin treatment for up to 48 h, although the ability of baclofen to inhibit calcium channel currents was blocked by pertussis toxin. These results indicate that the pertussis toxin-induced increase in glutamate release may be due to an increase in dihydropyridine binding sites, possibly localized to the presynaptic terminals.

N-methyl-D-aspartate responses in rat cerebellar granule cells are modified by chronic depolarisation in culture

Following culture in high (25 mM) K+ conditions cerebellar granule cells only respond with a rise in cytosolic free calcium concentration ([Ca2+]i after removal of external Mg2+. When granule cells are grown in low (5 mM) K+ N-methyl-D-aspartate (NMDA) exerts a neurotrophic effect. We show that at the critical time for this effect NMDA will elicit a rise in [Ca2+]i in 5 mM K+ cultures even in the presence of Mg2+ and that growth in 25 mM K+ induces the rapid appearance of a Mg2+ block of NMDA receptors in granule cells. This suggests firstly, that a rise in [Ca2+]i could be involved in the neurotrophic effect of NMDA and secondly, that the characteristics of the NMDA responses in granule cells are modified as a result of growth under depolarising conditions.

Squamous cell carcinoma of the equine external genitalia: a review and assessment of penile amputation and urethrostomy as a surgical treatment

A retrospective analysis was performed on 48 cases of suspected neoplasia involving the equine external genitalia. Forty nine squamous cell carcinomata (SCC) and 23 squamous papillomata (SP) were identified. Two cases of epithelial hyperplasia and one case of habronemiasis were also recognised histopathologically. The glans penis was the most common site of tumour development accounting for 53 per cent of cases of SCC and 61 per cent of SP. The urethral diverticulum, urethral process or urethra was involved in 27.6 per cent (8/29) of cases of SCC. Twelve per cent (5/41) of cases of SCC were confirmed to have metastatic involvement of the local lymph nodes. Papillomata showing pre-malignant changes were identified in five cases. Seventy five per cent (36/48) of the animals presented were ponies. All were geldings, mean age 16.5 years. Penile amputation and urethrostomy, preputial ablation and proximal urethrostomy or local excision were used in the surgical management of these animals; three cases were inoperable and destroyed at presentation. Oedema, haemorrhage and stenosis of the urethrostomy site were encountered as post operative complications. Sixty six per cent (6/9) of animals with SCC of the glans penis (without urethral involvement), which had a known history over the follow up period, treated by penile amputation and urethrostomy survived for longer than 18 months. Similarly, of those with urethral involvement only 28.6 per cent (2/7) survived for a similar follow-up period. SCC not uncommonly affects the external genitalia of aged pony geldings and frequently the glans penis. If the lesion is identified before local metastasis occurs, penile amputation and urethrostomy is indicated and the prognosis is favourable.

Possible homologies between photorefractoriness in sheep and birds: the effect of thyroidectomy on the length of the ewe's breeding season

Comparisons are drawn between the photoperiodically driven breeding cycles in "long-day" birds and "short-day" mammals, emphasizing the importance of photorefractoriness as a key regulator in the timing processes. It is argued that the two types of breeding cycle may not be so radically different as previously thought and, indeed the cycles may be strictly homologous. Evidence in support of this comes from the role of the thyroid glands in seasonality. In starlings and quail, thyroidectomy prevents refractoriness developing and the birds remain in breeding indefinitely under long days. If the processes underlying refractoriness are similar across species then thyroidectomy should greatly alter the ewe's breeding cycle. In two experiments, Welsh Mountain ewes were thyroidectomized in the summer during anoestrus and their subsequent periods of oestrus monitored under various daylengths. There was no effect of thyroidectomy on the time when oestrous cyclicity began in the Autumn but the onset of anoestrus was profoundly disrupted. All the ewes continued to cycle well beyond the end of the normal breeding season and a number have continued throughout the entire period of anoestrus.

Abnormalities in the immune system of children with beta-thalassaemia major

We have studied both the humoral and cell mediated immune systems of 23 children with beta-thalassaemia major. In children who had not been splenectomized, a 3-fold expansion in the number of circulating B cells and a modest polyclonal gammopathy was present. Of these patients 70% had decreased numbers of circulating T4 cells; 83% were unresponsive to skin testing with Candida albicans, and the majority had decreased lymphocyte proliferative responses in vitro. In children who had been splenectomized, there was a 10-fold increase in the number of circulating B lymphocytes and a 2-fold increase in the number of T4 and T8 cells present in peripheral blood. Additionally, these patients as a group were more responsive to both skin testing and lymphocyte stimulation in vitro with Candida albicans. Seven patients had an inverted T4/T8 ratio. One child has positive serology to HIV by ELISA and Western Blot techniques with a normal T4/T8 ratio. Thus, while children with thalassaemia are at risk for exposure to HIV, the immunological abnormalities associated with the disease and/or its treatment necessitates cautious interpretation of any AIDS-related immunological changes.

Comparison of the Leicester Micropalliator and the Cardiff Palliator in the relief of postoperative pain

Two devices for providing patient-controlled, on-demand analgesia were compared for 24 h after abdominal surgery. The Leicester Micropalliator delivered a mandatory background infusion of 1 mg h-1 in addition to on demand bolus doses of morphine 2 mg i.v. while the Cardiff Palliator provided only bolus doses of morphine 2 mg i.v. The Leicester Micropalliator provided analgesia superior or equivalent to that of the Cardiff Palliator in patients who had undergone hysterectomy or cholecystectomy, respectively, and there was no increase in side effects. The total doses of morphine administered over 24 h did not differ significantly between the two devices.

The intravenous intralipid tolerance test

The half-life of an intravenously injected bolus of intralipid 20% was measured in normal rats in order to asess its relationship to reticuloendothelial system (RES) activity. Groups of animals were studied following various treatments, and the results compared to measurement of carbon clearance in similar groups. The RES effects of silica and C parvum were confirmed by the carbon clearance test, but no effect was seen on the half-life of intralipid. Intralipid clearance was shortened by fasting and the administration of intravenous heparin, neither of which affected carbon clearance. It is concluded that the intravenous intralipid test has no place in the asessment of RES function.

Urolithiasis in the horse - a review of 13 cases

The presenting signs, treatment and postoperative progress of 13 horses with vesical and urethral calculi are reviewed. Single, discrete stones were present in 10 animals in which the results of treatment were generally good. In three horses with sabulous cystic deposits, urolithiasis was associated with bladder paralysis and the response to treatment was poor.