Noradrenergic mechanisms in the brain and peripheral organs of normotensive and spontaneously hypertensive rats at various ages

Previous studies of noradrenergic mechanisms in spontaneously hypertensive rats (SHR) have yielded conflicting results, as many have used: 1) rats of only one age; 2) a single organ such as heart or brain; or 3) either Wistar-Kyoto (WKY) or an outbred normotensive control rat. We have studied the turnover of norepinephrine (NE) in three brain areas (cortex, hypothalamus, brain stem) and three peripheral organs (duodenum, skeletal muscle, kidney) of SHR, WKY, and Wistar rats at 5, 9, and 18 weeks of age. The rate of decline of norepinephrine [NE] in tissue was determined with a fluorescence assay at 0, 2, 4, and 8 hours after inhibition of tyrosine hydroxylase with alpha-methyltyrosine. Differences in NE turnover were inferred by comparing slopes of regression lines calculated for the plot of log [NE] (expressed as a percent of the initial concentration) vs time. Systolic arterial pressure of SHR was similar to that of WKY and Wistar rats at 5 weeks of age, but increased to 150 mm Hg by 9 weeks and reached an average of 190 mm Hg by 18 weeks. The turnover of NE in 5-week-old SHR compared to two normotensive strains was significantly lower in the cortex and significantly higher in the kidney and skeletal muscle. By 9 weeks, in SHR, NE turnover had increased significantly in the hypothalamus and brain stem, while decreasing significantly in the kidney and duodenum. No such changes were seen in these organs of WKY or Wistar rats when comparing turnover of NE at 5 and 9 weeks. At 18 weeks, there were no further differences in the organs of SHR when compared to values obtained at 9 weeks. These data support the hypothesis that the turnover of NE may be altered in central and peripheral organs of young SHR, and may initiate or contribute to the development of hypertension. Changes in turnover of NE in the brain and peripheral organs between 5 and 9 weeks in SHR suggest compensatory responses to increasing arterial pressure; however, similar changes in turnover were not seen between 9 and 18 weeks, although arterial pressure continued to increase.

Cerebrospinal fluid cyanide after nitroprusside infusion in man

Sodium nitroprusside (SNP) is frequently used as an hypotensive agent for clipping of intracranial aneurysms, repair of arteriovenous malformations and resection of vascular tumours. Cyanide (CN), which is its main metabolic product, has been recovered from the cerebrospinal fluid (CSF) of the rat after intravenous administration of CN, but recovery of CN from CSF after SNP has not been reported in man. Seven consenting adults were studied. Adequate premedication was provided with pentobarbitone 2 mg x kg-1 and atropine 0.4 mg one hour before operation. Anaesthesia was induced with thiopentone 8 mg x kg-1 and maintained with nitrous oxide 60 per cent with oxygen and supplemental fentanyl 0.05 mg and pancuronium 0.5-1 mg as needed. Lumbar subarachnoid, radial artery, central venous, and Foley urinary catheters were inserted. Arterial carbon dioxide tension (PaCO2) was maintained between 4.6-5.32 kPa (35-40 torr) with an Air Shields ventilator. Red cell, plasma and CSF cyanide were measured using a digital ionanalyzer before and at 30 minutes interval after infusing SNP at a rate sufficient to maintain the blood pressure at two thirds of the pre-operative level. Average total dose of SNP was 0.51 mg x kg-1. CN concentration in the red blood cells increased from 9.5 +/- 2.05 to 75.12 +/- 17.12. Plasma CN increased from 0.54 +/- 0.05 to 1.09 +/- 0.14 micrograms per cent. CSF CN increased from 0.11 +/- 0.04 to 0.72 +/- 0.07 micrograms per cent. Significant increase in red cell, plasma and CSF CN occurred five minutes after the start of SNP and returned to the preoperative level 19 hours later. Conclusion CN crosses the blood-brain barrier. Large doses of SNP in patients with neurovascular brain disorders warrants caution because cytotoxic cerebral oedema and CN encephalopathy have been described in rats after intravenous injection of sodium cyanide or exposure to hydrogen cyanide.

Noradrenergic mechanisms in brain and peripheral organs after aortic nerve transection

Noradrenergic mechanisms were studied in the hypothalamus, midbrain, medulla, kidney, duodenum, and skeletal muscle of Wistar rats at 3 or 13 days after either bilateral transection of the aortic depressor nerve (ADN) or a sham operation. The rate of decline of tissue norepinephrine (NE) concentration after inhibition of tyrosine hydroxylase with alpha-methyltyrosine was used as an index of NE turnover. Three days after ADN transection, arterial pressure and heart rate were elevated significantly, and NE turnover was increased in all three brain areas, kidney, and skeletal muscle but not in duodenum. The largest change occurred in skeletal muscle, where the time required for tissue NE concentration to decline to 50% of control decreased from 9.0 to 2.5 h. In rats 13 days after ADN transection, arterial pressure was significantly higher than in sham-operated controls, but heart rate was similar to control values. NE turnover was slightly increased in hypothalamus but was not significantly different in muscle and kidney when compared to sham-operated controls. These results suggest that 3 days after ADN transection in the rat, arterial pressure is elevated as a result of increased activity of noradrenergic neurons in the hypothalamus and brain stem, which is translated into increased sympathetic nerve activity to peripheral organs, particularly skeletal muscle. The normal turnover of NE in peripheral organs 13 days after ADN transection suggests that mechanisms other than increased sympathetic activity are responsible for maintaining the elevated arterial pressure.

Extradural analgesia revisited. A statistical study

The results of 334 lumbar extradural analgesics, administered in a standard manner, allowed reassessment of some factors influencing the spread of local anaesthetic solution in the extradural space. There was no evidence of increased spread in patients with degenerative vascular disease when compared with a control group free from such disease. The patient's height and age had a small effect on spread. The results contradict the earlier assumption of a direct relationship between the volume of anaesthetic solution injected and the number of segments blocked.

Comparative effects of nondepolarizing muscle relaxants on succinycholine-induced fasciculations and postoperative pain

The effectiveness of pancuronium (1.0 to 1.5 mg), d-tubocurarine (3 mg), and gallamine (20 mg) administered three minutes before succinylcholine (1 mg/kg) in preventing muscle fasciculations and postoperative muscle pains was compared in 100 patients. Pretreatment with pancuronium abolished fasciculations and produced rapid and excellent muscle relaxation for endotracheal intubation. Both d-tubocurarine (dTc) and gallamine administered prior to succinylcholine (SCh) were inconsistent in prevention fasciculations. Muscle relaxation was significantly delayed in onset, shorter in duration, and was inadequate for intubation in the majority of patients. The 45% incidence of postoperative muscle pains in the control group decreased after pretreatment with gallamine, dTc, and pancuronium to 20%, 15%, and less than 5%, respectively. It was concluded from the present study that pancuronium is superior to dTc and gallamine for preventing SCh-induced fasciculations and postoperative muscle pains without compromising the muscle relaxation for intubation. However, pancuronium administered for pretreatment may significantly prolong the action of succinylcholine and caution is to be exercised in patients having short surgical procedures and when additional doses of muscle relaxants may be required.

Electrocardiographic abnormalities in the sick elderly

From a study of routine electrocardiography on 300 ill elderly patients in an acute geriatric unit, it is evident that the incidence of atrial fibrillation, ventricular extrasystoles, myocardial ischaemia and myocardial infarction is much higher than in the general population of similar age group. In females, the incidence increases with advance in age. It is suggested that the time is ripe for a large multicentre study which would help to decide the true incidence and significance of the abnormalities.

The effect of assisted ventilation on arterial carbon dioxide

The effect on the arterial carbon dioxide tension of assisting spontaneously breathing patients under halothane anaesthesia has been studied. A reduction in PaCO2 is usually seen, but it was reduced below 40 torr in only 30 per cent of cases, while a rise was recorded in 20 per cent.