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SWALLOWED NEONATAL ENDOTRACHEAL TUBE
421 some other container for dipping and a third container used for transmission to the laboratory (few wide-mouthed containers are watertight). This difficulty leads me to prefer the Mackey spoon. The plastic Mackey spoons used to be resistant to heat and capable of re-use. It seems that because of this it was not profitable to make them and now only polyethylene spoons, which melt when heated, can be obtained. This makes the Mackey-spoon technique more expensive than it used to be, but it is still much cheaper than uricult slides. The spade-shaped dip-spoon recently devised by Oxoid Ltd. is likely to be as good as the Mackey spoon, but if a " good " MacConkey medium is made there is no need to use two different media on the same dip-spoon or slide. Public Health
Winchester.
Department of Obstetrics and Gynecology, Kaiser Foundation Hospital, San Francisco, California.
ARON STORCH.
PLASMA-CATECHOLAMINE ESTIMATIONS SIR,-We would like to point out that our article on the validity of plasma-catecholamine estimationswas in no way intended to detract from the method of McCullough,2 as might be inferred from the letter of Miss Davis and Mr. Sheridan (Aug. 15, p. 364), but rather to add to it. For example, we found that both the sensitivity and reproducibility of the method could be considerably improved by certain modifications, particularly by stabilising the temperature of the final fluorescent mixture, of which the original McCullough method makes no mention. It is well recognised3 that failure to do this, especially at low concentrations of catecholamines, may cause variations of up to 14°per degree centigrade change in temperature. The common occurrence of variation in laboratory temperature of up to 10°C has been regarded as invalidating all methods where this has not been taken into account.33 Further, the McCullough method only states that the blood-sample should be chilled in ice for an unspecified
period, until centrifuged. In our experience this may result in considerable losses, as may be seen in tables IV and v of our article. Their point about the presence of catechol-o-methyl transferase in red blood-cells, we ourselves endeavoured to illustrate in fig. 3. Our work also suggests that each of the wide range of amine oxidases in blood is likely to be highly substrate-specific, which makes it difficult to ensure their absence from any particular
fraction. Carruthers, M., Taggart, P., Conway, N.,
Bates,
D., Somerville, W.
Lancet, July 11, 1970, p. 62. H.
Courtauld Institute of Biochemistry and Department of Cardiology, Middlesex Hospital, London W.1, and Institute of Ophthalmology, London W.C.1.
M. H. HUGHES.
SWALLOWED NEONATAL ENDOTRACHEAL TUBE SIR,-With reference to the article by Dr. Abrahams and his colleagues (July 18, p. 135) may I refer you to an article in the July, 1970, issue of the Journal of Pediatrics (p. 123) ? In this, Dr. G. C. Calderwood and I suggested the attachment of a silk suture, or any other nonabsorbable type of suture, to the end of the endotracheal tube. This prevents any problem arising if the tube is swallowed, since the suture allows easy removal. The suture, inserted in the horizontal plane to prevent kinking of the tube, does not interfere with any attachment to the tube. Obviously the redesigned tube, possibly with an extension of the initial tube, would be preferable even to this method.
2. 3.
we note
can
MALCOLM CARRUTHERS PETER TAGGART WALTER SOMERVILLE.
Laboratory,
Royal Hampshire County Hospital,
1.
under " the effect of prolonged storage ", influence the rate of decay of catecholamines. However, experiments on deproteinised plasma indicate that blood pH is unlikely to be the factor responsible for the in-vitro decay which we have demonstrated. We hope that the points we made will prove helpful to other investigators and narrow the scope for potential error, so that this useful method of investigation will not fall into disreoute.
As
pH
McCullough, J. clin. Path. 1968, 21, 759. Gerst, E. C., Steinsland, O. S., Walcott, W. W. Clin. Chem. 1966, 12, 659.
GLUCAGON AND THE HEART
SiR,-Your excellent editorial on glucagon (July 18, p. 137) requires further comment. You quote the results of Glick1 comparing the effects of glucagon, noradrenaline, isoprenaline, and dopamine on renal blood-flow; but these are based on an unphysiological experimental design. Noradrenaline, isoprenaline, and dopamine are rarely if ever used clinically or experimentally by single-bolus injection, as they were in this investigation. In addition, the concentration of dopamine used is known to produce peripheral and renal vasoconstriction. In physiological doses by constant infusion, dopamine decreases renal resistance as as increasing cardiac output.2,3 Cardiology Service Department of Medicine, Montefiore Hospital,
well
Bronx, N.Y. 10467.
ROBERT ROSENBLUM.
COXSACKIE MYOCARDITIS OF THE NEWBORN SIR,-In 1958,4 we reported on 8 cases of Coxsackie-B, myocarditis in newborn children. 4 lived, and we have traced 3 of them, now aged 13 years. Prof. V. Schrire, of the cardiology department, University of Cape Town, has lately examined them and reports that they are clinically, radiologically, and electrocardiographically normal. P. V. SUCKLING Cape Town, L. VOGELPOEL. South Africa.
COMPARISON OF ANTIHYPERTENSIVE AGENTS SIR,-Imust take issue with
(Aug. 8,
p.
Dr. liibb and his
colleagues
275) for the levity with which they dismiss the
contribution of thiazide in the reduction of blood-pressure of the patients in whom they compared bethanidine, tx-methyldopa, and reserpine. The level of untreated pressure of their patients was not remarkably high (mean diastolic pressure about 116 mm. Hg). The dose of thiazide used was substantial, but, as might have been expected, the doses of trial drugs which had to be added to the thiazide were small. There is no evidence that the reduction in blood-pressure achieved in their patients could not be attributed in great part to the thiazide, and that the contribution of the trial drugs in the doses in which they were used was not trivial and incidental. Without a control group treated with thiazide alone I fear that no meaningful conclusions about the relative merits of bethanidine, oc-methvldopa, and resernine can be drawn from their work. Mater Hospital, Dublin 7. 1. 2.
AUSTIN T. CARTY.
Glick, G. Clin. Res. 1970, 18, 307.
McDonald, R. H., Jr., Goldberg, L. I., McNay, J. L., invest. 1964, 43, 1116. 3. Rosenblum, R., et al. Clin. Res. 1970, 18, 326. 4. Suckling, P. V., Vogelpoel, L. Med. Proc. 1958, 4, 372.
et
al. J. clin.
Winchester.
Department of Obstetrics and Gynecology, Kaiser Foundation Hospital, San Francisco, California.
ARON STORCH.
PLASMA-CATECHOLAMINE ESTIMATIONS SIR,-We would like to point out that our article on the validity of plasma-catecholamine estimationswas in no way intended to detract from the method of McCullough,2 as might be inferred from the letter of Miss Davis and Mr. Sheridan (Aug. 15, p. 364), but rather to add to it. For example, we found that both the sensitivity and reproducibility of the method could be considerably improved by certain modifications, particularly by stabilising the temperature of the final fluorescent mixture, of which the original McCullough method makes no mention. It is well recognised3 that failure to do this, especially at low concentrations of catecholamines, may cause variations of up to 14°per degree centigrade change in temperature. The common occurrence of variation in laboratory temperature of up to 10°C has been regarded as invalidating all methods where this has not been taken into account.33 Further, the McCullough method only states that the blood-sample should be chilled in ice for an unspecified
period, until centrifuged. In our experience this may result in considerable losses, as may be seen in tables IV and v of our article. Their point about the presence of catechol-o-methyl transferase in red blood-cells, we ourselves endeavoured to illustrate in fig. 3. Our work also suggests that each of the wide range of amine oxidases in blood is likely to be highly substrate-specific, which makes it difficult to ensure their absence from any particular
fraction. Carruthers, M., Taggart, P., Conway, N.,
Bates,
D., Somerville, W.
Lancet, July 11, 1970, p. 62. H.
Courtauld Institute of Biochemistry and Department of Cardiology, Middlesex Hospital, London W.1, and Institute of Ophthalmology, London W.C.1.
M. H. HUGHES.
SWALLOWED NEONATAL ENDOTRACHEAL TUBE SIR,-With reference to the article by Dr. Abrahams and his colleagues (July 18, p. 135) may I refer you to an article in the July, 1970, issue of the Journal of Pediatrics (p. 123) ? In this, Dr. G. C. Calderwood and I suggested the attachment of a silk suture, or any other nonabsorbable type of suture, to the end of the endotracheal tube. This prevents any problem arising if the tube is swallowed, since the suture allows easy removal. The suture, inserted in the horizontal plane to prevent kinking of the tube, does not interfere with any attachment to the tube. Obviously the redesigned tube, possibly with an extension of the initial tube, would be preferable even to this method.
2. 3.
we note
can
MALCOLM CARRUTHERS PETER TAGGART WALTER SOMERVILLE.
Laboratory,
Royal Hampshire County Hospital,
1.
under " the effect of prolonged storage ", influence the rate of decay of catecholamines. However, experiments on deproteinised plasma indicate that blood pH is unlikely to be the factor responsible for the in-vitro decay which we have demonstrated. We hope that the points we made will prove helpful to other investigators and narrow the scope for potential error, so that this useful method of investigation will not fall into disreoute.
As
pH
McCullough, J. clin. Path. 1968, 21, 759. Gerst, E. C., Steinsland, O. S., Walcott, W. W. Clin. Chem. 1966, 12, 659.
GLUCAGON AND THE HEART
SiR,-Your excellent editorial on glucagon (July 18, p. 137) requires further comment. You quote the results of Glick1 comparing the effects of glucagon, noradrenaline, isoprenaline, and dopamine on renal blood-flow; but these are based on an unphysiological experimental design. Noradrenaline, isoprenaline, and dopamine are rarely if ever used clinically or experimentally by single-bolus injection, as they were in this investigation. In addition, the concentration of dopamine used is known to produce peripheral and renal vasoconstriction. In physiological doses by constant infusion, dopamine decreases renal resistance as as increasing cardiac output.2,3 Cardiology Service Department of Medicine, Montefiore Hospital,
well
Bronx, N.Y. 10467.
ROBERT ROSENBLUM.
COXSACKIE MYOCARDITIS OF THE NEWBORN SIR,-In 1958,4 we reported on 8 cases of Coxsackie-B, myocarditis in newborn children. 4 lived, and we have traced 3 of them, now aged 13 years. Prof. V. Schrire, of the cardiology department, University of Cape Town, has lately examined them and reports that they are clinically, radiologically, and electrocardiographically normal. P. V. SUCKLING Cape Town, L. VOGELPOEL. South Africa.
COMPARISON OF ANTIHYPERTENSIVE AGENTS SIR,-Imust take issue with
(Aug. 8,
p.
Dr. liibb and his
colleagues
275) for the levity with which they dismiss the
contribution of thiazide in the reduction of blood-pressure of the patients in whom they compared bethanidine, tx-methyldopa, and reserpine. The level of untreated pressure of their patients was not remarkably high (mean diastolic pressure about 116 mm. Hg). The dose of thiazide used was substantial, but, as might have been expected, the doses of trial drugs which had to be added to the thiazide were small. There is no evidence that the reduction in blood-pressure achieved in their patients could not be attributed in great part to the thiazide, and that the contribution of the trial drugs in the doses in which they were used was not trivial and incidental. Without a control group treated with thiazide alone I fear that no meaningful conclusions about the relative merits of bethanidine, oc-methvldopa, and resernine can be drawn from their work. Mater Hospital, Dublin 7. 1. 2.
AUSTIN T. CARTY.
Glick, G. Clin. Res. 1970, 18, 307.
McDonald, R. H., Jr., Goldberg, L. I., McNay, J. L., invest. 1964, 43, 1116. 3. Rosenblum, R., et al. Clin. Res. 1970, 18, 326. 4. Suckling, P. V., Vogelpoel, L. Med. Proc. 1958, 4, 372.
et
al. J. clin.