753 known pressor factors. We do not feel, however, that the two cases presented necessarily support this claim. When renal-vein-renin ratios are close, especially with low renin levels, determinations of renal blood-flow may be required to establish whether a kidney is secreting renin inappropriately. The development of new inhibitors of angiotensin 11 formation or true competitive antagonists of this vasoactive peptide may help to select more reliably patients with renin-

dependent hypertension. Department of Medicine,

General Infirmary, Leeds LS1 3EX

S. G. BALL R. D. THOMAS M. R. LEE

THE SEARCH FOR "MENOTOXIN"

SIR,- There are enough resemblances between plant and human biochemistry to make "menotoxin" (an acetone-soluble substance extractable from menstrual fluid and toxic to plants’-3) more than just a curiosity. In physiological amounts any "toxic" effects it may have on the menstruating woman herself are much less than the dramatic effects demonstrable on some plants, but if menotoxin could be isolated subtler effects on the human body might be sought. First, however, a more reliable plant test system is needed. Crude extracts containing mainly lipid material were made4 from menstrual dressings provided by students not taking oral contraceptives and, as controls, from unused tampons and towels. The method of extraction excludes bacterial contamination at this stage. The succulent plant Kalanchae blosfeldtiana may be induced to flower by exposure to a short-day regimen, followed by transfer to a long-day regimen. Individual plants may produce scores of flowers all in a similar stage of development.Flowers which are removed from the plant and incubated in humidity chambers at 250C with their stalks in a solution containing antibiotics (chloramphenicol and streptomycin, each at 25 g/ml) and the plant-growth substance kinetin (5 pLmoI/1) remain healthy for up to 20 days. Eventually, the petals lose their red colour and turn brown, probably because of the oxidation of polyphenols released during cell lysis. This loss of pigmentation followed by lysis and browning is similar to that seen in ageing leaves; and, as in leaves, senescence of Kalanchl1e flowers is much accelerated by the plant-growth substance abscisic acid (at 1 mmol/1). Senescence of excised Kalanchoe flowers was also much accelerated by menstrual extracts (made up in antibiotic-kinetin solution), whereas extracts from unused tampons did not have this effect. The acceleration was not due to acidity (pH 5-4) because menstrual extracts buffered at pH 7-4 had similar effects to unbuffered extracts, and control solutions buffered at pH 5.4 did not accelerate senescence. Nor was it due to more rapid growth of microorganisms in menstrual extracts, for, when we incubated flowers in solutions containing no antibiotics and sucrose (0-2mol/1) as an extra carbon source, the resultant heavy microbial contamination did not accelerate flower senescence. We conclude that a component of menstrual extracts causes an acceleration of senescence in excised Kalanchöe flowers. That much is fact; what follows is largely speculation. Since high concentrations of prostaglandin E1 (P.G. E1) induce the development of plant acid phosphatasecould "menotoxin" be one or more of the prostaglandins6 found in menstrual extracts? We tested prostaglandins E l’ E2’ F 1 cx, and F:zcx in concentrations similar to those found in menstrual extracts, and found them inactive on our system; so were p.G.A.1, A2. and 1. Reid, H. E. Lancet, 1974, 1, 988. 2. David, G. ibid. p. 1172. 3. Pickles, V. R. ibid. p. 1292. 4. Chtheroe, H. J., Pickles, V. R. J. Physiol. Lond. 1961, 156, 255. 5. Curry, S. C., Galsky, A. G. Plant Cell Physiol. Tokyo, 16, 799. 6. Pickles, V. R., Hall, W. J., Best, F. A., Smith, G. N. J. Obstet. Commonw. 1965, 72, 185.

many other prostaglandins and related substances not yet tested. An alternative approach might be to seek in menstrual extracts substances known for their toxic effects on plants. One possibility is fusaric acid, a plant-growth inhibitor produced by fungi and sometimes used for treatment of hypertension because it inhibits dopamine-p-hydroxylase. A concentration of 1 mmol/1 was clearly active in our experimental system, having effects similar to those of abscisic acid and the menstrual extracts. Hartmann and Keller-Tescfikel found that 600 mg of fusaric acid followed by three 500 mg doses of oral levodopa produced temporary effects that might be called psychotomimetic. So far as we know, fusaric (5-butylpicolinic) acid has not been identified as a product of human or mammalian metabolism, although picolinic acid is an isomer of nicotinic acid. We are not suggesting that the mood changes before or during menstruation are exactly like those found by Hartmann and Keller-Teschke, and even less that the menotoxin is fusaric acid-indeed, there is no evidence that the menotoxin is a single substance or that the menstruating uterus is its only human source. However, the example of fusaric acid does show the possibility of there being substances capable of interacting both with plant and human metabolism, in a manner relevant to the mood changes in the menstrual but there

B,,

phase. Departments of Botany and University College,

Br.

J. A. BRYANT

of Physiology,

D. G. HEATHCOTE V. R. PICKLES

P.O. Box 78, Cardiff CF1 1XL

CIRCADIAN VARIATION IN HUMAN BRAIN ENZYMES

SIR,-While investigating the effects of various factors

on

cerebral enzyme activities in

patients with no neurological or psychiatric abnormality we found that enzyme activity varied significantly with time of death. Most of the enzymes so far measured in the frontal cortex (including glutamate decarboxylase, choline acetyltransferase, hexokinase, and acetylcholinesterase) appear to undergo fluctuations throughout the 24 h period. The size and phase of these changes differed in the various enzymes. Data for acetylcholinesterase, which hydrolyses the putative neurotransmitter acetylcholine, are shown in the table. The ACETYLCHOLINESTERASE ACTIVITIES IN FRONTAL CORTEX (BRODMANN AREA 10) OF NORMAL SUBJECTS

* Estimated by the method of Ellman

et

al.’ and

expressed

as

mean-rS.E.M.

f Difference (estimated by (P

Circadian variation in human brain enzymes.

753 known pressor factors. We do not feel, however, that the two cases presented necessarily support this claim. When renal-vein-renin ratios are clos...
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