SUMMARY The diagnosis of autonomic neuropathy frequently depends on results of tests which elicit reflex changes in heart rate. Few well-documented normal ranges are available for these tests. The present study was designed to investigate the effect of age upon heart rate variability at rest and in response to a single deep breath, the Valsalva manoeuvre, and standing. A computerised method of measurement of R-R interval variation was used to study heart rate responses in 310 healthy subjects aged 18-85 years. Heart rate variation during each procedure showed a skewed distribution and a statistically significant negative correlation with age. Normal ranges (90% and 95% confidence limits) for subjects aged 20-75 years were calculated for heart rate difference (max-min) and ratio (max/min) and standard deviation (SD). Heart rate responses were less than the 95th centile in at least one of the four procedures in 39 (12-6%) out of the 310 subjects, and were below this limit in two or more tests in five (1 6%) subjects. In view of the decline in heart rate variation with increasing age, normal ranges for tests of autonomic function must be related to the age of the subject.

Biochemical cure of acromegaly was more strongly associated with pretreatment GH than with tumour size. Random/basal GH measurements are useful and convenient for the audit of treatment outcome in acromegaly. Ways of improving the biochemical outcome of acromegaly should be sought.

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The circadian rhythm of melatonin secretion from the pineal body is entrained to the light-dark cycle and is controlled via sympathetic fibres originating from the superior cervical ganglia. We have therefore examined plasma melatonin profiles in diabetics with and without evidence of autonomic neuropathy and in normal matched controls. The physiological increase in nocturnal plasma melatonin concentration was not observed in diabetics neuropaths. There was no consistent pattern in the diabetics without neuropathy; only three out of the eight subjects in this group had a sustained nocturnal increase in melatonin. Normal diurnal variation of plasma cortisol was present in all groups of subjects. The present study shows that diabetic patients with evidence of autonomic neuropathy lack the normal circadian changes of plasma melatonin concentration. This provides confirmation for the control of pineal function via the sympathetic nervous system in man. The impaired melatonin profiles observed in diabetic patients without apparent autonomic neuropathy suggest that a subclinical state of sympathetic denervation may exist in this group of diabetics.