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When rats are fed a protein deficient (PD) diet for 7 days, rates of proteolysis in skeletal muscle decrease by 40-50% (N. E. Tawa, Jr., and A. L. Goldberg. Am. J. Physiol. 263 (Endocrinol. Metab. 26): E317-325, 1992). To identify the underlying biochemical adaptations, we measured different proteolytic processes in incubated muscles. The capacity for intralysosomal proteolysis, as shown by sensitivity to methylamine or lysosomal protease inhibitors, fell 55-75% in muscles from PD rats. Furthermore, extracts of muscles of PD rats showed 30-70% lower activity of many lysosomal proteases, including cathepsins B, H, and C, and carboxypeptidases A and C, as well as other lysosomal hydrolases. The fall in cathepsin B and proteolysis was evident by 3 days on the PD diet, and both returned to control levels 3 days after refeeding of the normal diet. In muscles maintained under optimal conditions, 80-90% of protein breakdown occurs by nonlysosomal pathways. In muscles of PD rats, this ATP-dependent process was also 40-60% slower. Even though overall proteolysis decreased in muscles of PD rats, their capacity for Ca(2+)-dependent proteolysis increased (by 66%), as did the activity of the calpains (+150-250%). Thus the lysosomal and the ATP-dependent processes decrease coordinately and contribute to the fall in muscle proteolysis in PD animals.

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SUMMARY Autonomic function was assessed in subjects with acute intermittent porphyria and age-and sex-matched controls using five different bedside tests of cardiovascular reflexes. During the acute attack both parasympathetic and sympathetic tests were impaired, but subsequently improved during remission. Early parasympathetic dysfunction was also detected during remission and in latent asymptomatic acute intermittent porphyria.Acute intermittent porphyria is an autosomal dominant inborn error of metabolism characterised by a partial deficiency in the activity of the haem biosynthetic enzyme, porphobilinogen deaminase (PBG). Consequently the porphyrin precursors delta-aminolaevulinic acid (ALA) and porphobilinogen (PBG) accumulate in blood and are excreted in excessive amounts in the urine.' 2The clinical manifestations of acute intermittent porphyria have been attributed to a widespread neurological dysfunction caused by the block in haem biosynthesis.34 Abdominal pain is the commonest and often the most troublesome symptom which occurs in more than 90% of cases.5 It has been explained on the basis of splanchnic autonomic dysfunction, thus providing a mechanism for the intestinal dilatation and stasis occasionally noted radiologically and at laparotomy in patients suffering from an acute attack.6 Indeed, many of the accompanying features of an acute attack are suggestive of autonomic neuropathy; namely, the inappropriate sinus tachycardia, labile hypertension, postural hypotension, excessive sweating, severe vomiting, constipation and occasional diarrhoea and sphincteric bladder problems.5 78 Ridley et al have reported that tachycardia invariably preceded the development of peripheral neuropathy and respiratory paralysis, and they postulated that the tachycardia of porphyria might be due to autonomic cardioneuropathy.5 The transient and labile hypertension which commonly accompanies the acute attack has also been given a neurogenic explanation follow-

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