We determined the total activity and isoenzyme distribution of lactate dehydrogenase and creatine kinase in serum and biopsy specimens from skeletal muscle of nine normal individuals and nine patients with Duchenne muscular dystrophy (I), five with collagen disease (II), and four with non-progressive unclassified myopathy (III). Mean total serum creatine kinase in patients with Duchenne muscular dystrophy (867 U/liter, SD = 197) was 31-fold that in the control group (28 U/liter, SD = 14). There was also a small (3.3-fold) increase in the mean total serum creatine kinase of patients with III, but none in the serum from patients with II. Changes in the creatine kinase isoenzyme distribution of skeletal muscle were primarily in the MB isoenzyme. The mean percentage of creatine kinase-MB activity in muscle from patients with I (2.81, SD = 1.15) and patients with III (1.69, SD = 1.07) significantly (P less than 0.005) exceeded that of the control group (0.43, SD = 0.18). Muscle from patients with II showed little change. The most striking changes in lactate dehydrogenase were also observed in patients with I, in whom the mean total serum activity (356 U/liter, SD = 115) was 3.4-fold that of serum from the control group (105 U/liter, SD = 19). Skeletal muscle from these patients also showed a significant decrease in mean percent isoenzyme 5 activity (from 50 to 23) and an increase in that of isoenzymes 1 and 2 (from 1 to 9 and 8 to 20, respectively). These changes in the distribution of these two sets of isoenzymes in muscle were reflected in the serum.

The relationship between age and TSH response to TRH was studied in 40 men with unipolar major depressive disorder (range 24-65 years, mean 44.7 years) and 36 healthy male volunteers of similar ages. Both groups were subdivided into younger and older than 40 years of age. "Blunted" TSH response to TRH was observed in 58% of depressed men and in 28% of controls, using a dTSH maximum of less than or equal to 6 microU/ml as a cut-off criterion. Older healthy men had a higher blunting rate (40%) than the younger group (19%). In depressed patients, by contrast, the blunting rate was 50% in the older group and 65% in the younger group. Higher mean maximum dTSH, higher basal TSH and lower mean circulating FT4 levels were also noted in older depressed men, suggestive of a subtle thyroid subsensitivity to TSH stimulation and subclinical primary hypothyroidism that may have contributed to the depression. Age is known to be a confounder of TRH test results. There may be a subset of depressed patients over 40 where the confounding effect of age is associated with an exaggerated, rather than decreased TSH response to TRH.

Levels of circulating total thyroxine (TT4), free thyroxine (FT₄), total triiodothyronine TT3 and thyrotropin (TSH) were determined in 27 men with unipolar major depressive disorder ages 24–50, mean ± SEM 36.9 ± 2.9 years, and 38 healthy controls (HC) ages 20–50, mean ± SEM 34.2 ± 3.1 years. No significant differences were observed between HC and depressed men with regard to TT4 and FT4. Mean TT3 levels were lower, and mean TSH levels higher in depressed patients than in HC, p < 0.05 for both, compatible with possible subclinical primary hypothyrodism in depressed patients. Consistent with this, an inverse correlation between basal TSH values and TT₃ (r = –0.38, p < 0.05) was noted in depressed but not in HC subjects.

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