The mechanism involved in the decreased numbers of several trans-
membrane proteins such as
sodium pump sites,
sodium-
lithium countertransport,
sodium potassium cotransport
proteins,
proteins mediating the passive efflux of
sodium and
insulin receptors in erythrocytes from patients with
hyperthyroidism is not known. The
ATP-dependent proteolytic system which is involved in the loss of trans-
membrane proteins during the maturation of the reticulocyte may be involved in the accelerated loss of these
membrane proteins. Therefore, the effect of
thyroid hormones on the
ATP-dependent proteolytic activity of reticulocyte lysates was examined in this study.
Reticulocytosis was induced in 14 guinea pigs by
phenylhydrazine hydrochloride injections for 5 consecutive days followed by 2 days of rest. T3 (10 micrograms/100 g
body weight) was injected into 7 animals on day 4 and day 6. Reticulocyte-rich blood was withdrawn on day 8. Oxygen consumption determined 24 hours after injection of T3 was 25% higher (p less than 0.01) and T3 treated animals had a 2.5 fold higher (p less than 0.01)
weight loss than control animals. The
ATP-dependent proteolytic activity measured in reticulocyte lysates using 125I labelled
lysozyme was 3.6 fold higher in the T3 than in the control group of guinea pigs (p less than 0.01). We conclude that
thyroid hormones induce the
ATP-dependent proteolytic activity of reticulocyte lysates which may be responsible for the reduced number of several trans-
membrane proteins found in erythrocytes from patients with
hyperthyroidism.