Induction of the ATP-dependent proteolytic system in guinea pig reticulocyte lysates by triiodothyronine

Abstract

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. T 3 (10μg/100g 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 Reticulocyte-rich blood was withdrawn on day 8.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 T 3 was 25% higher (p<0.01) and T 3 treated animals had a 2.5 fold higher (p<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 T 3 than in the control group of guinea pigs (p<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.