Propranolol withdrawal and thyroid function in the rabbit

ABSTRACT

Propranolol without manifestations is now known to have strong correlation to thyroid hormones. Conflicting results are reported by different workers regarding the influence of sudden propranolol withdrawal on the different parameters related to thyroid functions. The present study was conducted on adult male rabbits to explore the effect of propranolol administration [30 mg/kg/day orally] for four weeks and its subsequent withdrawal on the pituitary thyroidaxis; namely, serum TSH, total T4, free T4, total T3 and free T3. The withdrawal period ranged from one day and extended up to 12 days. Total serum T3 was found to be significantly reduced following the prolonged daily oral administration of propranolol, while propranolol withdrawal led to a significant elevation of serum free T3 as compared with three and six days following drug cessation. These results emphasized the importance of free T3 in the production of propranolol withdrawal manifestations, while the nonsignificant changes of serum total T3 on propranolol withdrawal may be due to changes in serum protein binding capacity affecting total T3 but not free T3