INTERACTIONS OF ADRENERGIC BLOCKING DRUGS WITH THE IN VIVO RELEASE OF THYROID HORMONE INDUCED BY THYROTROPHIN AND THE LONG-ACTING THYROID STIMULATOR

Abstract

ABSTRACT The interactions of adrenergic blocking drugs with the thyroid hormone-releasing effects of thyrotrophin (TSH), the long-acting thyroid stimulator (LATS) and l-isoprenaline (IPNA) were studied by measuring blood radioiodine levels in 131I-injected, thyroxine-blocked mice. Pretreatment with the alpha adrenergic blocking drug phenoxybenzamine (PhBA) reduced the 2 h blood 131I response to TSH, and also reduced the 2 and the 8 h responses to LATS, whereas the TSH-like response to IPNA was either augmented or unaffected. Similar results were obtained with another alpha blocker, phentolamine (PhA). Neither the l- nor the d-isomer of the beta blocker propranolol (l-Pro and d-Pro) reduced the responses to TSH or LATS, although l-Pro abolished the response to IPNA. These findings support the concept of a common mechanism for the actions of TSH and LATS, on the in vivo release of thyroid hormone. The same mechanism may be involved in the TSH-like effect of several biogenic monoamines, since the blood 131I responses to these, according to previous findings, are also inhibited by alpha blockers. The non-biogenic IPNA, however, seems to differ from TSH and the biogenic monoamines in its initial interaction with the thyroid cell.