The effect of hGH on hypothalamic-pituitary-thyroid function in patients with pituitary dwarfism

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Abstract
The effect of growth hormone (hGH) on the hypothalamic-pituitary-thyroid function was studied in patients with pituitary dwarfism. Twenty-six patients were given KABI hGH, 0.5 U[units]/kg per wk, for a period of 4-18 mo. Three groups of patients were identified according to their T4 [thyroxine] levels before and during the treatment. Group I: T4 levels were initially normal and stayed in the normal range throughout a course of treatment. Group 2: T4 levels were initially normal but dropped to the subnormal range after hGH. Group 3: T4 levels were initially subnormal and decreased further after hGH. Changes in T4 levels after hGH in groups 2 and 3 were accompanied by a decrease in plasma T3[triiodothyronine]RSU without concomitant decrease in plasma T3. Clinically, most of them lacked symptoms and signs of hypothyroidism and exhibited a good growth response to hGH. Plasma TSH [thyrotropin] response to TRH [thyroliberin] in these patients revealed a sustained delayed pattern, which was suggestive of hypothalamic hypothyroidism. This pattern of TSH response to TRH became further exaggerated after hGH therapy. TSH response to TRH among patients in group 1 was normal and was not influenced by hGH. Administration of 4.0 U of KABI hGH daily for 21 consecutive days to 3 patients resulted in a shortened half-life of T4 and inversely prolonged that of T3. Various degrees of TRH deficiency apparently exist among patients with idiopathic pituitary dwarfism. Therapy with hGH discloses a mild TRH deficiency by accelerating the half-life of T4. This also causes a further drop in the T4 levels in those with marked TRH deficiency. The development of clinical hypothyroidism is not so obvious in these patients because of inverse delay in half-life of T3 by hGH.

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