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

Abstract

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/kg/week, for a period of 4—18 months. Three groups of patients were identified according to their T4 levels before and during the treatment. Group 1: 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 T3RSU 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 response to TRH 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. In contrast, 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. These results suggest that various degrees of TRH deficiency 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.