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Studies of thyroid activity following hypothalamic lesions have provided indirect evidence of TSH influence on the pars distalis of birds. The present study examined the influence of hypothalamic lesions on TSH assays of the rostral and caudal lobes of the pars distalis. Lesions of the septomesencephalic tract increased TSH levels in the rostral lobe but had no influence on the caudal lobe. Lesions of the supraoptic or ventrolateral nuclei neither stimulated nor depressed TSH in either lobe of the pars distalis.

Metabolic clearance (MCR) and production rates (PR) of human thyrotropin (hTSH) were determined by the constant infusion to equilibrium method 57 times in 55 patients. 16 control patients had a mean hTSH MCR of 50.7 ml/min. The mean hTSH MCR was significantly (P < 0.02) higher in 19 euthyroid men (51.6 ml/min) than in 12 euthyroid women (43.0 ml/min), but this apparent sex difference disappeared when the MCR were corrected for surface area, 25.8 (men) versus 25.2 ml/min per m(2) (women). Hypothyroid patients had significantly (P < 0.005) lower hTSH MCR (30.9 ml/min), and hyperthyroid patients had significantly (P < 0.05) higher hTSH MCR (60.9 ml/min) than controls. The hTSH MCR in patients with "decreased thyroid reserve" (40.9 ml/min), hyperfunctioning thyroid nodule (53.8 ml/min), and "empty sella syndrome" (46.6 ml/min) were not significantly different from controls. The mean hTSH PR in controls (104.3 mU/day) was significantly (P < 0.005) different from that in patients with "decreased thyroid reserve" (956 mU/day), hypothyroidism (4,440 mU/day), hyperthyroidism (< 43.9 mU/day) and a hyperfunctioning thyroid nodule (< 38.7 mU/day). In primary hypothyroidism intravenous triiodothyronine therapy (50 mug/day) for 10 days decreased the hTSH PR (from 4,244 to 2,461 mU/day) before changes in the hTSH MCR (from 33.1 to 33.7 mU/day) were observed. These studies have demonstrated that changes in the serum concentration of hTSH are mainly due to altered pituitary hTSH secretion with only a minor contribution from the change in hTSH MCR.

A cytological and optical microscopic study of the anterior lobe of hypohysis in the Wistar adult rat 10, 30 or 60 minutes after intravenous injection of 50 mug of synthetic TRH discloses modifications of thyrotropic cells and prolactin cells. It's possible to recognize a quick degranulation of the prolactin cells (with a maximum at the 10th minute) and a slower degranulation of the thyrotropic cells (perceptible at the 10th minute and very pronounced at the 60th minute). The somatrotopic cells did not show any modification.

Ten patients (8 women, 2 men) with the "empty sella syndrome" were studied to evaluate the pituitary reserve of human thyrotropin (hTSH) and prolactin (hPRL). None of the patients had signs or symptoms of hypopituitarism or primary hypothyroidism. All patients had normal baseline thyroid function tests except for 2 patients with mild elevations in total triiodothyronine as measured by competitive protein displacement assay (T3D). Eight of ten patients had normal hTSH responses to thyrotropin releasing hormone (TRH), whereas the 2 patients with elevated T3D had blunted TRH responses. In the 4 patients studied, the metabolic clearance (MCR) and production rates (PR) of hTSH were normal. In 9 of 10 patients normal baseline serum hPRL levels were detected, and each responded to TRH. In one case serum hPRL was undetectable and failed to respond to TRH. The assessment of other anterior pituitary function revealed few minor abnormalities. In summary, like other anterior pituitary hormones, the pituitary reserve in "empty sella syndrome" of hTSH and hPRL is usually normal. When abnormalities do occur, they are attributable to other co-existent endocrine pathology.

The author discusses the problems of hormonal functions of normal placenta with particular reference to thyrotrophin of chorionic origin. The chemical structure and physiological activity of chorionic thyrotrophin are described and clinical syndromes caused by thyrotrophin secretion by pathologically changed placenta are discussed.