Additional recombinant hormones now approved

Two additional recombinant hormones have recently gained marketing approval thyroid-stimulating hormone and calcitonin. 

TSH is approved for medical use as a diagnostic aid in the detection of thyroid cancer/thyroid remnants in post-thyroidectomy patients. Thyroid cancer is relatively rare, exhibiting the highest incidence in adults, particularly females. First-line treatment is surgical removal of all or most of the thyroid gland (thyroidectomy). This is followed by thyroid hormone suppression therapy, which entails administration of T3 or T4 at levels sufficient to maintain low seum TSH levels through the negative feedback mechanism mentioned earlier. TSH suppression is required 

Calcitonin is a polypeptide hormone which (along with parathyroid hormone and the vitamin D derivative, 1,25-dihydroxycholecalciferol) plays a central role in regulating serum ionized calcium (Ca +) and inorganic phosphate (P,) levels. The adult human body contains up to 2 kg of calcium, of which 98% is present in the skeleton (i.e. bone). Up to 85% of the 1kg of phosphorus present in the body is also found in the skeleton (the so-called mineral fraction of bone is largely composed of Ca3 (P04)2 which acts as a body reservoir for both calcium and phosphorus). Calcium concentrations in human serum approximate to O.lmg/ml and are regulated very tightly (serum phosphate levels are more variable). 

Calcitonin lowers serum Ca + and P, levels, primarily by inhibiting the process of bone resorption, but also by decreasing resorption of P, and Ca + in the kidney. Calcitonin receptors are predictably found primarily on bone cells (osteoclasts) and renal cells, and generation of cAMP via adenylate cyclase activation plays a prominent role in hormone signal transduction. 

Calcitonin is used clinically to treat hypercalcaemia associated with some forms of malignancy and Paget s disease. The latter condition is a chronic disorder of the skeleton in which bone grows abnormally in some regions. It is characterized by substantially increased bone turnover rates which reflects over-stimulation of both osteoclasts (promote bone resorption, i.e. degradation of old bone) and osteoblasts (promotes synthesis of new bone). 

Most superovulatory regimes utilizing p-FSH entail its administration to the recipient animal twice daily for 4-5 days. Regular injections are required due to the relatively short half-life of FSH in serum s.c. administration helps prolong the duration of effectiveness of each injection. The 4 or 5 days of treatment with FSH is followed by a single dose of LH, promoting final follicular maturation and ovulation. 

The causes of variability of superovulatory responses are complex and not fully understood. The general health of the animal, as well as its characteristic reproductive physiology, is important. The exact composition of the gonadotrophin preparations administered and the exact administration protocol also influence the outcome. The variability of FSH LH ratios in many p-FSH preparations can affect the results obtained, with the most consistent superovulatory responses being observed when FSH preparations exhibiting low LH activity are used. The availability of recombinant FSH and LH will overcome these difficulties at least. 

TSH is approved for medical use as a diagnostic aid in the detection of thyroid cancer/thyroid remnants in post-thyroidectomy patients. Thyroid cancer is relatively rare, exhibiting highest 

Human parathyroid hormone (hPTH) is an 84 amino acid polypeptide that functions as a primary regulator of calcium and phosphate metabolism in bones. It stimulates bone formation by osteoblasts, which display high-affinity cell surface receptors for the hormone. PTH also increases intestinal absorption of calcium. 

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