Immunoassay for Human Growth Hormone

Since highly purified human pituitary growth hormone has become available, much information concerning its metabolic effects has been accumulated. However, simple and specific methods of measuring endogenous levels of human growth hormone have been difficult to achieve. Attempts to assay human growth hormone by injecting whole serum into hypophysectomized rats and measuring the width of the tibial plate have generally failed to show any activity in normal serum, although some acromegalic sera have been found to contain stimulating activity (1-3). More recently, Gemzell (4) assayed extracts of plasma using the tibial-line assay and found up to 12.3 ,ug growth hormone activity per ml of plasma in acromegalic subjects. Growth hormone-like activity was also found in plasma extracts from certain patients with diabetes, liver disease, and several other conditions; however, no activity was detected in extracts of normal plasma (5). The variability, insensitivity, and questionable specificity of the tibial assay system have raised doubts as to the significance of these results. In this laboratory, measurement of the serum sulfation factor has proved a useful indicator of growth hormone activity, but it is, nevertheless, not a direct measurement of growth hormone (6). Immunologic methods for assaying human growth hormone have recently attracted much attention. Li, Moudgal and Papkoff (7) have been able to detect as little as 2.5 ug of growth hor-