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A radioimmunoassay for rat growth hormone capable of measuring levels in plasma is described in detail. Several experimental conditions were studied, both to validate the method and to determine factors which regulate GH secretion in this species. In fasting Sprague-Dawley rats weighing 150-200 g, mean plasma GH concentration in females was 94.2±17.3, and in males, 54.9±12.0 mμg/ml. GH levels in lactating rats were determined to be in the normal range for females, thereby providing evidence that this assay does not detect prolactin. GH levels were not elevated in pregnant rats. Hypophysectomy led to a fall below detectable levels of GH. Intraocular pituitary transplants failed to raise GH levels in hypophysectomized hosts. GH levels in male, but not in female, rats are depressed by brief periods of ether anesthesia. These findings and the results of pituitary transplantation experiments are further evidence that the nervous system is involved in the regulation of GH secretion. (Endocrinology79: 275, 1966)
Schalch et al. (Mon,) studied this question.