Immunoreactive Rat Growth Hormone: Physiological Variations in Serum and Urine

Immunoreactive rat growth hormone (GH) in serum and urine was measured by a double antibody procedure. Anti-rat growth hormone (anti-RGH) serum was obtained from chickens immunized with three successive 0.25 mg doses of the hormone antigen. Standard amounts of RGH incubated with rat serum were recovered quantitatively. The assay can be used for the determination of GH in rat pituitary extracts as well as for the measurement of hormone secreted from incubated pituitaries. Serum GH concentrations were determined in eight male and 11 female Wistar rats under five different physiological conditions, which were produced in each animal at weekly intervals. GH concentrations in the serum of overnight fasted and ether anesthetized rats were 7.8 ± 2.4 in males and 5.3 ± 0.7 ng/ml in females. Normal feeding or prolonged (48 h) starvation did not significantly alter serum GH in either sex. Exercising for 20 min decreased the serum GH in males to 1.9 ± 0.3 ng/ml and in females to 3.9 ± 0.4 ng/ml. When blood samples were obtained without ether anesthesia GH concentrations were not changed in overnight fasted males (10.2 ± 2.2 ng/ml) and were elevated in females (7.8 ± 0.5 ng/ml). A dialyzable substance, present in the urine of normal rats, interferes with the GH immunoreaction. However, GH was detected in the dialyzed urine of hypersomatotropic rats. These animals had greatly elevated circulating GH due to the pituitary tumor MtT-W15.