Hormonal Specificity of thein VitroAction of Growth Hormone on Amino Acid Transport into Rat Muscle

Abstract

Various pituitary hormones were tested for their ability to stimulate in vitro the transport of AIB into the cells of isolated hypophysectomized rat diaphragms. Crude and purified TSH, purified FSH, purified LH, purified MSH, posterior pituitary extracts and synthetic oxytocin andvasopressin were all ineffective at the concentrations tested. Three ovine prolactin preparations stimulated AIB transport into muscle when present in the incubation medium at high concentrations. This activity was abolished, however, when the prolactin solutions were adjusted to pH 8 and heated for 20 minutes at 100 C. The heating procedure also eliminates the action of growth hormone on amino acid transport but does not alter the ability of prolactin to stimulate the pigeon crop sac. Thus, it is conceivable that the amino acid transport stimulating activity present in ovine prolactin is due to growth hormone contamination. These experiments indicate that growth hormone is the only pituitary hormone which interacts to any extent with the amino acid transport system of muscle.