Studies on the nature of plasma growth hormone

The paper presents further evidence for the existence of two discrete forms of growth hormone in human plasma, one which is detectable by both radioimmunoassay and bioassay and is immunoreactive, and the other, termed 'bioactive', which is detected by tibial bioassay but shows little reactivity with currently available antisera to pituitary growth hormone. The same division of immunoactive and bioactive growth hormone occurs in rats, though with less disparity. Tests on rats indicated that the bioactive hormone is preferentially released into jugular vein plasma and that plasma concentrations of the bioactive hormone can be enhanced by insulin administration. The bioactive hormone was detectable by tibial assays in Cohn fractions IV, IV-1, and IV-4, and could be concentrated about 40-fold by fractionation with (NaPO3)6 and (NH4)2SO4.