Growth hormone and prolactin variants in normal subjects. Relative proportions in morning and afternoon samples

There are multiple molecular forms of both growth hormone (GH) and prolactin (PRL). Traditionally the two hormones have been measured by radioimmunoassay (RIA) techniques. Recently, several molecular variants of these hormones have been discovered using Western blotting techniques: four GH size variants, 27K GH, 22K GH (the classical form), 20K GH (an alternatively-spliced form), and 17K GH, and two PRL structural variants, a glycosylated (G-PRL) and a nonglycosylated form. In this study, we measured these GH and PRL variants in 18 normal subjects in the morning in a fasting state and in the afternoon in a non-fasting state. Contrary to expectations, the predominant serum GH form in both morning and afternoon samples was found to be 17K, not 22K GH, accounting for 82-89% of the total circulating GH. The predominant serum PRL form was found to be the nonglycosylated variant, constituting 83-84% of the total circulating PRL. None of the GH or PRL variants were significantly different when comparing morning to afternoon samples. These results provide, for the first time, evidence for the existence of two new GH-immunoreactive components in human sera, the 17K and 27K GH, the former in proportions often higher than those of the classical 22K GH, and argue for the need to measure them individually.