Immunolike growth hormone substance in tissues from human embryos/fetuses and adults.

GH immunolike reactivity was measured by RIA and IRMA tests in the extracts of tissues from human fetuses (8-32 weeks) and adults. For some fetal tissues a comparison was made with the T4 values obtained in a previous study. Both hormones were already measurable in peripheral tissues at 8 weeks of gestation. The increase in GH was faster than for T4 and it reached the zenith at approximately 20 weeks; thereafter, the GH concentration declined until delivery. In contrast, T4 progressively increased until term. Thirteen tissues were studied both in fetuses and in adults: the GH concentration was about 10 times higher in fetal tissues, with the exception of the brain and the pancreas. The brain showed the lowest GH concentration throughout fetal life and adulthood, whereas the highest GH levels were recorded in adults' pancreas, but they resulted to be artifacts since the RIA values were not confirmed by the IRMA test. In both groups of subjects the highest GH concentrations were found in kidneys, liver and small intestine; the lowest, beyond the brain, in red muscle and cartilage. Thus, the pattern of the quantitative distribution of GH in fetal tissues is the same as in adults, suggesting a functional role of the hormone in the developing human during the prenatal period, in contrast with the concept that high tissue levels of GH are a mere reflection of high GH blood levels. Moreover, in all tissues examined no correlation was found between GH and T4 concentration.