Specific somatotropic and lactogenic uptake in vivo in the livers of transgenic mice expressing bovine growth hormone gene.

The distribution of labeled hGH, oGH and mPRL in different tissues of MT-bGH transgenic and normal mice was investigated using an in vivo technique. This technique allows comparisons of tissue uptake of radioactivity after the labeled hormone was injected alone (20 ng/50 g BW) or together with an excess (300 micrograms/50 g BW) of unlabeled hormone. Liver, kidney and spleen are the organs that concentrate a significant amount of radioactivity 20 min after the injection of labeled hormones, but the uptake of radioactivity decreased in the presence of unlabeled hormones only in the liver. Graphical analysis showed that the disappearance curves were described by the sum of 3 compartments alpha, beta and gamma. The first two are similar in transgenic and in normal mice but the third had a t1/2 of 56 +/- 9 min in transgenic and 71 +/- 8 min in normal mice. The inhibition of liver uptake was related to the dose of unlabeled hormone injected and a half maximal displacement was obtained with 4 micrograms and 10 micrograms of hGH per 50 g of body weight for normal and transgenic mice, respectively. The 125I-hGH taken up in vivo by the liver of transgenic mice was bound to a molecular species with Stokes radius of approximately 64 A (which is consistent with the molecular size reported for the hormone-receptor complex).(ABSTRACT TRUNCATED AT 250 WORDS)