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Studies of GH receptor (GHR) gene expression in human tissues have been hampered by the limited amount of tissue available for analysis and the low sensitivity of conventional methods. We have developed a quantitative reverse transcriptase-PCR assay for measurement of GHR messenger ribonucleic acid levels in small human tissue biopsies. To compensate for sample to sample variation, an internal RNA standard, which differs from the wild-type GHR transcript by only a few nucleotides, was reverse transcribed and amplified together with the GHR transcripts. PCR was carried out using one biotinylated primer to permit the purification of single stranded PCR products on streptavidin-coated microtiter plates. The ratio between the wild-type and mutated transcripts was determined by two separate minisequence reactions in which a primer, annealed immediately 3' of a variable nucleotide, was extended by a single 3H-labeled nucleotide, complementary to either the wild-type or mutated sequence. The assay range was 0.125-8 x 10(5) transcripts/sample, the mean intraassay coefficient of variation was 8.7%, and the lower limit of detection was 0.125 x 10(5) transcripts/sample. GHR messenger ribonucleic acid levels were detectable in small amounts (10-100 ng) of total RNA extracted from adipose tissue, skeletal muscle, and liver. The GHR gene expression in liver was approximately 10-fold higher than that in skeletal muscle, whereas intermediate levels were found in adipose tissue. In nine patients undergoing elective abdominal surgery, GHR gene expression in skeletal muscle was reduced on day 3 after surgery compared to the baseline level. The decrease in GHR gene expression was accompanied by a decrease in skeletal muscle glutamine. This suggests that the postoperative protein catabolism may be caused at least partly by acquired GH insensitivity due to reduced expression of the GHR gene.

GH has multiple effects on growth and metabolism, and these functions are mediated through binding to specific cell surface receptors. The human GH receptor (GHR) exists in two known isoforms; in one form exon 3 is present (GHR3+), and in the other, exon 3 is absent (GHR3-). Recent reports have suggested that the expression of the two isoforms is tissue specific and/or developmentally regulated. We used a reverse transcription-polymerase chain reaction assay to study the expression pattern of the two isoforms in a variety of tissues from normal subjects and patients with acromegaly. In skeletal muscle from both normal subjects and patients with acromegaly, the GHR3+ transcript was expressed, either alone or together with the shorter (GHR3-) transcript. When multiple tissues from six subjects were tested, the expression of the two isoforms varied among subjects, whereas different tissues from the same subject showed the same expression pattern. These results indicate that the expression of the GHR isoforms is not tissue specific. Instead, the expression of the GHR isoforms appears to be specific for each individual, suggesting that it is under the control of factors that affect all tissues in the body.