Insulin receptor ribonucleic acid levels and alternative splicing in human liver, muscle, and adipose tissue: tissue specificity and relation to insulin action.

The absolute levels and alternative splicing of insulin receptor RNA molecules were determined in samples from liver, muscle, and adipose tissue from 17 nondiabetic individuals. Both the absolute levels and alternative splicing varied in a tissue-specific manner. In all tissues, a majority of the insulin receptor RNA molecules contained exon 11. Liver tissue had a lower percentage of RNA molecules without exon 11 (Ex 11-) than muscle and adipose tissue, but the absolute number of Ex 11- RNA copies was higher due to higher overall levels of insulin receptor RNA. Insulin receptor RNA levels in adipose tissue showed significant correlation with obesity, expressed as body mass index (kilograms per m2) as well as with in vivo insulin action, as measured by the insulin tolerance test. In this study, obesity and insulin action were not correlated with insulin receptor RNA expression in liver or muscle. Within individuals, no relation was detected between the number of insulin receptor RNA copies in a tissue and the number or percent Ex 11- RNA in the same tissue. Also, the absolute levels or Ex 11- percentages in one tissue could not predict corresponding measurements in the other two investigated tissues from the same individual.