Growth hormone regulation of somatomedin C/insulin-like growth factor I production and DNA replication in fetal rat islets in tissue culture.

The regulation of DNA replication by growth hormone and the production of somatomedin C/insulin-like growth factor I (SM-C/IGF-I) and insulin by fetal rat islets in culture has been studied. Islets were cultured for 3 days in medium containing 2.7 or 16.7 mM glucose, various concentrations of fetal calf serum (FCS), and 100-1000 ng/ml human growth hormone (GH). DNA replication was determined by incorporation of [3H]thymidine into islet DNA; SM-C/IGF-I and insulin secreted into the medium were measured by specific radioimmunoassays. Glucose caused a twofold stimulation of islet DNA replication in medium containing greater than or equal to 1% FCS but failed to stimulate DNA replication at lower serum concentrations. In the presence of 16.7 mM glucose, GH (100-1000 ng/ml) stimulated DNA replication at all serum concentrations. In medium containing 2.7 mM glucose, GH was stimulatory only in the presence of 1% FCS. Somatomedin C/IGF-I release into the culture medium could be detected in all experimental groups. Glucose alone did not affect SM-C/IGF-I release, and in serum concentrations less than 0.1% FCS, GH also failed to increase the release of the peptide. In medium containing 1% FCS and 16.7 mM glucose, 100-1000 ng/ml GH caused a 50-100% increase in SM-C/IGF-I release into the medium. Addition of 100 ng/ml exogenous SM-C/IGF-I to medium containing 16.7 mM glucose and 0.1-1.0% FCS caused a twofold stimulation of the islet DNA replication. This effect could be abolished by the addition of an antibody to SM-C/IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)