Changes in immunoreactive basic somatomedin in conscious and anaesthetized male rats

Basic somatomedin (B-SM) like insulin-like growth factor-I or somatomedin-C belongs to the basic group of somatomedins. In preliminary studies on the control system for B-SM, we have found that plasma levels of immunoreactive B-SM (IRSM) fluctuate in conscious adult male rats. The peaks average 85% of the local baseline level (minimum of 6 points) and occur with an interpeak interval of 2.1 h. In rats anaesthetized with nembutal (50 mg/kg) very few peaks were found. After approximately 3.4 hr. of anaesthesia, plasma IRSM levels dropped precipitously with a calculated T1/2 of 50 minutes. These results suggest that IRSM levels may be related to serum CH levels which occurred 4 hr previously and that part of variation seen in serum levels in conscious rodents may be due to physiological fluctuations.