Centrally administered insulin-like growth factor II fails to alter pulsatile growth hormone secretion or food intake.

Abstract

Insulin-like growth factor II (IGF-II) peptide, mRNA, and receptors are widely distributed in the central nervous system, yet the physiological role of IGF-II in brain remains largely unknown. In the present study, we examined the in vivo effects of central administration of recombinant human IGF-II on pulsatile GH secretion and food intake. The IGF-II preparation used was shown to stimulate 3H-thymidine incorporation in MG-63 human osteosarcoma cells in vitro. Free-moving adult male rats bearing chronic intracerebroventricular (icv) and intracardiac venous cannulae were icv administered 10 microliters of either IGF-II (in doses of 300 ng and 1 microgram) or the vehicle solution, and blood samples were obtained every 15 min for 6 h. Vehicle-injected control animals exhibited the typical pulsatile pattern of GH secretion with most peak GH values greater than 100 ng/ml and trough levels less than 1.2 ng/ml. Central administration of IGF-II, at both doses, failed to alter the spontaneous 6-hour GH secretory profile; there were no significant differences in either GH peak amplitude, GH trough level, GH interpeak interval, or mean 6-hour plasma GH level, compared to vehicle-injected controls. There was also no effect of icv administered IGF-II on mean plasma glucose or insulin levels. Compared to vehicle-injected control rats, the icv injection of IGF-II (at doses of 300 ng and 1 microgram) did not significantly alter 24-h food intake or body weight gain in normal feeding rats.(ABSTRACT TRUNCATED AT 250 WORDS)