Impaired growth hormone secretion in VMH lesioned rats

To investigate impaired growth hormone (GH) secretion in ventromedial nuclei (VMH) lesioned rats, we examined spontaneous plasma GH secretion, and plasma GH responses to arginine, clonidine and growth hormone releasing factor (GRF) under unanaesthetized and unrestrained conditions. Spontaneous GH secretion was blunted with 75% decrease of peak value in VMH lesioned rats, while it clearly existed in control rats. When rats were pre-treated with chlorpromazine (1-2 mg/kg, i.v.) which eliminates pulsatile GH secretion, no difference was observed in the plasma GH response to arginine (1 g/kg, i.v.) or to clonidine (100 micrograms/kg, i.v.) between VMH lesioned and control rats, but response to GRF (10 micrograms/kg, i.v.) was enhanced in the former animals. Administration of antiserum against somatostatin (1 ml) plus chlorpromazine significantly elevated the basal plasma GH level and GH response to arginine in control rats, but did not elevate them in VMH lesioned rats. These results suggest that reduction of both hypothalamic GRF and somatostatin release contribute to the impaired GH secretion in VMH lesioned rats. Reduction of somatostatin caused enhanced GH response to GRF and no increase in basal GH level with pre-treatment of antiserum against somatostatin. Reduction of GRF resulted in a failure to restore GH response to arginine with pre-treatment of antiserum against somatostatin. Reduction of both GRF and somatostatin caused blunted spontaneous GH secretion and normal GH response to arginine and clonidine.