Loss of tissue sensitivity to growth hormone during maternal deprivation in rats

Abstract

Ovine growth hormone (oGH) (100 μg) was given intracisternally (i.c.) or subcutaneously (s.c.) to 8 day old rat pups that had been separated from the mother for 2 hours before injection or left undisturbed in the home cage, and ornithine decarboxylase activity (ODC) was determined in brain and liver. GH (s.c.) increased liver ODC to 400% of control in undisturbed pups but had no effect on liver ODC activity when given to maternally deprived pups. Similarly, i.c. administration of oGH increased brain ODC activity to 150% of control in undisturbed pups but had no effect in maternally deprived pups. The response of liver ODC to oGH returned when the deprived pups were returned to the mother 2 hours prior to administration of GH. A similar suppression of the liver ODC response to GH was observed in pups placed with a urethane-anesthetized mother, although urethane administration itself did not decrease the response of liver ODC to GH. Placing the pups with a mother whose nipples had been ligated did not decrease the stimulation of liver ODC evoked by oGH administration. Ovine placental lactogen (oPL) (100 μg) also failed to stimulate liver ODC activity in maternally deprived rat pups, although it stimulated liver ODC in control pups. In contrast to these results, s.c. administration of dexamethasone (.2 mg), dibutyryl cAMP (.8 mg), PGE-1 (50 μg) or insulin (10 μg) stimulated liver ODC activity comparably in both maternally deprived and control pups. Similarly, intracisternal adminstration of dibutyryl cAMP (50 μg) stimulated brain ODC activity in both maternally deprived and control pups. These results suggest that maternal deprivation is associated with a specific suppression of tissue response to the growth promoting peptide hormones GH and oPL. This suppression is reversed rapidly when pups are returned to the mother, and appears to be triggered by the removal of active mothering behavior, not by nutritional deprivation or the removal of passive sensory stimuli associated with the mother.