| Popis: |
We have previously reported that maternal deprivation of rat pups causes a decrease in tissue responsiveness to growth hormone that is mediated by the loss of maternal tactile stimulation. We now report that liver responses to alpha and beta adrenergic agonists as well as glucagon and vasopressin decrease during maternal deprivation. However, the decreased responsiveness to these agents is mediated by short-term food deprivation (FD) rather than loss of maternal tactile stimulation. When 8-day-old rat pups were separated from the mother or placed with a nipple-ligated mother for 2 hr and then injected with phenylephrine, isoproterenol or glucagon, liver ornithine decarboxylase (ODC) activity did not increase, although ODC activity increased markedly in control pups after administration of these agents. This loss of responsiveness appears to be both tissue- and drug-specific, as liver ODC responses to dexamethasone, dibutyryl cyclic AMP and prostaglandin E-1 and heart ODC responses to phenylephrine were not affected. FD had only a slight effect on glycogen phosphorylase activation by phenylephrine and had no effect on phenylephrine-induced glycogen depletion. Finally, FD did not affect the number of alpha-1 or beta receptors in liver of rat pups. These findings suggest that short-term FD selectively decreases liver ODC responses to certain agonists including alpha and beta adrenergic agonists by postreceptor mechanisms. |
