The goal of this project is to determine which second messenger pathways are involved in neurotransmitter and hormonal regulation of rat adrenal medulla enkephalin levels. Rat adrenal medulla offers a simple model system which can be readily manipulated both in vivo and in vitro. We hope to apply much of what we have learned using bovine adrenal medulla (BAM) cells to rat medulla; the receptors involved in calcium regulation seem similar in rat and bovine medulla cells. An advantage of rat medulla is that enkephalin levels are low, but respond more robustly to stimuli than do BAM cells. As a result we should be able to study regulatory pathways which may be missed in BAM cells. For example, we have found that lactating mother rats and aged rats have higher adrenal enkephalin and precursor levels than do young adult rats. Prolactin is a candidate regulatory agent since haloperidol administration, which increases prolactin secretion, also increases adrenal enkephalin. Processing of proenkephalin may also be regulated. During development, a pronounced decrease in precursor to processed enkephalin ratio was observed prior to weaning. Repeated nicotine administration, which mimics neuronal activity, produced a precocious fall in this ratio. Inhibitory as well as stimulatory pathways appear important in regulation. Denervation of the rat adrenal has been reported to increase enkephalin and particularly proenkephalin levels, but not tyrosine hydroxylase, and the basis of this specific negative neuronal regulation is being sought.
