Stress suppression of growth hormone secretion in the rat: effects of disruption of inhibitory noradrenergic afferents to the median eminence.

The participation of a growth hormone (GH) inhibitory noradrenergic input to the median eminence in stress-induced suppression of rat GH secretion was investigated in animals with median eminence catecholamine lesions produced by intravenous injection of 6-hydroxydopamine (6-OHDA). Unstressed lesioned rats exhibited an enhanced frequency of GH secretory bursts, but both intact and lesioned rats responded to stress with suppression of GH (controls: 56% suppression, 6-OHDA lesioned: 43% suppression, not significantly different). Thus noradrenergic projections to the median eminence, if they participate at all in stress-induced GH suppression, appear to have only a minor role. This study does not exclude the possibility that circulating adrenaline of adrenal medullary origin might obscure defects in GH control produced by noradrenergic denervation of the median eminence.