Influences of Catecholamines on Growth Hormone Release in Female Goldfish, Carassius auratus

Publisher Website
Google Scholar
Abstract
The influence of catecholamines on growth hormone (GH) release in female goldfish was investigated by monitoring serum GH [growth hormone] levels following injections of drugs known to alter catecholamine synthesis and neural activities. I.p. injection of 6-hydroxydopamine, a catecholaminergic neurotoxin, or .alpha.-methyl-p-tyrosine, a catecholamine synthesis inhibitor, decreased serum GH levels. I.p. injection of L-dopa increased serum GH concentrations in a dose-dependent manner. The L-dopa-induced increase in serum GH was potentiated by i.p. injection of carbidopa which would increase the avilability of L-dopa to brain tissues by blocking the peripheral conversion of L-dopa to dopamine (DA). Apparently, L-dopa or one of its catecholamine metabolites acts centrally to increase GH release. Intraventricular (i.v.t.) injection of DA and i.p. injection of apomorphine, a DA agonist that crosses the blood-brain barrier, increased serum GH. I.p. injection of DA did not alter circulating GH levels in normal fish or fish bearing preoptic lesions that abolish an inhibitory hypothalamic influence on GH release; DA increased serum GH in fish which had their blood-brain barrier destroyed by sham operation procedures. Apparently, DA acts centrally to stimulate GH secretion, possibly by inhibiting the release and/or synthesis of GH release-inhibitory factor. Serum GH concentrations were decreased in a dose-dependent manner by i.p. injection of norepinephrine (NE); i.v.t. injection of NE did not alter serum GH levels. Evidently, NE acts outside of the blood-brain barrier to decrease serum GH levels in the goldfish, possibly by directly influencing pituitary GH cells. An .alpha.-adrenergic mechanism stimulating GH release in the goldfish may also be present, although the level of this action is not known.