ISSN:
1365-2826
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
It is well known that the adrenergic system has both stimulatory and inhibitory influences on growth hormone (GH) secretion probably by modulating GH-releasing hormone (GHRH) and/or somatostatin release. To better understand the mechanisms by which these influences take place, we investigated the effects of α- and β-adrenergic agonists and antagonists on both basal and GHRH-induced GH release in 23 male adult volunteers. The GH-releasing effect of clonidine (0.15 mg infused iv over 10 min), an α2-adrenergic agonist, was significantly blunted by yohimbine (30 mg orally at −50 min), a relatively specific α2-adrenergic antagonist area under the response curve, mean±SEM: 672.6 ± 143.0 versus 219.6 ± 16.7 μg/l/h; P〈0.05). On the other hand, the GHRH (1 μg/kg iv as a bolus)-induced GH increase was unaffected by yohimbine (339.3 ± 19.1 versus 518.1±172.8 μg/I/h). Concomitant blockade of α1-/α2-adrenoreceptors by phentolamine (0.5 mg/ml/min infused iv from −60 to +30 min) abolished the GHRH-induced GH rise (645.5± 106.0 versus 189.0±58.8 μg/l/h; P〈0.01). Finally, the GHRH-stimulated release was blunted by β2-adrenergic stimulation with salbutamol (10 μg/min infused iv from −5 to +15 min) (324.3 ± 99.7 versus 112.7 ± 48.8 μg/l/h; P〈0.02).In conclusion: 1) The evidence that yohimbine is able to blunt the clonidine-induced GH release but fails to inhibit the GHRH-induced GH rise indicates that, as in animals, in man too the GH-releasing effect of clonidine is specifically mediated by α2-receptor activation, and may occur via endogenous GHRH release; 2) the inhibitory effect on GH release of β, namely β2, receptor activation is probably mediated by the somatostatinergic system; 3) an unopposed β-adrenergic activation would account for the inhibitory effect on GHRH-induced GH release of concomitant α1–/α2-adrenoreceptor blockade by phentolamine.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2826.1990.tb00435.x
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