CONTINUOUS INTRACEREBROVENTRICULAR ADMINISTRATION OF A CORTICOTROPIN-RELEASING HORMONE ANTAGONIST AMPLIFIES SPONTANEOUS GROWTH-HORMONE PULSES IN THE RAT

Involvement of endogenous corticotropin releasing hormone (CRH) in the regulation of spontaneous growth hormone (GH) secretion was investiga ted. A CRH antagonist, ct helical CRH 9-41, was intracerebroventricula rly infused for 36 h at a rate of 1 mu g/0.5 mu l/h to freely moving, cannulated adult male rats. Serial blood samples were drawn every 20 m in for the last 8 hours of a helical CRH 9-41 infusion. The treatment induced a marked increase in GH peak amplitude without affecting eithe r trough levels or numbers of peaks. In parallel, levels of growth hor mone releasing hormone (GHRH) mRNA in the arcuate nucleus, but not of somatotropin release inhibiting hormone (SRIH) mRNA in the periventric ular and arcuate nuclei, were increased. These data suggest that, in a ddition to its action in the stress-induced inhibition of GH secretion through regulation of periventricular SRIH neurons, CRH can also act as a modulator of endogenous GH secretion through regulation of arcuat e GHRH neurons. Whether the modulatory effects of CRH on GHRH neurons are direct or indirect remains to be established.