Effect of continuous somatostatin and growth hormoneμreleasing hormone (GHRH) infusions on the subsequent growth hormone (GH) response to ghrh: Evidence for somatotroph desensitization independent of GH pool depletion

Continuous infusions of growth hormone-releasing hormone (GHRH) attenuate the subsequent growth hormone (GH) response to GHRH. To test whether this phenomenon can occur in the absence of GH pool depletion, we examined the effects of continuous infusions of 10 nM GHRH and of 10 nM somatostatin (SRIH), separately or in combination, on dispersed, perifused rat anterior pituitary cells. Columns of these cells were given either GHRH alone for 5 h, GHRH and SRIH together for 3 h followed by GHRH alone, or SRIH alone for 3 h followed by GHRH or medium. SRIH blunted both basal GH release and the GH response to GHRH, without affecting the subsequent GH responses to GHRH. The GHRH infusions attenuated the subsequent GH response to GHRH, even when GH release was initially prevented bythe concurrent infusion of SRIH. Furthermore, the degree of attenuation was similar in the presence or absence of SRIH. suggesting that pool depletion plays little role in the desensitization process under these experimental conditions. Theresults are consistent with the hypothesis that a short-term infusion of GHRH leads to attenuation of the GH response inrat anterior pituitary cells primarily through receptor effects rather than through GH pool depletion.