Effect Of Homologous Desensitization Of CRH-R1 On The Regulation Of CRH Secretion In Rats' Hypothalamus Paraventricular Nucleus Early After Trauma

Objective: To study the distinct distribution and the time-course changes of the G protein-coupler receptor kinase (GRK) and corticortropin-releasing hormone (CRH) expressions in the hypothalamus paraventricular nucleus (PVN) of rats following trauma and 10nM CRH adminstration on the cultured hypothalamus slices. Methods: The traumatic model that severe thorax impact injury with fracture of femur was established in rat, and in vitro 10nM CRH was given to the cultured hypothalamus slices with or without the nonselective GRK inhibitor heparin or calmodulin's (CaM) specifical antagonist W-7.The distribution of GRK was studied with histochemistry, and its protein was semi-quantified with Westernblot. RT-PCR, a semi-quantitative method, was used to detect the mRNA of GRK2 and CRH.Results: The positive stain of GRK2/3,not GRK6, was found mostly in the PVN and periventricular nucleus in hypothalamus. GRK2/3 decreased significantly 30min after the trauma (p<0.05) and nearly recovered 90min after trauma without significant changes of GRK2 mRNA. A marked increase of CRH mRNA was observed 30min after trauma (p<0.05), and more significant 60, 90min after trauma (p<0.01). In the cultured hypothalamus slices, 10nM CRH given for 30, 60min can also stimulate the increase of CRH mRNA (p<0.01). However, a very significant decrease of GRK2/3 was measured after 30min CRH exposure (p<0.01) and marked attenuation after 60min exposure (p<0.05) without significant alteration of GRK2 mRNA. 1uM heparin preincubation for 2h can inhibit GRK2/3 and GRK2 mRNA and increase the CRH mRNA very significantly (p<0.01). 50uM W-7 incubation for 2h can reverse the inhibition of CRH on GRK2/3 and attenuate CRH mRNA notably (p<0.01) without GRK2 mRNA significant change. Conclusion : Homologous desensitization of CRH-R1 may not occur or be inhibitated early after trauma and CRH administration in cultured hypothalamus slices in rats' PVN. This could give rise to the downregualtion of GRK2/3 not GRK2 mRNA. CaM may stimulate ultrashot positive feedback regulation of CRH secretion in PVN by way of inhibit GRK2/3 early after trauma.