The kidneys stimulate vasopressin release during hemorrhage in rats with chronic NTS lesions

Elimination of baroreceptor afferent input to the brain produced by chronic lesion of nucleus of the solitary tract (NTS) does not alter vasopressin (VP) release during hypotensive hemorrhage in conscious rats. To investigate whether the kidneys play a critical role in stimulating VP release during hemorrhage in chronic NTS-lesioned rats, we examined the effects of removing potential signals arising from the kidneys. In NTS- lesioned rats, nephrectomy or renal denervation, but not captopril injection, markedly attenuated (but did not abolish) hemorrhage-induced VP release. In contrast, none of these manipulations attenuated the VP response in NTS- intact rats. Hemorrhage increased plasma renin activity in control and NTS- lesioned rats, and this response was not altered by renal denervation. In rats with NTS lesions and renal denervation, hemorrhage induced the expression of Fos in hypothalamic magnocellular VP neurons in a pattern similar to that of hemorrhage in intact rats. Collectively, these results indicate that in chronic NTS-lesioned rats an afferent signal arising from the kidneys stimulates VP release during hemorrhage, possibly through renal nerves. However, with the NTS intact or after the selective removal of arterial baroreceptor inputs, such a role for the kidneys is not apparent. Furthermore, in the absence of the NTS and renal nerves, another signal generated by hypotensive hemorrhage continues to stimulate VP neurons.