Date of Award
Doctor of Philosophy
Hypothalamic and peripheral noradrenergic systems have been implicated in baroreflex control of arteria pressure. However, the relationship between changes in the hypothalamic noradrenergic activity and changes in peripheral sympathetic activity is unclear. The first study examined this relationship in conscious Wistar rats following changes in baroreceptor input to the CNS produced by: (1) transection of aortic depressor nerve (ADN) (removal of specific baroreceptor input), (2) acute hypotension for 60 min produced by infusion of nitroprusside, and (3) acute hypertension for 60 min produced by infusion of phenylephrine. An index of norepinephrine (NE) turnover was used to assess the noradrenergic activity by measuring the decline in endogenous concentration of NE after inhibition of NE synthesis.;ADN transection, caused a significant elevation in arterial pressure, heart rate and NE turnover in the hypothalamus, midbrain, medulla, skeletal muscle, and kidney but not in the duodenum. Acute hypotension produced a reflex increase in heart rate and an increased NE turnover in the posterior hypothalamus (PH) and all peripheral organs examined (skeletal muscle, kidney and duodenum). Acute hypertension produced no significant changes in NE turnover in the hypothalamus or the peripheral organs examined.;Recent electrophysiological evidence suggests that baroreceptor information and afferent renal fibers may interact at the level of the hypothalamus. To determine the nature of such an interaction, the effect of renal denervation on hypothalamic and peripheral noradrenergic responses to changes in baroreceptor input were examined. Renal denervation normalized the elevated arterial pressure and increased NE turnover in the hypothalamus and skeletal muscle seen after ADN transection. In the acutely hypotensive group renal denervation abolished the increased NE turnover in PH but not in the peripheral organs. Renal denervation in the acutely hypertensive animals caused a significant decrease in NE turnover in the hypothalamus, unmasking an inhibitory influence of "loaded baroreceptors".;In conclusion there is an inhibitory influence from the baroreceptor afferent and an excitatory influence from the renal afferents on the noradrenergic systems in the hypothalamus. Furthermore, hypothalamic and peripheral noradrenergic activity are not tightly linked, as dissociation of these two systems can be produced under certain conditions.
Patel, Kaushik Parbhubhai, "Hypothalamic And Peripheral Noradrenergic Responses To Changes In Baroreceptor Input In Conscious Rats With And Without Renal Nerves" (1983). Digitized Theses. 1282.