We studied the effect of brief periods of left atrial-pulmonary vein distention on the rate of renin secretion in sodium-restricted dogs anesthetized with chloralose and breathing spontaneously. Series 1 consisted of 32 trials in seven dogs with intact renal nerves and intact vagi. Renin secretion, calculated as the product of renal venous minus arterial renin activity (radioimmunoassay) times renal plasma flow (electromagnetic flowmeter), was depressed to 56% of control during atrial distention despite no change in arterial pressure, central venous pressure, or renal blood flow. Series 2 consisted of 58 trials in 12 dogs which had undergone unilateral renal denervation several days prior to the studies. Simultaneous, bilateral determinations indicated that renin secretion from the innervated kidney was depressed to 58% of control during atrial distention; secretion from the denervated kidney was unchanged. Series 3 consisted of 30 trials in six dogs with bilateral cervical vagotomy. Atrial distention evoked no changes in renin secretion. We conclude that left atrial distention reflexly reduces the rates of renin secretion via vagal afferent and renal sympathetic efferent pathways.
A long-term (14-24 h) telemetry recording of mean arterial pressure (MAP) and heart rate (HR) was obtained from conscious unrestrained dogs (n = 9) maintained in a closed environment. MAP and HR records were analyzed for their harmonic content by the fast Fourier transform method. The power spectral density functions of MAP and HR clearly revealed the existence of coherent ultradian rhythms of MAP and HR with a period of 1-2 h. HR and MAP are in phase and sustained during a 24-h period. To elucidate the nature of these rhythms, two additional studies were conducted (n = 4) in which clonidine (200 micrograms/kg) was administered systemically. In series I, a 7-h control period preceded the administration of clonidine, whereas in series II the order was reversed. Control (series I) and recovery (series II) periods were compared with a 0- to 7-h postinjection period. The results show that clonidine drastically and significantly reduces the amplitude of both MAP and HR oscillations for an average period of 7 h. This response was very consistent in both series and in all four dogs. These results implicate the central nervous system as the origin of these rhythms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.