American journal of physiology. Regulatory, integrative and comparative physiology
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Nov 2015
Variable Responses of Regional Renal Oxygenation and Perfusion to Vasoactive Agents in Awake Sheep.
Vasoactive agents are used in critical care to optimize circulatory function, but their effects on renal tissue oxygenation in the absence of anesthesia remain largely unknown. Therefore, we assessed the effects of multiple vasoactive agents on regional kidney oxygenation in awake sheep. Sheep were surgically instrumented with pulmonary and renal artery flow probes, and combination fiber-optic probes, in the renal cortex and medulla, comprising a fluorescence optode to measure tissue Po2 and a laser-Doppler probe to assess tissue perfusion. ⋯ Arginine vasopressin (3.3 ± 0.5 μg/h) caused similar decreases in RBF and renal oxygen delivery, but did not significantly alter renal oxygen consumption or cortical or medullary LDF or Po2. Captopril had no observable effects on cortical or medullary LDF or Po2, at a dose that increased renal oxygen delivery by 24%, but did not significantly alter renal oxygen consumption. We conclude that vasoactive agents have diverse effects on regional kidney oxygenation in awake sheep that are not predictable from their effects on LDF, RBF, or total renal oxygen delivery and consumption.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Nov 2015
Catecholaminergic neurons in the comissural region of the nucleus of the solitary tract modulate hyperosmolality-induced responses.
Noradrenergic A2 neurons of the nucleus of the solitary tract (NTS) have been suggested to contribute to body fluid homeostasis and cardiovascular regulation. In the present study, we investigated the effects of lesions of A2 neurons of the commissural NTS (cNTS) on the c-Fos expression in neurons of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, arterial pressure, water intake, and urinary excretion in rats with plasma hyperosmolality produced by intragastric 2 M NaCl (2 ml/rat). Male Holtzman rats (280-320 g) received an injection of anti-dopamine-β-hydroxylase-saporin (12.6 ng/60 nl; cNTS/A2-lesion, n = 28) or immunoglobulin G (IgG)-saporin (12.6 ng/60 nl; sham, n = 24) into the cNTS. ⋯ Contrary to sham rats, intragastric 2 M NaCl also increased arterial pressure in cNTS/A2-lesioned rats (16 ± 3, vs. sham: 2 ± 2 mmHg 60 min after the intragastric load; n = 9), an effect blocked by the pretreatment with the vasopressin antagonist Manning compound (0 ± 3 mmHg; n = 10). In addition, cNTS/A2 lesions enhanced hyperosmolality-induced water intake (10.5 ± 1.4, vs. sham: 7.7 ± 0.8 ml/60 min; n = 8-10), without changing renal responses to hyperosmolality. The results suggest that inhibitory mechanisms dependent on cNTS/A2 neurons reduce water intake and vasopressin-dependent pressor response to an acute increase in plasma osmolality.