UBC Theses and Dissertations
The effect of carotid sinus pressure on the osmoregulation of arginine vasopressin in anesthetized rabbits Scott, Christine Sharon
Studies in rat, dog and human show that changes in blood volume influence the relationship between plasma osmolality and plasma arginine vasopressin (AVP) concentration. It has not been proven whether the change in blood volume acts through stimulation of the low pressure receptors or arterial baroreceptors or both. The purpose of these experiments was to investigate the effect of changes in arterial baroreceptor stimulation on the relationship between plasma osmolality and plasma AVP in the anesthetized, artificially ventilated rabbit. Both carotid sinuses were isolated and perfused with blood at servo-controlled pressures of 40, 100, or 140 mmHg. The vagus and aortic depressor nerves were sectioned bilaterally to eliminate input from a trial and aortic arch baroreceptors. Saline (0.3%) was infused i.v. to lower plasma osmolality and 5% saline was infused to r a i s e plasma osmolality. At low (288 + 1 mosm/kg), medium (309 ± 1 mosm/kg) and high (323 + 1 mosm/kg) plasma osmolality, the carotid sinus pressure was changed from 100 mmHg t o 40 mmHg, to 140 mmHg and returned to 100 mmHg. Arterial blood samples were taken at each carotid sinus pressure 7 minutes after the change in pressure. Plasma immunoreactive AVP (iAVP) was measured by radioimmunoassay. At medium (309 mosm/kg) and high (323 mosm/kg) plasma osmolality, the levels of plasma AVP were higher at CSP 40 mmHg than at CSP 140 mmHg. The relationship between plasma iAVP and plasma osmolality was expressed as a linear regression at each of the carotid sinus pressures. The slope of the regression line at CSP 40 mmHg was greater than it was at CSP 140 mmHg. The x-intercepts of the regression lines were not significantly different. In the control rabbits, in which CSP was maintained constant at 100 mmHg, the slope of the AVP/Posm relationship was the same as that in the experimental animals at the same CSP. These results indicate that arterial baroreceptors, acting alone, can change the slope of the AVP/Posm relationship. Changes in carotid sinus pressure appear t o change the sensitivity but not the threshold of the osmotic control of AVP release.