Vasopressin and intrarenal blood flow distribution

Effect of leukotrienes of renal water excretion

To investigate the renal actions of leukotrienes (LT), we infused arachidonic acid into the renal artery of anesthetized dogs during systemic cyclooxygenase inhibition (with ibuprofen) alone or in combination with lipoxygenase inhibition or LTD4/LTE4 receptor antagonism. Renal arachidonic acid infusion following ibuprofen alone decreased urine osmolality (945 +/- 143 to 698 +/- 144 mosm/kg; p < 0.01) and increased urine flow rate (0.34 +/- 0.11 to 0.56 +/- 0.16; p < 0.05) without altering renal blood flow, glomerular filtration rate or sodium excretion. In separate groups, prior inhibition of lipoxygenase (propylgallate) or blockade of LTD4/LTE4 receptors (LY171883) prevented the changes in urine osmolality and urine flow rate. Intrarenal oleic acid infusion following ibuprofen had no effect on renal function. Analysis of the renal papillae at the end of the experiment indicated that interstitial osmolality and sodium, potassium and urea contents were the same in all groups, ruling out a decrease in papillary interstitial osmolality as the cause of the decrease in urine osmolality in the arachidonic acid-infused group. Our experiments suggest that renal LT can decrease urine osmolality and increase urine flow rate and may play a role in renal water excretion.

Effect of arginine vasopressin on renal medullary blood flow. A videomicroscopic study in the rat

The role of arginine vasopressin (AVP) in the regulation of renal medullary blood flow is uncertain. To determine if AVP has a direct vasoconstrictive action on vasa recta, the effect of AVP on erythrocyte velocity (VRBC), diameter, and blood flow (QVR) in descending vasa recta (DVR) and ascending vasa recta (AVR) was studied in the exposed renal papilla of four groups of chronically water diuretic rats using fluorescence videomicroscopy. There were three periods: control (period 1), experimental (period 2), and recovery (period 3). In periods 1 and 3, all groups received hypotonic saline. In period 2, group I rats (AVP) received AVP (45 ng/h per kg body wt); group II (time) received hypotonic saline alone; group III (AVP plus V1-inhibitor) received AVP plus its vascular antagonist, d(CH2)5Tyr(Me)AVP; and group IV (V1-inhibitor) received the vascular antagonist alone. Another group of rats (group V) was employed to demonstrate that the rise in blood pressure induced by a 3- or 10-ng/kg injection of AVP was virtually abolished by the prior infusion of the V1-inhibitor. The urine of group III as well as group I rats was concentrated (Uosm = 721 +/- 62 H2O vs. 670 +/- 39 mosM/kg), while urine remained dilute in groups II and IV. In period 2, VRBC and QVR in DVR and AVR decreased in group I, did not decrease in group III, and increased in groups II and IV. The vascular antagonist thus completely abolished the AVP-induced decrease in QVR in group III. These findings unequivocally establish that AVP in physiological amounts reduces medullary blood flow, at least in part, by a direct vasoconstrictive action on the medullary microcirculation. They also show that an effect of AVP on medullary blood flow is not necessary for its antidiuretic effect.

The effect of vasopressin on renal blood flow and its distribution in the rat

Anaesthetized Brattleboro rats with hereditary diabetes insipidus were infused with vasopressin at three different doses (1.3, 13 or 130 mu./hr) in order to study the effect of the hormone on renal blood flow and its distribution. Radioactive microspheres were used to determine intrarenal blood flow. The plasma vasopressin level during infusion of the lowest dose was calculated to be within the physiological range. At this dose vasopressin was antidiuretic but was without effect on arterial blood pressure or solute excretion, whereas the two higher doses were both pressor and natriuretic. All doses of vasopressin increased renal vascular resistance and decreased renal blood flow. The vasoconstrictor effect of the lowest dose was confined to the outer cortex, whereas the two higher doses affected the entire cortex. In separate experiments, [1-(beta-mercapto-beta, beta-cyclopentamethylenepropionic acid), 2(O-methyl) tyrosine] arginine vasopressin, an antagonist of the vascular action of vasopressin, was administered to anaesthetized Long Evans or Brattleboro rats. In the Long Evans rats the antagonist caused a decrease in renal vascular resistance and a consequent increase in renal blood flow, this effect being restricted to the outer cortex. In Brattleboro rats the antagonist had no effect on renal vascular resistance or renal blood flow. It is concluded that physiological levels of vasopressin influence the distribution of renal blood flow by causing vasoconstriction in the outer region of the renal cortex. Higher levels of the hormone increase vascular resistance throughout the cortex.