Rats with diabetes mellitus have an increase in UT-A1 urea transporter protein abundance and absolute urea excretion, but the relative amount (percentage) of urea in total urinary solute is actually decreased due to the marked glucosuria. Urea-specific signaling pathways have been identified in mIMCD3 cells and renal medulla, suggesting the possibility that changes in the percentage or concentration of urea could be a factor that regulates UT-A1 abundance. In this study, we tested the hypothesis that an increase in a urinary solute other than urea would increase UT-A1 abundance, similar to diabetes mellitus, whereas an increase in urine urea would not. In both inner medullary base and tip, UT-A1 protein abundance increased during NaCl-or glucose-induced osmotic diuresis but not during urea-induced osmotic diuresis. Next, rats undergoing NaCl or glucose diuresis were given supplemental urea to increase the percentage of urine urea to control values. UT-A1 abundance did not increase in these urea-supplemented rats compared with control rats. Additionally, both UT-A2 and UT-B protein abundances in the outer medulla increased during urea-induced osmotic diuresis but not in NaCl or glucose diuresis. We conclude that during osmotic diuresis, UT-A1 abundance increases when the percentage of urea in total urinary solute is low and UT-A2 and UT-B abundances increase when the urea concentration in the medullary interstitium is high. These findings suggest that a reduction in urine or interstitial urea results in an increase in UT-A1 protein abundance in an attempt to restore inner medullary interstitial urea and preserve urine-concentrating ability.sodium-potassium-2 chloride cotransporter; diabetes mellitus THE RENAL MEDULLA IS THE LOCATION in which water excretion is controlled through the production of concentrated or dilute urine. Several solute transport proteins play a major role in the urinary concentrating mechanism, including urea transporters and the NaϪ cotransporter (NKCC2/BSC1). Among the urea transporters, UT-A1 is expressed in the inner medullary collecting duct and is important for vasopressin-regulated urea reabsorption (reviewed in Ref. 21). UT-A2 and UT-B are expressed in the thin descending limb and descending vasa recta, respectively, and are important for intrarenal urea recycling (reviewed in Ref. 21). NKCC2/BSC1 is expressed in the thick ascending limb of the loop of Henle and is responsible for the active reabsorption of NaCl that drives the single effect to concentrate urine (reviewed in Ref. 22).Several studies show that UT-A1, as well as NKCC2/BSC1 and aquaporin-2 (AQP2), protein abundances increase after 5 days of uncontrolled diabetes mellitus due to streptozotocin (2,10,11,19,27). We showed that UT-A1 protein abundance does not change in streptozotocin-treated Brattleboro rats, indicating that vasopressin is necessary for the increase in UT-A1 protein abundance because Brattleboro rats lack vasopressin (11). When we administered vasopressin to Brattleboro rats and then induced diabetes melli...

The kidney responds to high levels of ANG II, as may occur during malignant hypertension, by increasing sodium and water excretion. To study whether kidney medullary transporters contribute to this response, rats were made hypertensive using ANG II. Within 3 days of being given ANG II, systolic blood pressure (BP) was increased (200 mmHg), vs control (130 mmHg), and remained high through day 14. Kidney inner medullary (IM) tip and base and outer medulla were analyzed for transporter protein abundance. There were significant decreases in UT-A1 urea transporter, aquaporin-2 (AQP2) water channel, and NKCC2/BSC1 Na(+)-K(+)-2Cl(-) cotransporter. To determine whether the decreases were a response to hypertension, ANG II, or an ANG II-induced increase in aldosterone, rats were given 1) norepinephrine (to increase BP) and 2) ANG II plus spironolactone (to block the mineralocorticoid receptor). Norepinephrine (7 days) increased BP, urine volume, sodium excretion, and decreased urine osmolality and UT-A1, AQP2, and NKCC2/BSC1 abundances, similar to ANG II. ANG II alone or with spironolactone yielded similar increases in BP, urine volume, and urine osmolality, and decreases in UT-A1 and AQP2 proteins in the IM tip. Plasma vasopressin was unaffected by treatment. Water diuresis did not change UT-A1 but decreased AQP2 and NKCC2/BSC1 abundances. We conclude that decreases in UT-A1, AQP2, and NKCC2/BSC1 proteins may contribute to the diuresis and natriuresis that occur following ANG II or norepinephrine-induced acute hypertension and do not appear to involve ANG II stimulation of aldosterone or thirst.

Infestation parameters are presented for 227 ticks, all Ixodes angustus Neumann, collected from individual mammals (n = 531) in southeastern and south-central Alaska from 1996 to 1999. This tick was recovered from 12 of the 19 mammal species examined, with four species of shrews (Sorex spp.), two species of voles [Clethrionomys gapperi (Vigors) and Clethrionomys rutilus (Pallas)], one species of mouse [Peromyscus keeni (Rhoads)], and the red squirrel [Tamiasciurus hudsonicus (Erxleben)] being the most frequently parasitized hosts. Larvae (n = 146) of I. angustus were collected most often, followed by nymphs (n = 50), females (n = 30), and a single male. The leptinid mammal-nest beetle Leptinus occidentamericanus Peck (1 male, 5 females) was also recovered from five individual small mammals; three of these were C. rutilus.